186 ttiE ENTOMotiOGIST* 



CONTRIBUTIONS to the CHEMISTRY of INSECT COLOURS. 



By F. H. Perry Coste, F.C.S., F.L.S. 



(Continued from p. 170.) 



VI. — The Biological Aspect {continued). 



In the next place, it has appeared to me very strongly 

 suggestive that so many varieties are obtained by breeding : with 

 certain red species, I believe, that by breeding on the large scale 

 a percentage of yellow varieties may be certainly expected :* now, 

 it is certain that in breeding insects the natural conditions of life 

 are never attained, and it is therefore not at all strange that a 

 certain derangement of the constitution should occur, leading to 

 imperfect colour development, i. e., to retrogressive varieties.f 

 Very strongly confirmatory, I think, of this view is a fact that I 

 found recorded in the ' Entomologist ' (xxiii. p. 134), by Mr. 

 Johnson, who states that a large brood of ^. caia, reared by him, 

 produced a large percentage of yellowish, &c., varieties, and also 

 very many cripples. I 



It must be noted further that, by this principle of indirect 

 action, through affecting the constitution, &c., we may equally 

 explain such varieties as the albino specimens of L. phlceas and 

 the various heath butterflies : it would be exceedingly interesting 

 and instructive if someone who has the opportunity would breed 

 such species on a large scale, keeping them short of food, or 

 otherwise exposing them to somewhat unhealthy conditions ; in 

 such case one ought to find — if the above view be correct — a 

 large number of albino varieties. And lastly, I may note a circum- 

 stance cited by Wallace — that there is an abnormally large per- 

 centage of pale or white varieties on islands, especially on small 

 ones. It must seem certainly well-nigh impossible to correlate 

 this with any chemical peculiarities of the soil,§ but it is easy to 

 undertand that the general conditions may so affect the con- 

 stitution as to arrest the development of pigment. i| Taking all 

 these facts into consideration, therefore, it does appear to me 

 that there are at least very strong grounds for hesitating to 

 invoke any so direct a factor as the chemical peculiarities of soil 

 or food in order to account for coloric variations ; and that there 

 is at least some reason to ascribe the variations to general 



* Cf,, however, a statement in Entom. xxii. p. 259. 



t Of course, it is necessary to the validity of this argument that a larger 

 percentage of such varieties should occur among bred specimens than among those 

 in the natural state. It would be interesting to know whether or not such is 

 the case. 



I Gf. also Mr. Mitchell's note in Entom, p. 171. Mr. Johnson does not state 

 whether any of the yellowish varieties were also cripples or not. 



§ If it be assumed that the presence of salt in the food has anything to do with 

 this, we ought to find similar varieties on all shore lines. 



II If, indeed, the whole question be not one of selection for some end, of which 

 we are at present ignorant. 



