Excretory & Reproductive System: Earthworm | Additional Study Material for NEET PDF Download

EXCRETORY SYSTEM

Excretory organ - "nephridia"
3 types of nephridia
Septal Nephridia - found on "inter segmental septa"
- Starting from 15-16 segment all posterior septa have nephridia
- arranged in two rows on each plane of septa. Each row has 20-25 nephridia".
- 40-50 nephridia on each face of septa.
- Septal nephridia on one septa (80-100)
- In 15th and last segment these are 40-50 septal nephridia

Structure of septal nephridia:-
(1) Nephrostome - A slit like hole.
(2) Neck :- After nephrostome this part is a straight tube like structure.
(3) Twisted loop :- made up of two limbs ie. ascending and descending limbs.  "No of twist - 9-13 twists"  Terminal end of distal-limb is in form of a straight lobe nephridia connected with inter-segmental septa with the help of straight lobe.
(4) Terminal duct :- last part of nephridia.
- one ciliated canal inside terminal duct.
- Nephridia absorb body fluid with the help of nephrostome.
In twisted loops - re-absorption process takes place, useful material absorbed and poured into the body cavity.
- all excretory substance gets concentrated and reaches to the "terminal-duct".
- All terminal ducts present at the one lateral side of septa fuses and forms a septal nephridial duct or septa excretory canal. It forms on the posterior part of septum.
- In 15th segment, septal nephridial duct is absent it first seen in 16^th segment.
- two large ducts are present at the dorsal side of alimentary canal. From 15th to last segment they are known as supra intestinal excretory duct.

S.N.D. - opens in S.I. excretory duct.
- Supra - intestinal excretory duct open through a small pore in each segment into alimentary canal.
- alimentary canal absorbs water from excretory materials.
- Excretory substances with undigested food thrown out from anus.
- Septal nephridia - "endonephric" or "entero nephric"
In order to check the loss of water excretory substances are thrown into alimentary canal. so septal nephridia help in "osmoregulation"

Terminal duct → S.N.D. → Supra Intestinal excretory duct → Alimentary canal

(2) Integumentary nephridia:-
- Present on the internal surface of body wall.
- After 6th segment - each segment - 200-250
In clitellar segments they are 10 times (2000-2500) They are known as "forest of nephridia"
- small in size so - they are known as "meronephridia"
- Holonephridia - septal nephridia are large in size and less in number
Nephrostome absent - called - "protonephridia"
If nephrostome present - meta nephridia.e.g. septal nephridia
Twisted loop `V' shaped
Their terminal duct - opens outside the body so are "exonephric".

(3) Pharyngeal nephridia :
Present on dorsal side of alimentary canal
- In 4-5-6- segment they are mixed with blood glands.
- In each group - 100 nephridia
- Total 600 nephridia size is same as septal nephridia.
Structure is same as integumentary nephridia.
Terminal ducts of each group unit to form a common duct.
Common ducts of 4-5th segment open in pharynx in 4 segment. While of 6th segment open in buccal cavity in 2nd segment.
- Called "enteronephric."
- They are not related with excretion, but perform the function of digestive glands.
Modern scientist - "peptonephridia"
Pheretima - "Ureotelic"
When moisture is more than "Ammonotelic"

REPRODUCTIVE SYSTEM
Earth worm is "monoecious" - hermaphrodite.
Reproductive organ - Present on ventral side of alimentary canal.

Male reproductive organ :-

- 10th & 11th segment has testes sac.
Testes sac. - formed by coelomic cavity each testes sac has a pair of testes.
Free end of testes is divided in 4 lobes, These lobes produce spermatogonia
Testes - mesodermal in origin.
Isttestes sac - smaller
IIndtestes sac- larger.
A pair of seminal vasicles associated with each testes sac.

1 pair - 11th segment - smaller seminal vesicle
I1 pair - 12th segment - large seminal vesicle

Each seminal vesicle is connected to testis sac by a pair of tubules.
- Spermatogenesis - in "Seminal Vesicle" testes forms only spermatogonia
- Monocystis protozoa, found in testes or seminal vesicle. they destroy the sperm - "male sterility
- From each testes sac arises a pair of vas deferentia.

They extends upto 18th segment
- A pair of prostate gland found from 17th to 20th segments.
- Vasadeferentia along with duct of prostate gland open by male genital pore. Three ducts opens in male gential pore.
- 2 Vasa deferentia and one prostate glands duct. Male genital pore is a group of three pores,

Female reproductive system :
- located In 13th segment is one pair of ovary they are connected to Inter-segmental septa
- The free end of ovary is divided into many lobes. In each lobe are found rows of eggs.
- Eggs - "acropetal order"
- Two oviducts located beneath ovary.
- both oviduct combine and open outside the body by female genital pore in I^st cliteller segment
- Spermatheca - from 6th to 9th segments, one pair in each.
- Two part of spermatheca.

1.Ampula    2.Neck
- A duct is associated with the neck this is known as diverticulum .After copulation sperms are stored in it.
- "Ampulla - Secretes nutritive liquid, this provides nutrition to sperms.

Accessary glands
- One pair in 17th and 19th segment.These opens outside the body at the apex of genital papilla secretion helps to bind to Pheretima during copulation.

Copulation-

Breeding season - At night of rainy season the two Pheretima come closer to each other and tie in opposite direction 18th segment of one comes in contact with 5th '6th segment of other Pheretima.

- A small tube (papilla) is formed around the male genital aperture. These are known as copulation tubes or copulation pegs.
- The copulation tube of one earthworm inserts into spermathecal pore of other.
- The transfer of sperms take place
- Spermatheca gets filled with sperms in one hour.

Cocoon formation :-

Pheretima is protandrous.
A slimy fluid is secreted by glandular cells of clitellum. This then comes in contact with air and forms a pouch around clitellum. This is known as cocoon.
- The eggs comes out from female genital pores and get filled up in cocoon.
- Earth worm wringles back side and cocoon proceeds towards front side.
- When cocoons passes over the spermatheca the sperms gets filled in it.
- Nutritive fluid is given by albumin gland of epidermis.
- Pheretima completely wringles out from the cocoon. fertilization takes place in cocoon only. this is known as "external fertilization".
- Only one egg develops and rest gets destroyed.

Developement:- In 2-3 weeks"
Pheretima gets fully developed and they come out by hatching. They donot have clitellum soon they develop clitellum.

In young earthworm - Setae present in clitellum part.

Cleavage - "unequal" "holoblastic" spiral, determinate.

Gastrulation - Invagination"
"Neurohormone" - Secreted from supra pharyngeal ganglion. these hormones control regeneration of injured tissue, development of clitellum, and other accessory sexual organs, maturation of gametes, cocoon-formation and shedding of gametes etc.

Uses of earthworm :-

Pheretima used to cure rheumatism, piles, asthama, pyorrhoea, impotency, ulcer, jaundice etc.

Losses :- It harms the root of betal

Natural life cycle of pheretima - 3.5 to 10.5 years

Economic Significance of Pheretima & other earthworms -
(1) The burrows makes the soil (land) porous.
(2) They are natural ploughmen of land. So they are friends of farmers.
(3) They act as bait for fishing process.

Harms caused by earthworms :-
(1) Increases soil erosion, Pheretima elongata - harms the roots of betal plant. Some earthworms also harms the plant of paddy and "elaichi plants - e.g. "Malabaria padudicola"

(2) A sporozoan protozoa - Monocystis - resides in seminal vesicles and testes as a parasite.

(3) Acts as hosts for transmission of some parasites (e.g. - gape worm of chickens )

(4) Some times they get burried with dead bodies thus they bring up the infection and harmful microbes with them on the surface.