Earthworm, Chapter Notes, Class 11, Biology PDF Download

HISTORY

(i) The word Pheretima was at first used by Kinberg is 1867.
(ii) At first Indian earthworm was completely described by prof. Karm Narayan Bhal.
(iii) Complete details of Indian earthworm was published in "The Indian zoological memoirs on IndianAnimal type".

2. CLASSIFICATION

Phylum   -      Annelida
                      Metamerically segmented &
                      usually elongated worm like.

Class    -      Oligochaeta
                    Segmentation distinct. No
                    parapodia. Head not distinct.
                    Mainly terrestrial earthworm.

Genus   -      Pheretima
                     Female genital pore single
                     while male one pair. Clitellar
                      segments 14, 15 & 16.

Species -           posthuma

Other species of earthworm are as follows-

(i) Megascolex - Found in South India.
(ii) Dravida - Found in South India.
(iii) Eutyphaeus - Found in North India
(iv) Lumbricus - Found in Europe. Most common species of earthworm.

3. HABITS AND HABITAT

(i) Earthworms are cosmopolitan in distribution.
(ii) They are found in moist soil.
(iii) According to Darwin one acre of land may contain 50,00 earthworms.
(iv) They are found 2 to 10 feet deep in the soil, so they are called Earthworm.
(v) They are nocturnal.
(vi) Their breeding season is from July to October.

4. EXTERNAL STRUCTURE

(i) It has a long, cylendrical, narrow, bilaterally symmetrical body, well adapted for burrowing. Length of
the body is 15 to 20 cm and diameter is 3 to 5mm.
(ii) The worm is brown or clay coloured due to the presence of porphyrin.
(iii) Dorsal surface is darker then ventral and carries a dark mid dorsal line due to dorsal blood vessels.
(iv) Body is metamerically segmented.
(v) The number of segments are 100 to 120 are called metameres or somites.
(vi) Earthworm has no distinct head and no conpicuous sense organ head appendages also lacks.
(vii) First segment of the body is called peristomium or buccal segment which bears mouth.

(viii)Fleshy lobefold overhanging the mouth is called prostomium.
(ix) Last segment called pygidium. The last segment of body is also known as anal segment as it
carries terminal anus.
(x) 14th, 15th and 16th segment modify to form band like glandular structure called clitellum. Clitellum
secretes mucous, albumin and form egg case or cocoon for eggs.
(xi) It divides the body into 3 parts-

(a) Pre-clitellar region
- Includes 1 to 13 segments.

(b) Clitellum region
- Includes 14 to 16 segments.

(c) Post clitellar region
- Includes 17 to last segments.

(i) In the middle of each segment a ring of tiny ciliated bristles called setae are present. They are made
up of chitin.

(ii) A setae measures 0.26 mm in length to 0.03 mm in width.

(iii) A setae is fiant yellow coloured S-shaped with a swollen middle part.

(iv) Its one third part projects above the surface of skin termed as neck, the embeded two third part is termed as base.

(v) Setae is locomotory structure.

(vi) The arrangment of setae in a ring in each segment is know as perichaetine arrangment.

(vii) Each segments possess 80 to 120 Setae.

(viii)There are no setae in the first and last segments and in the clitellum of a mature worm.

External Apertures

Mouth
(i) It is a terminal aperture located in the first segment peristomium.
(ii) Dorsally mouth is covered by prostomium like a hood.

AnusI
t is a small vertical slit present in the last segment.

Dorsal pores

Dorsal pores are present in the intersegmental groove starting from 12/13 upto last but one segment.
Coelomic fluid comes out of these pores to moisten the skin

Nephridiopores

(i) Except first 6 segment each of the body carries 200-250 nephridipores, which open out as minute
opening.
(ii) Cilitellar segment carries 2000 nephridiopores.

Spermathecal pores
Spermathecal pore are present in the intersegmental groove of 5/6, 6/7, 7/8 and 8/9 (4 pairs).

Female genital pore
Located on the mid ventral side of 14th segment.

Male genital pores
A pair of male genital apertures is located on the ventral side of the 18th segment.

Genital papillae
(i) They are also called copulatory papillae.
(ii) One pair of these papillae opens through apertures on latero-ventral sides on 17th segment. and the other pair on 19th segment.

Arrangment of selae. A - Perichaetine, B - Lumbricine

Body Wall

The bodywall of earthworm consists of the following four layers.

Cuticle

(i) Cuticle is the outermost layer, thin semi transparent composed of irregularly arranged collagen fibre.
(ii) It is a protective layer.
Epidermis(hypodermis)
Epidermis is composed of columnar epithelium lying on a basement membrane.

Four types of cells are found in epidermis-

(A) Supporting cells
(B) Gland cells
(C) Basal cells
(D) Sensory cells
(A) Supporting cells

These cells are maximum in number in epidermis. There are long columnar cells.

(B) Gland cells

In between supporting cells, gland cells are found. Two types of gland cells are found muscous cells and Albumen cells.

(a) Mucous cells
(i) Large in number.

(ii) They secrete mucous on the body surface which keeps body surface moist and slippery.

(b) Albumen cells
(i) Few in number
(ii) There cells secrete Albumen.

(c) Basal cells
(i) They replaces supporting and glandular cells so, also called repalcement cells.

(d) Sensory cells
(i) Found in group.
(ii) They possess numerous sensory hair which receive impulses from environment.

Muscular layer

(a) Circular muscular layer
Prophyrin pigment is found within circular muscular layer.

(b) Longitudinal muscle layer
(i) They are found below circular muscular layer.
(ii) Due to its contraction earthworm becomes short and thick.

Coelomic epithelium
They are lowermost layer of the body wall of earthworm.

Functions of body wall

(i) It maintains the shape of the body.
(ii) It protects the body from mechanical injuries.
(iii) Mucous secreted by gland cells of the body wall provides protection from harmful germs and also helps in plastering the burrows.
(iv) Sensory cells of the body wall receive external stimuli.

5. COELOM

(i) The earthworm is eucoelomate (schizocoelom)
(ii) The coelom is filled with a alkaline whitish fluid, called coelomic fluid.
(iii) It consists of water, salts, proteins and following four types of cells

Granulocyte

(i) Most numerous cells.
(ii) They are phagocytic, engulf harmful micro-organisms.

Leucocytes
They are round nucleated cells, which form about 10% of all coelomic cells.

Mucocytes
These are elongated feather like cells.

Chloragogen cells

(i) They are small star shaped yellow cells, each with several finger like projection.
(ii) The cells store excretory wastes and when fully packed with such material leave coelom through dorsal pores with coelomic fluid.

Functions of Coelomic Fluid

(i) It keeps the body wall moist by continuously passing out through dorsal pores to facilitate respiration.
(ii) Protects body surface from bacteria.
(iii) Coelomic fluid distributes digested food.
(iv) It helps in the removal of some excretory wastes through chloragogen cells.
(v) It acts as a hydrostatic skeleton.


6. SEPTA

(i) The earthworm is metamerically segmented i.e. divided into segments externally by grooves and internally by transverse partitions, called septa.
(ii) Septa are perforated. The apertures are sphinctered.
(iii) The septa are absent in first four segments.
(iv) The first septum is thin and membranous and present between 4th and 5th segments.
(v) The septa between segments 5/6, 6/7, 7/8, 8/9 and 10/11 are thick muscular and cone like which run obliquely backwards.
(vi) There is no septum between segments 9 and 10.
(vii) Septa without perforations exist between 11/12, 12/13 and 13/14.
(viii) Each septum bears about 100 sphinctered pores, through which coelomic fluid flows freely from one segment to another.

7. LOCOMOTION

(i) It takes place by contraction and relaxation of the circular and longitudinal muscles of the body wall aided by setae.
(ii) At a time 9 segments contract in Pheretima.
(iii) Speed of earthworm is 25cm/minute.

8. DIGESTIVE SYSTEM

Alimentary Canal
It is a long straight tube of varying diameter which runs through entire length of body beginning from mouth to anus.
It consists of following regions-

Mouth
(i) It is a aperture located in the peristomium.
(ii) The mouth is dorsally connected over by a small fleshy projection, called prostomium.

Buccal cavity
(i) The mouth opens into a short thin walled protrusible buccal cavity lined with cuticle.
(ii) It extends from the first to the middle of 3rd segment.
Diagram to illustrate locomotion in an earthworm

Pharynx
(i) The buccal cavity leads into a wide pear shaped pharynx.
(ii) It is located in the 4th segment.
(iii) The pharyngeal cavity is divided into a dorsal salivary chamber and a ventral conducting chamber due to the presence of horizontal shelves.
(iv) Above the dorsal salivary chamber lies a muscular, glandular and vascular pharyngeal mass or bulb that contains saliva secreting gland cells or chromophill cells.
(vi) These cells produce proteolytic enzymes.
(vii) The dorsal chamber is lined with ciliated cells.

Oesophagus

(i) The pharynx leads into a short thin walled narrow duct called oesophagus.
(ii) It lies between 5th to 7th segments.

Gizzard

(i) The oesophagus opens into an oval, hard, muscular, thick walled muscular organ, called gizzard which
lies in the 8th segment.
(ii) It grinds the food into fine particle.
(iii) Internally it is lined by a thick cuticle which is covered by thick circular muscle layer. 

Stomach

(i) It is a short tubular structure which extends from the 9th to 14th segment.
(ii) Its wall is glandular and internally produced into transverse folds.
(iii) In some species (eg. Lumbricus) calciferous glands are present in stomach which secrete calcium carbonate in suspension.
(iv) This neutralizes the acidic calcium present in the food and converts it into calcite.
Intestine
(i) The Stomach opens into a long, wide and thin walled tube, the intestine, which extends from the
15th to the last segment.
(ii) A portion of intestine internally bears a long fold of epithelium which hangs from mid dorsal side into the lumen. This villus like fold is called typhlosole.
(iii) It increases the absorptive surface of intestine.
(iv) Due to the presence of typhlosole, the intestine can be differentiated into the following three regions:

(A) Pre-typhlosolar region

(i) It extends from 15th to 25th segments.
(ii) Its internal lining is much folded and highly vascular.
(iii) In the 26th segment it gives off two short conical outgrowths the intestinal caecum, one on either side.
(iv) The intestinal caecae extend from 26th segment to 22nd body segment.

(B) Typhlosolar region

(i) The region is marked by the presence of a long fold of internal epithelium the typhlosole which hangs into lumens from mid-dorsal line.
(ii) This region consists of 50 to 70 segments beginning from 26th body segment.
(iii) The typhlosole is absent in about last 25 segments.
(iv) The typhlosole increases absorptive surface area of the intestine.

(C) Post typhlosolar region

(i) This region is also called rectum and it lies in the last 23 to 25 segments.
(ii) The rectum opens to the exterior on the last segment by a small aperture called anus.

Food and lngestion

(i) Earthworm is omnivorous.
(ii) The food of earthworm consists of soil rich in humus (dead leaves and remains of arthropods), small worms etc.
(iii) During ingestion the buccal cavity is protruded and by the contraction of muscular strands (dilatory muscles) the pharyngeal cavity is enlarged to such the food particles.

Digestion

(i) In pharynx the food is mixed with saliva secreted by glandular cells of pharyngeal bulb.
(ii) Saliva contains mucin and proteolytic enzymes.
(iii) Within gizzard food is grinded into fine powder.From gizzard the food reaches into stomach.
(iv) The gland cells of stomach secrete proteolytic enzymes which convert proteins and small peptides into amino acids.
(v) In the intestine the food is digested almost completely by the enzyme present in the juice secreted by the gland cells namely pepsin, trypsin, amylase, lipase, cellulose, invertase. Intestine is the principle site of digetion and absorption.
(vi) The digestion is completely extracellular.
(vii) Excreta is finally egested food out in the form of round balls or pellets called worm castings; while
those of Eutyphaeus make a large and tower-like heap.

9. EXCRETORY SYSTEM

Excretion is effected by numerous small microscopic, segmentally arranged, coiled tubules called nephridia.

According to their position, nephridia are of three types :
Septal nephridia
(i) It starts from the 15th segment.
(ii) It is found attached to both the faces of inter segmental septa behind 15th segment. After 15 segment
each segment possess septal nephridia 80 to 100.
(iii) A septal nephridium consists of four regions.

nephridial system in relation to the intestine.
Nephrostome or ciliated funnel
It is round, ciliated funnel having a slit-like opening by which it communicates with coelom.

Neck
The nephrostome leads into a short narrow, ciliated neck which is bent upon itself.

Body
(i) The neck opens into the main body of nephridium.
(ii) It is formed of a short straight lobe and long spirally twisted loop with a narrow apical part.
(iii) The loop can be distinguished into proximal limb and a distal limb both of which are spirally twisted around each other.
(iv) The distal limb is connected with straight lobe whereas the proximal limb joins with neck.

Terminal duct

(i) The proximal limb of the main body continues as a small terminal duct.
(ii) The nephridium bears four ciliated tracts i.e. one in the neck, two in the body and one in terminal duct.
(iii) Finally it passes through the terminal duct as a single tubule.
(iv) There are two rows of septal nephridia on the anterior face and two rows on the posterior face of each septum. Each row contains 20-25 nephridia.
(v) Terminal ducts of septal nephridia of each segment open into a pair of septal excretory canals which run inwards and open into a pair of supraintestinal excretory ducts lying mid-dorsally above the intestine.
(vi) Supra-intestinal excretory ducts extend from the 15th segment to the last segment of the body.
(vii) Each of ducts opens into intestine by a narrow ductule in each segment.

Pharyngeal nephridia

(i) The structure of pharyngeal nephridia is like the septal nephridia except that they have no nephrostomes.
(ii) They are found as three pairs of tufts in 4th, 5th and 6th segments.
(iii) Each tuft is located on either side of the alimentary canal.
(iv) The terminal ducts of nephridia of each tuft in a segment fuse to form a pharyngeal nephridia duct. common thick walled
(v) Tcahvei tyd.ucts of 4th and 5th segments open into the pharynx and those of 6th segment open into the buccal
(vi) Tnehpeyh raidlsioa dliiksec hsaerpgtea lt hneeirp herxidcriae.tory products into alimentary canal & hence they are Enteronephric

Integumentary nephridia

(i) They are only half the size of septal nephridia.
(ii) They have no ciliated funnels.
(iii) nTehep htreirdmioinpaol red.uct of each nephridium opens to the outside directly by a narrow aperture called
(iv) Since they open directly to the outside, they are called exo-nephric nephridia.
(v) TIsht eayn adr e2 nirdr esgeuglamrleyn atstt.ached to the inner face of the body wall or integument of each segment except
(vi) Itne ne aticmhe sse mgmoreen ti .eth. efirro nmu m20b0e0r rtaon g2e5s0 0fr ofomrm 2i0n0g ttoh e2 5s0o bcuatl leind cfloiterellasrt soefg nmeepnhtsri dthiae.ir number is about

Physiology of excretion

(i) The glandular cells of nephridia extract nitrogenous wastes and excess of water from the blood.
(ii) The nephridia are highly vascular.
(iii) lTuhmee rne mbyo vseedp teaxl carnedto rpyh waraysntgees aal rnee tphhroriwdnia o. utside the body by integumentary nephridia but into the gut
(iv) The earthworm is ureotelic.

10. CIRCULATORY SYSTEM

(i) In Earthworm circulatory system is closed type and include blood, blood vessel and heart.
(ii) lTehuec obcloyoteds e. arthworm is composed of plasma and tiny, colourless, nucleated corpuscles, which act as
(iii) The respiratory pigment erythrocruorin or haemoglobin remain dissolved in plasma.
(iv) Blood vascular system is different in first 13 segment related to number, arrangement blood vessel. and nature of

The main longitudinal vessels are :

(a) Dorsal blood vessel (b) Ventral blood vessel
(c) Lateral oesophageal vessels (paired) (d) Subneural vessel
(e) Supraoesophagel vessel (smallest)
(v) Prominent transverse vessel in first 13 segments are :

Lateral hearts (segments 7 and 9)
Anterior loops (segment 10 and 11)
Lateral oesophageal hearts (segments 12 and 13)

(vi) Dorsal blood vessel is considered true heart in earthworms.
(vii) Dorsal blood vessel extends from 1st to 13th segment as a distributing duct.
(viii) Dcoomrsmal ubslosoudra sle vgemsseenlt.s 14 onwards collects blood from dorso-intestinals and from subneurals through
(ix) Blood flows in dorsal vessel from posterior to anterior direction.
(x) Ventral vessel exists below the alimentary canal, blood flow from anterior to posterior direction.
(xi) oVregnatrna. l Avfetessr e1l 3g isveeg rmisee ntto ipt asierendd s i nptaeigreudm evnetnatrryo -vinetsessetilns ainl veeascshe slse ginm eeanct hto s seugpmpelyn bt ltooo din ttoe ssteingaml ewnatlal.l
(xii) Lcaantearla. lA ofteesro 1p3h asgeegaml evnets stheel ya ruen pitea irteod f olormca tae ds iinng tlhee ssuebgnmeeunrtasl 1v etsos 1e3l. on both sides of alimentary
(xiii) Subneural vessel extends from 14th segment up to last segment, below the ventral nerve cord.
(xiv) vLeastesreall thoe vaerntst ra- lT vheesys ealr.e one pair in 7th and one pair in 9th segment, they send blood from dorsal

(xv) Lateral oesophageal hearts - They are one pair in 12th and one pair in 13 segment, they send blood from supraoesophageal and dorsal vessel to ventral vessel.
(xvi) Anterior loops - Anterior loops are single paired found in 10th segment and one paired in 11th segment.
They send blood from lateral oesophageal vessel to supraoesophageal vessel.

Blood glands

(i) Blood glands are found in the segments 4, 5 and 6th.
(ii) Blood glands are red coloured bunchy structure.
(iii) They manufacture haemoglobin and blood corpuscles.

Lymph glands

(i) Lymph glands are present on both sides of dorsal blood vessel from 26th segment to last (one pair
per segment, small and whitish).
(ii) Lymph glands produces phagocytic cells.

11. SENSE ORGANS

Epidermal receptor
(i) Distributed all over the epidermis more abundant on lateral sides.
(ii) They are tactile in function and also respond to chemical stimuli as well as vibration of earth.

Buccal Receptors

(i) Confined to the epithelium of buccal chamber.
(ii) They are gustatory and olfactory (related to taste and smell) and also respond to chemical stimuli
(chemoreceptor).

Photo Receptors

(i) Restricted only to the dorsal surface and numerous on prostomium, reduce gradually on posterior side,
absent on clitellum.
(ii) Each consists of an ovoid cell with a nucleus clear cytoplasm, network of neurofibullae and a 'L' shaped
lens or optic organelle (Phaosome)
(iii) They enable the worm to judge the intensity of light and its direction.

12. NERVOUS SYSTEM

The nervous system is divided into-

Central nervous system
It comprises of the following parts-

Cerebral ganglia (Suprapharyngeal ganglia)

(i) There are two cerebral ganglia that fuse to form a single mass called "brain".
(ii) It lies dorsally in the groove between buccal cavity and pharynx in the third segment.

Sub-pharyngeal ganglia
A pair of these ganglia fuse to form a single mass lying beneath the pharynx in the fourth segment.
A pair of circum or peripharyngeal connectives

(i) They arise the sides of cerebral ganglia and run backwards and downwards surrounding the pharynx
and meet laterally with sub-pharyngeal ganglia.
(ii) The cerebral ganglia peripharyngeal connectives and sub-pharyngeal ganglia thus form a complete nerve ring around the pharynx.

Double ventral ganglionic nerve cord

(i) It is a long double cord like structure that arise from sub-pharyngeal ganglia and extend backward along the mid-ventral line beneath the alimentary canal upto posterior and of the body.
(ii) In each segment it bears paired ganglia.

Peripheral nervous System

(i) It consists of nerves that arise from the central nervous system and innervate various parts of body,
constitute PNS.
(ii) Each cerebral ganglion gives off laterally 8-10 nerves which innervate the prostomium and buccal cavity.
(iii) Nerves from sub-pharyngeal ganglia supply the structures in 2nd to 4th segments.
(iv) From each segmental ganglia three pairs of nerves arises which supply different organs of their respective
segments.

Sympathetic Nervous System

Also known as autonomic nervous system it consists of :
Nerve Plexus
Spread beneath epidermis and alimentary canal and connected with peripharyngeal connectives.

13. RESPIRATORY SYSTEM

(i) No special respiratory organs are present in Pheretima.
(ii) Respiration is cutaneous, i.e. exchange of gases takes place through moist and thin skin supplemented
by thin capillaries.
(iii) Haemoglobin dissolved in blood plasma.
(iv) For respiration moist skin is essential, if the skin gets dried up gaseous exchange stops and worm

14. REPRODUCTIVE SYSTEM

Earthoworm is hermaphrodite
Male Reproductive system

Male reproductive system include following structures-
 

Testes
(i) Two pairs of white lobed or palmate testes are found in earthworm.
(ii) One pair lies in 10th and other in 11th segment close to mid ventral line on either side of nervecord.
(iii) Testes is made up of a narrow base from which arise 4 to 8 small rounded cells or spermatogonia.

Testes Sac

(i) Testes of each segment is surrounded by wide, thin walled fluid filled testis sac.
(ii) Two testis sac are situated ventro laterally, one behind the other in 10th and 11th segments.
(iii) Testis sac of 11th segment is large enough to enclose seminal vesicle of that spermatogonia.

Seminal Vesicles

(i) They are two paired large, white structure in 11th and 12th segments. Also known as septal pouch
since they grow as outgrowth of septa.
(ii) Seminal vesicle of 11th segment is enclosed with testis sac and that of 12th segment lies free.

Spermiducal funnels

(i) They are two paired, ciliated, also known as "sperm rosettes".
(ii) They lie behind each testes, enclosed within same testis sac.

Vasa deferentia

(i) Spermiducal funnel leads into slender ciliated thread like sperm duct.
(ii) Two vasa deferentia of same side run close posteriorly upto 18th segment to join prostate gland.

Prostate Gland

(i) Prostate gland is paired, flat, solid, lobulate masses lying one on each side of gut from 16th to 17th
segment upto 20th to 21st segments.
(ii) Prostate gland produces a fluid function of which is not known. Few zoologist believe secretion is useful for activation of sperms. that prostatic

Accessory Gland

(i) They are two paired of white masses, a pair each in segment 17th and 19th are found.
(ii) oTnh evye notpreanl stiod ee.xterior by number of ducts on two pairs of genital papillae upon 17th and 19th segment
(iii) Their secretion helps in uniteing two worms during copulation.

Female Reproductive System

Ovaries

(i) Oofv saeripetsu mar ein 2 f rsomnta lol fw iht.ite structure that lies ventrally in 13th segment; attached to the posterior face
(ii) Each ovary is made up of finger like projections in which ova are arranged in linear series.
(iii) Ova are in various stages of development immature proximal part and mature on distal part.

Ovarian Funnel

(i) Saucer shaped much folded, and ciliated margins, lies behind each ovary in 13th segment.
(ii) It leads into short, conical oviduct.

Oviduct

(i) Two oviducts runs backward, perforate septum 13/14 to reach 14th segment.
(ii) They converge to meet in ventral body wall forming short common oviduct, which opens to exterior through female genital aperture on 14th segment.

Spermatheca

(i) Tsehgemy eanrte frfoomun d6 thi nt o4 9ptha. irs, small, flask shaped, present ventro-laterally, one pair in each
(ii) oEfaf cehlo snpgeartmeda tbhleincda ec aise cau mbr.oad pear shaped body the ampulla and short narrow neck of which gives
(iii) sSepgemrmeantthse. ca opens to exterior by spermathecal pores,situated in groups between 5/6, 6/7, 7/8, 8/9
(iv) During copulation the sperm are collected in caecum.

Copulation

(i) Two earthworms come to lie in opposite directions. They became attached to each ventral surface in such a way that the male genital apertures of one earthworm lie o tohpepro aslioten gto t htehier spermathecal pores of the other.
(ii) During copulation the male genital pore lies against a spermathecal pore.
(iii) aTnhde tgheen istaple prmapaitlilca ea nadre pirnossetratteicd finlutiod sp ocsotnetraioinr inmgo sstp epramir so fa rsep epmouartehde cinalt op osrpee romf aththee octah.er earthworm
(iv) Thus there is a reciprocal exchange of seminal fluid after which the two earthworms separate.

Cocoon Formation

(i) Ttoh efo grmla nadn c eellalss toicf cmliteemllubmra nseeocurest eg iard vleis coor ucso, cgoeolant eanroouunsd s ucblitsetallunmce. which on exposure to air, hardens
(ii) tGhlea ncdo ccoeolln a lisso s slipepcreedt ef oarnwoatrhdesr. tube called slime tube. The earthworm when wriggles backward them
(iii) cWohcoileo nm. oving over the female genital aperture on the 14th segment, the eggs are deposited inside the
(iv) Wspheermn atthhee cgaired laer ep aaslssoe sr eolevaesr etdh ein stop ethrme actohceocoanl .pores, the sperms of another earthworm stored in
(v) Sthoem eea rathlbwuomrmen csoemcrpelteetde lyb yw grilgagnlde sc eolulst ooff aitn.terior segments is also deposited into the cocoon before
(vi) The cocoon is some what spherical and light yellow in colour.
(vii) Several cocoons are formed in succession by a single earthworm.

Fertilization

(i) The earthworm is protandrous and therefore cross-fertilization takes place.
(ii) oSfi nrceep rtohdeu ecatirotnh.worm is hermaphrodite, all individual worms lay eggs. Hermaphroditism increase the rate
(iii) Fertilization takes place inside the cocoon. Out of several fertilized eggs only one develops.
(iv) The development is direct.The young earthworm comes out of the cocoon after 2 to 3 weeks.

15. ECONOMIC IMPORTANCE

Role in agriculture

(i) Earthworms are said to be the "friends of farmers", as they make the soil fertile.
(ii) By its various activities in soil, the earthworm contributes in no small measure to the soil and the healthy growth of crops. betterment of the
(iii) It has been said that the earthworm is a better cultivator than any machine invented by man.
(iv) Freirasdt,l yb ye bnuterrro twhirnogu ginhs etahrecshe o cf hfoaondn,e tlhse bwuotr mra ilnowosaetenrs athlseo s ofiinl pdasr taic lqesu iackn de fxoirtm frso cmo utnhtele sbsa schea onfn erloso.Atsir, enabling plants to grow more easily.
(v) Sineocrgoanndilcy, mfraestthe rs aonil dis n bitrroouggehnto unse asru tbhset asnucrefa (caes ine athrteh wfoorrmm 'os f efxincere ptoarryti cwleass toers waorerm a lcsaos ptsr easloenngt iwn iitth) which enrich the soil for plant growth.
(vi) Bcausrrtso wiss finin ethlye gfireinldd eadn di nb rtihneg gthizez adrede,p iet rh seolpil st oi nt hteh es ugrrfoawceth a nodf psloa natcst. as ploughing. Since the worm

As food bait

(i) Emaerdthicwinoersm.s are widely used as bait for fishing, they are also used in the preparation of Ayurevedic
(ii) They make favourite meals of birds, they are also used as experimental animals.

Harmful effects

(i) Tobacco plants are unable to stand on the loosened soil made by Pheretima.
(ii) rPohoetsre.tima elongata destroys the roots of creepers whereas Malabaria padaducola destroys paddy
(iii) The worm castings on sloping lands tend to be washed away by rain resulting into soil erosion.

16. SPECIAL POINTS

(i) Ereagrethnweorarmte ah atas ila b puot wtheer poof srteegrieonr ehraaltfi omn.a yIf o ra mwaoyr mno its recugte nine rtawtoe pthieec heesa tdh ep oarntitoenri.o Tr hheaylf hwaivlle u psouwalelyr to regenerate some segment cut accidentally.
(ii) The absence of appendages in earthworm help it to move in the soil without much difficulty.
(iii) tDou eex ttoe ritnsa ul nsdtiemrgurlio.und habitat eyes are not needed. The epidermal receptors are sufficient to respond
(iv) The slime secreted by the skin gland cells is used to plaster the walls of the burrows.
(v) Coelomic fluid powed over the body surface through dorsal pores help to moisten and disinfect the body.
(vi) Burrow is usually formed by eating the soil.
(vii) Tgihgearnet ica rfeo rambso uotf 13,6500 0m smp eicni elesn ogft he.arthworms ranging in size from animals less than 1 mm long to
(viii) Megascolex australls is the largest species of earthworm known.
(ix) iTnhtees etinntee.ronephric nephridia prevents loss of water. The water from excretory water is absorbed in the
(x) Trehsep ireaxtoionne.phric nephridia besides removing nitrogenous water keeps the integument moist to help
(xi) In the evolutionary history of animal kingdom, annelids are the first animals to possess true coelon.
(xii) The arrangement of setae in each body segment in called "perichaetine".
(xiii) The secretion of calciferous glands in the stomach neutralizes humic acid present in the soil.
(xiv) Life span of earthworm is 2 to 6 years.