THE WARBLE FLY. 53 



the female is a long flexible tube, telescopic in structure and quite 

 incapable of piercing the skin. 



The animal licks off the eggs, and the larvae hatched from them 

 are carried into the mouth by the tongue. 



The maggots then pass into the gullet, and penetrate the walls and 

 wander about in the tissues, finally taking up their position along the 

 back, immediately beneath the hide. 



They next become spiny, and at this stage commence to produce 

 considerable irritation. A swelling now arises the "warble" the 

 summit of which is perforated. Towards this aperture the tail end of 

 the bot (on which are two spiracles or pores) is directed, and through it 

 it breathes. 



Around the bot there is now formed a quantity of pus and blood 

 upon which it feeds, developing rapidly and undergoing a moult, it 

 becomes mature. By means of the spines it makes its way out of the 

 warble-cell and falls to the ground. It there enters the pupal or 

 chrysalis stage and in from three to six w r eeks time the fly escapes. 



The flies usually appear about the middle of May, and on until 

 September is well in. 



H.bovis is as yet imperfectly known. It is said to lay its eggs on 

 the skin. Other observers state that the eggs are always laid in the 

 middle line of the back, on each side of the spine, about the region of 

 the shoulders. But, strange to say no one seems to have found the eggs 

 there themselves. 



In a recent valuable paper Mr. A. D. Imms, (I) who has carefully 

 examined the evidence, states : 



u There are at least three possible courses for the life-history of the 

 larva of H.bovis, viz : 



That the larva on hatching immediately eats its way through the 

 hide and wanders for a short distance in the sub-cutaneous tissue. It 

 eventually returns to the surface and gives rise to the well-known 

 tumours or warbles (Ormerod and others). 



Or, having bored its way through the skin, it wanders very 

 extensively in the tissues of its host, frequently entering the spinal 

 canal through the intervertebral spaces. In other instances the larvae 

 wander to the oesophagus and become embedded in the walls. In both 

 cases they subsequently return to the sub-cutis, and there complete their 

 development (Koorevaar). 



Or, that the larvae do not bore through the skin at all, but are 

 taken into the throat of the ox, by means of the latter licking parts of 

 the body where the eggs are deposited. On reaching the oesophagus 

 they hatch out from the eggs, and slowly bore through the w 7 alls of the 

 former. They then wander about the tissues of the animal, working 

 their way upwards at the same time, and not infrequently effect an 



(i) Journ. Economic Biology, 1906, vol. i, pp. 74-91. 



