578 
D1PTERA. 
their escape from their winter quarters by breaking through 
one end of their shells and the remains of the leaves around 
them. In the “ Observations on the Hessian Fly,” written 
by Jonathan N. Havens, Esq., it is stated, that, “whenever 
the fly has been hatched in the house, it always comes 
forth from its brown case wrapt in a thin white skin, which 
it soon breaks, and is then at liberty ” ; and Mr. Havens 
supposes that the same thing occurs when the transforma- 
tion takes place abroad. Mr. Herrick states, that this 
skin or “ scarf,” as he calls it, “ splits on the thorax or 
back,” and the fly is disengaged from it by working through 
the rent. 
This process, and the appearance of the insect through 
the pupa-skin, is fully described in his letter of the 21st 
of February, 1848, from which the following extract is 
taken. It is from a memorandum made May 12, 1837. 
“ On looking over culms of wheat, which ripened last J ulv, 
I found a puparium of the Hessian fly ; began to cut it 
open; found within a fly nearly matured. Opened only 
the anterior part of the puparium ; but the animal soon 
squirmed itself out, enveloped in a thin scarf. The pupa- 
rium was left entirely clean. — The animal worked its abdo- 
men back and forth, and, in about twenty minutes, was 
detached from the scarf.” In one instance, Mr. Herrick 
found the empty scarf-skin “ attached to one end of the 
puparium.” Ordinarily, however, the insect seems to crawl 
entirely out of the puparium, or flax-seed shell, before dis- 
engaging itself from the pupa-skin, as stated above by Mr. 
Havens. Upon examining a puparium after the escape 
of the insect, I could not discover any vestige of larva or 
pupa skin within it. It was left entirely empty. 
Very soon after the flies come forth in the spring, they 
are prepared to lay their eggs on the leaves of the wheat 
sown in the autumn before, and also on the spring-sown 
wheat, that begins, at this time, to appear above the sur- 
face of the ground. They continue to come forth and lay 
