36 



Tha eggs of the horse (Estrus, which are white and of conical form, adhere to the 



horse's hair as shewn in 

 fig. 27. They are fur- 

 nished with an operculum 

 or lid which at the time of 

 hatching, about twenty- 

 days after they are depos- 



_ Fig. 27. Eggs of the Horse Breeze Fly deposited on the hah- of a horse i^ed openS to allow of the 



exit of the young larva. It was at first supposed that the horse licks off the eggs thus 

 deposited, and that they are by this means conveyed into the stomach, but Mr. Bracey 

 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 slight 

 est 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 or lid is 

 thrown open, and a small active worm is produced, which readily adheres Lo the moist sur- 

 face of the tongue, and is thence conveyed with the food to the stomach." Thus a horse 

 which has no ova deposited on him may yet have bots by performing the friendly office of 

 licking another horse that has." 



It is worthy of remark that it is probable the greater part of the eggs deposited by 

 this fly are taken up in consequence of the irritation of other flies, which by their sting- 

 ing cause the horse to lick himself, and thus receive the larvae of the (Estrus on the tongue 

 •and lips, whence they are conveyed into the stomach. 



The larva or grub when first hatched from the egg, is a small, active, rather long 

 worm, but as its growth advances it becomes thicker and broader, and set with bristles. 



Fif. 28.rPortionof the Stomach of a Horse with larv» of (Esfrus The bodv is of a whitish Or Vellowish red 

 eoizi adherinor tn it. i *' , . i f> i 



colour, and is composed oi eleven segments, 

 armed at the lower edge with a double row 

 of triangular spines or bristles, large and 

 small alternately, black at the point which 

 is always turned backwards. The larvae 

 usually hang in clusters from the lining of 

 the stomach, see fig. 28; they maintain 

 their hold by means of two dark brown 

 hooks with which their head is furnished. 

 The spines with which the whole surface of 

 the body is provided contribute to fix it 

 more solidly, preventing the grubs by the 

 manner in which we have seen they are 

 placed from being carried away by the food 

 which has gone through the first process 

 of digestion. 



The larvae are generally found adher- 

 ing to the white insensible lining or tissue of the stomach. They make small deep round 

 holes wherever they adhere to this lining, and sometimes penetrate through it, but not 

 through the other layers or coats of the stomach. 



When they are removed from the stomach with a sudden jerk so as not to injure 

 them, it is said that they will if fresh and healthy attach themselves to any flaccidfmem- 

 brane, and even to the skin of the hand. 



The larva when matured leaves the membrane to which it has been attached, and 

 traversing the whole length of the intestinal canal, leaves it by the anal orifice, and falls 

 to the ground, where seeking a suitable place of retreat it undergoes the change into a 

 chrysalis, the skin hardening, and becoming a dark reddish brown colour. After remain- 

 ing torpid for a few weeks in this state, the perfect insect having assumed its mature form 

 bursts the lid at the anterior end of the chrysalis, and makes its exit. In a few hours 

 afterwards having dried its wings it flies off and seeks its mates. 



It is curious to note the agitation and terror produced both by this fly and by ano- 

 ther horse breeze-fly {GasterojjJiilus hcemorrhoidalis, Leach), which deposits its eggs upon the 

 lips of the horse. This latter is described by Mr. Clark as " very distressing to the 



