OF HARTING. 441 



considerable numbers in two large cysts situated in 

 the pharynx of the deer. Those of another species of 

 -this family, the true Bot fly (G aster ophilus Equi), 

 actually pass their growing stage in the stomach of 

 the horse, and the establishment of its family by the 

 parent fly in a locality so difficult of approach, is one 

 of the wonders of insect economy. The eggs are 

 deposited on the coat of the horse, not at random, as 

 at first sight might be supposed by any one casually 

 witnessing the act of oviposition, but on the anterior 

 part only of the body of the animal, were it otherwise, 

 hundreds of the young grubs, failing to reach their 

 proper nidus, would infallibly perish in a few hours 

 without taking food. The manner in which the eggs 

 are deposited by the fly is thus described by Mr. 

 Bracey Clark, in "An essay on the bots of horses 

 and other animals," a standard work on the subject : 

 " Suspending herself before the part where she designs 

 to deposit her egg for a few seconds, she suddenly 

 darts upon it, and leaves the egg adhering to the 

 hair : she hardly appears to settle, but merely touches 

 the hair with the egg held out on the projected 

 abdomen : the egg is made to adhere by means of a 

 glutinous liquor secreted with it. She then leaves the 

 horse at a small distance, and prepares a second egg, 

 and, poising herself before the part, deposits it in the 

 same way. The liquor dries and the egg becomes 

 firmly glued to the hair. This is repeated by various 

 flies, till four or five hundred eggs are sometimes 

 placed on one horse." In a few days the hatching 

 takes place, and the attention of the horse being 

 called to the fact by the titillation resulting from the 

 uneasy movements of the larvae amongst its hairs, 

 the unsuspicious animal naturally licks the part 

 affected, which, thanks to the wonderful instinct of 

 the parent fly, is never out of reach of the horse's 

 tongue, the larvae adhere to the latter, and are thus 

 fairly on their way to the stomach. No doubt many 



