186 



could discover it, even when I knew within a tenth of an 

 inch where the puncture was, and employed an excessive mag- 

 nifyer. Such holes as are represented on the three central 

 stalks are very familiar to me, and were unquestionably made 

 by the parasites eating their way out from the puparium of the 

 Hessian Fly. The figures of the 0. destructor are only tole- 

 rable. In fig. 3 a. b., the antennas of 9 and $ are inter- 

 changed. The figures of the parasites are very much worse. 

 The antenna? of the male are pretty correct, but those of the 

 female could scarcely be recognized. 



As to the habits of the Hessian Fly, the account which con- 

 tains the least errors and the most truths is one by Dr. Chap- 

 man, in a volume (fifth, I think,) of the Memoirs of the Phil- 

 adelphia Agricultural Society. 



Of the genus Cecidomyia there are five or six other species 

 in this region ; one of which, as I said before, is often seen 

 about the heads of wheat while flowering, chiefly at or a little 

 before sunrise. I have made partial descriptions of some of 

 these, and did intend to publish descriptions of all the Ameri- 

 can species of this genus ; but I fear I shall never be able to do 

 it. The Hessian Fly is much the largest species (in size, of 

 course) of the genus, --among those found here, at least. 



The egg parasite of the Hessian Fly I discovered in 1833. 

 There are at least one hundred species of this genus Platygas- 

 ter already described and published, and I fear that this may be 

 one of the number ; but many of the descriptions are too im- 

 perfect for me to decide. 



My investigations of the history of the Cicada septendecim 

 have nearly satisfied me that taking any one region, the insects 

 do really come in swarms only every seventeenth year. Whether 

 they appear singly in intermediate years I am unable to say. 

 So many periods are now established in different parts of the 

 country, however, that we must suppose that the regularity of 

 their appearance is sometimes disconcerted by vicissitudes of 

 weather or other causes. 



