40 MANUAL OF THE MOLLUSCA, 



"with, snails (in cool weather) it is generally a degree or tvro 

 higher. 



The moUusca of temperate and cold climates are subject to 

 hyhernation ; during which state the heart ceases to beat, 

 respiration is nearly suspended, and injuries are not healed. 

 Thoy also cestivate, or fall into a summer sleep when the heat is 

 great ; but in this the animal functions are much less inter- 

 rr.pted. — {3IuUer. ) 



Reproduction of lost parts. It appears from the experiments 

 of Spallanzani, that snails, whose ocular tentacles have been 

 destroyed, reproduce them completely in a few weeks ; others 

 have relocated the trial with a like result. But there is some 

 doubt whether the renewal takes place if the brain of the animal 

 be removed as well as its horns. Madame Power has made 

 similar observations upon various marine snails, and has found 

 that portions of the foot, mantle, and tentacles, were renewed. 

 Mr. Hancock states that the species of eolis are apt to make a 

 meal off each other's p)apillce, and that, if confined in stalo 

 water, they become sickly and lose those organs ; in both cases 

 they are quickly renewed under favourable circumstances. 



Viviparous reproduction. This happens in a few species of 

 gasteropods, through the retention of the eggs in the oviduct, 

 until the young have attained a considerable growth. It also 

 appears to take place in the acephalans, because their eggs gene- 

 rally remain within some part of the shell of the parent until 

 hatched. 



Oviparous reproduction. The sexes are distinct in the most 

 highly organised (or dioecious) moUusca ; they are united in the 

 (moncecious) land-snails, pteropods, oj^isthobranchs, and in some 

 of the conchifers. The prosobranchs pair ; but in the dioecious 

 acephalans, the spermatozoa are merely discharged into the 

 water, and are inhaled with the respiratory currents by the 

 other sex. The monoecious land-snails require reciprocal 

 union; the limneids unite in succession, forming floating 

 chains. 



The cgrjs of the land-snails are separate, and protected by a 

 shell, which is sometimes albuminous and flexible, at others 

 calcareous and brittle ; those of the fresh-water sj)ecies are soft, 

 mucous, and transparent. The spawn of the sea-snails consists 

 of large numbers of eggs, adhering together in masses, or sjDread 

 out in the shape of a strap or ribbon, in which the eggs are 

 arranged in rows ; this nidamental rihhon is sometimes coiled 

 up spirally, like a watch- sjpring, and attached by one of its 

 edges. The eggs of the carnivorous gasteropods are enclosed 



