180 HELICID^. 



single brood in the year. The eggs are about the size 

 of a small pea, and much resemble in colour and con- 

 sistency the berries of the mistletoe. They are laid in a 

 kind of nest, which the mother snail makes in the loose 

 earth, in order to protect them from wet and the heat of 

 the sun. No incubation is necessary, and they are left 

 to the care of nature. The young are developed at the 

 end of from twenty-one to forty-five days, according to 

 the season and state of the temperature. The little snail, 

 when it is first excluded, lives only on the pellicle of the 

 egg, the whole of which is eaten by it. This provision 

 is similar or analogous to that which is appropriated to 

 the young of land vertebrate animals. The experiments 

 made by M. Gaspard with respect to the function of 

 those organs in snails which are called " eyes,'^ led him 

 to conclude that these mollusks are totally devoid of 

 sight and are quite insensible to light, that they do 

 not perceive an obstacle placed in their way until they 

 touch it, and that, after being deprived of their horns 

 which support the so-called eyes, they guide themselves 

 as surely as before. It may be observed that this 

 absence of sight and apparent insensibility to light are 

 quite consistent with the nocturnal habits of snails. 

 Perhaps the deficiency of this sense is supplied by the ex- 

 cessive susceptibility of the skin to outward impressions. 

 M. Gaspard remarks that he found in these pretended 

 optical bodies, or " eyes,^^ nothing more than the organs 

 of an exquisite sense of touch, arising from a large nerve 

 Avhich runs through the tentacles and is expanded over 

 their extremities. He also denies the existence of any 

 sense of hearing or smell in these mollusks ; but this 

 latter statement does not appear to agree with the ob- 

 servation of subsequent writers. 



