In the case of earthworm, sexual reproduction takes place.They are monoecious and hermaphrodite.They are protandrous and cross-fertilization and external fertilization takes place.
The male reproductive system of earthworm consists of following parts:
Testes lie in the 10thand 11th segment a pair each.They are minute, white loped structure with a narrow base and 4 to 8 digitate process.Testes produce spermatogonia.
A pair of testis sac which are thin walled and filled with wide structure fluid.Second testes sac is larger than the first testes sac because it surrounds or encloses seminal vesicle along with testes and periductal funnel.It is bi-lobe.
Two pair of the seminal vesicle is present.The second pair is larger because it is not enclosed by testis sac.The seminal vesicle is also called septal pouch and it is a fluid filled sac-like structure which supplements nutrition to spermatozoa.In seminal vesicle, spermatogonia convert to spermatozoa.1stpair is in 11 segment and 2nd pair is in 12 segments.
The periductal funnel is enclosed by testes sac.1st pair lies in 10th segment and 2ndpair lies in 11th segment.They are wide ciliated funnel and play the role in the collection of spermatozoa and pass posteriorly.
The spermiducal funnel proceeds posteriorly to form slender, elongated, cylindrical thread like ciliated tube called vasa deferentia.It opens into male genital pore which lies ventrolaterally in 18th segment.
Prostate gland lies in the 16th or17th segment to 20th to the 21st segment.It is the white lobulated large flat solid gland.It consists of two parts glandular and non-glandular part.The glandular part is lobulated racemose like which secrete a nutritive substance for spermatozoa.The non-glandular part consist of many ductules of the gland and this ductule combines to form the common prostate duct which opens into the male genital pore.
Accessory gland lies in segment 17 and 19 a pair each and is a rounded whitish gland which secretes sticky substance and opens into genital papillae through minute ductules.The secretion helps in the temporary union during the mating process.
Female reproductive system of earthworm consists of following parts:
A pair of small whitish compact and lobulated or digitate process which lies in the 13 segment and attached to 12-13 septa. Ovary consists of many ovarian lobules with ova.The immature ova lies in proximal part and mature ova lies in distal part.When fully matured, the ova are set free into coelomic cavity.
The oviducal funnel is saucer shaped with folded and ciliated margin and they lie in the 13th segment and play an important role in the collection of matured ova.
A pair of oviduct lies in the 14th segment.They are conical, short and ciliated and the two oviduct meets ventrally and posteriorly perforate the septa 13/14 and form common oviduct which opens out through female genital pore lying in 14th segment.
Four pairs of spermathecae which are flask-shaped with broad pear shaped ampulla and a short diverticulum or caecum having a narrow neck.The ampulla store nutritive substance produced by prostate gland whereas in diverticulum spermatozoa are stored.It opens intersegmental ly and ventrolaterally in 5/6, 6/7, 7/8, 8/9 a pair each.
Mating takes place during the rainy season when it is damp or moist and warm.The two earthworm come in contact with each other and are ventrally applied in opposite direction in the inverted position.The male genital pore lies opposite to spermathecal pore and fits into the spermathecal pore.The spermatozoa are transferred from one earthworm to another.The sixth spermatheca is lastly filled.Then the earthworm separates after one hour of the mating process.When ovary matures, the clitellum becomes active. It contains different types of cell which secrete different substances.
Cocoon forming cell:
The cocoon forming cell secrete viscous gelatinous substance which on contact with air, convert into a membranous elastic tube or girdle.
The mucous cell becomes active and secretes slime tube inside the cocoon.
The albuminous cell secretes albumen inside it.
The earthworm wriggle backward and the cocoon slips forward and on its way, cocoon carry fully matured eggs, spermatozoa as well as albuminous fluid from anterior region.The cocoon slips off and both the end are closed.Many cocoons are laid one after another.The cocoon is rounded or oval in the structure of 2.5 mm length and 2mm wide and yellow in color.There are many fertilized eggs in each cocoon but out of that only one develops into young one.The other fertilized eggs serve as nurse cell and provide nutrition to the developing embryo.The albuminous fluid also supply nutrition.Only one hatch out from each cocoon.It takes 2-3 weeks for development.The young one are small in size and without clitellum.