698 



ZOOLOGY 



SECT. 



FIG. 604. Follicles of the hermaphrodite gland of the Gas- 

 tropoda. A, of Helix hortensis (Pulmonata) ; B, of 

 the Eolidac. a. a ova ; b. masses of sperms ; c. common 

 efferent duct. (From Gegenbaur.) 



with the oviduct, a number of narrow accessory oviducal glands 

 (muc. #/.), frequently a gland termed prostate connected with the 

 spermiduct, an eversible sac the sac. of the dart (d. s.) contain- 

 ing a crystalline stylet, and a penis (pen.}, which is perforated by a 



canal, and is capable 

 of being retracted by 

 a special muscle. The 

 duct may be simple 

 or may be incom- 

 pletely divided longi- 

 tudinally into two 

 parts. In the Pul- 

 monata the first part 

 (hermaphrodite duct 

 proper) is simple, and 

 serves for the passage 

 of both ova and 

 sperms ; the middle 

 part is incompletely 

 divided internally into 

 two passages, one serving as oviduct, the other as spermiduct. In 

 the distal part oviduct and spermiduct are completely separate. 

 Where the spermiduct enters the penis, there is given off a long, 

 slender, tapering diverticulum, the flagellum (flag.), in which the 

 sperms are made up into elongated masses or spermatophores. 



Development. The limpets (Patella) are exceptional in laying 

 the eggs one by one and unfertilised impregnation taking place 

 in the water after they have been discharged. In almost all the 

 Gastropoda fertilisation is internal, and the eggs are laid in great 

 masses, embedded in jelly each egg having its own hyaline 

 envelope. Very often the mass of spawn consisting of the jelly- 

 like substance, with the eggs embedded in it, attains a relatively 

 considerable' size. Inform it varies greatly: very often it is in 

 the shape of long strings which are cylindrical or band-like : some- 

 times several such strings are twisted together into a cord. 

 Sometimes the spawn is fixed to sea- weed or other objects ; some- 

 times it 'is unattached, and may float about freely. In the 

 Streptoneura (Fig. 605), instead of a jelly-like mass, the eggs are 

 enclosed in a firm parchment-like capsule, in which is contained, 

 in addition to the eggs, a quantity of an albuminous fluid, serving 

 to nourish the developing embryos. The shape of the capsule 

 (Fig. 605) varies greatly in the different genera ; sometimes it is 

 stalked, sometimes sessile ; in some cases there is a lid or oper- 

 culum, the opening of which permits of the escape of the embryos. 

 Very commonly large numbers of these capsules are aggregated 

 together, and usually they are attached to a rock or a sea-weed, 

 or similar object. In many cases only a limited number, some- 





