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Reproductive System of Earthworm
Reddish-brown in colour, earthworms have their dorsal side characterized by the dark line of the blood vessels, while their ventral side is characterized by the openings of the genitals. They have both the male and the female parts of the reproductive system. The process is simple as they are hermaphrodites.
Earthworms help farmers by improving soil quality. They have a body that has metameric segments with a cylindrical shape. They are found in reddish brown colour. Earthworms’ locomotion is controlled by their S-shaped setae. Earthworms are of hermaphrodites or monoecious type, which means they have both female and male reproductive organs in their bodies. Cross-fertilization is the most common fertilization type found in earthworms. Earthworms have a great contribution in maintaining the balance of ecosystems. The male and female reproductive parts are located in certain segments of their body. Copulation occurs in earthworms where sperms enter the female reproductive system from the male reproductive part.
Figure 1: Earthworm reproductive system
Lumbricus Terrestris is the most known earthworm that illustrates the standard reproductive organs of an earthworm. Earthworms’ reproductive system doesn’t have many complications. Parthenogenetic is an asexual reproduction form that occurs in earthworms but it is not mandatory for all earthworms.
Male Reproductive System
Earthworms’ male reproductive system mainly has the following components −
Four seminal vesicles are present in earthworms’ male reproductive organs. Some theories about earthworms explain that these vesicles evolved about a million years ago preceded by the parthenogenesis process. Spermatozoa is matured from spermatogonia in these vesicles. The testes produce these mature sperm.
Testes and Testes Sac
Four testes are found in earthworms’ male reproductive organs in segments 10 and 11. Spermatogonia is produced by testes. The sac is full of fluid and surrounded by wide walls. The bi-lobed sac is white-coloured. In the tenth segment, the first sac is larger than the other one, and seminal vesicles are also housed in it.
The count of seminal funnels is four in earthworm’s male reproductive organ. The arrangements of seminal funnel are found in the 11th and 10th segments. Spermatozoa is passed to vasa deferentia and onwards by these ciliated funnels.
Female Reproductive System
The female reproductive system mainly has the following parts.
The structure of the oviducal funnel is saucer-shaped. This part can be found in segment 13 of the earthworm’s female reproductive system. An earthworm ovary produces matured ova which are collected afterward by oviducal funnel. The end part of this funnel is called the oviduct. It is a short conical tube-like structure. In segment 14, a couple of oviducts meet. Then these oviducts open out into the external genital pore.
In the 13th and 12th septa, there is an attachment of an ovary pair. The ovary of earthworms is the resting place for multiple ovarian lobules and ova. The ova complete its maturity and proceeds with gradual movement toward the coelomic cavity. They take a rest in the dorsal end of an ovary until they become mature.
In every earthworm body, there are four pairs of spermatheca. A short diverticulum is present on these flask-shaped spermatheca. Spermatheca works as sperm storage. Segment 9 and 5 is the location of spermatheca.
Earthworms are said to be nocturnal and hermaphrodites and reproduction is generally executed through cross-fertilization. The process of copulation, according to studies, has been found to be occurring in the rainy season which is from the month of July to October, and at the time of night or morning dawn. The process takes about one hour to complete.
In that process, the earthworms lie in contact with each other in the opposite direction. The inclination is such that the male genital apertures of one earthworm are in the proximity of the spermathecal pores of the other earthworm. The sperm droplets from the male pore are carried by a seminal groove, to the clitellar region whereupon it gets collected and makes their entry to the spermatheca, of the other earthworm with the aid of the tubercula pubertal.
Figure 2: Copulation
After the process of copulation, both the earthworms make cocoons and a number of fertilized ova. The cocoons that are resistant are normally gathered near the surface of the soil except in weather when it gets dry. That time they are laid in deep layers. The eggs in the cocoons are laid after some days of copulation. A feature of copulation is that they do not have any larval stage. Young earthworms emerge from cocoons in complete form without any clitellum.
Earthworms are segmented, cylindrical, and tubular in form, and can grow up to fourteen inches and dig up to seven inches. They play a significant role in the maintenance of the environment. The reproductive system of a single earthworm contains both male and female parts. Copulation of two earthworms leads to fertilization in both earthworms.
Q1. Where are the reproductive organs of the earthworms located?
Ans. Earthworms are said to be hermaphrodites. This implies that the male and the female reproductive parts are both contained in the same organism. The reproductive organs are located in segments nine to fifteen.
These creatures have one or two pairs of testes contained within the sacs. Two or four pairs of seminal vesicles produce, store, and release the sperm through the male pores. Ovaries and the oviducts in segment thirteen release eggs through female pores in segment fourteen.
Q2. What is the structure and function of reproduction in an earthworm?
Ans. Being hermaphrodites, each earthworm possesses the male and the female parts of reproduction within their segmented body. During the process of copulation, the individual earthworms exchange the sperms and fertilize the eggs of the other earthworm. Both the earthworms have male and female genital pores.
The structure and function of the band are called clitellum. They make another tube of mucus. The band is passed toward the mouth of the worm. On moving forward the mucus passes over the eggs that stick to the slime.
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