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able letters I found that you had noted the condition of the 

 Hessian Fly after it had taken the flaxseed form, and before it 

 had any trace of the wings and limbs of the fly about it. You 

 spoke of its lying within its flaxseed case " a motionless grub." 

 Mr. Worth mentions something similar. He says that soon after 

 the change of color, if the insect be gently rubbed with the 

 finger, the flaxseed skin may be detached, and the animal with- 

 in will be disclosed in the maggot form, or words to this effect. 

 Putting these facts in comparison with what I had myself seen 

 in the other species, I was led to the conclusion that the 

 condition of the insect between that of the active or feeding 

 larvag and the fully developed pupa, in which it still retained 

 the larva form, could not properly be called the pupa state. 

 I have not come to this conclusion hastily, or without fully 

 considerins; all the circumstances attendino; the transformations 

 of the four species above named. C. salicis retains the larva 

 form till a few days before the evolution of the fly, and it is 

 converted to a mature pupa without casting off" or detaching 

 itself from a larva skin. The same occurs with 0. robinice. 

 C. tritici, in ninety-nine cases out of a hundred, casts off" one 

 larva-skin before it leaves the wheat ears, then still retaining 

 the larva form, it descends to the ground and penetrates a little 

 way below the surface, where it remains unchanged till a few 

 days before the fly is disengaged. The pupa state is very 

 brief, and the form of the insect in this state is similar to 

 that of others, and is assumed without again casting off" its skin. 

 In a very few cases, the larva does not cast off" its skin 

 till just as it is entering the earth. You seem to agree with 

 me that the matured pupa is a different thing from the larva, in 

 form ; for it shows the rudimental members of the fly beneath 

 the " scarf" skin of the pupa. You also have observed that the 

 Hessian Fly insect retains the form of a larva after its flaxseed 

 skin has become detached from its body. These two important 

 points you have the credit of making known before they were 

 discovered or announced by Dr. Fitch. Whether " the insect 



