Anatomy of finfish and shellfish

Unit 13- Mollusca

13.4.8. Reproductive System
The sexes are separate. The males are usually smaller; less rounded dorsally, and possess slightly longer arms.
Male reproductive system
The large, oval, yellowish and saccular testis lies near the apex of- the visceral mass. Sperms produced in the testis are passed into its lumen which opens into small ciliated aperture on the left side into a long sperm duct or vas deferens, which opens into a long seminal vesicle. Here, the sperms are rolled up into long and narrow bundles enclosed in elaborate chitinous capsules, called the spermatophores.

Fig.12. Sepia.Male reproductive system.

A spermatophyte like an automatically explosive bomb; at one end et has a complex spring-like arrangement which ruptures its wall and discharged the sperms after copulation. The terminal part of seminal vesicle gives on two blind folds, one of them being the prostate or accessory gland. The seminal vesicle terminates into a wide reservoir, the sperm sac or Needham's sac, which opens into the mantle cavity by the genital aperture lying on a papilla or the pent to the left of the anus.

Fig. 13. Sepia.Male reproductive system.

Female reproductive system
The largo rounded white and saccular ovary is also situated, like the tests m the male, in a chromic sac near the apex of the visceral mass. The oviduct, leaden: from the codomlc sac is a short, thin-walled, wide tube which opens into the mantle cavity to the left of the anus. The narrower distal end of the ovidud has truck glandular wails forming the oylducal gland, the function of which is to secrete the outer coat of the ova. A pair of large oval and flattened nidamental glands lies one on either side of the ink duct each opens by its dad anteriorly into the mantle cavity. A pair of orange coloured accessory nidamental glands is situated in front of the nidamental glands, opening into the mantle cavity by numerous minute pores. All these glands serve to secrete the elastic egg Capsules.
Copulation
In Septa, the fourth left arm of the male is specially modified as an intromittent organ for copulation by the suppression of some basal rows of suckers, and is called the hectocotylus. The male inserts it in the own mantle cavity to extract the spermatophores, or the elastic capsules felled with sperms. Next this arm is thrust into the mantle cavity of the female with its load of spermatophores which are quilted on the bursa copulatrix, or a modified part of the funnel.
The eggs are larger and the developing embryos feed on large amount of stored food yolk. The young ones that hatch out are like the adults.

Fig. 14. Sepia. A cluster of eggs.