CHAPTER IX 



EXPERIMENTS WITH SNAILS, MOTHS, AND BEETLES 



THE European snails, Helix hortensis and Helix nemoralis, 

 have been studied by Lang, whose experiments in breeding them 

 have extended over several years and, though still in progress, 

 have already yielded decisive results on a number of important 

 points. The young snails require at least two years, generally 

 three, and often four years to reach maturity. The animals, 

 although hermaphroditic, do not self-fertilize, as isolation experi- 

 ments have shown. The sperm, received during copulation, 

 may remain alive for several years in the receptaculum seminis, 

 therefore wild individuals cannot be used safely in breeding ex- 

 periments, but the young snails must be first reared and isolated 

 and paired in order that the parentage of their offspring can be 

 certainly known. 



The bands of pigment on the shell are the chief characters 

 that Lang has studied in his experiments. Colonies of snails 

 are sometimes found in which only two kinds of individuals are 

 met with, those with five bands and those without bands, no 

 intermediate types existing in such colonies. These colonies 

 furnish the best materials for breeding experiments. In such 

 colonies the banded individuals are "pure," that is, they breed 

 true to their type. It is more difficult to obtain "true" indi- 

 viduals without bands. Those are most likely to breed true 

 that are found in colonies in which only bandless individuals 

 exist. 



If virgin banded and bandless individuals are allowed to 

 pair and are then separated, each will make a nest in the ground 

 and deposit from 40 to 60 eggs, or more. The banded indi- 



