HOUSE FLIES AND BLUEBOTTLES 



209 



which contains those ganglia that may be regarded as 

 equivalent to a brain, soon ceases to show any signs of 

 life; but the body, if touched, will for hours after 

 decapitation respond to the stimulus by reflex move- 

 ments of the legs and wings. The ganglia in the thorax, 

 therefore, are all-important as the centres of animal life, 

 and it is by crushing them that the life of the insect is 

 most effectually and speedily destroyed. There is all 

 the more reason for this with the Muscidce than with 

 other insects, because of the remarkable concentration 

 of the nervous system in that family. The whole of the 

 ganglia belonging to that part of the nerve-chain which 

 lies behind the head have become fused into one mass, 

 and that mass is situated in the thorax (Fig. 67); it 

 may easily be discovered in a blue- 

 bottle by removing the skin from 

 the upper surface of the thorax, and 

 then cutting away the masses of 

 muscle which are thus exposed, as 

 well as that part of the alimentary 

 canal which lies immediately beneath 

 them. The nervous mass is then 

 seen as a whitish body from which 

 threads pass in various directions. 

 This dissection should be performed 

 under water. 



There is a very pretty fly called 

 Pollenia rudis, which is often 

 common on the window panes in 

 the spring, before M. domestica 

 appears. It is about the size of the latter species, and 

 hibernates in the house, whence its presence on the 

 windows. It is of a shining brownish-black colour, the 

 thorax being sprinkled with thin golden hairs in addition 







FIG. 67. Thoracic Gan- 

 glia of Bluebottle. 

 (After Lowne.) 



