NOVEMBEE 25, 1910] 



SCIENCE 



735 



mann obtained similar results with the 

 same species. E. Fischer obtained parallel 

 results with Arctia caja, a brightly colored 

 diurnal moth of the family Bombycidaj. 

 Pupffi of this moth were exposed to a tem- 

 perature of 8° C, and some of the butter- 

 flies that emerged were very dark-colored 

 aberrant forms. A pair of these dark aber- 

 rants were mated, and the female pro- 

 duced eggs, and from these larvae and pupse 

 were reared at a normal temperature. The 

 progeny was for the most part normal, but 

 some few indi^dduals exhibited the dark 

 color of the parents, though in a less de- 

 gree. The simple conclusions to be drawn 

 from the results of these experiments is 

 that a proportion of the germ-cells of the 

 animals experimented upon were affected 

 bj' the abnormal temperatures, and that the 

 reaction of the germ-cells was of the same 

 kind as the reaction of the somatic cells 

 and produced similar results. As every- 

 body knows, Weismann, while admitting 

 that the germ-cells were affected, would 

 not admit the simple explanation, but gave 

 another complicated and, in my opinion, 

 wholly unsupported explanation of the 

 phenomena. 



In any ease tliis series of experiments 

 was on too small a scale, and the separate 

 experiments were not sufficiently carefully 

 planned to exclude the possibility of error. 

 But no objection of this kind can be urged 

 against the careful and prolonged studies 

 of Tower on the evolution of chrysomelid 

 beetles of the genus Lcptinotarsa. Leptino- 

 tarsa — better known, perhaps, by the name. 

 Doryphora — is the potato-beetle, which has 

 spread from a center in north Mexico 

 southwards into the isthmus of Panama 

 and northwards over a great part of the 

 United States. It is di^-isible into a large 

 number of species, some of which are domi- 

 nant and widely ranging; others are re- 

 stricted to very small localities. The spe- 



cific characters relied upon are chiefly refer- 

 able to the coloration and color patterns of 

 the epicranium, pronotum, elytra and under- 

 side of the abdominal segments. In some 

 species the specific markings are very con- 

 stant, in others, particularly in the com- 

 mon and wide-ranging L. decemlineata, 

 they vary to an extreme degree. As the 

 potato-beetle is easily reared and main- 

 tained in captivity, and produces two 

 broods every year, it is a particularly 

 favorable subject for experimental investi- 

 gation. Tower's experiments have ex- 

 tended over a period of eleven years, and 

 he has made a thorough study of the geo- 

 graphical distribution, dispersal, habits 

 and natural history of the genus. The 

 whole work appears to have been carried 

 out with the most scrupulous regard to 

 scientific accuracy, and the author is un- 

 usually cautious in drawing conclusions 

 and chary of oft'ering hypothetical expla- 

 nations of his results. I have been greatly 

 impressed by the large scale on which the 

 experiments have been conducted, by the 

 methods used, by the care taken to verify 

 every result obtained, and by the great 

 theoretical importance of Tower's conclu- 

 sions. I can do no more now than allude 

 to some of the most remarkable of them. 



After showing that there are good 

 grounds for believing that color produc- 

 tion in insects is dependent on the action 

 of a group of closely related enzymes, of 

 which chitase, the agent which produces 

 hardening of chitin, is the most important, 

 Tower demonstrates by a series of well- 

 planned experiments that colors are di- 

 rectly modified by the action of external 

 agencies — viz., temperature, humidity, 

 food, altitude and light. Food chiefly 

 affects the subhypodermal colors of the 

 larv£E, and does not enter much into ac- 

 count ; the most important agents affecting 

 the adult coloration being temperature and 



