170 



HEALTH AND DISEASE 



The eggs of the bot-fly are deposited on the hairs of the horse's legs in 

 the early summer, and they are soon hatched by the sun. The newly- 

 hatched larvae by their movements cause a certain amount of irritation 

 and are licked off by the horse, and in this way are quickly conveyed 

 to the stomach, to the mucous memiirane of which they at once attach 

 themselves by means of the hooked mandibles with which they are 

 provided. The larvae remain attached to the cuticular membrane of the 



F C 



Fig. 273. — Metamorphoses of the Bot-Fly 



A, Egg of Bot-Fly as it appears stuck on a hair. B, Egg of Bot-Fly, showing the OpercuUim or lid. c, Lid 

 pushed aside and the larva escaping. D, Larva fully developed after having been in the stomach of the horse. 

 E, Head of Larva, showing Booklets by which it anchors on to the mucous membrane of the stomach. F, Bot-Fly 

 developed from D. G, Larvre of Bot-Fly anchored on to mucous membrane of the stomach of the horse. 



stomach for some months, proba1)ly the greater part of a year. When 

 sufficiently developed they relax their hold and are expelled. It may be 

 noted here, however, that treatment is of no avail; there are no safe 

 remedies which Avill cause the bots to abandon their position until the 

 proper time. But the fact of quitting their hold naturally calls attention 

 to their existence, and the u.se of any remedy at this period is sure to 

 be attended with an apparent success. 



The smaller red variety, the (Estrns hcemorrhoidcdis, deposits its eggs 

 on the lips of the horse, whence the larvae are transferred to the stomach. 

 They are much less common than the larvae of the (Estrns equi. 



Of the nematodes which infest the intestines of the horse a large white 

 or pale-yellow worm, the Ascaris megalocei^hala, is the most common. 



