Reproductive System of Earthworm

Earthworms are known as farmers’ friends. They have a cylindrical shape metamerically segmented body. They are reddish-brown in colour. Dorsal side is characterized by a dark line of blood vessels and the ventral side is characterized by the genital openings. The body consists of S-shaped setae, which help in locomotion.

Reproductive System of Earthworm

Earthworms are monoecious or hermaphrodites, i.e. they contain both male and female reproductive organs. Reproduction is mostly by cross-fertilization in earthworms.

Reproductive organs are present on 9th to 15th segments.

Male Reproductive System

The male reproductive system comprises testes, testis sacs, seminal vesicles, spermatic funnel, prostate glands and other accessory glands.

Testes:      

• Two pairs, present on 10th and 11th segment.
• Each testis consists of 4 to 8 finger-like projections.
• Testes contain spermatogonia cells in the lobules.
• They produce sperm.

Testis Sacs:

•  Testes are present within fluid-filled sacs called testis sacs.
•  Large spermatic funnel is present.
•  Testis sacs are connected to seminal vesicles.
• Spermatogonia cells pass from testis sacs to seminal vesicles, where they mature to form spermatozoa.

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.

Spermatic Funnel:

• Two pairs, present on 10th and 11th segment behind each testis.
• They are folded and ciliated.
• It connects testis sacs to vasa differentia. Sperms matured in seminal vesicles come back to testis sacs and transported to vasa differentia via spermiducal funnel.

Female Reproductive Organ

The female reproductive system of earthworm comprises ovaries, oviduct and spermatheca.

Ovaries:

• One pair of ovaries, present at 13th segment.
• Each ovary consists of several finger-like projections.
• In these projections, developing ova are present in a row, which looks like a series of beads.
• The mature ova are found at the distal end and immature ova are found at the proximal end of the lobules.

Oviduct:

• One pair of the ovarian funnel is present at 13th segment, below ovaries.
• These funnels are ciliated and folded and open in the oviduct.
• Oviducts are a short conical funnel. they are ciliated.
• Both the oviducts converge and form a single female genital aperture at the 14th segment.

Spermatheca:

• Four pairs, situated inter-segmentally between 5-6, 6-7, 7-8, and 8-9th segment.
• They are also known as seminal receptacles as they store sperms from another earthworm during copulation.
• Each spermatheca is flask shaped.
• The main body of spermatheca is called the ampulla, which stores sperms and short small lobe called diverticulum.
• In Pheretima, the diverticulum stores sperms.
• The spermatheca opens externally by small ducts.

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.

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