126 THE INFLUENCE OF INANIMATE SDKEO ENDINGS. 



as is often assumed, necessarily indicate tHe completion of in- 

 dividual growth. They may no doubt coincide, but they need 

 not ; and instead of being surprised, as is frequently the case, 

 at finding that larvae, i.e. animals not yet fully grown, are sexu- 

 ally mature — e.g. Salamandra, Siredon, Blatta, and others — we 

 ought rather to wonder that it is only quite recently that such 

 cases have been investigated and considered worthy of record. 

 An example of this kind, recently observed by me, is offered by 

 the land-snails of the Mediterranean province. It is tnown 

 that on high mountains or in high latitudes land-snails are fre- 

 quently hindered by the low temperature from assimilating 

 within a given time as much nourishment as others of the same 

 species living on the plain or in a warmer climate, so that they 

 never attain the same size, though they are capable of reprodvic- 

 tion. In this case it would be possible that the first sexual 

 maturity and the last stage of growth might coincide, although 

 the mature animal was of a small size. It is quite otherwise 

 with the snails of the warm Mediteri'anean region. These, as I 

 know from my own observations, are brought to sexual matu- 

 rity by the time they are six months old by the intense heat 

 combined with the sufficient moisture of the spring, though 

 they are not fully grown ; after a summer's rest of thi'ee 

 months, occasioned by the drought, a second period of egg 

 deposition occurs at the beginning of winter, although the full 

 size of the animal, as indicated by the completion of the margin 

 of the mouth of the shell, is not attained tUl the second period 

 of sexual sictivity. Thus species of the same genera, perhaps 

 even the very same species, in our damp and cold climate, do 

 not produce a new generation till they are fully grown, while 

 in the dry warm region of the Mediterranean they have pro- 

 duced two generations before they are fully grown. This is 

 probably the true explanation of what are known in the ter- 

 minology of the zoologist as Larva-forms,^^ a narce given to all 

 animals which possess the characters of the larvae of other 

 species and are nevertheless capable of sexual reproduction, 

 Such larva-forms occur in almost every group, in Vertebrata, 

 Mollnsca, Ascidians, "Worms, &c. A very striking example 

 occijrs, among creatures of such high physiological development 



