578 DIPTERA. 



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, 1843, 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 July, 

 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 



