X WARBLE FLY. 



The above are the main differences connected with the moult to the 

 final form of the maggot, and, following on these alterations in its 

 structure, and especially on the power of keeping up a constant irrita- 

 tion by means of the muscular expansion and contraction of its 

 prickly skin, we find tlie lining membrane of the cell increasing in 

 thickness, until it becomes well defined as a tough wall round the 

 perforation, continuous with the upper part of the cell. Fig. 12 

 shows a cell drawn in section, and slightly magnified after maceration 

 in water. The lowest end of the maggot-chamber appears full of foul 

 matter, caused by the irritation of the friction and suction of the 



Fig. 12. Fig. 13. 



Fig. 12. — Warble-cell, slightly larger than life. Fig. 13. — Chrysalis of Ox Warble 

 Fly, side view, and showing contained fly. 



maggot ; and, after the creature has crawled from its hole, a pressure 

 on the empty warble is followed by a discharge of some amount of 

 purulent matter. 



When the warble-maggot is full-fed it presses itself gradually out 

 of the opening at the top of the warble, which at first sight looks much 

 too small for the exit, but the opening can be squeezed somewhat 

 larger, the soft maggot is compressible, and is further helped in 

 dragging itself out by the ringed shape and roughened skin, which 

 prevent its slipping back again into its former hole. "When it has 

 fallen to the ground it creeps to some shelter, under a stone, a clod, 

 or where may be convenient, and there the skin hardens into a chrysalis 

 coat much like the grub, excepting in being dark brown or blackish in 

 colour, and somewhat flattened on one side (see fig. 13). From these 

 chrysalids the Warble Flies come out, in favourable weather, in about 

 four weeks from the dropping of the maggot from the back of the 

 cattle ; in cold weather the time required for the change is longer.* 



When the maggot has gained the condition mentioned above it 

 undergoes no further great change until it turns to the chrysalis-state. 

 The spiracles become less radiated and darker, the maggot also 

 becomes darker as it increases in size ; but the main points of its life 

 now are to form, at the expense of the animal in which it lives, the 

 material from which the fly will presently be developed. 



* For details see ' Essay on Bots,' by Bracy Clark ; ' Monographie der ffistriden,' 

 by Friedricli Brauer and other writers. 



