Samacheer Class 11 Bio Zoology - Organ and Organ Systems in Animals

• Earthworms are classified as epigeics, anecics and endogeics based on their ecological strategies.
• Epigeics are the surface dwellers e.g., Perionyx excavaus and Eudrilus eugeniae.
• Anecics are found in the upper layers of the soil e.g., Lampiro mauritii, Lumbricus terrestris.
• Endogeics are found in deeper layers of the soil e.g., Octochaetona thursoni.

The internal structure of the earthworm reveals a segmented body plan adapted for its burrowing lifestyle. The body wall is remarkably moist, thin, soft, skinny, and elastic, providing both protection and flexibility. It is composed of several distinct layers: the outermost cuticle, which is a non-cellular protective layer; the epidermis, which lies beneath the cuticle and consists of various cell types including supporting cells for structural integrity, gland cells for mucus secretion to keep the body moist, basal cells for regeneration, and sensory cells for detecting stimuli. Beneath the epidermis are layers of muscles, including circular and longitudinal muscles, which are crucial for locomotion. The innermost layer of the body wall is the coelomic epithelium, which lines the coelomic cavity. This coelom is a fluid-filled body cavity that acts as a hydrostatic skeleton, providing support and facilitating movement through muscular contractions against the fluid.

The coelom of the earthworm is a prominent and essential feature of its internal anatomy. It is a spacious, fluid-filled body cavity located between the outer body wall and the inner alimentary canal. This coelom is not merely an empty space; it contains coelomic fluid and plays a crucial role as a hydrostatic skeleton. The fluid within the coelom provides internal support against which muscles can contract, enabling the earthworm's characteristic burrowing and crawling movements. The coelomic fluid is milky and alkaline, and it is rich in various types of coelomocytes, including granulocytes or eleocytes, amoebocytes, mucocytes, and leucocytes. These coelomocytes are known to have significant functions in regeneration, allowing the earthworm to recover from injuries, and they also contribute to the immune system, defending against pathogens. Furthermore, they are involved in wound healing, ensuring the rapid repair of damaged tissues. Thus, the coelom and its fluid are integral to the earthworm's locomotion, structural integrity, and physiological well-being.

Earthworms can be identified in gardens by their fecal deposits known as worm castings on the soil surface. The key characteristics used to identify earthworms include a long and cylindrical narrow body with bilateral symmetry. The body is typically light brown in colour with a purple tinge at the anterior end. The body is divided into many segments or metameres, and the dorsal surface is marked by a dark mid-dorsal line that runs along the length of the organism. In mature worms, segments 14 to 17 are noticeably swollen with a glandular thickening of the skin called the clitellum, which is a distinctive feature of sexually mature individuals. These characteristics collectively make earthworms easily recognizable and distinguishable from other soil-dwelling organisms.

Chyme is the semi-fluid, pulpy mass of partially digested food that is formed in the stomach. The process begins when food enters the stomach, where it is subjected to both mechanical and chemical digestion. Mechanical digestion involves the churning action of the stomach muscles, which mixes the food thoroughly. Chemical digestion occurs through the action of hydrochloric acid and various gastric juices, including enzymes like pepsin, which are secreted from the walls of the stomach. Hydrochloric acid provides the acidic environment necessary for pepsin to function and also helps to kill harmful microorganisms. As a result of these digestive processes, the food is broken down into a thick, acidic, and creamy consistency known as chyme. This chyme is then gradually released from the stomach into the small intestine for further digestion and absorption.

Earthworms respire through a unique and efficient method known as cutaneous respiration, which means they breathe directly through their skin. For this process to be effective, their body wall must remain consistently moist, thin, and permeable. Oxygen from the surrounding environment, whether it's the air in soil pores or dissolved in water, diffuses across the moist surface of their skin and into the dense network of capillaries located just beneath the epidermis. Simultaneously, carbon dioxide, a waste product of cellular respiration, diffuses from the blood in these capillaries out through the skin into the environment. The constant secretion of mucus by gland cells in their epidermis helps to keep their skin moist, which is absolutely critical for the gases to dissolve and diffuse efficiently. If an earthworm's skin dries out, gas exchange cannot occur, leading to suffocation.

Cockroaches are considered pests for several important reasons. They destroy food and contaminate it with their offensive odour, making stored food and kitchen items unsuitable for consumption. Cockroaches are known carriers of a number of bacterial diseases that can be transmitted to humans through contamination of food and surfaces. The cockroach allergen can cause asthma and other allergic reactions in sensitive people, making them a health hazard in residential and commercial spaces. Additionally, their rapid reproduction rate, ability to survive in various environments, and nocturnal habits make them difficult to control once an infestation occurs. Their presence in homes and food storage areas poses significant public health risks and makes them one of the most common household pests.

• The photoreceptors of the cockroach consist of a pair of compound eye on the dorsal surface of the head.
• Each eye is formed of about 2000 simple eyes called the ommatidia.

The male frog possesses several specialized structures that enable it to attract females for mating. The male frog has a pair of vocal sacs located on the ventral side of the body, which serve to amplify the croaking sound produced during mating season. Additionally, the male frog has a nuptial pad on the ventral side of the first digit of each forelimb, which aids in gripping the female during amplexus. The male makes a characteristic loud croaking sound by forcing air through the vocal sacs, which resonates and carries over considerable distances. This distinctive sound serves as a mating call that attracts receptive females to the male's location, facilitating successful reproduction.

Frog respires on land and in the water by two different methods. In water, skin acts as aquatic respiratory organ (cutaneous respiration). Dissolved oxygen in the water gets exchanged through the skin by diffusion. On land, the buccal cavity, skin and lungs act as the respiratory organs. In buccal respiration on land, the mouth remains permanently closed while the nostrils remain open.
The floor of the buccal cavity is alternately raised and lowered, so air is drawn into and expelled out of the buccal cavity repeatedly through the open nostrils. Respiration by lungs is called pulmonary respiration. The lungs are a pair of elongated, pink coloured sac-like structures present in the upper part of the trunk region (thorax). Air enters through the nostrils into the buccal cavity and then to the lungs. During aestivation and hibernation, gaseous exchange takes place through skin.

• The dorsal wall of the intestine of earthworm is folded into the cavity as the typhiosole.
• This fold contains blood vessels and increases the absorptive area of the intestine.

The peristomium and prostomium are two distinct structures at the anterior end of the earthworm. The peristomium is the first segment of the earthworm body, and the mouth is located in the centre of this segment. The prostomium is a small flap-like structure that overhangs the mouth and functions as an upper lip. The prostomium is not a true segment but rather a lobe that extends from the anterior end above the mouth opening. While the peristomium forms the actual first body segment containing the mouth, the prostomium serves as a protective and sensory structure that helps the earthworm in burrowing and feeding activities.

In mature earthworms like Lampito mauritius, the clitellum is located on segments 14 to 17, appearing as a swollen, glandular thickening of the skin that secretes mucus for cocoon formation during reproduction. The spermathecal openings are three pairs of small ventrolateral apertures situated in the intersegmental grooves between segments 6/7, 7/8, and 8/9. These openings lead to the spermathecae, which are pouches that store sperm received from another earthworm during copulation. The clitellum's position in the anterior-middle region and the spermathecal openings' location in the more anterior segments reflect the reproductive anatomy of earthworms, with the spermathecae positioned to receive sperm before the clitellum produces the cocoon.

The clitellum is a specialized structure found in mature earthworms, consisting of segments 14 to 17 that appear swollen due to a glandular thickening of the skin. This thickened region is a distinctive feature of sexually mature earthworms and plays a crucial role in reproduction. The clitellum secretes a mucus sheath that helps in the formation of the cocoon, which is the protective egg case containing developing earthworm embryos. During mating, the clitellum produces the material necessary to form this cocoon, making it an essential reproductive structure. The presence and development of the clitellum indicates that an earthworm has reached sexual maturity and is capable of reproduction.

The mouthparts of the cockroach are directed downwards. The head is small, triangular lies at a right angle to the longitudinal body axis. Hence it is called hypognathous.

• The two sex organs of earthworm mature at different times and hence self fertilisation are prevented.
• The sperm develops earlier than the production of ova. This process is known as protandrous.
• It transmits the diseases like cholera, dysentery, and tuberculosis hence it is known as vectors.

Compound eyes are large, sessile, and reniform or kidney-shaped visual organs present as a pair on the head of cockroaches. Each compound eye is composed of approximately two thousand simple eyes or visual units called ommatidia. Each ommatidium consists of a lens, crystalline cone, and photoreceptor cells. The vision produced by the combined action of all ommatidia is called mosaic vision, which provides a fragmented or mosaic-like image of the surroundings. This type of vision is particularly effective for detecting movement and is well-suited to the nocturnal lifestyle of cockroaches. Compound eyes allow for a wide field of view and rapid detection of predators and prey.

Cockroaches possess two pairs of wings that are important for their locomotion and protection. The first pair of wings, called elytra or tegmina, are hardened and leathery in texture and serve primarily as protective covers for the delicate hind wings when the insect is at rest. These forewings are not used for flight but instead protect the functional wings beneath them. The second pair of wings, known as the hind wings or flight wings, are membranous and functional, used for actual flight. The hind wings are larger and more delicate than the forewings. When the cockroach is in flight, the elytra are held at an angle to allow the hind wings to unfold and generate the lift and thrust necessary for movement through the air.

The abdomen of a cockroach consists of ten segments, each of which is composed of sclerites or hardened plates arranged on different sides. The sclerites on the dorsal or upper side of each abdominal segment are called tergites, which form the dorsal surface of the abdomen. The sclerites on the ventral or lower side are called sternites, which form the ventral surface. The sclerites on the lateral or side regions are called pleurites, which connect the dorsal and ventral regions. Together, these three types of sclerites form a complete ring around each abdominal segment, providing structural support and protection to the internal organs while allowing for flexibility and movement of the abdomen.

The respiratory systems of humans and cockroaches differ significantly in structure and mechanism. Humans possess lungs as the primary respiratory organs, where gas exchange occurs in the alveoli, and breathing is controlled by the diaphragm and intercostal muscles. In contrast, cockroaches have a tracheal respiratory system with spiracles and tracheae. The spiracles are small openings located on the sides of the abdomen and thorax that can open and close to regulate gas flow. During inspiration, the spiracles open and oxygen enters the haemocoel through these openings. The oxygen then travels through the tracheae and tracheoles, which branch extensively throughout the body, delivering oxygen directly to the tissues. Gas exchange occurs at the level of the tracheoles where they come into contact with the hemolymph and body cells. This direct delivery system in insects is more efficient for their smaller body size and metabolic needs compared to the centralized lung system in humans.

A cockroach can survive for approximately one week without its head because respiration in cockroaches is independent of the head. Unlike humans and many other animals, cockroaches do not have nostrils or lungs located in the head region. Instead, their respiratory system is distributed throughout the body. The abdomen contains ten pairs of spiracles that are directly connected to the tracheal system and tracheoles. These spiracles allow oxygen to enter the haemocoel and facilitate gas exchange with the hemolymph and body tissues. Since the spiracles are located on the thorax and abdomen rather than the head, the cockroach can continue to respire even after decapitation. However, the headless cockroach will eventually die due to inability to feed and drink water, not from respiratory failure. This remarkable adaptation demonstrates the efficiency of the insect tracheal respiratory system.

Cockroaches possess compound eyes that produce mosaic vision with relatively lower resolution compared to the simple eyes of vertebrates. The compound eye is composed of hundreds of small functional units called ommatidia. Each ommatidium contains its own lens, cornea, retina, and optic nerve, and each one independently forms a small image of the visual field. These hundreds of individual images formed simultaneously by all the ommatidia are combined together in the brain to create a single composite image known as mosaic vision. The resolution of this mosaic vision is lower than that of simple eyes because each ommatidium captures only a portion of the visual field with limited detail. However, this type of vision provides cockroaches with excellent motion detection and a very wide field of view, which is advantageous for detecting predators and navigating their environment quickly.

Compound eyes and simple eyes differ significantly in structure and function. Compound eyes are found in insects and crustaceans and are formed of hundreds of small functional units called ommatidia. Each ommatidium contains its own lens, cornea, retina, and optic nerve. Each ommatidium forms a separate small image, and all these images together create an unclear mosaic vision. Simple eyes, found in vertebrates including humans, consist of a single eye with only one lens, one cornea, one retina, and one optic nerve. A simple eye forms a single clear and detailed image. Although compound eyes have lower resolution and produce less clear images compared to simple eyes, they provide a much wider field of view and are extremely sensitive to motion, making them well-suited for the lifestyle of insects and other arthropods. Simple eyes, on the other hand, provide high-resolution vision with excellent detail perception, which is advantageous for vertebrates that require precise visual information for hunting, navigation, and other complex behaviors.

• The heart of birds and mammals have four chambers. The oxygenated and deoxygenated blood is carried by separate blood vessels and transports to body parts and the purifying organ.
• The frog has a three-chambered heart. The oxygenated and deoxygenated blood mixes here. This mixed blood is reaching all the parts.

• In the elasmobranhs amphibians, reptiles egg laying mammals the faeces and urine pass through this opening.
• This passage is also a genital passage for the deposition of sperm. This is called cloacal aperature.

• Earthworm have setae which are small hair like bristles. They are not composed of the same material as human hair.
• They will be helpful in feeding mating and locomotion.

Intestinal caeca are specialized structures found in the digestive system of earthworms, particularly in Metaphire posthuma. A pair of cone-shaped bulgings or outgrowths are present in the 26th segment of the earthworm. These structures are known as intestinal caeca. The intestinal caeca secrete amylolytic enzymes, which are enzymes that break down starch into simpler sugars. This enzymatic secretion significantly aids in the digestion of starch and other carbohydrates present in the food consumed by earthworms. The presence of intestinal caeca increases the surface area available for enzyme secretion and absorption, making the digestive process more efficient. These structures represent an important adaptation that allows earthworms to effectively digest plant material and organic matter in the soil.

Earthworms can be classified into three ecological categories based on their habitat preferences and ecological strategies. Epigeic earthworms, such as Perionyx excavatus, live on the surface of the earth in leaf litter and organic matter. They are typically smaller, more pigmented, and feed on decomposing organic material. Anecic earthworms, exemplified by Lampito mauritii, burrow deep into the earth and come out of the soil to feed on surface litter, creating permanent burrows that extend deep underground. These earthworms are larger and play an important role in soil aeration. Endogeic earthworms, such as Octohaetona thurstoni, live within the earth in the soil layers and feed on soil organic matter. They create horizontal burrows and are intermediate in size. This classification system helps ecologists understand the different roles earthworms play in soil ecosystems and their contributions to soil health and nutrient cycling.

• Micro chaetus rappi is an African giant earthworm can reach a length of 6.7 meter (22 feet)
• Drawida nilamburansis is a species of earthworm in Kerala reaches a maximum length upto 1 meter (3 feet).

• Photo receptors – Found on the dorsal surface of the body.
• Gustatory – Sense of taste are found in the buccal cavity.
• Tactile receptors Sense of touch
• Chemo receptors Seen in the prostomium and the bodywall.
• Thermo receptors

The statement that a cockroach can survive without its head is correct. A cockroach can live for approximately one week without its head, which is a remarkable adaptation that distinguishes insects from many other animals. The reason for this survival ability lies in the cockroach's open circulatory system, where blood is not confined to vessels but bathes the organs directly in the body cavity. More importantly, cockroaches breathe through a system of spiracles, which are small holes or openings located on each of their body segments. These spiracles allow the cockroach to obtain oxygen directly from the air without depending on the mouth or head for respiration. Therefore, even without a head, the cockroach can continue to breathe through these segmental spiracles and maintain basic metabolic functions for a limited period until other vital processes fail.

• Brain or supra oesophageal ganglion or brain.
• It acts as a sensory and an endocrine centre.
• Sub – oesophageal ganglion
• It acts as a motor centre controls the movements of the mouthparts legs and wings.

• The photoreceptors of the cockroach consist of a pair of compound eyes at the dorsal surface of the head.
• Each eye is formed of about 2000 simple eyes called ommatidia.

• During breeding the sexual dimorphism is seen clearly.
• The male frog has a pair of vocal sac and a; nuptial pad on the ventral side of the first digit i of each fore limb.
• Vocal sacs assist in amplifying the croaking sound of frog.

• Epigeics – Surface living (Eg.) Eudrilus eugeniae
• Anecics-Found in upper layers of the soil. (Eg.) Lampito mauritii.
• Endogeics – Found in deeper layers of the soil. (Eg.) Octochaetona thurstoni.

• Earthworm has no special respiratory organ like lungs or gills.
• Respiration takes place through the body wall.
• The outer surface of the skin is richly supplied with blood capillaries which helps in the diffusion of gases.
• Oxygen diffuses through the skin into the blood.
• Carbondi-oxide from the blood diffuses out.
• The skin is kept moist by mucous and coelomic j fluid and facilitates exchange of gases.

• The brain composed of bilobed mass of supra-pharyngeal ganglia. On the third segment j supra-pharyngeal nerve ganglion and on the 4th segment sub-pharyngeal nerve ganglion is seen.
• The brain and the sub-pharyngeal ganglia are connected by a pair of cirum-pharyngeal connectives.
• The double ventral nerve cord runs backward from the sub-pharyngeal ganglion.

The nephridia are the excretory organs of the earthworm, responsible for the removal of nitrogenous wastes and osmoregulation. Nephridia are present in multiple segments throughout the earthworm's body and are classified into three distinct types based on their location and structure. Pharyngeal or tufted nephridia are found in segments 5 to 9 and are associated with the pharyngeal region. Micro nephridia, also called integumentary nephridia, are found in segments 14 to 19 and are located near the body wall. Mega nephridia, also called septal nephridia, are found from segment 19 onwards to the last segment and are typically larger and more prominent than the other types. Each type of nephridium has a specific structure and function, but collectively they work to filter waste products from the coelomic fluid and expel them through nephridiopores.

• Vermi wash is a liquid manure or plant tonic obtained from an earthworm.
• It is used as a foliar spray and helps to induce plant growth.
• It is a collection of excretory products, mucus secretion micronutrients from the soil organic molecules.

A wormery, also known as a worm bin, is a specially designed container system used for the recycling and composting of organic waste materials using earthworms. In a wormery, earthworms are introduced to decompose waste food, leaf litter, and other biomass materials. The earthworms break down these organic materials through their digestive processes, converting them into nutrient-rich compost. This compost produced in a wormery is of superior quality compared to regular compost because it is enriched with earthworm castings, which are highly beneficial for soil fertility and plant growth. Wormeries are an excellent sustainable method for managing household and garden waste while simultaneously producing a valuable fertilizer. They are compact, odor-free when properly maintained, and can be kept indoors or outdoors, making them suitable for both urban and rural settings.

Sensory receptors in cockroaches are distributed throughout various parts of the body, each specialized for detecting different types of stimuli. Thigmoreceptors, which respond to touch and pressure, are located on the antennae, maxillary palps, and anal cerci. Olfactory receptors, responsible for smell, are present on the antennae, which are highly sensitive to chemical odors in the environment. Gustatory receptors, which detect taste, are found on the maxillary palps and labium, allowing the cockroach to taste food before ingestion. Thermoreceptors, which sense temperature changes, are located on the tarsal segments of the legs, enabling the cockroach to detect warm and cold environments. Chordotonal organs, which respond to air-borne and earth-borne vibrations, are present in the anal cerci and other parts of the body, providing the cockroach with the ability to detect vibrations and sound waves. This distribution of sensory receptors throughout the body allows cockroaches to have a comprehensive awareness of their environment and respond appropriately to various stimuli.

• The entire body is covered by a hard chitinous exoskeleton.
• In each segment exoskeleton has hardened plates called sclerites which are joined together by a delicate and elastic articular membrane.
• The sclerites of the dorsal side are called tergites. Ventral side are called sternites lateral side are called pleurites.

The mouthparts of cockroaches are specialized for biting and chewing and are therefore classified as mandibulate or orthopterus type mouthparts. The mouthparts consist of several distinct components arranged around the mouth opening. The labrum serves as the upper lip and forms the anterior boundary of the mouth. A pair of mandibles are the primary chewing structures that move laterally to bite and process food. A pair of maxillae are located behind the mandibles and assist in food manipulation and sensory perception. The labium functions as the lower lip and forms the posterior boundary of the mouth. The hypopharynx, also called the tongue, is a median structure that aids in food movement and manipulation within the mouth cavity. Together, these mouthpart structures enable the cockroach to bite, chew, and consume a wide variety of food materials.

• The wide mouth opens into the buccal cavity.
• On the floor of the buccal cavity lies a large muscular sticky tongue.
• The tongue is attached in front and free behind.
• The free edge of the tongue is forked.
• A row of small and maxillary teeth is found on the inner region of the upper jaw.
• Vomerine teeth are present one on each side of the internal nosteils.

The blood of a frog consists of two main components: plasma and blood cells. Plasma comprises approximately 60 percent of the total blood volume and serves as the liquid medium in which blood cells are suspended. The remaining 40 percent consists of blood cells, which include three main types. Red blood cells, or erythrocytes, are the most abundant and contain hemoglobin for oxygen transport. White blood cells, or leukocytes, are present in smaller numbers and include several types with different functions. Neutrophils are the most abundant white blood cells and function in phagocytosis and defense against bacteria. Basophils are involved in inflammatory responses and release histamine. Eosinophils participate in immune responses against parasites and allergens. Lymphocytes are crucial for specific immune responses and antibody production. Monocytes are large phagocytic cells that engulf pathogens and cellular debris. Additionally, platelets, which are cell fragments, play an important role in blood clotting and hemostasis. This composition of frog blood is essential for oxygen transport, immune defense, and maintaining homeostasis.

• Earthworm has along and cylindrical body.
• It is 80-210 mm in length. It is light brown in colour.
• The body is encircled by a large number of grooves which divides it into a number of compartments called segments ormetameres.
• The mouth is found in the centre of the first segment of the body called the peristomium.
• Overhanging the mouth is a small flab called prostomium.
• The 14 – 17th segments become swollen called clitellum.
• There are pair of female genital opening in the 14th segment and pair of male genital opening in the 18th segment.
• In the segments 6/7, 7/8, 8/9 lies the spermatheca.
• In all the segments of the body except the first last and clitellum there is ring of chitinous body setae. They all involved in locomotion.
• The last segments bear anus.

1. The alimentary canal runs as a straight tube throughout the length of the body from the mouth to anus.
2. The mouth opens into the buccal cavity which occupies the 1st and 2nd segments.
3. The thick muscular pharynx lies in the 3rd and 4th segments and is surrounded by the pharyngeal glands.
4. A small narrow oesophagus lies in the 5th segment and the 6th segment contains muscular gizzards. Which helps in grinding the soil and decaying leaves.
5. The intestine starts from the 7th segment and ’ continues upto the last segment.
6. The dorsal wall of the intestine is folded into the vascular cavity called typhlosole.

In earthworm closed type of blood vascular system is seen which contains blood vessels, capillaries and lateral hearts.
* Two median longitudinal vessels run above and below the alimentary canal as dorsal and ventral vessels of the earthworm.
* There are paired valves in the dorsal vessels which prevent the backward flow of the blood.
* From 6 to 13 segments with the 8 pairs of commissural vessels which connects the dorsal and the ventral vessel called lateral hearts.
* The blood is pumped from the dorsal vessel to the ventral vessel.
The blood glands present in the anterior segments of the earthworm produce blood cells and haemoglobin and gives red colour to the blood.

The earthworm is a hermaphrodite organism the male and female reproductive organs are found in the same individual.
Male reproductive system:
* Two pairs of testes are present in the 10th and 11th segments. The testes give rise to the germ cellor spermatogonia.
* Two pairs of seminal funnels called ciliary rosettes are situated in the same segments as the testes. Three pairs of spermathecalies in the 7,8,9 segments.
* The vas deferens arise from the ciliary rosettes run upto the 18th segment and open exterior through the male genital aperture which contains two pairs of penial setae.
* A pair of prostate glands lie in the 18th and 19th segments.
* The secretion of the prostate cement the spermatozoa into a bundle of spermatophores.
Female reproductive system:
* A pair of ovaries lying in the 13th segment. Ovarian funnels are present beneath the ovaries continue as an oviduct and opens in the 14th segment as a female genital opening.
* There are three pairs of spermathecae lie in the 7th, 8th and 9th segment.
* They receive spermatozoa during copulation.
* The two earthworms mate juxtaposition opposite gonadal openings and exchanging sperms mature egg cells in the nutritive fluid are deposited in the cocoons produced by the glands cells of the citellum which also collects the partner’s sperm from the spermathecae.
* Fertilization and developments occurs in the cocoon.
* After 3 weeks baby earthworm are released.

• The earthworm normally crawls with the help of their body muscles setae and buccal chamber. The outer circular and inner longitudinal muscle layers lies below the epidermis of the body wall.
• The contraction of circular muscles make the body long and narrow while the longitudinal muscles make the body short and broad and hence due to the contraction of longitudinal muscle the earthworm moves.
• The alternate waves of extensions and contractions are aided by the leverage afforded by the buccal chamber and setae.

• A cockroach is a bilaterally symmetrical segmented animal which is divisible into head thorax and abdomen.
• The entire body is covered with a chitinous exoskeleton.
• Each segment consists of sclerites. The head is small and triangular and the mouthparts are directed downwards hence known as hypognathous. The head bears a pair of compound eye. Each compound eye is composed of unit of ommatidia.
• The mouthparts are of mandibulate type. It consists of labrum pair of mandibles a pair of maxillae labium and a tongue.
• The thorax consists of prothorax mesothorax and metathorax. Each thoracic segment bears a pair of walking legs.
• Due to the presence of 3 pairs of leg, they are called Hexapoda. Each leg consists of five segments they are coxa, trochanter femur tibia, and tarsus.
• It has two pairs of wings. It is called tegmina or elytra. The wings arise from the mesothorax protect the hind wings when at rest. The second pair of wings arise from metathorax and used inflight.

The alimentary canal is divided into three regions namely foregut midgut and hindgut.
Foregut:
* It includes pre-oral cavity mouth pharynx oesophagus and the posterior region contains crop.
* The food is stored in the crop. The crop is followed by gizzard which have chitinous teeth helps in the grinding of the food particles.
Midgut:
* At the junctional region of the gizzard are eight finger like tubular blind processes called the hepatic caecae or enteric caecae.
* At the junction of midgut and hind gut lies 100 – 150 yellow coloured malphigian tubules. It excretes the nitrogenous wastes from the haemolymph.
Hindgut:
* The hind gut is broader than the midgut.
* It consists of ileum colon andrectum. The rectum opens out through anus.
* Digestive glands
* Salivary glands
* Hepatic caeca

The circulatory system of cockroaches is an open type of circulatory system, which differs significantly from the closed circulatory system found in vertebrates. The coelom, or body cavity, is filled with a fluid called hemolymph that bathes all the internal organs directly. The heart is an elongated, muscular tube that lies mid-dorsally beneath the thorax and extends through multiple segments of the body. The heart consists of 13 chambers, and on either side of each chamber are small openings called ostia. Blood from the surrounding sinuses and body cavity enters the heart through these ostia. Once inside the heart, the hemolymph is pumped anteriorly toward the head region and then flows out into the sinuses and body cavity again, where it comes into direct contact with the organs and tissues. In each segment of the body, there are triangular muscles called alary muscles that are attached to the heart. These alary muscles contract and relax, assisting in the circulation of hemolymph throughout the body. Additionally, a pulsatile vesicle is present at the base of each antenna, which also functions to pump blood and assist in circulation. This open circulatory system, though less efficient than closed systems, is adequate for the metabolic needs of insects like cockroaches.

• The malphighian tubules are the main excretory organs of cockroach which help in eliminating the nitrogenous wastes from the body in the form of uric acid. Excretion is uricotelic.
• In addition fat body, nephrocytes cuticle and urecose glands are also excretory in function. The malpighian tubules are attached at the junction of midgut and hindgut. There are about 100-150 in number present in 6 – 9 bundles.
• Each tubule is lined by glandular and ciliated cells and the waste is excreted out through the hindgut.
• The glandular cells of malpighian tubules absorb water salts and nitrogenous wastes. The cells of the tubules reabsorb water and inorganic salts.
• By the contraction of the tubules nitrogenous waste is pushed in to the ileum. The remaining waste with solid uric acid is exceeded along with the faecal matter.

• The male reproductive system consists of a pair of testes vasa deferentia an ejaculatory duct utricular gland phallic gland and the external genitalia.
• A pair of 3 lobed testes lies on the 4th and 6th abdominal segments. The vas deferens opens into the male gonopore which lies ventral to anus.
• The mushroom-shaped gland is a large reproductive gland which opens into the anterior part of the ejaculatory duet.
• The sperms are stored in the seminal vesicles as bundles of spermatophores. Surrounding the male genital opening are few chitinous structures called phallometric or gonopophyses which help in copulation.

• The female reproductive system consists of a pair of ovaries vagina genital pouch collaterial glands speromthecae and the external genitalia.
• A pair of ovaries lie in the segmetn of 2nd and 6th abdominal segment. Each ovary is formed of eight ovarian tubules. Oviducts of each ovary unite into a common oviduct known as vagina which opens into the genital chamber.
• A pair of spermathecae is present in the 6th segment and opens in to the genital pouch.
• During copulation the ova descend to the genital chamber and fertilised by the sperm. The collateral gland secreta a hard case called ootheeca around the egg.
• The ootheca is dropped to a crack or crevice of high relative humidity near a food source. The nymphs are released from this ootheca and they grows by moulting about 13 times to reach the adult form.

The body of frog is streamlined to help in swimming. Body is divided into head and trunk.
Head:
* The head is triangular and has an apex which forms the snout.
* The mouth is at the anterior end on the head contains pair of external nostrils, pair of eyes with unmovable upper eyelid movable lower eye lid which protects the eye.
* The nictitating membrane protects the eye when the frog is underwater.
* A pair of ear drum lies behind the eyes. There is no external ear neck and tail.
Trunk:
* It bears a pair of fore limbs and a pair of hind limbs. The hind limbs are longer than the forelimbs. At the posterior end between the hind limbs is the cloacal aperture.
* Forelimbs help to bear the weight of the body. It consists of upper arm forearm and a hand. The hind limbs consist of thigh shank and foot.
* Foot bears five long webbed toes and one small spot called the sixth toe cloacal aperture.
* Forelimbs help to bear the weight of the body. It consists of upper arm forearm anda hand.
* The hind limbs consist of thigh shank and foot. Foot bears five long webbed toes and one small spot called the sixth toe.

In hymenopteran insects such as honeybees, ants and wasps, a mechanism of sex determination called haplodiploidy mechanism of sex determination is common. In this system, the sex of the offspring is determined by the number of sets of chromosomes it receives. Fertilized eggs develop into females (Queen or Worker) and unfertilized eggs develop into males (drones) by parthenogenesis. It means that the males have half the number of chromosomes (haploid) and the females have double the number (diploid), hence the name haplodiplody for this system of sex determination.
This mode of sex determination facilitates the evolution of sociality in which only one diploid female becomes a queen and lays the eggs for the colony. All other females which are diploid having developed from fertilized eggs help to raise the queen’s eggs and so contribute to the queen’s reproductive success and indirectly to their own, a phenomenon known as Kin Selection. The queen constructs their social environment by releasing a hormone that suppresses fertility of the workers.

• The heart consists of three-chamber. Two auricle and one ventricle. Heart is covered by pericardium. On the dorsal side of the heart is a triangular chamber called sinus venosus.
• Truncus arteriosus is a thick-walled structure which is obliquely placed on the ventral surface of the heart.
• It divides into right and left aortic trunk. Each divides into carotid systemic and pulmocutaneous arteries.
• The systemic trunk of each side is joined posteriorly to form the dorsal aorta. They supply blood to the posterior part of the body. The pulmo-cutaneous trunk supplies blood to lungs and skin.
• The sinus venosus receives the deoxygenated blood from the pre and post venacava and delivers the blood to the right auricle.
• The left auricle receives oxygenated blood through the pulmonary vein.

Eugenics refers to the study of the possibility of improving the qualities of the human population through various scientific and social methods. The methods of eugenics can be broadly categorized into preventive and positive approaches. Preventive methods include sex education in schools and public forums to promote awareness about reproductive health, promoting the use of contraception to prevent the birth of children with genetic disorders, compulsory sterilization for individuals with severe mental retardation and criminals to prevent the transmission of harmful traits, and prenatal diagnosis of genetic disorders followed by medical termination of pregnancy (MTP) to avoid the birth of affected children. Positive methods aim to improve the genetic quality by encouraging reproduction among healthy individuals through egg donation and sperm donation from healthy donors, and artificial insemination by donors to ensure healthy offspring. Advanced biotechnological methods include gene therapy which can correct defective genes at the molecular level, and cloning which can produce genetically identical individuals with desired traits. These methods collectively represent attempts to enhance the human gene pool and reduce the incidence of genetic diseases in the population, though they raise important ethical and social considerations.

• The nervous system is divided into the central nervous system, peripheral nervous system and the autonomous nervous system.
• Peripheral nervous system consists of 10 pairs of cranial nerves and 10 pairs of spinal nerves. The autonomous nervous system is divided into sympathetic and parasympathetic nervous system.
• CNS consists of brain and spinal cord. Brain is covered with pia mater and dura mater. The brain is divided into the forebrain mid-brain and hindbrain.
• Forebrain Consists of a pair of olfactory lobes and cerebral hemisphere and diencephalon. The olfactory lobes contain a small cavity called the olfactory ventricle.
• The midbrain includes two large optic lobes and has cavities called optic ventricles.
• Hindbrain consists of the cerebellum and medulla oblongata. The medulla oblongata passes out through the foramen magnum and continues as spinal cord.

• The earthworm normally crawl with the help of their body muscles setae and buccal chamber.
• The outer circular and inner longitudinal muscle layers lies below the epidermis of the body wall.
• The contraction of circular muscles make the body long and narrow while the longitudinal muscle make the body short and broad and hence due to the contraction of longitudinal muscle the earthworm moves.
• The alternate waves of extensions and contractions are aided by the leverage afforded by the buccal chamber and setae.

Lampito mauritii and Metaphire posthuma are two common earthworm species used in zoological studies, and they exhibit several distinct morphological differences. In terms of shape and size, Lampito mauritii is cylindrical measuring 80 mm to 210 mm in length with a width of 3.5 mm to 5.0 mm, while Metaphire posthuma is also cylindrical but smaller, ranging from 115 mm to 130 mm in length with a width of 5 mm. The colouration differs significantly, with Lampito mauritii being light brown and Metaphire posthuma being dark brown. Segmentation also varies between the two species, with Lampito mauritii having 165 to 190 segments and Metaphire posthuma having approximately 140 segments. The clitellum, which is the reproductive region, is located at the 14th to 17th segments in Lampito mauritii (spanning 4 segments) and at the 14th to 16th segments in Metaphire posthuma (spanning 3 segments). A notable difference is the presence of intestinal caeca, which are absent in Lampito mauritii but present in Metaphire posthuma at the 26th segment. Both species have their male genital pores located at the 18th segment and female genital pores at the 14th segment, showing similarity in this characteristic. These morphological differences are important for taxonomic identification and understanding the diversity within earthworm species.

Characters
Lampito mauritii
Metaphire posthuma
1. Sperma thecal opening
Three pairs 6/7, 7/8 and 8/9
Four pairs 5/6, 6/7, 7/8 and 8/9
2. Pharynx
3rd – 4th segment
Runs up to 4th Segment
3. Oesophagus
5th segment
8th segment
4. Gizzard
6th segment
8th – 9th segment
5. Intestine
7th segment to anus
15th segment to anus
6. Lateral hearts
8 pairs from 6 th to 13 th segments
3 pairs from 7 th to 9 th segments
7. Pharyngeal nephridia
5th _ 9th segment
4th – 6th segment
8. Micronephridia
14th to last segment
7th to last segment
9. Meganephridia
19th to last segment
15th to last segment

Male and female cockroaches display several distinct morphological and anatomical differences that allow for easy identification. The abdomen is long and narrow in males but short and broad in females. When examining the abdominal segments, males display nine visible segments while females show only seven visible segments. A characteristic feature unique to males is the presence of anal styles, which are completely absent in females. The terga, or dorsal plates, differ in their coverage pattern: in males, the 7th tergum covers the 8th tergum, whereas in females, the 7th tergum covers both the 8th and 9th terga. Females possess a brood pouch, an adaptation for carrying and protecting eggs, which is absent in males. The antennae also show sexual dimorphism, being longer in males compared to females. The wings extend beyond the tip of the abdomen in males, providing them with better flight capability, while in females the wings extend only up to the end of the abdomen. These differences reflect the distinct reproductive roles and behavioral patterns of male and female cockroaches in their life cycle and survival strategies.

Frogs and toads, though both amphibians, belong to different families and exhibit numerous morphological and physiological differences. Frogs belong to the family Ranidae while toads belong to the family Bufonidae. The body shape differs markedly, with frogs having a slender body structure suited for jumping and aquatic movement, whereas toads have a bulkier, more compact body. The legs of frogs are notably longer, facilitating their characteristic jumping locomotion, while toads have shorter legs adapted for walking and crawling. Webbed feet are present in frogs, enabling efficient swimming in aquatic environments, but are absent in toads. The skin texture and structure also differ significantly: frogs possess smooth and moist skin that aids in respiration and water absorption, while toads have dry skin covered with wart-like glands that secrete toxic substances for defense. Regarding dentition, frogs have both maxillary and vomerine teeth, whereas toads completely lack teeth. Additionally, their reproductive patterns differ in egg-laying behavior: frogs lay their eggs in clusters or masses, while toads lay their eggs in long strings. These differences reflect the distinct ecological niches and evolutionary adaptations of these two amphibian groups.