206 



immature pupa.^ A mature pupa it certainly is not, till it is 

 provided with limbs, etc. The wheat-fly (C. tritici) during this 

 same period has likewise the form of a larva ; but instead of re- 

 maining dormant all the while, it actually possesses the power of 

 locomotion ; and though unprovided with legs, crawls down from 

 the wheat ears to the ground, and burrows in the earth. Can 

 it be in the pupa state while doing this? I trow not. It was 

 this fact with others that induced me to change my opinion re- 

 garding the time when the insect may be said to become a real 

 pupa. 



In the Patent Office Report you allude to Raddi's account, 

 as you do in your last letter ; but have not stated where it is to 

 be found. For this reason I have not referred to it. Dr. Fitch 

 seems to have made a strange geographical mistake about the 

 places Avhere the Hessian Fly was observed in Europe, as 

 stated by Ivollar. Altenburg is in Hungary, at the confluence 

 of the Leith and Danube, forty miles south-east of Vienna, and 

 seventeen south of Presburg. Weikendorf is in Austria, six- 

 teen miles north-east of Vienna : the former more than four 

 hundred, and the latter above three hundred and seventy-five, 

 miles from Hesse Cassel. 



Did I tell you that 0. salicis is nearly twice as large as the 

 Hessian Fly? The magnitude of the larva makes it an ex- 

 cellent subject for observation of the (to me) extraordinary 

 peculiarities in the transformations of the Cecidomyice. These 

 peculiarities seem to be wholly unknown to European entomolo- 

 gists, and are not distinctly stated even by Dr. Fitch. With 

 the exception of these insects, there is no instance on record 

 of an insect passing from the larval to the pupal form Avithout 

 casting off or becoming detached from the skin with which its 



1 I was disposed formerly to consider the insect in this sta^^e as analogous to what 

 the French writers term houle allongee; but the active condition for awhile of the wheat- 

 fly larva, after its feeding state is over, and after it has moulted its skin, has induced 

 me to change my opinion. Moreover in C salicis and C. robinice there is no moulting 

 at all till the fly is developed. 



