The Reproductive System.—Broadly speaking, the complicated arrangements which are found in Mollusca resolve themselves into modifications of three important factors:—

(a) The gonads or germ-glands, in which are developed the ova and the spermatozoa. These glands are generally known as the ovary in the female, the sperm-gland or testis in the male.

(b) The channels which provide for the passage of the seminal products; namely, the oviduct in the female, the vas deferens or sperm-duct in the male.

(c) The external generative organs.

Fig. 49.—Generative and other organs of Littorina obtusata L., female.

(After Souleyet.)

Fig. 50.—Generative and other organs of Littorina obtusata L., male.