ii8 INJURIOUS AND USEFUL INSECTS 



stomach. An experienced observer of insects might have 

 predicted that the fly would not feed, from the mere fact that 

 all the eggs are laid in a single mass. Where the eggs are laid 

 one by one, the female must fly from place to place, and select 

 the best sites for the future larva. This may occupy days or 

 weeks, during which time she must be supported by food. 

 But where all the eggs are laid together, the business can be 

 transacted in a very short time, and then the fly commonly 

 does not feed at all. Nature cares nothing about the spent fly, 

 which perishes speedily. The nervous system is taken over from 

 the larva with no very important change. One thing, however, 

 is noteworthy. In the fresh-hatched larva the brain lies where 

 we naturally expect to find it — that is, in the head, close to the 

 feelers, eyes, and mouth. After a few days it is withdrawn 

 into the thorax, where it is to be found during the rest of the 

 larval stage. Why should the braip be thus retracted into thp 

 thorax ? I think it may be because the future head of the fly 

 is to be formed there. The head, when completed and duly 

 expanded, will again enclose the brain. For this purpose the 

 brain must be behind and not in front of the rudiments of the 

 head, which have to extend backwards as they open out. But 

 why is the head of the fly formed in the thorax, and not, as 

 usual, within the larval head ? Perhaps because there is much 

 more room in the capacious thorax for the deep folds which 

 give rise to the head. When once this plan is adopted, and 

 the head of the fly is made to develop within the thorax of the 

 larva, it is plain that the head of the larva may be still further 

 reduced in size, for a chief part of its contents has been re- 

 moved elsewhere. In the thorax of the fly the predominance 

 of the middle segment, or mesothorax, is to be remarked. The 

 prothorax and mesothorax are insignificant in comparison. 

 Here, as in the blow-fly (p. 142), the functional wings and the 

 muscles attached thereto call for an enormous enlargement of 

 the corresponding segrnent. 



One peculiarity of the fly of Chironomus enables us to 

 distinguish it at a glance from other Diptera of the same size 

 and general appearance. It does not bring its fore legs to the 

 ground when resting, but keeps them stretched out in front. 

 Some may-flies (Ephemerse) have the same habit. Gnats 

 extend their hind legs, and wave them about. This peculiar 

 poising of the fore legs, like the arms of a tight-rope dancer. 



