GASTEROPODA. 



401 



Fig. 199. 



Mule organs of Buccinum. 



able by the enormous penis attached to the 

 right side of the neck (jig. 199), which is not, 

 as in the last division, capable of retraction 

 within the body, but remains permanently ex- 

 ternal, being, when not in use, folded back and 

 lodged within the branchial cavity, from which 

 however it is frequently protruded without any 

 apparent object. 



In the female there is no rudiment of such 

 a structure, but the generative aperture is seen 

 to be situated a little within the edge of the 

 pulmonary cavity, being a simple hole leading 

 to the oviduct. The internal organs of the 

 male, represented in the annexed figure, con- 

 sist simply of a testicle and its excretory canal. 

 The testis is of considerable size, sharing with 

 the liver the smaller convolutions of the shell ; 

 from this arises the vas deferens, which forms 

 by its convolutions a kind of epididymis 

 (jig. 199, 6), and then increasing in diameter 

 enters the root of the penis, through which it 

 passes by a tortuous course (d) to the tubercle at 

 the extremity of this organ, where it opens 

 externally. The penis when opened, as re- 

 presented in the engraving, is seen to contain 

 strong transverse fasciculi of muscle, which 

 probably cause the erection of this organ ; they 

 will at the same time lengthen it, so as to 

 destroy in a great measure the zig-zag turns 

 into which the vas deferens is thrown in its 

 usual relaxed state. 



In the female the position of the testicle is 

 occupied by the ovary, while the vas deferens 

 is represented by a thick and glandular oviduct. 



In Murex the penis of the male is pro- 

 portionally smaller ; and, instead of a com- 

 plete vas deferens, penetrating to its extremity, 

 there is merely a groove along its surface, along 

 which the semen flows. In Valuta the ex- 

 terior groove only runs to the base of the penis, 

 and in Strombus the male organ is a mere 

 tubercle. 



In the Pulmonalia operculata the organs of 

 both sexes are in every respect similar to those 

 of the Pectinibranchiate order. In Paludina 

 alone (Helix vivipara, Lin.) the penis is retrac- 



tile,issuingfrom ahole found in the right tentacle, 

 and from the disparity in size between the 

 tentacles, arising from this cause, the male is 

 readily distinguished. The females of this 

 genus are not unfrequently ovo-viviparous, 

 the ova remaining in their capacious oviduct 

 until they are hatched. 



Spallanzani asserts that, if the young of 

 Paludina are taken at the moment of their 

 birth, and kept entirely separate from others of 

 their species, they can reproduce without im- 

 pregnation, like the Aphides and Monoculi, 

 in which the same connexion with the male 

 is found to fecundate not only the female 

 herself, but her offspring for several generations. 

 Nevertheless, whether Spallanzani's observa- 

 tions be correct or not, the males are fully as 

 numerous as the females, so that it would be 

 difficult to imagine the object of such a de- 

 viation from the ordinary proceedings of na- 

 ture. 



Ova. The spawn of the Gasteropod Mol- 

 lusca is found under diverse forms ; it is 

 usually in the marine species attached to the 

 surface of stones, shells, or sea-weed, the ova 

 being connected with each other in long ri- 

 bands or delicate festoons, which are some- 

 times extremely beautiful and curious. The 

 Doris and Tritonia deposit their ova in this 

 manner, and the mass of eggs deposited by 

 them resembles a frill of lace of extreme 

 beauty. In Aplysia the spawn is found to 

 resemble long gelatinous threads, in the centre 

 of which the ova are seen, varying in tint, so 

 as to give different colours to different parts of 

 the thread; the whole strikingly resembles 

 strings of vermicelli, and the Italians in fact 

 have applied to them the name of vermicelli 

 marini. In Helix and Bulimus the eggs are 

 naked and protected by a hard shell, whilst in 

 Buccinum, Voluta, Murex, and other marine 

 species, the ova are enveloped in membranous 

 sacs agglomerated together in large bunches ; 

 these sacs have been erroneously regarded as 

 the eggs themselves; they are, however, merely 

 coriaceous envelopes, answering the purpose 

 of the gelatinous coating enclosing the eggs of 

 other species, several eggs being contained in 

 each bag, in which, when mature, the young are 

 easily seen. It would seem that extraordinary 

 provisions have been made by nature for the 

 multiplication of these creatures, in spite of 

 the numerous enemies which devour them, or 

 the vicissitudes of temperature to which, espe- 

 cially in the terrestrial species, their eggs are 

 necessarily subject. We are indebted to M. 

 Leuchs for several interesting observations 

 concerning the ova of slugs, which explain in 

 a great degree the quantities of them \vhich in 

 some seasons infest gardens and vineyards, 

 becoming, from the devastation which they 

 cause, serious plagues to the agriculturist. 

 The number of eggs varies with the healthiness 

 of the animal, the supply* of food, or the tem- 

 perature of the season ; yet it is probable 

 that a single slug will lay five hundred, under 

 ordinary circumstances: thus, supposing a 

 thousand of these creatures to be collected in 



