70 Veterinary Medicine. 



These are common in America, and in Europe, Asia and Africa. 

 The female has her abdomen prolonged into an ovipositor, by 

 means of which she lays her eggs from June to October, mainly 

 on the legs of solipeds, during the heated hours of the day. 

 Following the horse she poises opposite the point selected, her 

 ovipositor curved forward beneath the abdomen, darts to the spot 

 deposits her egg and instantly flies back. This is repeated again 

 and again, and the long hairs of the fore-limbs (fore-arm, carpus, 

 and metacarpus) are literally covered with eggs. 



The egg is dull white, conical, and cemented by the button at 

 its apex to a hair. In 24 hours it hatches out and the embr3'0, 

 crawling under the hairs, creates an itching which leads the horse 

 to lick or bite the part, and the embryo adhering to the damp 

 tongue is taken in and swallowed. The embryos just about to 

 escape from the ovum are taken in by the tongue at the .same time. 



An embryo on reaching the stomach at once attaches itself by its 

 buccal hooks, and especially to the left .sac. It is then the size 

 of the egg from which it eiscaped, and of a blood red color, but 

 in the course of the next winter and spring it undergoes three 

 moultings becoming larger on each occasion, and changing to a 

 yellowish brown color. 



The mature larva (^bot) as found in the stomach in spring and 

 early summer, measures 7 to 9 lines in length, has a yellowish 

 brown color, and is formed of a series of ten rings, all excepting 

 the two last are furnished with a closely set row of spines directed 

 backward. The ninth ring has a few short spines at the side 

 only. The rings which in the embryo were soft and fleshy are 

 now firm and resi-stant. Many reach maturity from May to 

 October and pass out with the faeces, showing little disposition to 

 hook themselves on to the intestine in their course. They remain 

 in the manure or burrow in the earth and in 24 hours the envelope 

 becomes hard and horny, the stage of nympha having been reached. 



In 30 to 40 days, according to the temperature, the nympha 

 opens and the perfect fly escapes. 



CEstrus Haemorrhoidalis (Gastrus Hemorrhoid alis. Gas- 

 TROPHii<us Hemorroidalis, Red-tailed Bot Fi.y) is a small 

 fly, barely 4 lines in length, very hairy ; the thorax olive gray 

 with a black band in the middle ; the abdomen white in front, 

 black in its median part, and orange red at the end ; and its wings 

 spotless. It is common in North America and Europe. 



