ANIMAL GALLS. 409 



was at first conjectured, that the horse Hcks off the 

 eggs thus deposited, and that they are by this means 

 conveyed into its stomach; but Mr Clark says, " I 

 do not find this to be the case, or at least only by 

 accident; for when they have remained on the hair 

 four or five days, they 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 thence con- 

 veyed with the food to the stomach." He adds, 

 that '' a horse which has no ova deposited on him 

 rnay yet have botts, by performing the friendly office 

 of licking another horse that has."* The irrita- 

 tions produced by common flies {Jlnthomijice me- 

 teoricce, Meigen), are alleged as the incitement to 

 licking. 



The circumstance, however, of most importance to 

 our purpose, is the agitation and terror produced 

 both by this fly, and by another horse breeze-fly 

 [Gasterophilus haimorrhoidalis, L.each), which de- 

 posits its eggs upon the lips of the horse, as the 

 sheep-breeze fly (CEs/rMS oris) does on that of the 

 sheep. The first of these is described by Mr Clark 

 as " very distressing to the animal, from the excessive 

 titillation it occasions; for he immediately after rubs 

 his mouth against the ground, his fore-feet, or some- 

 times against a tree, with great emotion; till finding 

 this mode of defence insufficient, he quits the spot in 

 a rage, and endeavours to avoid it by galloping away 

 to a distant part of the field, and if the fly still con- 

 tinues to follow and teaze him, his last resource is in 

 the water, where the insect is never observed to pur- 



* Liun. Trans, iii. 305. 

 VOL. IV. 34 



