195 



HERRICK TO HARRIS. 



New Haven, Feb. 21, 1843. 



As regards the moulting of the Cecidomyia destructor^ I must 

 reply almost wholly from memory, for I am so much occupied 

 and interrupted that I cannot make a thorough examination of 

 my voluminous observations. I think, however, that I shall 

 not state anything about the matter which is not substantially 

 true. 



The Hessian Fly mother lays an egg on the young wheat 

 plant : in a few days it hatches, and the larva crawls out of the 

 fine pellicle, which is left in situ. Here is one covering thrown 

 off. After feeding on the juices of the plant, the larva be- 

 comes plump and tense, and in process of time turns brown. 

 In two or three weeks after this change of color the animal 

 within becomes entirely detached from the old larva-skin, and 

 lies a motionless grub. Here is another covering thrown off. 

 The process of growth goes on, and by and by, on opening the 

 leathery maggot-skin (now a puparium) you find the pupa so 

 far advanced that some of the members of the future imago 

 are discernible through the scarf which envelops and fetters it 

 on all sides. In due time this scarf splits on the thorax, and 

 the imago works out, literally, — and, as I suppose, at or about 

 the same time forces the puparimn, and comes forth in full- 

 winged maturity. In the entire life of the insect, then, there 

 are three moultings. 



I recollect distinctly finding among my wheat stalks one 

 bearing a pupa of the Hessian Fly ; and attached to one end 

 of the puparium (and, I believe, partly engaged in it) was this 

 scarf-skin ; showing that the emergence from the puparium' 

 must have been somewhere nearly contemporaneous with the 

 disengagement from the scarf. A paper lies before me con- 

 taining memoranda made May 12, 1837, of which I will give 

 an abstract. 



" On looking over culms of wheat from my garden,, which 



