74 THE LIFE-STORY OF INSECTS [CH. 



Gastrophilus, lick the newly-hatched larvae into their 

 mouths. The 'bot,' or maggot of Gastrophilus, comes 

 to rest in the horse's stomach ; often a whole family 

 attach themselves by their mouth-hooks to a small 

 patch of the mucous coat of that organ. The maggot 

 is relatively short and stout, with rows of strong 

 spicules surrounding the segments, and with spiracles 

 capable of withdrawal through a cup-like inpushing 

 of the tail-region of the body, so that the parasite is 

 preserved from drowning when the host drinks water. 

 The young maggot of Hypoderma (fig. 22 e) is elongate 

 and slender, spends its first two stages burro win- 

 in the gullet wall and then wandering through the 

 dorsal tissues of its host; ultimately it arrives 

 beneath the skin of the back and assumes for its 

 third and fourth instars a broad barrel-like form 

 (fig. 22 b). The supply of free oxygen within the ox's 

 tissues being now insufficient, the warble-maggot 

 bores a circular hole through the skin and rests 

 with the tail spiracles directed upwards towards the 

 outer air. When fully grown the maggot works its 

 way through the hole in the host's skin, and falling 

 to the ground pupates in some sheltered spot, the 

 life cycle occupying about a year. Similarly the 

 Horse-bot escapes from the host's intestine with the 

 excrement, and pupates on the ground. 



A curious modification of the maggot is noticeable 

 in the larva of the Hover-flies (Syrphus). These, 



