404 THE BIOLOGY OF INSECTS 



(1922) the paired hooks and the central spine are reduced 

 to minute conical processes (Fig. 83, E) ; the larva has no 

 further occasion to bore or migrate. The cuticle of the 

 fourth-stage maggot is pale and comparatively feeble. 

 When some weeks later the final (fifth) larval stage is reached, 

 the mouth-armature is still further reduced, as the hooks 

 are altogether wanting (Fig. 83, F). The cuticle is firm and 

 tough, and most of the body-segments have transverse rows 

 of strong spines on both the dorsal and ventral surfaces, 

 as well as groups of spines on the lateral areas of the body. 

 After the moult which ends the fourth stage the fifth-stage 

 larva is pale, but as it ages it becomes darker in colour and 

 when ripe assumes a grey or brown hue. In form it is stout, 

 widest at the middle and tapering towards the rounded head 

 and tail regions ; at the latter the almost black, firm, 

 spiracular plates are very conspicuous (Plate XVI, C). 

 These may be seen through the hole in the host's skin, which 

 is raised into a hemispherical prominence over the hollow 

 swelling or tumour (** warble ") in which the maggot during 

 its two last stages lives and feeds (Plate III, C). The 

 surrounding subcutaneous tissue and muscle undergo 

 destructive Hquefaction through the irritation and secretion 

 of the parasite, which is thus able to secure by suction an 

 abundant and nutritious supply of food. 



The spiny armature of the ripe maggot enables it to 

 work its way through the hole in the host's skin, as the 

 armature of the young larva assists its emergence from the 

 egg. The firm tough cuticle is adapted for the maggot's 

 short life in the outer world, and becomes modified, as in 

 muscoid transformations generally, into the hard puparium 

 (Plate XVI, D) within which the imaginal structures are 

 developed. About five or six weeks after the ripe maggot 

 has worked its way out of the host animal's back, fallen 

 to the ground, and sought shelter under a clod or stone, 

 the fly breaks out of the puparium, and the female after 

 pairing starts anew the yearly life-cycle by laying her eggs 

 on the hairs of the cattle. It is interesting to notice how, 

 in the seasonal adaptation of these insects to their hosts 



