OP SEL BORNE. 151 



advances that this (Estrus is the parent of that wonder- 

 ful star-tailed maggot which he mentions afterwards ; 



systems, the Gasterophilus Equi, LEACH ; the generic appellation being 

 founded on the aptitude of the maggots for residence in the stomachs of 

 living animals. 



Mr. Bracy Clark, who has well described the habits of these insects 

 in his Observations on the Genus GEstrus, published in the third volume 

 of the Linnean Transactions, and subsequently in an Essay on the Bots 

 of Horses, dwells with more detail on the fact recorded in the text. 

 Speaking of the spotted-winged bot-fly, he says, " The mde pursued by 

 the parent fly to obtain for its young a situation in the stomach of the 

 horse is truly singular, and is effected in the following manner: When 

 the female has been impregnated, and the eggs are sufficiently matured, 

 she seeks among the horses a subject for her purpose, and approaching 

 it on the wing, she holds her body nearly upright in the air, and her tail, 

 which is lengthened for the purpose, curved inwards and upwards : in 

 this way she approaches the part where she designs to deposit the egg; 

 and suspending herself for a few seconds before it, 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 point 

 of the 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. 



" The inside of the knee is the part on which these flies are most fond 

 of depositing their eggs, and next to this on the side and back part of 

 the shoulder, and less frequently on the extreme ends of the hairs of the 

 mane. But it is a fact worthy of attention, that the fly does not place 

 them promiscuously about the body, but constantly on those parts which 

 are most liable to be licked with the tongue ; and the ova therefore are 

 always scrupulously placed within its reach. Whether this be an act of 

 reason or of instinct, it is certainly a very remarkable one. I should 

 suspect, with Dr. Darwin, it cannot be the latter, as that ought to direct 

 the performance of any act in one way only." 



The eggs thus deposited are not, in Mr. Bracy Clark's opinion, removed 

 from the hairs by the moisture of the horse's tongue, aided by its rough- 

 ness, in the act of licking, and thus conveyed to the stomach : but remain, 

 he conceives, attached to the hairs for four or five days until they have 

 become " ripe, after which time the slightest application of warmth and 

 moisture is sufficient to bring forth in an instant the latent larva. At this 

 time, if the tongue of the horse touches the egg, its operculum is thrown 

 open, and a small active worm is produced, which readily adheres to the 

 moist surface of the tongue, and is from thence conveyed into the 

 stomach." For the manner in which the larva affixes itself in the 

 stomach by means of the two hooks with which it is furnished at its 

 smaller extremity ; its mode of growth ; its detachment, when fully 



