40 - MANUAL OF THE MOLLUSCA. 
with snails (in cool weather) it is generally a degree or two 
higher. 
The mollusca of temperate and cold climates are subject to 
hybernation; during which state the heart ceases to beat, 
respiration is nearly suspended, and injuries are not healed. 
They also cestivate, or fall into a summer sleep when the heat is 
_ great; but in this the animal functions are much less inter- 
rupted.—( Miller.) 
Reproduction of lost parts. It appears from the experiments 
of Spallanzani, that snails, whose ocular tentacles haye been 
destroyed, reproduce them completely in a few weeks; others 
have repeated 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 papiile, and that, if confined in stale 
water, they become sickly and lose those organs; in both cases 
they are quickly renewed under fayourable 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 dieciows) mollusca; they are united in the 
(monecious) land-snails, pteropods, opisthobranchs, and in some 
of the conchifers. The prosobranchs pair; but in the dicecious 
acephalans, the spermatozoa are merely discharged into the 
water, and are inhaled with the respiratory currents by the 
other sex. The moncecious land-snails require reciprocal 
union; the lmneids unite in succession, forming floating 
chains. 
The eggs 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 species are soft, 
mucous, and transparent. The spawn of the sea-snails consists 
of large numbers of eggs, adhering together in masses, or spread 
out in the shape of a strap or ribbon, in which the eggs. are 
arranged in rows; this nidamental ribbon is sometimes coiled 
up spirally, like a watch-spring, and attached by one of its 
edges. The eggs of the carniyorous gasteropods are enclosed 
