112 ENTOMOLOGICAL NEWS. [April, '05 



the last segment. I separated these larvae from the healthy 

 ones, and upon the next morning I found most of them to have 

 changed to a blue-black, some of them spotted and others very 

 dark, and it could be plainly seen that the spots developed from 

 within the larvae. They did not feed again until the change 

 of color was completed, which was generally on the third day. 

 The pupation of these specimens was delayed just the number 

 of days which it required for this color change. Every one 

 of these larvae developed into glaucus females, while the green 

 and brown larvae developed into the yellow form. My next 

 object was to try find the reason. I succeeded in obtaining 

 eggs of the second generation and again reared a large number 

 of the larvae with exactly the same result. 



After those larvae which changed their color as above had 

 gone through their last moult I examined the foliage upon 

 which they had fed, and I discovered that the leaves were 

 sprinkled over with fine black spots and were completely cov- 

 ered over with a gummy substance. The nature of the phe- 

 nomena I could not determine, but do not doubt that botanists 

 can explain it. I now placed a number of green larvae on this 

 diseased foliage, and after one to two days feeding they changed 

 their color, although not so intensely, the reason for which, in 

 my judgment, is that they were too near pupation, these latter 

 larvae developed into specimens bearing a more or less large 

 yellow spot in the centre of the anterior wings. To prove that 

 my observations were well founded I reared a number of larvae 

 of the next generation on healthy foliage and a number on dis- 

 eased foliage — I call it diseased as it turns yellow and withers 

 much before the other — and the result was, healthy foliage, 

 yellow females ; spotted foliage, black females. In. the pupae I 

 could not distinguish any differences upon which to base facts, 

 but I am convinced that the dimorphism is a diseased condi- 

 tion, brought about by diseased food plants, and as far as I am 

 able to judge at this time I believe the albino and melanic 

 forms of other species, particularly of Colias philodice, will be 

 ascribed to the same cause. But why only the one sex should 

 become so affected is a problem which must be left for a scien- 

 tist to solve. 



