ADAPTATION IN COLORATION. 21 5 



tion of the germ cells, shields them from external stimuli by its capacity to 

 absorb or compensate therefor. Of more importance, however, is the fact 

 that animals, or Leptinotarsa, at any rate, reproduce or mature the germ 

 cells only under favorable conditions, and then within narrow limits. Of 

 still greater moment is the fact that the germ cells are not equally sensi- 

 tive to stimuli in all their stages of development. Thus, in Leptinotarsa, 

 in both tropical and temperate latitudes, the germ cells do not develop nor 

 reproduction take place until the conditions of temperature and moisture are 

 favorable. For example, I have found specimens of signaticollis which 

 were active as early as April 15, whose germ cells did not begin to grow or 

 that did not begin to reproduce until about June 1, when the arrival of the 

 rainy season insured the necessary amount of moisture. In the dry plateau 

 of northern Mexico and the southwestern part of the United States Leptino- 

 tarsa may emerge from aestivation weeks before the rains come, but they 

 do not breed until the rains begin. Likewise, in the northern United States 

 and Canada, decemlincata may emerge from the ground in April, but the 

 germ cells do not begin to grow until the coming of the warm, moist days in 

 May, or possibly June. In experiment it has been my most difficult problem 

 to induce these beetles to breed under changed conditions. Germ-cell growth 

 and reproduction for a given species takes place, therefore, only under condi- 

 tions within the narrow limits to which it is adapted, but after the eggs are 

 fertilized and laid, hot, cold, wet, or dry spells act as stimuli upon the soma 

 and produce results like those which we have already described under "Place 

 and geographical variation." 



Permanent, heritable color modifications of Leptinotarsa have been found 

 in nature, and are indistinguishable from somatic variations excepting in their 

 capacity for being transmitted to subsequent generations. They, however, 

 have no relation to the variations herein described. 



ADAPTATION IN COLORATION. 

 WARNING COLORATION. 



Almost all the species of Leptinotarsa are conspicuously colored white and 

 black, yellow and black, red and black, metallic green, or blue ; and all, both 

 larva; and adults, live freely exposed upon their food plants. The combina- 

 tions of yellow, white, or red with blacks are regarded as warning colors, 

 especially by the supporters of the theory of natural selection, and serve to give 

 notice of the supposed inedibility of the possessor of the colors. This theory 

 of warning colors has been developed mostly by the English naturalists, Dar- 

 win, Wallace, and Bates, and by Miiller, Hasse, and others from observations, 

 and by Poulton from experimentation, all of whom consider warning color- 

 ation to be due to natural selection. I have had an opportunity to examine 

 this phenomenon quite extensively in Leptinotarsa, and to obtain data from 

 nature and in experiment that goes to support the idea of utility in the above 

 color combinations. 



