THE SNAIL 81 



the uppermost whorl but one of the spire. It consists of 

 a number of digitiform follicles, lined by a germinal epithe- 

 lium which, produces both ova and spermatozoa in each 

 follicle. The generative ducts and accessory organs of the 

 snail are shown in fig. 17. The ova and spermatozoa when 

 ripe pass outwards through the hermaphrodite duct, a single 

 much-convoluted tube, the distal end of which enters the 

 substance and receives the ducts of the large conical albumen 

 gland. From this point onwards the ova and spermatozoa 

 travel by different passages, firstly along the different sides of a 

 widish duct incompletely divided by a longitudinal partition 

 into a sacculated oviducal and a narrower spermiducal channel. 

 After a course of about three inches this conjoined duct 

 divides to form a separate oviduct and sperm duct, and finally 

 the two, after entering into relations with various accessory 

 organs, unite again to open at the common genital pore. 



The oviduct is short and thick walled, and is generally 

 spoken of as consisting of the oviduct proper and the vagina, 

 the latter being that portion of the tube which lies between 

 the openings of the accessory female organs and the genital 

 pore. The accessory organs are the dart-sac, the mucous 

 glands and the spermatheca. The first named is a thick- 

 walled cylindrical sac opening into the vagina. It contains a 

 quadrangular calcareous spicule, the so-called dart or spiculum 

 amoris which is used in copulation. The mucous glands open 

 into the vagina on either side of the opening of the dart-sac. 

 Each gland consists of a number of simple finger-like glandular 

 tubes which unite to form the mucous duct of either side. 

 The spermatheca is a long, slender outgrowth of the vagina 

 lying alongside of the conjoined oviduct and sperm-duct. Its 

 upper end is dilated into a globular vesicle, and in Helix 

 aspersa it also presents an elongated diverticulum on its course. 



The male accessory organs are the penis and flagellum. 

 The former is nothing more than a muscular portion of the 

 sperm-duct which is capable of being protruded through the 

 genital pore and withdrawn by means of a special retractor 

 muscle. The shape and relations of the long tubular flagellum 

 can best be studied in the figure. 



The spermatozoa before extrusion are lodged in a spermo- 

 phore, an elongate plate of hardened mucus formed in the 

 flagellum and rolled up to form a sort of cylinder in which the 



II. F 



