440 THE NATURAL HISTORY 



of our domestic animals, principally the horse, ox, 

 sheep, and fallow deer, other herbivorous quadrupeds 

 are also subject to their attacks, and several instances 

 are even recorded of their presence within the human 

 body. Each species of fly is not only appropriated to 

 one particular species of quadruped, but confines its 

 attacks to special parts of the animal on which it is 

 parasitic. For instance, CEstrus Bovis oviposits on the 

 backs of cattle, and every egg so deposited, whether 

 in the hide, as some assert that it is, or on it, according 

 to others, is followed by a gradually increasing open 

 tumour, in which the larva resides and subsists on the 

 purulent secretion resulting from the constant irritation 

 it occasions until it has attained its full development, 

 it then forces its way out, and allows itself to drop to 

 the ground, into which it burrows for the purpose of 

 undergoing its final transformations. As many as 

 thirty or forty of these tumours, each containing a 

 grub, are sometimes met with in the back of one 

 animal. CEstrus Ovis (Cephalemyia Latr.} glues its 

 eggs to the inner margins of the nostrils in sheep, in 

 spite of the frantic attempts of the latter by running 

 away, violently shaking their heads, or burying their 

 noses in the herbage, to escape the infliction. The 

 grubs, when hatched, make their way up the nostrils 

 to the maxillary and frontal sinuses, where they com- 

 plete their development, and when full grown, like the 

 larvae of CEstrus Bovis, pass through their final changes 

 under ground. It would be interesting to ascertain 

 whether the maggots sometimes found making their 

 exit between the eye-ball and the nasal duct, in the 

 inner angle of the orbit, are the larvae of this fly. 



Another species of CEstrus which we have not 

 identified, although we have every season good pre- 

 sumptive evidence of its presence in the park, is a 

 source of constant annoyance to the Fallow deer, 

 causing them to snort incessantly, in the day time. 

 The larvae of this fly have sometimes been found in 



