128 COLORATION IN LEPTINOTARSA. 



EFFECT OF ENVIRONMENT UPON COLORATION. 



Many well-known facts point to the immediate action of temperature, mois- 

 ture, food, light, etc., upon the coloration of insects. That changes in tem- 

 perature can and do effect modifications in coloration and dimorphism is 

 abundantly proven by the work of Dorfmeister, Edwards, Weismann, Merri- 

 field, Urech, Fischer, and Standfuss, while the last two authors have been 

 able to produce an inheritance of the modification in the second genera- 

 tion. Seasonal variations as the result of the varying conditions of wet and 

 dry seasons are of common occurrence in the tropics. As a rule, however, 

 the modifications produced in experiments along this line have not been 

 inherited in subsequent generations ; and this has given Weismann, Poulton, 

 and others a basis for strong arguments against the possibility of the validity 

 of the Lamarckian doctrine of evolution in insect coloration through the 

 inheritance of acquired characters. 



PROTECTIVE RESEMBLANCE, WARNING COLORATION, MIMICRY. 



Wallace's theory of warning coloration and Darwin's theory of protective 

 resemblance, with its special phase of mimicry elaborated by Bates and 

 Muller, have secured strong support from the observations in nature of 

 Bates, Midler, Weismann, Tremen, and others, and from the experimental 

 researches of Poulton and Finn. These phenomena can at present be best 

 explained by the hypothesis of selection. Attempts at explanation by other 

 theories always show lamentable weakness or peculiarities of logic not easily 

 explained. In fact, natural selection as a cause of evolution in insect color- 

 ation receives its strongest support from the data and observations cen- 

 tered about these phenomena. Arguments against the theory of protective 

 resemblance, warning coloration, and mimicry are few and of doubtful valid- 

 ity ; and the facts used are cases of convergent evolution of questionable 

 application. Altogether, no other phenomena, I believe, argue as strongly and 

 successfully for the truth of the principle of natural selection as these mar- 

 velous phenomena of insect coloration. 



THE PROBLEMS OF INSECT COLORATION TO-DAY. 



It was truly and well said by Darwin that "the coloring of insects is a 

 complex and obscure subject." Before we can proceed much farther in the 

 subject we must understand better the nature, source, and development of 

 color and color-producing substances and their relation to the physiology of 

 the animals in question. When we have this knowledge at hand then shall we 

 be prepared to investigate the action of environment upon coloration, and to 

 understand more fully whether evolution has been along definite lines 

 according to an orthogenetic principle, or fortuitous, guided by natural 

 selection. 



