IV.J THE COMMON SNAIL. 277 



ccecal diverticulum of the base of the penis which secretes 

 a mucilaginous investment for the spermatozoa ; the sper- 

 matophores or packets of spermatoza thus formed are trans- 

 ferred, during copulation, to a corresponding ccecal diver- 

 ticulum of the oviduct known as the receptaculum seminis. 

 Fleshy valves are developed within the lips of the genital 

 cloaca and at the orifices of the genital ducts which open 

 into it, and the whole condition of the organs is such as to 

 obviate the possibility of self-fertilization. 



In the spiculum amoris, an accessory to the female portion 

 of the apparatus (see Sect. G. 3 f.) we have a structure, 

 almost without parallel in the whole animal kingdom. It 

 reaches maturity during the breeding season, and is forcibly 

 ejected from individual to individual during the amorous 

 overtures, which last for a period of some hours. 



The spermatozoa are long filiform bodies, each with 

 an enlarged nucleus-bearing "head." The ova are chiefly 

 noteworthy on account of the absence of a distinct vitelline 

 membrane ; they are comparatively large and are provided 

 with a nutritive food-yolk. 



The reproductive elements of opposite sexes ripen alter- 

 nately, the maturation of a given batch of spermatozoa pre- 

 ceding that of the ova they are destined to fertilize, and in 

 view of the facts above related it follows that the sperma- 

 tozoa must be transferred, during copulation, to the body of 

 the second individual — there to await the descent of the ova. 



Fertilization takes place as the ova leave the body, and 

 there are to be found in the haunts of these animals during 

 the summer months, usually beneath some stone or de- 

 caying wood or more rarely buried in the earth itself, 

 aggregates of 100 or more eggs, each invested in an albu- 

 minous envelope, within which the early developmental 

 phenomena are undergone. 



