UNIT SIX : DETAILED STUDY OF EARTHWORM
Class : 11
Reproductive system of Earthworm
The earthworm is hermaphrodite or monocious i.e. male and female reproductive organs are found in same individual.
Male Reproductive System
Testes: there are two pairs of testes. One pair is situated at 10th segment and another pair at 11th segment. Each testis consists of 4 to 8 digits.
Testes Sacs: Testes are enclosed by fluid filled sacs called testes sacs. One testes sac is found at 10th segment and other is at 11th segment. Two testes sacs communicate each other.
Seminal Vesicle: there are two pairs of seminal vesicles. One pair is situated at 11th and other at 12th segment. Each seminal vesicle communicates with testes sac. The spermatogonia are passed from testes into testes sacs and then they are passed into seminal vesicles where they develop into sperms. The mature sperms again go back into testes sac and pass into seminal funnel.
Seminal Funnel: There are two pairs of seminal funnel. One pair is found in 10th segment and another pair in 11th segment. They are ciliated and found below testes.
Vasa differentia: There are four tubes, which start running from 12th segment to 17th segment. In 17th segment, they unite with the duct of prostate gland to form common prostatic and spermatic duct.
Prostate gland: There are two prostate glands. They are larger, irregular, flat, and wide. They extend from 16th or 17th segment to 20th to 21st segment. Each prostate gland has small curved duct, which joins with spermatic ducts and opens through male genital aperture at 18th segment.
Accessory gland: There are two pairs of accessory gland. One pair in 17th segment and another pair are in 19th segment. They are small and round in structure. They bear small ductules, which open through genital papillae.
Female Reproductive Organ
Ovaries: There is a pair of ovary situated at the 13th segment hanging on septum between 12th and 13th segment. Each ovary has finger like projections, which contained ova in series. The mature ova are found toward end and immature ova are found on the base of the lobules of the ovary.
Oviducal Funnel: One pair funnel like structures at 13th segment found below ovary with ciliated mouth called oviducal funnel. Each funnel opens into short conical tube called oviduct. Two oviducts fuse together at 14th segment and open outside through female genital aperture.
Spermathaceae: There are four pairs of spermathecae. Each pair is found between 5-6, 6-7, 7-8, and 8-9th segment. Each spermatheca is flask shaped. The main body of spermathaca is called ampulla and short small lobe found attached at its side is called diverticulum. They store sperms.
Copulation
In rainy season, two earthworms copulate at night. During copulation, two earthworms get attached through their ventral surface with their anterior end pointing in opposite direction. The male genital aperture become erected and inserted into the spermathecal pore of each other. During the process sperms are exchanged together. Then they separate after about an hour.
Coocon Formation
After copulation, a membrane is secreted around clitellum by membrane secreting glands. The membrane starts to move towards anterior end of earthworm whereas the worm starts withdrawing itself backward. During the process, the membrane receives ova coming from female genital aperture and sperms coming from spermathecal pores. Lastly, the membrane is laid out on the ground. The elastic opening of membrane becomes closed. The structure is called cocoon (ootheca). Within cocoon, one of the sperm fertilized with ovum to form zygote and young worm is developed that comes out of cocoon about 2-3 weeks. A dozen of cocoons is formed after each copulation by each conjugant.
Tags:
Biology