Animal Galls. 431 



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 

 conveyed with the food to the stomach." He adds, that " a 

 horse which has no ova deposited on him may yet have botts, 

 by performing the friendly office of licking another horse 

 that has/'* The irritations produced by common flies 

 (AnthomyicB meteoricce, 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 hcemor- 

 rhoidalis, LEACH), which deposits its eggs upon the lips of 

 the horse as the sheep breeze-fly (CEstrus ovis) 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 sometimes 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 continues to follow and teaze him, his last 

 resource is in the water, where the insect is never observed 

 to pursue him. These flies appear sometimes to hide them- 

 selves in the grass, and as the horse stoops to graze they 

 dart upon the mouth or lips, and are always observed to poise 

 themselves during a few seconds in the air, while the egg is 

 prepared on the extended point of the abdomen."^ 



The moment the second fly just meotioned touches the 

 nose of a sheep, the animal shakes its head and strikes the 

 ground violently with its fore-feet, and at the same time 

 holding its nose to the earth, it runs away, looking about on 

 every side to see if the flies pursue. A sheep will also smell 

 the grass as it goes, lest a fly should be lying in wait, and if 

 one be detected, it runs off in terror. As it will not, like a 

 * Linn. Trans, iii. 305. t Ibid, 



