NATURAL SCIENCES OF PHILADELPHIA. 215 



These characters would seem to imply a case of hybridism, but 

 I think differently. Having raised scores of the males and 

 females of both species in the same box, I have never observed a 

 single irregular union the males of both invariably seeking their 

 own kind. So deeply is the sexual instinct implanted in them 

 that the females, ratlier than submit to copulation with species 

 essentially unlike, deposit their ova unfertilized. I am inclined 

 to the belief that G. i-egalis, l)eing a higher type of insect than D. 

 imperialis had been evolved from the latter in obedience to inter- 

 nal changes brought about through the medium of nutrition; said 

 changes having been moderately sudden instead of slow and 

 gradual. 



That nutrition plays such an important part in the evolution of 

 species, may seem to be speculation, without facts to sustain it. 

 If nutrition should be proved to be the means by which the sexes 

 in insects are controlled, as a paper in " The American Naturalist," 

 b}' Mrs. Mary Treat, would indicate, I cannot discern why it should 

 not be applicable to a certain extent to the production of species. 



In the case under consideration, the change from diet contain- 

 ing but a small percentage of nutritive matter, as leaves of 

 conifers possess, to more nutritious food, has, in my estimation, 

 been the agent in producing the changes above indicated. That 

 these changes have not been going on for indefinite periods, but 

 have been the work of a short time, I think is evident. 



If, through the medium of nutrition, D. imperialis is brought 

 to assume many of the prominent characters of C. regalis, I do 

 not see the propriety of placing the former in a distinct genus 

 from the latter, in consequence of a slight difference in the size of 

 the antennae, and in the position of the posterior wings in a state 

 of rest in the adult state : as the close resemblance which obtains 

 between the two larvae when young, seems to imply a near rela- 

 tionship. Harris, in referring D. imperialis, of Drury to Dryo- 

 campa, did so under considerable hesitation. The fact that there 

 is such a near alliance, backed up by those set forth in this paper, 

 if they are rightly interpreted, would seem to warrant its rein- 

 statement in the old genus Ceratocampa, 



