90 SHEEP. [1900 



contraction, vary in apparent size ; the back very convex, or arched, 

 the under surface somewhat flat, and the general shape of a long oval; 

 or, rather, the sides parallel, with the head end prolonged, and the tail 

 end blunt. The colour at this stage has gradually become yellowish, 

 and on the back of each segment, excepting on the first and last, is a 

 transverse dark streak. Beneath, oa the abdomen, are rows of spines, 

 all pointing backwards, which assist the grub in moving. 



The head end is furnished with two well-defined dark brown hooks, 

 and between them is a little hollow, which answers the purposes of a 

 mouth (see figure, p. 89). The last segment of the tail extremity is 

 truncated upwards (see figure) with a circular margin projecting over 

 the dark breathiug-poies, and a kind of lip below bearing small spines. 



The method of attack is for the Sheep's Nostril Fly to deposit its 

 living larva (or maggot) at or just within the opening of the [Sheep's 

 nostrils, from which it begins at once to make its way upwards to the 

 inside of the nostrils by means of its head-hooks and its spines. At 

 this first stage of growth the maggot is a very little thing, only about 

 (or less) tlian a twelfth of an inch in length, legless, as it is throughout 

 its life, the shape elongated, and the skin white and transparent ; but 

 little of the structure can be made out without the help of a magnifying 

 glass, unless it may be the little head-hooks (see figure, p. 89). The 

 colour gradually alters with age of grub up to maturity, as mentioned 

 above. 



After starting in young state on its journey inside the Sheep's 

 nostril, the maggot progresses upwards by fixing its two hooks in the 

 mucous membrane inside the nostiil, and thus it is enabled to hold 

 fast and draw^ the rest of the body after it, and then, pressing on the 

 abdominal spines (mentioned above), which all point backwards, it by 

 this means keeps itself in place whilst it loosens the head-hooks and 

 reaches this part forwards to take a new hold. But this method of 

 progression is not altogether harmless to the Sheep, as it is re- 

 corded: — "If one may judge from the black dots, indicating a previous 

 haemorrhage, scattered over the mucous membrane, the irritation set 

 up by the wandering embryos is very considerable." " 



As the maggots grow, they make their way into tlie recesses and 

 furthest chambers of the nose ; in some cases finding their way when 

 still small into situations from which, when at a larger size, they 

 cannot escape, and consequently perishing there. 



When full-grown, if all has gone on in regular course, the maggots 

 loose hold of their hooks on the mucous membrane, and drop to the 

 ground ; sometimes are expelled by being sneezed out. From the 

 the middle of April to the end of July is the time noticed as the most 



* 'Animal Parasites of the Sheep.' By Cooper Curtice, D.V.S., M.D. U.S. 

 Dept. of Agriculture, Washington. U.S.A. 1890. 



