DIPTERA. 477 



moulting, together 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 transparent skin, which retains nearly its original form 

 and dimensions, and extends a little beyond the included in- 

 sect 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 tlie 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 en- 

 closed within its loosened filmy skin. It is somewhat remark- 

 able that the true nature of this covering of the maggot should 

 not have been ascertained by English naturalists. Mr. Kirby, 

 as before stated, supposed it to be a thin membrane, formed 

 by the insect for the protection of its body from the cold of 

 winter. According to Professor Henslow's account, the larvae 

 "spin themselves up in a very thin and transparent web, which 

 is often attached to a sound grain, or to the inside of one of 

 the chaff-scales." f Mr. Curtis observed on the backs of some 

 of the shrivelled grains " a long narrow filmy sac, on opening 

 which a bright orange granulated maggot came out alive; and 

 when shut up in a tin box, many voluntarily left their cases 

 and wandered about." J Having carefully watched the insect 



* " Proceedings of the Academy of Natvyral Sciences of Philadelphia," Vol. 

 IV., p. 210. 



f " Journal of the Royal Agricultural Society of England," Vol. II., p. 22. 

 j "Journal of the Royal Agricultural Society of England," Vol. VI., p. 145. 



