Earthworm - reproductive system - class-XI

Earthworm is a bisexual or hermaphrodite but always shows cross-fertilization due to polyandrous conditions.

The number of ovaries present in Earthworm is one pair of ovaries. One pair of ovaries is attached at the intersegmental septum of the 12th and 13th segments. Ovarian funnels are present beneath the ovaries which continue into the oviduct and open on the ventral side.

Earthworms are monoecious or hermaphrodite (have both male and female sex organs) but are protandrous. The testes mature earlier than ovaries and hence, self-fertilisation is avoided.
Thus, the correct answer is option A.

Earthworm is hermaphrodite. There are two pairs of testes present in the 10th and 11th segments. Their vasa deferentia run up to the 18th segment where they join the prostratic duct. The prostate and spermatic duct open to the exterior by a pair of male genital pores on the ventrolateral side of the 18th segment. 

Four pairs of spermathecae are located in 6th-9th segments. They receive and store spermatozoa during copulation. One pair of ovaries is attached at the inter-segmental septum of the 12th and 13th segments. Ovarian funnels are present beneath the ovaries which continue into the oviduct, join together and open on the ventral side as a single median female genital pore on the 14th segment.

In Earthworm there are four pairs of spermathecae which are located in the 6th - 9th segments one pair in each segment. They receive and store spermatazoa during copulation. One pair of ovaries is attached at the inter-segmental septum of the 12th and 13th segments.

A pair of male genital pores is present on the ventrolateral sides of the 18th segment. Numerous minute pores called nephridiopores open on the surface of the body. In each body segment, except the first, last and clitellum, there are rows of S-shaped setae, embedded in the epidermal pits in the middle of each segment.

Asterias, Musca domestica and butterfly include a larval stage in their life cycle. Whereas in the case of Pheretima, there is no larval stage involved and the development is direct mode of development.

Answer is option A i.e. "One hour"
Copulation lasts for about an hour. Then the worms separate and later (after some day) they lay their eggs in cocoon. Cocoon formation takes place after copulation, when ovaries mature.

Spermathecae, which are four pairs are arranged one each in 6,7,8 and 9 th segments. Spermathecae are also called as seminal receptacles as they store spermatozoa from another worm  in the diverticular region during copultion. The ampulla of spermathecae nourish the sperms.

In earthworms, the male genital pores are located on the 18th segment, not the 9th segment.

The oviduct funnel located below ovary opens into a short conical tube called oviduct. Two oviducts fuse together and open outside through female genital aperture located in the 14$^{th}$ segment.

Earthworms are hermaphrodites but they cannot fertilize their own eggs because of their relative position of male and female genital aperture and they are protrandous (i.e. male sex mature earlier than female gametes). So, cross-fertilization takes place instead of self-fertilization.

The clitellum plays an important role in reproduction. Its glands produce mucous which becomes a sheath containing nutritive material. The sheath slides forwards, collecting eggs and sperm from the genital openings of the worm. The sheath finally slides off from the head of the worm. As it separates from the worm, its ends are sealed. It now becomes a cocoon.

Genital pores for both male and female organs are present on the ventral side of the earthworm. Also, setae are present on the ventral side.

The anterior region of Pheretima consists of a thick, saddle-like ring found in the epidermis known as Clitellum This structure is easily visible with naked eyes hence a person can easily distinguish the anterior and posterior end of pheretima.

Cross-fertilization occurs in many hermaphrodite animals as in earthworm. It is due to the fact that their male and female reproductive organs mature at different times.

In Pheretima, a cocoon contains many fertilised eggs but only one embryo completes development, while other ova serve as nurse cells. The development is direct without a free larval stage. After the development of 2-3 weeks, the young worm crawls out of the cocoon. So, the correct answer is option A.

There are two pairs of testes, which are situated in the 10$^{th}$ and 11$^{th}$ segments on each side of the alimentary canal. The germinal epithelium of the testis gives rise to the sperm cells by spermatogenesis. So, the correct answer is option B.

Earthworms are hermaphrodites; that is, they have both male and female sexual organs.  The two or four pairs of seminal vesicles produce, store and release the sperm via the male pores. Ovaries and oviducts are in segment 13 release eggs. Ovarian funnels are present beneath the ovaries which continue into the oviduct, join together.

The spermathacae are also called as receptaculum seminis. species of earthworms have four pairs of spermathecae one pair each in the 6th, 7th, 8th, and 9th segments. The spermathecae receive and store the spermatozoa of another earthworm during copulation. They are lined with epithelium and are variable in shape: some are thin, heavily coiled tubes.

Two pairs of accessory glands are present in 17th and 19th segments. Four pairs of spermathecae are located in 6th-9th segments. They receive and store spermatozoa during copulation. One pair of ovaries is attached at the inter-segmental septum of the 12th and 13th segments.