193 



the sheath and culm, two other larvae whose history is unknown 

 to me, but which appear not much related to the Hessian Fly. 



HAKRIS TO HERRICK. 



CAMBRIDGE, Jan. 14, 1843. 



Hoping that you may be induced to favor me with some of 

 your promised notes on my Treatise, and being particularly 

 desirous at this time for some further explanation of Mr. Ha- 

 vens' remarkable statement respecting the transformation of 

 the Hessian Fly, which, if true, I should be glad to be able to 

 make use of in some observations on transformations that I am 

 now drawing up for a lecture, I beg leave to call your attention 

 to the statement of Mr. Havens, quoted on page 428 of the 

 Treatise. " Whenever the fly has been hatched in the house, 

 it always comes forth from its brown case, wrapped in a thin 

 white skin which it soon breaks, and is then at liberty." 



You are aware, I suppose, that the transformations of insects 

 from the pupa to the imago, consists in some of a single, and in 

 others of a double, moulting. Permit me, however, to name 

 some examples of the course of transformation, illustrating 

 these castings of the skin or skins. 



The maggots of most flies become pupas within the indurated 

 maggot-skin, which then forms a puparium, or natural cocoon, 

 for the insect ; and which, if carefully opened a few days or 

 hours before the last transformation, will be found to contain a 

 real pupa, not greatly unlike the pupa of a beetle, having like 

 the latter the legs and abortive wings unconfined. When 

 about to come forth in the fly state, the inclosed insect breaks 

 off the end of its puparium or old larva-skin, and at the same 

 time divests itself of the thin and delicate pupa-skin, leaving 

 the latter within the hardened puparium. This is an example 



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