400 



GASTEROPODA. 



(436.) The sac of the dart first requires our attention. This 

 viscus, when unin verted, for it must be turned inside out in order 

 to expose the we t apon within it, is a thick muscular bag (Jig. 183, 

 a?) ; and, on opening it, it is found to contain the dart attached to 

 a nipple-like protuberance at the bottom of the sac. The dart 

 itself is four-sided ; and as it grows by the constant addition of cal- 

 careous particles deposited at its base from the surface of the 

 vascular protuberance to which it is fixed, so, if broken off, it is 

 speedily reproduced in a similar manner. 



(437.) The male part of the generative system is composed of 

 a testicle, vas deferens, and the whip-like penis above described. 



The testicle is considered by Cuvier* to consist of two distinct 

 portions: one, a soft whitish oval mass (Jig. 183, p) ; while the 

 other is elongated, thin and granular (y) 9 being imbedded among 

 the convolutions of the oviduct (z*?). The vas defer ens forms the 

 excretory duct of both these portions, and terminates in the side of 

 the penis ; its orifice becoming of course external when that organ 

 is protruded by evolution. The intromittent organ itself, as seen 

 when lodged within the body of the snail, consists of two parts, 

 a muscular bag which forms its body (b') 9 and a long whip-like 

 portion z ; the latter is hollow, but not perforated. The reader 

 will now have little difficulty in understanding how this remarkable 

 apparatus is protruded. The generative sac, common to both the 

 male and female organs, first becomes inverted ; the body of the 

 penis (>') then undergoes inversion in a similar manner, so that the 

 orifice of the vas deferens appears externally ; and lastly, the long 

 appendage to the penis, z 9 being likewise turned inside out by the 

 action of the muscles that compose its walls, completes this strange- 

 ly constructed instrument. Its subsequent retraction into the 

 visceral cavity is effected partly by the assistance of a special re- 

 tractor muscle (a), which acts upon the body of the penis, but 

 principally by the same contractility that accomplished its evo- 

 lution. 



(438.) The female system next demands our notice ; and this 

 will be found to present for our investigation an ovary and lengthy 

 oviduct, to which are appended certain auxiliary organs, namely, 

 the spermatheca and the multifid vesicles. 



The ovary (Jig. 183, s) is found situated in the inmost recesses 

 of the shell, and partially imbedded in the substance of one of 

 the lobes of the liver. From the ovary a long oviduct (g) is de- 



* Loc. cit. 



