246 Biology in America 



settlors bronglit with them plenty of English grit, Scotch 

 whiskey ;iml Irish ])otatoes; and the beetles, finding the lat- 

 ter more to their liking than their native food, soon showed 

 proper appreciation of the good things set before them, and 

 became inveterate potato feeders. After this change in the 

 diet, it was not long before they had overrun all of the 

 eastern United States and lower Canada. 



There are many species of these beetles, distributed in 

 different parts of the range of the genus, and most of them 

 show considerable variation. There are two generations each 

 season, the duration of each varying both with the species and 

 the locality. The beetles retire for the winter underground 

 and upon emergence in spring, seek out the potato plants, 

 upon which the eggs are laid. From these hatch the grub- 

 like larvae, which after a varying period cease feeding, and 

 drop to the ground into which they burrow and there pupate, 

 surrounding themselves with a thin shell. From this the 

 adult beetles escape, make their way to the surface and pro- 

 ceed to a repetition of this performance, the second brood 

 of beetles hibernating in the earth at the end of summer. If 

 the larvae are taken soon after hatching and kept in experi- 

 mental cages at higher or lower temperatures than normal, 

 or in more or less humid atmospheres, or in various combina- 

 tions of temperature and humidity, until development is com- 

 plete, the adult beetle developing from them will be lighter 

 or darker in shade and will show many differences from the 

 usual color pattern, these differences in many cases closely 

 corresponding to differences in beetles from different locali- 

 ties. Thus it was possible to produce in the laboratory in 

 Chicago beetles resembling closely those occurring in nature 

 in Arizona, The same stimulus produced different results 

 depending upon its strength. Thus a moderate increase of 

 temperature made the beetles darker in color, while a greater 

 increase made them lighter, and precisely similar results were 

 obtained by lowering the temperature, and by raising and 

 lowering the relative humidity. 



But these results were temporary, lasting for one genera- 

 tion only, and were not inherited. If on the other hand the 

 beetles, shortly before egg-laying occurred, were subjected to 

 similar conditions, variations were produced which persisted 

 in subsequent generations. In the former case only the 

 "soma" or body cells of the individual were affected; in the 

 latter, the germ cells at a sensitive stage in their develop- 

 ment — at least so Professor Tower interprets his results. 

 Samples of some of his "creations" are shown in the accom- 

 panying figure. 



Not alone by laboratory experiment is it possible to control 



