REPRODUCATION IN EARTHWORM

Reproductive system in earthworm

Earthworms are hermaphrodites, and reproduction mostly occurs through cross-fertilization by copulation. ... The earthworms lie in contact with each other in the opposite direction, such that, the male genital apertures of one earthworm is near to the spermathecal pores of the other earthworm

male reproductive system

Organs

a) testes

b) testis sac

c) seminal vesicle

d) vasa deferentia

e) prostate gland

f) accessory gland

TESTES

Testes are very minute structures that are whitish in colour.
There are two pairs of testes and they are lobed.
One pair each is present in segment 10^th and 11^th that are found attached with the posterior surface of 9/10 and 10/11 inter-segmental septa.
Each testis possess 4-8 finger like lobules that contains rounded cells in masses termed as spermatogonia.
Testes are enclosed within testis sac.
During the young stage of the earthworm, the testes are fully developed whereas they get degenerated in the adult stage.

TESTES SAC

Testis sacs are whitish, wide bilobed sacs that encloses testis.
They are thin-walled and fluid-filled sacs.
On the ventrolateral sides of the ventral nerve cord, the two testis sacs are located in the 10^th and 11^th segments beneath the stomach.
In the testis sac, a large spermatic funnel having folded and ciliated margins is present behind each of the four testes.
The testis sacs links with a pair of seminal vesicles.
The spermatogonia are casted into the testis sacs then, they are passed into the seminal vesicles.

SEMINAL VESICLE

Two pairs, present on 11th and 12th segment.
Each seminal vesicle is connected to the testis sac.
Spermatogonia cells pass from testis sacs to seminal vesicles, where they mature to form spermatozoa.

Spermiducal funnel

They are cup like curvature found in two pairs.
They are ciliated sperm funnels, lying below each testis in the segment 10th and 11th segment and enclosed within the same testis sac.
Function
Mature sperms from seminal vesicles move back to the testes sac and pass through the spermiducal funnel into vasa differentia

. Prostate glands:

Prostate glands are large, whitish, flat solid, irregularly shaped glands.
These are found in pair and are located one on either side of the alimentary canal in the segments from 16^th to 20^th or 17^th to 21^st .
Maximum portion of prostate glands are glandular region while a small part is non-glandular region.
A thick curved prostatic duct arises from each prostate gland in 18^th segment.
The prostatic duct is connected to the two vasa deferntia of its own side and forms a common prostatic and spermatic duct.
On the ventral side of 18^th segment, prostatic duct opens via a male genital aperture.
Hence, each genital aperture has three distinct apertures, two of the vasa deferentia and one of the prostatic gland.
In earthworm the prostatic secretion is useful for the activation of sperms.
It also aids in motility of sperms.

ACCESSORY GLAND

In each each segment 17 and 19 is found a pair of rounded accessory gland on the ventral body on either side of nerve chord. they open to the exterior by the number of ducts on two pair of genital papillae. their secretion helps in uniting to worm during copulation

Female Reproductive Organs of Earthworm:

Female reproductive organs consist of the ovaries, oviducal funnel, oviducts and spermathecae.
Female reproductive organ includes:

Structure	Number	Location
Ovaries	1 pair	13^th segment
Oviducal funnels	1 pair	13^th segment
Oviducts	1 pair	13^th and 14^th segment
Female genital aperture	single	14^th segment
Spermathecae	4 pairs	6^th, 7^th, 8^th, and 9^th segments ventrolaterally

i. Ovaries:

Ovaries are white, small, lobulated structures that are found in a pair.
In the 13^th segment, ovaries are located one on either side of the ventral nerve cord.
It is attached with the posterior region of the inter-segmental septum of 12/13 segments.
Each ovary consists of various finger like projections where developing ova are found in a row, giving the beaded appearance.
In each ovarian lobe, the ova exhibits several stages of its development where mature ones lie in the distal part and the immature ones are found in the proximal part.

ii. Oviducts:

A small, ciliated ovarian funnel with folded margins are present below each ovary in 13^th segment.
Each ovarian funnel opens into a short and conical oviduct.
Oviducts are ciliated.
The oviducts of both the sides unite below the nerve cord.
Here, it open by a single median female genital pore ventrally in the 14^th segment.
The ova after maturation are released from the ovaries and are received by the ovarian funnel.
Then, it passes through the oviduct and that is discharged out via the female genital pore.

iii. Spermathecae:

Spermathecae are four pairs and each pair is located ventro-laterally in the 6^th, 7^th, 8^th, and 9^th segments.
Each spermatheca is flask shaped structure.
Each spermathecum is made of ampulla and neck (upper short tubular part).
the main body is the ampulla.
At the junction of the ampulla and neck, a small sac is found.
This sac is termed as diverticulum.
Spermathecae are also termed as seminal receptacles as they are designed for receiving sperms from another worm during copulation and temporary storage of sperms.
The diverticulum of spermathecae in Pheretima posthuman stores sperms, which reach here after copulation.
But in other species of earthworm, sperms are store in ampulla.
In Pheretima posthuma ampulla aids nourishment to the sperm but in other species of earthworm, diverticulum provides nourishment.
Spermathecal duct opens outside by small pores situated in the grooves of 5/6, 6/7, 7/8, and 8/9 segments.

iv. Female genital pore:

It is single pore and is located in the 14^th segment

COPULATION

Earthworms are hermaphrodites, and reproduction mostly occurs through cross-fertilization by copulation. Copulation mostly occurs during the rainy season, early in the morning at dawn.

The earthworms lie in contact with each other in the opposite direction, such that, the male genital apertures of one earthworm is near to the spermathecal pores of the other earthworm.

A seminal groove, carry sperm as droplets from the male pore to the clitellar region, where it collects, and eventually enters the spermathecae of the partner earthworm with the aid of the tubercula pubertal.

After copulation both the mated individuals produce cocoons with variable numbers of fertilized ova.The resistant cocoons are usually deposited near the soil surface, except in dry weather when they are laid in deeper layers.

Fertilization in earthworm:

Fertilization occurs inside the cocoon and normally there is only one embryo in a cocoon.
Cocoon is found in moist and cool places and young one hatch out after 2-2.5 months.
Albumen cells provide nutrition to the embryo.
Cleavage is holoblastic and unequal.
Development is direct without any larval stage

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