208 DISEASES DUE TO INTERNAL PARASITES. 



and biilboias at their bases. There are a few hairs on the head 

 and quite a number on the body, sides and limbs. It has no 

 mouth, or appreciable proboscis, its object in life seeming to be 

 the propagation of its species, which when the male has im- 

 pregnated two or three females, marks the end of his existence. 

 The male gad-fly in size is as large as the female, but its head is 

 narrow. They do not attack the sheep, and, as above stated, 

 only exist to impregnate the female. The female gad-fly is sup- 

 posed to deposit not the eggs, but live larvae within the nostrils 

 of the sheep, few only being placed on any one animal owing to 

 the agitation and violent movements exhibited by the sheep on 

 the approach of the fly. These larvae are exceedingly small in 

 size when first deposited. Their bodies are elongated and white. 

 On examination with a lens they show that the body consists of 

 eleven segments, with two hooks at its anterior end to be used to 

 attach itself to tli€ tissues and also to draw its body upwards and 

 forwards; the posterior end is furnished with two stigmata, or 

 breathing pores. The under surface is covered with minute 

 spines. The bodies are transparent, close examination revealing 

 the respiratory and digestive apparatus. The larvae as it ma- 

 tures changes in appearance, attaining a considerable size (about 

 three-quarters of an inch), the body becomes dark and striped 

 with black bands, the spines also turn black. When this condi- 

 tion is reached the grub escapes from the nostrils of the sheep, 

 and falling: on the ground immediately bores into it. It remains 

 in the ground for a period of from one to two months (the length 

 of time depending on the weather conditions). "When the fly 

 is matured within the chrysalis, it pushes up the upper end of the 

 case and reaches the surface of the ground by the same hole the 

 larvae made in the first instance. - On arriving at the surface 

 the fly appears at first sluggish and dull, the body and wings 

 needing exposure to the air to cause them to harden. When 

 this has taken place and the right time comes — that is when the 



