Zoological Society. 499 



their natural powers : and what is most remarkable, utero-gestation 

 resumed its process to accomplish the period, from the time it had 

 been arrested, as though no circumstance had suspended the opera- 

 tion, and the time destined by Nature for its completion. I conclude 

 the Helix to be insusceptible of prospective fecundation, that is, one 

 communication of the sexes being sufficient for more than one con- 

 ception, or there would probably before this time have been another 

 brood of young ones, as the parent is still living and flourishing. 



To render this paper more perfect, I will add a few other exam pies 

 relating to the same subject. Dr. Baird has recorded in the 'Annals 

 of Natural History ' for July last, the circumstance of an Egyptian 

 Helix, the " Snail of the Desert," the Helix maculosa of De Ferussac, 

 having remained gummed to a tablet in a show-case of the British 

 Museum during four years, when the existence of an apparently re- 

 cently formed epiphragm being observed, it was removed from the 

 tablet and placed in tepid water, and in a short time crawled away. 

 It fed on cabbage-leaf, and began very soon the completion of a re- 

 pair of the aperture of its shell, which had been broken prior to its 

 capture, the suspension of animation having arrested the execution of 

 the work. It resuscitated on the loth of March last, but has shown 

 neither signs nor result of fecundation, although still living. 



I am indebted to Mr. T. Vernon "Wollaston (who interspersed his 

 entomological pursuits, during a two seasons' residence on the island, 

 with a no less fruitful and valuable research in terrestrial concho- 

 logy) for several species of living mollusks, principally Helices, indige- 

 nous to Madeira and its adjacent rocks : all these had lain in a box in 

 drv canvas bags for a year and a half, and had been restored to vitality 

 bv placing them in water. They were put under glass shades, on 

 flower-pots filled with mould, or in large glass cases, and all fed well. 

 Three individuals of the Helix undata of Lowe, within forty hours, 

 deposited more than two hundred small, white, semipellucid pearl-like 

 eges, which, on exposure to the air, soon became of an opake white ; 

 not in a covering, nor agglutinated, but together, loose in the earth. 

 One portion or nidus, about sixty in number, I immediately restored 

 to their situation, about three-quarters of an inch below the surface, 

 covering them with mould, hoping therefrom to learn the period of 

 incubation. The parents burrowed their heads and bodies into the 

 earth, remaining in that position some twenty or thirty hours, or 

 forced themselves, shell and all, below the turf, and so deposited their 

 ova. Other species have also produced eggs. 



Curious and instructive as these facts may be, perhaps the conti- 

 nuance of the vital principle in mollusks removed from their native 

 element may seem still more so, especially iu the case of a bivalve, 

 which has so much less perfectly the power of excluding the influence 

 of atmospheric air on its animal substance ; yet the latency of ani- 

 mation is a quality obviously necessary for the inhabitants of ponds 

 and other shallows, which of course at certain seasons are liable to be 

 dried, or the existence of the species would soon become extinct. An 

 Unio, which lives in ponds, and much resembles the British species, 

 T'nio tvmidus of Retzius, but is somewhat higher and shorter, was 



