Detail study of Earthworm for class 11 NEB B

Detail study of Earthworm for grade XI NEB Board NEPAL

1. Pheretima posthuma Fig. Pheretima posthuma (Dorsal view) (Ventral view) Systematic position/ Classification Kingdom: Animalia Phylum: Annelida Class: Oligochaeta Genus: Pheretima Species: posthuma Common name: Earthworm

2. Habitat Pheretima posthuma (Earthworm ) is widely distributed animal found all over the world. It is abundantly found in top soil rich in humus. It is frequently found in gardens, lawns and agricultural fields.

3. Habit Burrowing It lives in burrows in damp soil. Their burrows are usually in the superficial layers of soil upto the depth of 12-18inches. However, during dry season they burrow deeper , sometimes upto six feet height. Nocturnal Earthworm is a nocturnal animal ie . They are active during the night time . Detritivores animal It is the common inhabitants of moist soil and feed upon dead and decaying organic matter. 5 marks 1 mark

4. Behavior It lacks well developed sense organs but possess simple receptors to receive various kinds of stimuli. Regeneration They shows a particular type of regeneration. It can regenerate its posterior end from the anterior end but its posterior end cannot regenerate its anterior end instead may develop its posterior end. Thus, the earthworm may die due to Starvation. Anterior end Posterior end

5. Reproduction It is hermaphrodite or bisexual i.e. both the male and female reproductive organs are present within the same individual. Self fertilization is impossible. Cross fertilization takes place between the two earthworm and development is direct. Locomotion Setae are locomotory organ of earthworm. Setae are present in each segment except 1st st , last and clitellum region.

6. External structures which are visible from outside is called external features or external morphology. The important external features are as follows: Shape :  Earthworm is elongated, long, narrow and cylindrical. The anterior end is tapering while the posterior end is more or less blunt type. Body surface :  Body consists of dorsal and ventral surfaces. Size :  A mature earthworm measures about 15cm in length and 3-5 mm in width. External Morphology of Earthworm 5 marks

7. Color of the body : Dark-brown (clay) in color due to the presence of porphyrin pigment which is found in dorsal surface of the body. Dorsal surface is relatively darker than ventral surface. Porphyrin protects the body from injurious effect of UV-rays. Respiratory pigment : Hemoglobin which is found in blood plasma that gives bright color of the blood. Segmentation :  Segmentation of the body is true i.e. external segmentation corresponds to internal segmentation. Hence, the segmentation of earthworm is called metamerically segmented . Body consists of about 100-120 segments. 1 mark

8. Symmetry:   Bilaterally symmetrical : A type of arrangement of the parts and organs of an animal in which the body can be divided exactly and equally into two halves that are mirror image of each other along one median plane only. Anterior end Earthworm lacks distinct head and sense organs. No eyes instead of eyes phasomes act as photoreceptor. It contains prostomium and peristomium .

9. Prostomium (Gr. Pro: before stoma: mouth) A fleshly lobe-like structure, which is present before the mouth. It helps in feeding mechanism. It is also the digging organ of the earthworm. Peristomium (Gr. Peri : around stoma: mouth) The first segment of the earthworm which is present around the mouth is called Peristomium . It is also called buccal segment which bears crescentic mouth. 1 mark

10. What is Cingulum ? Clitellum It is the prominent circular band of glandular tissue present after the 13 th segment of the earthworm. Female genital pore is present in the middle of 14 th segment ventrally. It covers the three segments ie . 14 th , 15 th  and 16 th  segment . S ignificance of Clitellum in Earthworm . Note: MAC It is highly glandular in nature as it contains various types of gland like: C ocoon forming gland- helps in cocoon formation M ucous secreting gland - secretes mucous A lbuminous gland – Albumen gives nourishment to the growing embryo and it also indicates the sexual maturity of the worm. 5 marks

11. Due to the presence of Clitellum , the body of earthworm is divided into three regions: Pre - Clitellar region- 1 st segment to 13 th segment Clitellar region- 14 th segment to 16 th segment Post - Clitellar region- 17 th segment to the last segment Why Clitellum is called Forest of Nephridia ? The number of integumentary nephridia is about 200-250 in each segment but in clitellum region the number increases by 10 th times ie . 2000-2500 in 14 th ,15 th and 16 th segment.

12. Setae Setae are locomotory organ of earthworm. T hey are yellowish , about 80-120 per segment in number. Setae are arranged in a ring around the body in the middle of the each segment. Such type of arrangement of setae is known as Perichaetine arrangement. Setae are made up of chitin . Setae are present in each segment except 1 st , last and C litellum region. 5 marks

13. It is about 0.26mm in length. It is slightly 's' shaped. It contain a curved neck, a swollen nodule and slightly curved root. The root remain inside the setal sac which is internally lined with germinal layer. The worn out setae are regenerated continuosly by the germinal layer of setal sac. Setae are provided with protractor and retractor muscles which helps in movement of setae. 5 marks Click to add text

14. There are many apertures present in earthworm which have their own functions. Some of them are given below: Mouth Anus Genital pore Genital papillae Nephridiopores   Spermathecal pore and Dorsal pores External Apertures/pores/openings of Earthworm

15. Mouth:   Mouth is the first opening of alimentary canal present in the first segment ( Peristomium ) of the body just below the prostomium . It is crescentic in shape. It is used for feeding. Anus:  Anus is the last opening of the alimentary canal present in the last segment (anal segment) through which undigested food pass out as worm casting.

16. Genital pore/opening :   Earthworm is bisexual or hermaphrodite so both male and female genital aperture are present in same individual. i ) Female genital aperture : A single medium female genital aperture is present in the 14 th  segment ventrally . Through this pore, female gamete (ova) are discharged.

17. ii) Male genital aperture:   A pair of male genital pores are present in the 18 th  segment latro -ventrally . Through these pores, male gametes (sperm) are discharged during copulation. Genital papillae or copulatory papillae:   Two-pairs of circular, small and conical genital papillae are found in the 17 th  and 19 th  segment latroventrally . They act as suckers and helps in holding the two worm during copulation. So, they are also called Copulatory papillae.

18. Nephridiopores   They are the openings of nephridia . Nephridia are the excretory organ of earthworm. Large number of very minute nephridiopores are found in all segments except first three segment. Metabolic waste products are released out through these pores. Clitellar region contains 2000-2500 nephridiophores while other contain 200-250. These pores are the apertures of integumentary nephridia .

19. Spermathecal pore Opening of spermathecae are called Spermathecal pore. Four pairs of spermathecal pores are found latroventrally and intersegmentally between the grooves of segment 5/6, 6/7, 7/8, 8/9 respectively. Spermathecae are present in 6 th ,7 th ,8 th ,9 th segment and these are called Sperm bag or sperm receptacle. They receive sperm from another earthworm during copulation and store sperm for cocoon formation.

20. Dorsal pores Minute dorsal pores are present one in each intersegmental groove in the mid-dorsal surface after the 12 th  segment (12/13 th  segment) to 2 nd  last segment. Coelomic fluid release out through these pores to kill-harmful bacteria, lubricates and keeps the skin moist for respiration. 1 mark

21. The process of breaking down of complex insoluble food materials into simple, soluble form with the help of enzymes is called digestion. The organs which are concerned with digestion are called digestive organs . These organs collectively form digestive system . Digestive system of earthworm consists of Alimentary canal and Digestive glands Alimentary Canal Alimentary canal is the food passing tube. It is long and straight. It extends from mouth to anus. Digestive System of Earthworm 8 marks

22. It consists of following parts : Mouth : 1 st segment Buccal Cavity : 1 st –mid 3 rd segment Pharynx : mid 3 rd – 4 th segment Oesophagus : 5 th -7 th segment Gizzard : 8 th - 9 th segment Stomach : 10 th – 14 th segment Intestine : 15 th up to last segment Anus : last segment

23. The alimentary canal is long tube, which starts from mouth and ends to anus. Mouth Mouth is the first opening of alimentary canal present in the first segment ( Peristomium ) of the body just below the prostomium . Mouth is small crescentic aperture. It helps in feeding. Buccal Cavity It is thin walled, short tube behind mouth, which extends from 1 st segment to mid 3 rd segment. It covers two and half segments. It helps to ingest food. It leads into Pharynx.

24. Pharynx : It is small, wide, thick-walled, muscular chamber , which extends from mid 3 rd to 4 th segment. It covers one and half segments. It is pear-shaped chamber. It is differentiated from the buccal chamber by a dorsal groove where the brain of an earthworm is present. Two chambers are found in pharynx. They are: dorsal chamber and ventral chamber. On inner dorsal side of the pharynx, there is salivary gland. Two lateral infolding are also present called shelves. The dorsal part of the pharynx has a pharyngeal bulb, which is made up of muscle fibre , connective tissues, blood vessels and salivary glands.

25. Salivary glands are unicellular and known as chromophil cells. Chromophil cells secrete saliva which contains proteolytic enzymes protease which converts protein to amino acids. Mucin is the other enzyme present, which makes the food soft. The pharyngeal wall is connected to the body wall through muscular strands which contract or dilate the pharyngeal lumen. It acts as a suction pump. Pharynx acts as sucking and pumping organ during feeding. Pharynx helps to pump the food inside the mouth. It leads into oesophagus . T.S. of Pharynx

26. Oesophagus : It is narrow, elongated, thin walled tube extends from 5 th segment up to 7 th segment . It covers 3 segments. It acts as food pipe. It has no glands. It passes food to the gizzard. Gizzard: It is oval, hard, thick walled, highly muscular organ, which extends from 8 th segment to 9 th segment . It covers two segment. It has an inner lining of the cuticle which makes it the hardest part of the alimentary canal. Internally, it is lined by chitinous cuticle which helps in mechanical digestion of food materials. It helps in the grinding of soil particles and decaying leaves. It acts as grinding machine in the earthworm. It leads into the Stomach.

27. Stomach: It is a narrow, thin walled tube, wider than oesophagus which extends from 10 th segment to 14 th segment . It covers 5 segments. It is a highly vascular and tubular structure. It is longitudinally internal folded and consist of various types of glands such as Calciferous gland Amylolytic gland and Proteolytic gland Three pairs of Calciferous glands are present in the 10-12segment, which produces carbonate of lime and helps in neutralising humic acid present in the humus. It secrets calcium containing fluid that neutralizes the acidity of ingested food. Amylolytic gland secretes amylase that help in digestion of carbohydrates. Proteolytic gland of the stomach secrete proteolytic enzymes which help in digestion of proteins. Stomach leads to the intestine.

28. Intestine: It is very long, wide tube, which extends from 15 th segment to anus . Internally intestine is highly folded and also consist of various types of glands. These foldings are called villi . These villi increase the effective area of absorption in the intestine. The intestine is divided into 3 parts: Pre- typhlosolar region Typhlosolar region Post- typhlosolar region

29. Pre- typhlosolar region:  Present from 15-26 segment. It contains villi but no typhlosole. . There is a short conical projection on the 26 th  segment, which is known as intestinal caeca. Intestinal caeca extend forwards upto 23 rd  segment and secrete amylase enzyme. Amylase helps in the digestion of carbohydrates. b. Typhlosolar region:  Present after the 26 th  segment, 27 th segment to the infront of last 23 rd or 25 th segment (above the anus.) Contains both villi and typhlosole. Typhlosole is the large internal median fold of the dorsal wall of the intestine forming a longitudinal ridge. Typhlosole increase the area of absorption in the intestine

30. c . Post- typhlosolar region:  It is the last 23 rd or 25 segments of intestine and also known as rectum. Intestinal villi and typhlosole are absent in this region. It stores fecal pellets and leads to the anus. Anus: Anus is a small round aperture present in the last segment. It is the last opening of the alimentary canal present in the last segment (anal segment) through which undigested food pass out as worm casting.  

31. What is Intestinal caecum ? In 26 th segment , two lateral finger like projections move forward upto 22 nd or 23 rd segment, which is called Intestinal caeca. It is highly glandular which secretes amylolytic enzymes (amylase) which help in digestion of carbohydrate. What is Typhlosole ? A median dorsal muscular fold projecting into the space of intestine in earthworm. It increases the absorptive area of the intestine. 5 marks

32. Typhlosole is the second part of the intestine that lies between 27 th segment to the infront of last 23 rd or 25 th segment (above the anus.) Due to the presence of Typhlosole , intestine of the earthworm is divided into three regions: Pre- typhlosolar region- 15 th segment to 26 th segment Typhlosolar region- 27 th segment to infront of last 23 rd or 25 th segment Post - typhlosolar region- last 23 rd or 25 th segment (Rectum of the Earthworm)

33. Digestive glands Pharyngeal glands Muscular, glandular, muscular mass on the roof of pharynx. The glandular cells are called chromophil cells which secrete mucus in the lumen of pharynx. Saliva contains mucus that helps in lubrication of food and proteolytic enzymes for proteins digestion. b. Gastric glands Secrete gastric fluid which contains proteolytic enzyme for protein digestion. Also contains calciferous glands which produce calcium and CO2. Calcium neutralizes the acidic nature of food in the stomach.

34. c. Intestinal glands Secrete intestinal fluid which contains proteolytic, amylolytic and lipolytic enzymes for digestion of proteins, carbohydrates and lipids. It also contains chitinase and cellulase enzymes for the digestion of chitin and cellulose respectively. d. Intestinal caeca They are small, tubular outgrowths arising from 26 th segment and extend backwards upto 22 nd and 23 rd segment. Are richly supplied with blood vessels and internally contain villi. They secrete a digestive fluid that contains amylolytic enzymes for the digestion of carbohydrates.

35. Physiology of digestion The mechanism of digestion includes following steps: Food and feeding mechanism(ingestion) Taking in of food into the buccal chamber through mouth is called ingestion. Earthworm is detritivores animal feeding upon dead and decaying organic substances. It directly feeds upon algae, mosses, seeds and seedlings. While feeding, the buccal chamber is everted out of the mouth and the soil containing dead and decaying substances is drawn into it by sucking action of pharynx. Thus, earthworm ingests large amount of soil for the sake of dead and decaying substances.

36. 2. Digestion: The process of conversion of complex organic matter into the simple forms by the action of enzymes. The ingested food in the conducting chamber of pharynx is acted upon by proteolytic enzymes secreted by pharyngeal mass- the partial digestion of proteins takes place. The food enters the gizzard where the mechanical digestion takes place by the grinding from the gizzard. Finely masticated food enters the stomach and chemical digestion takes place. The food is acted upon by proteolytic enzymes ( trypsin ), amylase secreted by amylolytic glands.

37. The calciferous glands secrete calcium containing fluid which neutralizes the acidic effect of stomach. The partially digested food enters the pre- typhlosolar region and get completely digested by the action of intestinal enzymes. The carbohydrates is digested into glucose by amylase, cellulose is digested into glucose by cellulose, proteins is converted into amino acids by trypsin and fats into fatty acids and glycerol by the action of lipase. Finally, the complete digestion occurs in the intestine.

38. 3 . Absorption The digested food enters into the surrounding coelomic fluid from the intestinal lumen through the simple epithelium. The absorption of food takes place by two methods. They are: passive and active absorption. Passive absorption (diffusion) Active absorption: The villi and typhlosole of pre and typhlosolar region absorbs the digested food. 4. Assimilation The process of distribution o f digested food to the cells and the tissues. The process is done by coelomic fluid and the blood. The digested food from the coelomic fluid and blood is transported to the cells and tissues of the body.

39. 5. Egestion The process of elimination of undigested food materials through anus. The post typhlosolar region helps in formation of fecal matters by the reabsorption of water from the undigested food (consolidation). The faecal matter is removed by the anus in the form of pellets called worm castings.

40. BODYWALL OF EARTHWORM The body wall of the earthworm covers the internal parts and also provides protection. Mucus protects the body wall from bacteria and other pathogens that lie on the body wall. Mucus also assists in respiration by keeping the skin moist. Body wall also serves as a receptor organ. The body wall consists of cuticle, epidermis, musculature and coelomic epithelium Cuticle:  Cuticle is non-cellular layer which covers entire body. Cuticle is made up of collagen and gelatin. Cuticle is produced by the underlying epidermis. It gives protection to all the inner body parts. 5 marks

41. b . Epidermis:   It is formed by a single layer of thick ectodermal epithelial cells. There are four types of cells in the epidermis. Glandular cells:  The glandular cells are of two types namely, mucus secreting cells and albumen secreting cells. Mucous cells are largest cells which are ovoid, rounded at the distal end and narrow at the proximal end. The distal end contains mucous granules whereas the proximal end contains cytoplasm and nucleus. Also mucous cells are more in number. On the other hand the albumin secreting cells are columnar and few in number. Secretory granules are uniformly distributed in these cells. The nucleus of these cells lies at the basal end.

42. ii. Supporting cells:  These cells are narrow and tall with an oval nucleus at the center. These cells are more in number than that of the gland cells. iii . Basal cells:  Basal cells are the smallest cells of all the cell types of the epidermis. The most important feature of these cells is that they are totipotent in nature. iv. Receptor cells:  Three types of receptor cells are present in the epidermis namely epidermal receptor cells, buccal receptor cells and photoreceptor cells. Receptor cells are sensory in function. These cells occur in groups with their outer ends giving out hair-like appearance.

43. c . Musculature:   Epidermis lies above the basement membrane. The basement membrane is a thin layer of connective tissue below which muscles are present. The muscles of the body wall are arranged in two layers namely outer circular muscle layer and the inner longitudinal muscle layer. The circular muscles are continuous and protractor muscles of setal sac are attached to this layer. The longitudinal muscles are arranged in bundles, alternating with the setal sacs. The contraction and relaxation of the circular and longitudinal muscles help in locomotion of the earthworm.

44. d . Coelomic epithelium:   The innermost layer of the body wall that covers the coelom. It forms the outer coelomic epithelium, which is a derivative of the mesoderm. The parietal layer forms the septa and the primordial germ cells. It contains single layered squamous epithelium so involved in protection.

45. Functions of Body wall Maintains body form due to its elasticity Protects against mechanical injuries Secretes mucous which helps in plastering the internal walls of the burrow, keeps the body surface slimy and kills harmful bacteria. Sensory epidermal cells serve for reception of external stimuli The body wall consists of setae which help in locomotion The musculature of the body wall helps in movement The body wall also helps in gaseous exchange being moist and vascular The cocoon forming glands of clitellum region secretes albumen which gives nutrition for the embryos which develop inside the cocoon.

46. COELOM OF EARTHWORM Coelom also known as perivisceral cavity is the space between the body wall and the alimentary canal. Coelom is filled with an alkaline fluid called as coelomic fluid. The coelom of earthworm is schizocoelom and it is divided into two compartments by the septa. The coelom of the first four segments is undivided. The first septum is thin and membranous. It lies between the fourth and fifth segments. The intersegmental septa present between 5-6, 6-7, 7-8, 8-9 and 10-11 segments are thick and muscular. No septum is present between the 9-10 segments. 5 marks

47. These septa are not horizontal but are oblique in disposition forming six cones with their apices directed backwards. These septa form complete partitions without perforations on them. The intersegmental septa of 11-12, 12-1 and 13-14 are transverse and non-perforated. The septum between 14-15 segments is typical as all the septa that follow it are characterized by the presence of minute oval or circular sphinctered pores. These pores are the characteristic of Pheretima posthuma . By closing the septal pores, the flow of coelomic fluid is stopped making a particular region turgid and stiff. This turgidity helps in locomotion. Hence, coelomic fluid is described as hydraulic skeleton. In the coelomic fluid four types of cells are present. They are: Amoebocytes /Phagocytes Mucocytes Circular nucleated cells Chloragogen cells

48. Phagocytes   Phagocytes are numerous and largest nucleated cells. They have several membranous folds on the surface. These are phagocytic in nature. They are produced by lymph glands which are situated on the dorsal blood vessel from 26th segment onwards till the last segment. Each of these glands arises from the complex folding of anterior face of the septum and consists of masses of phagocytes. b. Circular Nucleated Cells They are spherical cells with centrally placed nucleus responsible for the internal transport of various substances such as nutrients, respiratory gases and nitrogenous wastes. c. Mucocytes :  These are elongated cells with a nucleus at one side and expanded fan like process at the other end. These cells secrete mucus.

49. d. Chloragogen cells These are small cells and are numerous in number. They are intense yellow in color and so they are also called as yellow cells. They have characteristic vesicular bulging. These are specialized cells derived from the inner coelomic epithelium. They collect nitrogenous wastes from the coelomic fluid and from the blood supplied to the intestinal wall. They also take part in deamination of amino acids and synthesis of urea They are chief centers of glycogen synthesis and storage They play an important role in intermediary metabolism similar to cells of liver in higher animals. So these are functionally similar to liver cells of vertebrates. They help in excretion of nitrogenous waste materials.

50. Functions of coelomic fluid It keeps the body moist which facilitates respiration. It kills bacteria of the soil which comes on the body surface of the worm. It helps in removing the excretory wastes from the body. Helps in the transportation of materials from one part of body to other. Helps in destroying harmful bacteria, microorganisms and foreign materials. Helps in fixing the setae into the ground during locomotion. The luminosity produced by some earthworms is due to the coelomic fluid. It helps in the internal transport of various substances such as nutrients, respiratory gases and nitrogenous wastes.

51. Reproductive system The process of giving birth to young ones of their own kind for continuation of generation is called reproduction. The organs which are concerned with reproduction is called reproductive organs . These organs collectively form reproductive system . Earthworm is a hermaphrodite or bisexual or monoecious animal i.e both male and female reproductive organs are present in the same individual. But self-fertilization is impossible as testes and ovaries mature at different timings and the relative position of male and female genital openings. Therefore, cross fertilization takes place by copulation . 8 marks

52. Male reproductive system Testes sacs (10 th and 11 th seg ) Testes (10 th and 11 th seg ) Seminal vesicle (11 th and 12 th ) Vasa differentia (12 th to 18 th seg ) Prostate gland (16 th ,17 th to 21 st seg ) Accessory gland (17 th and 19 th seg )

53. Testes sacs : These are two fluid filled spaces on ventral surface. There are pairs of testes sacs present in the 10 th and 11 th segment . Testes sacs contain testes . Testes sac of 10 th segment is smaller . Testes : Testes are the male gonads . There are two pairs of testes present inside the testes sac first pair present in 10 th segment and the second pair present in the 11 th segment . Each testes contains at least 5-8 finger like peojections . Testes forms sperms (male gamete ) by the process of spermatogenesis Testes forms immature sperms.

54. Seminal vesicle : There are two pairs of seminal vesicle, first pair present in the 11 th segment and second pair in the 12 th segment . They are somewhat sperical or oval in shape . Testes sac of the 10 th segment communicate with the seminal vesicle of 11 th segment . Similarly testes sac of 11 th segment communicate with the seminal vesicle of 12 th segment . Immature sperms enter the seminal vesicles through seminal funnel for maturation. After maturation, mature sperm returns to their own testes sac . Then, they pass mature sperm through the vasa deferentia . 5 marks

55. Vasa deferentia These are the ducts for passing sperms . So, they are also called spermatic ducts . They are elongated narrow ciliated thread like tubular structure which extends from 12 th to 18 th segment. They are found in two pairs and each pair lie on either side of alimentary canal. They extends from 12 th to 18 th segment. In 18 th segment they join together with a thick prostatic duct and forms common prostatic and spermatic duct . They collect sperm from spermatic funnel and give to prostate gland.

56. Prostate gland There are a pair of large, white, flat, solid, irregular shaped and lobulated gland, extending from 16 th or 17 th segment to 21 st segment . From each prostate gland emerges a short, thick curved prostatic duct in 18 th segment. The prostatic duct joins the two vasa deferentia of its own side unite to form a common prostatic and spermatic duct. Prostatic duct opens separately through a male genital aperture on the ventral side of 18 th segment. Function It produce prostatic fluid which is alkaline in nature. It activates sperms and also it keeps sperm motile.

57. Accessory glands These are two pair of whitish, spherical structures found in the 17 th and 19 th segment. They open to the exterior by a number of ducts on two pair of, situated in 17 th and 19 th segment. The secretion of these gland pass out through genital papillae It helps in holding two worms during copulation( Adhesion ) Male genital pore It is found in one pair located in 18 th segment latroventrally . Function Through these pores, male gametes (sperm) are discharged during copulation.

58. Female reproductive organ Ovaries Ovaries are female gonads . A pair of small, whitish and lobulated ovaries located in the 13 th segment . Each ovary consists of a number of filaments which have beaded like appearance . Each ovary consists of several finger like processes in which ova are arranged in various stage of development. The process of formation of ova from the ovary is called oogenesis . The mature ova lies in the tip of the ovary and detaches. Function: They form ova .

59. Spermathecae There are 4 pairs in each of 6 th , 7 th , 8 th , 9 th segment situated ventro laterally. Each spermatheca is flask shaped consisting pear-shaped ampulla , short narrow neck and a short narrow elongated diverticulum . Spermathecae open outside through 4 pairs of spermathecal pores, situated in the grooves between 5/6, 6/7, 7/8, 8/9 th segment ventrolaterally . Spermathecae are also called Sperm bag or sperm receptacle as they store spermatozoa from another worm during copulation. Function: They receive sperm from another earthworm during copulation and store sperm for cocoon formation. Female genital pore It is a single, unpaired, small pore It lies in 14 th segment ventrally . Through this pore, female gamete (ova) are discharged .

60. Cocoon formation Cocoon is a barrel shaped protective egg case secreted by clitellum around 14 th , 15 th and 16 th segment. Cocoon is yellowish in color. The cocoon formation takes place after copulation, when ovaries mature ,with the help of clitellum . The clitellar region (14th, 15th 16th) is highly glandular in nature as it contains various types of gland like: Cocoon forming gland- helps in cocoon formation secrete wall of cocoon. Also secrete a gelatinous viscid and sticky substance which form a membrane girdle. Mucous secreting gland - secretes mucous Albuminous gland - produce albumen; serves for nourishment of the growing embryo, which is deposited between the girdle and body wall. 5 marks

61. The girdle soon harden on exposure to the air, into a tough but elastic tube which is called cocoon or egg capsule. Then the worm starts to wriggle behind so that the girdle slipped forward. As the girdle pass over the female genital pore, it receives ova and when it passes over spermathecal , it receives sperm through spermathecal pores. Finally, the girdle is thrown off from the anterior end and soon the elasticity of its wall closes up two ends to form a cocoon or ootheca . Several cocoon are formed after each copulation because the spermatozoa in spermathecae do not pass out all at one time. The cocoon are barrel shaped, light yellow in color and measuring about 2-2.5µm in length and 2.5-2µm in diameter.

62. Nervous system The group of organs which are responsible for receiving and conducting nerve impulses forms Nervous System. The nervous system can be studied under three main headings: (a) Central nervous system (b) Peripheral nervous system and (c) Sympathetic nervous system Fig: Nervous system of Earthworm

63. Central Nervous System Central nervous system lies along the mid-line of the body. It consists of 2 parts: Nerve ring and Ventral nerve cord. 1. Nerve ring It is ring like spherical structure which lies around the pharynx in 3 rd  and 4 th  segment. Nerve ring has 3 parts: i . Supra-pharyngeal ganglia (Brain) ii. Circum-pharyngeal connectives iii. Sub-pharyngeal ganglia A pair of brain, a pair of circum-pharyngeal connectives and sub-pharyngeal ganglia which collectively form a ring like structure in the nervous system of the earthworm called nerve ring.   1 mark

64. i . Supra-pharyngeal ganglia Also called cerebral ganglia They are bi-lobed in structure A pair of whitish pear-shaped supra pharyngeal ganglia fused to form brain. Lies dorsally in the 3 rd  segment in the depression between the buccal cavity and pharynx . ii. Circum-pharyngeal connectives/ Peri -pharyngeal connectives From either side of supra-pharyngeal ganglia, a pair of thick, short band circum-pharyngeal connectives arise which enclose the pharynx. It is outer bulging part which extends from 3 rd  to 4 th  segment.. Fig: Nervous system of Earthworm

65. iii. Sub-pharyngeal ganglia Found in lower region of nerve ring which lies in 4 th  segment . Circum-pharyngeal ganglia meet with a pair of sub-pharyngeal ganglia. Thus a complete nerve ring is formed around the pharynx.  2. Ventral nerve cord It is long thread like double layered structure, which arises from the posterior part of sub-pharyngeal ganglia and runs the posteriorly upto the last segment of the body. Extends from 5 th  to last segment . It has swelling bulb like structure in each segment called segmental ganglion . Fig: Nervous system of Earthworm

66. Peripheral Nervous System Those nerve which arise from different parts of central nervous system are called peripheral nervous system. Following pairs of nerve arise from brain: 8 to 10 pairs of nerve arise from brain which communicates or innervate or supply to prostomium , buccal cavity and pharynx. 2 pairs of nerve arise from circum-pharyngeal connectives which supply to the wall of prostomium and peristomium segment. 3 pairs of nerves arise from sub-pharyngeal ganglia which supply to the 2 nd , 3 rd  and 4 th  segment. 3 pairs of nerves arise from each segmental ganglion which supply to the various parts of segment, gut wall, body wall and other internal organ.

67. Sympathetic Nervous System   Sensory and motor nerve fuse to form nerve plexuses which moves ventrally through alimentary canal. It is situated below the skin (body wall) and on the alimentary canal . These plexuses are connected with the circum -pharyngeal connectives. It controls the visceral organs ( heart and alimentary canal). So, this system is also called Visceral Nervous system

68. Excretory System The process of elimination or removal of metabolic waste products including nitrogenous material like ammonia, urea, uric acid, amino acid, etc. from the body of earthworm is called Excretion. The annelid excretory system is made up of long tubular organs called Nephridia ( micronephridia or meronephridia ) Nephridia is of three types: Septal nephridia Pharyngeal nephridia Integumentary nephridia 1 mark 8 marks

69. Septal Nephridia or Typical Nephridia They are well developed and the largest nephridia which are found attached from 15/16 th intersegment to the last segment. Each septum has 40-50 septal nephridia and they are arranged in two rows. So, each septum has 80-100 septal nephridia. It consists of 3 main part : Nephridiostome:   Body Terminal duct Nephridiostome:   It is also called  Nephrostome . It is funnel shaped and externally ciliated, opening into the coelomic cavity. It consists of mouth like opening, which is surrounded by larger upper lip and smaller lower lip.

70. b. Body It is the main tubular part of the nephridia which is coiled around at its axis. It consists of two parts: 1. Short straight lobe- It is one half of the twisted loop. It is short, straight tube which remains attached to the twisted loop. 2. Long twisted loop with narrow apical lobe.- The twisted loop consists of proximal and distal limb, which are spirally twisted upon each other. The number of twist varies from 9-13 loops. c. Terminal duct It is the end part of the main body. It collect the excretory products and transfer them to a pair of supra-intestinal excretory duct. . 3 marks

71. Function of septal nephridia: Septal nephridia discharge the waste products through canal and ducts into the lumen of the intestine and finally through anus. So, they are enteronephric nephridia . 2. Pharyngeal nephridia They are found as paired and lie one pair in each of the 4th, 5th and 6th segment . They are similar to septal nehridia in structure but they lack nephrostome . They have 3 pair of nephridial canal/duct. The duct arise from 6 th  segment which opens into buccal cavity in 2 nd  segment, The ducts of 4 th  and 5 th  segment opens into the pharynx in 4 th  segment.

72. Function of Pharyngeal nephridia They discharge the waste products directly into the buccal cavity and pharynx from where these are passed outside with undigested food through the anus. So, they are called enteronephric nephridia .

73. 3. Integumentary Nephridia They are attached to the inner side of the body wall from 7 th  to last segment. They are smaller than septal nephridia. Each nephridium is V-shaped with short straight lobe and twisted loop without nephridiostome or funnel. The number of integumentary nephridia ranges from 200-250 in each segment but in clitellar region, their number is about 2000-2500. So clitellum is called forest of nephridia. Their terminal nephridial ducts are also very short which open on the outer surface of the body wall by nephridiopores . Function of Integumentary nephridia : They discharge the waste products directly into the exterior through individual openings called nephridiopores . So, they are called exonephric nephridia.

74. [phone] [email protected] Sudhir singh