351 
No. 150.] 
dually withdraws its several members, the antennae, wings and legs, 
from the cases in which they are respectively enveloped—a process 
analogous to that of withdrawing the hand and its several fingers 
from a tight glove ; until at length entirely freed, the now full- 
fledged and perfectly formed fly leaves its pupa skin and mounts 
into the air. 
Peculiarity in its metamorphoses .—It is sufficiently apparent from 
the account that has now been given, that the Hessian fly differs 
notably from all its congeners in one important point in its transfor¬ 
mations. From all the observations that have been hitherto made, 
the cecidomyians correspond with the other tipulides in this promi¬ 
nent particular—that their pupae are naked. Other species, at least 
many of them, after completing their growth, cleave from their 
skins in the same manner that the Hessian fly does, but when the 
separation is formed, the inclosed worm invariably crawls from and 
forsakes its larva case. It is thus, even, contrary to what has been 
hitherto supposed, with the C. tritici. Since my essay upon that 
species was published, I have clearly ascertained that the mature or 
dormant larva does cast its skin. Indeed, this fact is distinctly re¬ 
lated by Dr. Harris, in his treatise, to whom is due the credit of 
having first announced it. His statement had escaped my observa¬ 
tion when previously alluding to this subject. So far as I am aware, 
moreover, the cast skins in the several species are translucent, and 
of a membranous texture. In the Hessian fly, however, it becomes 
opake, changes its color, and is of a firm or coriaceous texture. 
The inclosed worm, also, does not leave it, but remaining, eventu¬ 
ally changes within it to a pupa, the same case thus forming its 
puparium. Its metamorphosis thus approximates it to the Muscidae 
or true flies, the Stratiomidae or soldier-flies, &c., and its pupa, in 
technical language is “ coarctate” and not “ incomplete,” like the 
pupae of the other cecidomyians. Should usage, therefore, settle 
down upon the name midge as distinctive of the minute tipulides, 
there will still be a marked propriety in continuing to this species 
its old name, Hessian Jly* 
* I doubt, however, whether the Hessian fly will continue to be the sole member of 
this genus having a coarctate pupa. Quito recently a species has occurred to my no¬ 
tice, analogous to (ho Hessian fly flax soed in every point that I havo been able to 
