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Reproductive system of Earthworm

Earthworms are cylindrical and metamerically segmented. They play a significant role in maintaining the sustainability and ecosystem, which is why they are called farmer’s friends.

Earthworms are hermaphroditic or monecious or bisexual because they possess both female and male reproductive organs. The same earthworm contains testes and ovaries as well. They are protandrous, i.e. testis matures earlier than the ovary. Earthworms reproduce sexually where they undergo copulation and cross-fertilization.

Male Reproductive System of Earthworm

The male reproductive system of earthworms comprises testes, testis sac, seminal vesicles, spermatic funnel, vasa deferentia, prostate gland, and other accessory glands.

Testis:

  • Testes are two pairs. The 10th segment houses one pair and 11th segment contains the other pair.
  • Testes are lobed and minute whitish structures.
  • Each testis is enclosed in a testes sac.
  • Spermatogonia cells are present in the lobules of each testis.
  • Testis produces sperms for copulation.

Testis:

  • Testes are two pairs. The 10th segment houses one pair and 11th segment contains the other pair.
  • Testes are lobed and minute whitish structures.
  • Each testis is enclosed in a testes sac.
  • Spermatogonia cells are present in the lobules of each testis.
  • Testis produces sperms for copulation.

Testis:

  • Testes are two pairs. The 10th segment houses one pair and 11th segment contains the other pair.
  • Testes are lobed and minute whitish structures.
  • Each testis is enclosed in a testes sac.
  • Spermatogonia cells are present in the lobules of each testis.
  • Testis produces sperms for copulation.

Testis sac:

  • Fluid-filled sacs containing testis are called testis sacs.
  • Testis sacs are bilobed with thin walls.

Seminal vesicles:

  • Seminal vesicles are two pairs - one pair each in the 11th and 12th segments.
  • The spermatogonial cells reach seminal vesicles through the testis sac, where they mature into spermatozoa.
  • The key functions of seminal vesicles are the maturation and storage of sperms.

Vasa deferentia:

  • Vasa deferentia are two pairs.
  • Each vasa deferentia arises from spermiductal funnels. The prosatic duct join the vasa deferentia in the 18th segment.

Prostatic gland:

  • Prostatic glands are irregularly shaped solid white masses.
  • They are situated on either side of the gut. The prostate glands extend from the 16th to the 20th segment or the 17th to the 21st segment.
  • The common prostate spermatic duct connects to the exterior using a pair of male genital pores present in the 18th segment.

Accessory glands:

  • The male reproductive system of earthworms has 2 pairs of accessory glands.
  • One pair can be found in the 17th segment and the other in the 19th segments.

Female Reproductive System

The female reproductive system of earthworms comprises ovaries, oviducts, and spermatheca.

Ovaries:

  • There’s one pair of ovaries present along the inter-segmental septum of the 12th and 13th segments.
  • Ovaries are whitish and small lobulated structures.
  • The ovarian lobes constitute the ova that are in different stages of maturation.
  • The distal end of the lobe contains mature ova, whereas the proximal end contains immature ones.

Oviducal funnels:

  • Each oviducal or ovarian funnel arises from both ovaries.
  • Oviducal funnels appear as large saucers consisting of ciliated margins.

Oviducts:

  • Each ovarian funnel continues into the oviduct.
  • Both the oviducts converge and open on the lower front side as the only female genital pore in the 14th segment.

Spermatheca:

  • Spermathecae are 4 pairs - one pair each in the 6th, 7th, 8th, and 9th segments.
  • Spermatheca appears as a flask-shaped structure.
  • The key function of spermatheca is to receive and store spermatozoa from another earthworm during copulation. Hence, spermatheca is also referred to as seminal receptacles.
  • Ampulla, the main body part of the spermatheca, stores the spermatozoa.
  • The spermatheca also contains a short and small lobe-like stricture called the diverticulum. The diverticulum is the storage site for sperms in Pheretima.
  • The spermatheca opens to the exterior via small ducts.

Copulation:

Copulation in earthworms takes place in the rainy season during the month of July to October. As said above, earthworms are bisexual, and copulation occurs by cross-fertilization.

Cross-fertilization is a process where two earthworms come together and exchange spermatozoa with one another. Two earthworms of adjacent burrows contact each other juxtaposing opposite gonadal pores. Cocoon or ootheca formation begins when ovaries mature.

Once the mutual exchange of sperms completes, both the worms separate from one another and lay eggs in cocoons. Egg cells, mature sperms, and nutritive fluid are deposited in the cocoon. The cocoons are deposited in the soil in which the fertilization of sperm and ova takes place. Because sperms and eggs are fertilized outside the organism, the fertilization is termed External. The cocoon holds the embryos formed after fertilization. Each cocoon finally results in 2 to 20 baby worms with an average of 4 in about 3 weeks. The development of earthworms is direct which means that there is no larval stage.

Economic importance of earthworms:

Earthworms are of significant economic value to humans. In agriculture, earthworms enhance soil fertility by a process called vermicomposting. They improve soil porosity, thereby permitting aeration and water absorption by the soil. The faeces of earthworms contain chemical substances significant for plant growth and development. They are also utilized as bait in game fishing. Because of all these reasons, Earthworms are better known as “friends of farmers”.

 

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