206 NATURAL HISTORV. [CH. XI^ 



Other species of the cesirus infest the intestinal ca- 

 vity of the horse. The osstrus equi is found in the 

 stomach ; the parent insect deposites its eg-g- about 

 the shoulder of the horse, where it can be easily 

 reached by the tongue ; the irritation causes the ani- 

 mal to lick the part ; and by this means the bot is 

 introduced into the only place which affords the vis- 

 cid nutriment and due heat requisite for its full de- 

 velopement. 



The aslrus hemorrhoidalis chooses the anal extre- 

 mity of the horse to deposite its egg. According to 

 Clark, the egg is deposited on the edge, and the larva 

 creeps through the whole length of the intestines. 

 Dr. Gaspari saw the perfect insect hover about one 

 of his horses apparently for the purpose of laying 

 its egg ; its attempts caused the animal to plunge, 

 kick, and run, and, in short, excited that furor, which 

 induced the ancients to give tliese insects tlieir de- 

 signation of xsirus. Not being successful, the crea- 

 ture insinuated itself with less noise under the tail 

 of another horse which was feeding quietly by itself. 

 Its attack seemed at first to excite itching, and the 

 fly profited by the irritation thus produced to effect 

 a lodgment. Soon after this happened, the horse 

 ran about, plunged, and then" threw himself on the 

 ground ; and did not recommence feeding until after 

 the lapse of a quarter of an hour. The worm is pro- 

 vided with hooks, by means of which it retains its 

 place. It also, when sufficiently developed, falls off 

 the horse, and, like the cestrus bovis, undergoes its 

 metamorphosis on the ground. 



A third species of oestrus is found in the nostrils 

 of sheep, goats, and various other animals. The 

 egg is lodged in the frontal sinus, ii^the midst of the 

 mucus which they contain. 



"In Lapland,'* says Linnaeus, "there is a fly co- 

 vered with a downy hair, called the rein-deer gad- 

 fly; it hovers all day over these aminals; their legs 

 tremble under them, they prick up their ears and flee 



