MAGGOTS OF THE AMERICAN WHEAT-FLY. 595 



kernels never fill out at all. Pinched or partly filled kernels 

 are the consequence of their attacks when the gram is more 

 advanced. The hulls of the impoverished kernels will al- 

 ways be found split open on the convex side, so as to expose 

 the embryo. This is caused by the drying and shrinking of 

 the hull, after a portion of the contents thereof has been 

 sucked out by the maggots. 



Towards the end of July and in the beginning of August, 

 the full-grown maggots leave off eating, and become sluggish 

 and torpid, preparatory to moulting their skins. This pro- 

 cess, which has been alluded to by Judge Buel and some 

 other writers, has been carefully observed by Mrs. Gage, 

 who sent to me the maggots before and after moulting, to- 

 gether with some of their cast skins. It takes place in the 

 following manner. The body of the maggot gradually shrinks 

 in length within its skin, and becomes more flattened and less 

 pointed, as may easily be seen through the delicate trans- 

 parent skin, which retains nearly its original form and dimen- 

 sions, and extends a little beyond the included insect at each 

 end. The torpid state lasts only a few days, after which 

 the insect casts off its skin, leaving the latter entire, except 

 a little rent in one end of it. Mrs. Gage observed many 

 of the maggots in the very act of emerging from their skins. 

 The cast skins are exceedingly thin, and colorless, and, 

 through a microscope, are seen to be marked with eleven 

 transverse lines. Great numbers of the skins are to be found 

 in the wheat-ears immediately after the moulting process is 

 completed. Sometimes the maggots descend from the plants, 

 and moult on the surface of the ground, where they leave 

 their cast skins, as described by Mr. J. W. Dawson, of 

 Pictou, Nova Scotia.* Late broods are sometimes harvested 

 with the grain, and carried into the barn without having 

 moulted. This seems to have often happened in England, 

 where the insect has been repeatedly noticed in the transition 

 state, still enclosed within its loosened filmy skin. 



* Proceedings of the Academy of Natural Sciences of Philad., Vol. IV. p. 210. 



