228 SNAILS AND SLUGS [CH. VII 



Further forward the two portions actually become distinct : 

 the (male) vas deferens passes under the retractor muscle 

 of the right tentacle to the muscular penis ; the (female) 

 oviduct proceeds nearly straight on to open into the 

 vagina. Eventually both penis and vagina open at their 

 common genital aperture upon the right side of the head. 

 Attached to these chief organs are numerous accessory 

 structures, some belonging to the male, others to the female 

 portion of the system. Springing from the junction of the 

 vas deferens with the penis is the long whip-like flagellum : 

 this, together with the hinder part of the penis secretes 

 an elongated band of hardened mucus whose edges are 

 rolled round to form a groove. The spermatophore, as this 

 structure is called, receives into its groove masses of 

 spermatozoa from the vas deferens and holds them as in 

 a case. In the act of mating the spermatophore and its 

 contents is transferred to the other snail via the penis 

 introduced within the vagina of the mate : it is received 

 into the duct of the receptaculum seminis (a long tube 

 terminating posteriorly in a spherical head) which is given 

 off from the posterior end of the vaginal cavity. In a few 

 days the spermatophore is dissolved and the contained 

 spermatozoa liberated in the receptaculum seminis. Here 

 they remain until the ova of the impregnated snail are 

 ready to be laid and are passing from the oviduct into the 

 vagina. They then descend the duct of the receptaculum 

 and fertilise the ova in the vagina. There are yet other 

 organs, namely the mucous glands (multifid vesicles) and 

 the singular dart-sac, connected with the vagina. The 

 mucous glands secrete a highly refractive fluid which they 



