321 
No. 150.] 
tails are given by M. Kollar, is identical with Say’s Cecidomyia de¬ 
structor. He even intimates a doubt whether the European species 
is a Cecidomyia, for, from all that had been observed, this genus in 
its pupa state, is naked, like the other Tipulida;, and not enclosed in 
a case. Having himself received specimens irom Dr. Ilammer- 
schmidt of Vienna, and still in the straw near the roots, he found 
tne insect “ enclosed in a leathery case,” on opening which, he dis¬ 
covered the larva shrivelled up and dead. Now this nice point, so 
particularly noted, and so strikingly showing the acuteness of dis¬ 
crimination possessed by that eminent naturalist, we think must dis¬ 
pel the last lingering doubt as to the identity of the American and 
European insects. As will fully appear in a subsequent part of 
this paper, the Hessian fly presents this singular anomaly, that its 
pupa is coarctate, or enclosed in a case like those of the other fami¬ 
lies of dipterous insects, but unlike all the pupte of the Cecidomyians 
and other Tipulidae that have been hitherto observed ! The very 
fact, therefore, which leads Mr. Westwood to suspect the European 
insect is not a Cecidomyia, all but demonstrates that it is the Hes¬ 
sian fly ! 
Its Introduction into America. 
The existence of the Hessian fly in Europe being premised, so 
many circumstances conspire to render it probable that it w r as intro¬ 
duced into this country in the mode originally supposed, that scarce¬ 
ly a doubt can now be entertained upon this point. 
When the habits and transformations of the insect itself are con¬ 
sidered, it will be perceived that these interpose great obstacles to 
its being transported across the Atlantic, at a period when two 
months or more were required for the voyage. Its passing through 
two generations in a year, makes its continuance in any one stage of 
iiS existence comparatively briel. I he first of these generations oc¬ 
cupies about seven months, from October to April inclusive. This 
generation is nurtured at the roots of the young plants, and there is 
no probability that any of these plants would be taken up, so that 
the insect could thus be conveyed away. The second generation is 
nurtured in the lower joints of the straw. The worm attains matu¬ 
rity in May, becomes a dormant “ flax seed ” iu June, continues in 
[Assembly, No. 150.] 23 
