No. 145.] 
787 
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 Perla 
and chrysops of the old authors, or the American representatives 
of those species, Ihe 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, attach¬ 
ed near each othen, 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 sapne 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 form¬ 
ing 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 
present season I discover that these individuals which have the 
ends of their veinlets black or dark green come from cocoons 
which are 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 
