FLIES. 



427 



mouth. Here, for a period of nine or ten months, they feed upon the substance of the 

 stomach and the suppurative matter produced in the deepened cavities they cause. 

 When only a few are present they cause little apparent injury to the animal, but when 

 they exist in large numbers they may produce sufficient inflammation or loss of blood 

 to cause death. When at last they are ready to undergo their transformation, they 

 loosen themselves from the stomach and are carried through the intestinal canal and 

 ejected with the excrement. The pupal state, which occupies thirty or forty days, is 

 passed in the earth, whither the larvae have previously entered, or in the excrement 

 with which they fell. 



G. hcemorrhoidalis, which also infests the horse, deposits its eggs only on the lips 

 and hairs of the lips, thereby causing much annoyance. When a fly makes its appear- 

 ance the horse will endeavor to evade it by rubbing his nose upon the ground or on 

 the trunks of trees, or he will take refuge in water. The flies will hide them- 

 selves in the grass and seize the opportunity to quickly deposit their eggs when the 

 horse is feeding. They have a sharp and peculiar smell which horses seem to recog- 

 nize, as is evidenced by their actions. The eggs are black, and hence not so easy to 

 distinguish as the light-colored ones of the preceding species. The larvss differ also 

 in seldom attaching themselves to the membrane of the stomach, but pass on to the 



!j 



small intestines, where they lodge. When nearly ready to pass out they fasten them- 

 selves to the external orifice, and loosen themselves and escape at any time. 



The eggs of Hypoderma are deposited on the hair about the front shoulders, neck, 

 and groins of artiodactyls only. It was thought for a long while that the female 

 thrust the eo-o-s within the skin, but such is now known not to be the case. Hence it 



Sv^ ' 



is that the great fear that animals show at their approach, and which has often been 

 observed since the oicnnog of 

 Homer, is the more remarkable. 

 Cattle seem especially to fear 

 them. As soon as one makes 

 its appearance in a herd it will 

 cause the most unmistakable 

 signs of anxiety, the cattle run- 

 ning about with their tails erect, 

 bellowing and pawing the earth, 

 and if possible seeking refuge in 

 water. The eggs are of peculiar 

 structure. They are elongate, 

 flattened oval, with a five-sided 

 projection at one end, and the 

 covering is very firm and tough. The larvae when first hatched are small, slender, 

 and cylindrical, with their mouth-parts adapted for boring their way into the skin. 

 Here they remain concealed till the following season and until they have shed 

 their first larval skin. In the latter part of their larval state, which extends over 

 two or three months, they become much larger, measuring about an inch in length, 

 their skin becomes hard and tough, and it is now necessary to seek an external 

 communication with the air. This they do by means of a small orifice in the large 

 ulcerative sac within which they are enclosed, and through which orifice the stigmata 

 protrude. Here they remain, feeding upon the suppurative matter which they cause, 

 in a quiescent condition, till they are nearly ready to escape. They have the peculiar 



FIG. 538. Hijpodernia bovis, bot-fly and larva, enlarged. 



