INSECTS AND OTHER ORGANISMS 401 



then developed, with its strong segmental spiny armature 

 and its pair of relatively large and powerful mouth-hooks, 

 diverging laterally with a sharp median process forwardly 

 directed between them (Fig. 83). H. Glaser (191 3) has 

 described how the little maggot alternately draws back and 

 thrusts forward the head- region so that the sharp point of 

 the forwardly directed spine strikes strongly from within 

 at the pole of the egg-shell, at length piercing it. Then the 

 paired mouth-hooks come into play, tearing a slit in the end 

 of the egg-shell, through which the maggot works its way 

 out, the rows of backwardly pointing spines on the body- 

 segments holding successively to the edge of the slit and 

 preventing slips backwards. Out of its egg-shell at last, 

 the little maggot crawls along towards the root of the hair, 

 and taking advantage of the hair-follicle, begins to pierce 

 and bite its way through the skin, disappearing completely 

 in a few hours (Plate III, A). Entrance to the beast's body 

 is thus made just wherever the eggs happen to have been 

 laid by the mother-fly. The position of the eggs varies 

 considerably but, as mentioned in a previous chapter 

 (p. 109), they are always placed comparatively low, usually 

 on the heels or hind-quarters, less often on the fore-limbs 

 or flanks. The general course of their wanderings has 

 already been described, upwards and forwards beneath the 

 skin and through the tissues to the sub-mucous coat of the 

 gullet where many may be found in the second and third 

 stages from August to January, resting or wandering to and 

 fro in the gullet- wall. The second-stage maggot (Plate II, D) 

 is relatively slender, from five to ten times as long as the newly 

 hatched instar, which it closely resembles in the form of its 

 mouth-hooks and the spiny armature at the hinder end of 

 its body around the tail spiracles. There are transverse 

 rows of spines on the body-segments, which, though as large 

 as those of the first-stage maggot, are far less conspicuous 

 because more widely spaced. The mouth-hooks and spines, 

 together with the complex musculature, enable the little 

 larvae to carry out their extensive migrations through the 

 tissues of the host- animal. The third-stage maggot of 



2 D 



