Mo. 4.3 Rep r mis. 224 



most commonly, however, on the forelegs and shoulders. The 

 method of deposition has been frequently observed. The female 

 hovers near the horse in a position which appears to be nearly 

 vertical, since the body is bent downward, and the extended 

 abdomen is thrust forward under the body to its full extent. The 

 fiy then darts toward the horse, the egg is glued to the hair in an 

 instant and the fly retreats a yard or two to hover till another egg is 

 ready to be deposited. The operation is repeated at very short 

 intervals, so that hundreds of eggs may ba deposited upon a horse 

 in a comparatively short time. The eggs are held by a sticky fluid, 

 which quickly dries and thus glues them firmly to the hairs. They 

 are about one-sixteenth of an inch in length, and taper a little 

 toward each end, though the attached end is the smaller. The outer 

 end is provided with a little cap (operculum), which is set quite 

 obliquely to the axis of the &gg^ though some authors represent it as 

 cutting the egg square off at the end. This cap or operculun 

 breaks or is pushed off when the grub hatches. Bracy Clark wrote 

 that the eggs do not hatch until twenty-five to thirty days old, while 

 Joly found them to hatch in four or five days. Verrill says : — 



" The eggs contain more or less perfectly developed larvae when laid ; and when 

 they are mature or have been a few days attached to the hair they burst open 

 and allow the young to escape almost instantaneously, when moistened. Thus 

 when the horse licks itself or its companions, the moisture hatches the eggs and 

 the young larvae are transferred to the mouth by the tongue or lips, and thence 

 to the stomach, where they fasten themselves to the lining membrane by their 

 two hooks." 



Evidently some such condition is essential to the hatching of the 

 eggs, as we have removed hairs containing eggs from the horse and 

 keeping them, where not subject to moisture they failed entirely to 

 hatch, and even after a year's time do not appear greatly shrivelled. 

 Doubtless they must hatch in a comparative short time or lose their 

 vitality, for moisture does not effect a hatching in those long kept 

 away from the horse. The empty egg shells may cling to the horse 

 for some time after the hatching of the larvs and give it the 

 appearance of being coated with eggs. Examination, however, 

 will readily disclose the absence of the operculum in the hatched 

 eggs. 



In order to determine more certainly as to the exact condition 

 of hatching and the time involved, I undertook in 1893 some obser- 

 vations which were reported in Bulletin No. 32 of the Division of 

 Entomology (pp. 46-49). Eggs collected from a horse while flies 

 were depositing, and therefore probably not long laid, were opened 



