APPLE LEAVES — GENUS CHRYSOPA. 83 



this genus presented black dots and other marks upon the head 

 and thorax, but they were in all other respects so much like 

 others destitute of these spots, that I was in doubt whether they 

 were anything more than mere varieties of two species, the Pcrla 

 and chrysops of the old authors, or the American representatives 

 of those species, the one having the veinlets pale green, the other 

 having them varied more or less with black. Awaiting for some 

 fact that would throw light upon this subject, I several years ago 

 met with ten chrysalids upon the leaves of a yellow pine, attached 

 near each other, and all obviously the progeny of one parent. 

 It occurred to me that when these disclosed the perfect insect 

 they would furnish evidence whether the same species presented 

 those slight differences in its markings which I had noticed 

 among different individuals of this genus. I accordingly gathered 

 them, and in a short time obtained from them the mature flies. 

 These were all alike in every respect, and were destitute of any 

 dots or other marks except a tawny yellow spot upon the cheeks. 

 I therefore regarded this mark upon the cheeks as forming the 

 distinctive character of a species. All the specimens which 

 were obtained in the manner stated, had the veinlets of their 

 wings pale green; other individuals, however, occurred, having 

 the same tawny yellow spot upon the cheeks, but in which the 

 ends of the veinlets were dark green or black. These I had been 

 inclined to regard as only varieties of the species, until the pre- 

 sent season I discover that these individuals which have the 

 ends of their veinlets black or dark green come from cocoons 

 which a.re globular, white, with a rough ragged surface from nu- 

 merous loose fibers of silk adhering to them, whilst those which 

 were gathered upon pine leaves were oval, pale green and smooth. 

 From the cocoons, therefore, it is evident that they are of dif- 

 ferent species. It is thus shown that a variation in the color of 

 the veinlets of the wings, as well as in the dots and other marks 

 upon the head and body in this genus, is to be regarded as indi- 

 cating a difference in the species. The general reader is com- 

 monly inclined to the opinion that naturalists make their favorite 

 science unduly complicated and obscure by founding multitudes 

 of species upon what appear to be slight and unessential dis- 

 tinctions. But the facts here stated will show him some of the 



