184 DIPTERA OF NORTH AMERICA. 



of the same genus, it is a question, according to Winnertz, whether 

 they take the same food with their hosts, or live on their excre- 

 ments. Ferris (Mem. de Lille, X, p. 274, with figures) found 

 Cecid. entomophila in an insect-box, living on the excrements of 

 the minute Acari abounding in such boxes ; he compares them, 

 apparently with good reason, with the larvae of Cecidomyia found 

 under the bark of trees, among the excrements of the xylophagous 

 insects. These larvae underwent their transformation in the cor- 

 ners of the box. 



It is very probable that the larvae of Cecidomyia, like most of 

 the dipterous larvae, do not undergo several moultings. I do not 

 find any mention about it in the authors. Only Dr. Harris states 

 that C. tritici casts off its skin before going under ground for 

 transformation. 



Before assuming the papa state, some larvae of Cecidomyia leave 

 their galls and abscond themselves under ground, under dry leaves 

 or moss, or under the bark of trees. Other larvae, on the contrary, 

 undergo their transformation within their gall.* In both cases 

 the pupae are frequently, although not always, inclosed in a cocoon. 

 Winnertz positively denies that the larvae spin this cocoon ; ac- 

 cording to his observation, the latter is, so to say, exuded by the 

 larva. He found that larvae which had fastened themselves to a 

 leaf, were encircled within twenty-four hours by a white halo, con- 

 sisting of tiny thread-like particles, which seemed to grow some- 

 what like crystal-needles ; the larva during this time remained 

 perfectly motionless. The cocoon is perfected within a few days, 

 and even then, under a strong magnifying power, no genuine 

 thread is perceptible. 



The mode in which the pupa state is assumed has been de- 

 scribed by Dr. Harris in a posthumous paper published in the 

 Proceedings of the Boston Soc. of Nat. Hist, 1860, p. 179. 

 " The approaching change is marked by an alteration of the color 

 of the anterior segments of the larva, which (in the case of Cecid, 

 salicis Fitch) from orange become red and shining, as if distended 

 by blood. Soon afterwards, rudimentary legs, wings, and antennae 

 begin, as it were, to bud and put forth, and rapidly grow to their 

 full pupal dimensions, and thus the transformation to the pupa is 



* The larva of Cecid. terminalis Lw., according to Winnertz, varies in 

 its habits. It sometimes goes under ground, and sometimes transforms 

 within the willow leaves deformed by it. 



