62 HUMBLE CEEATUaES. 



upon the central chord, a nervous ganglion, from 

 which hUateral branches proceed in a similar manner 

 to those in the Worm, showing a somewhat superior, 

 but still low stage of development. But now, if we 

 compare these structures with the nervous system of 

 the Ply, we shall find a marked progress, indicated 

 by a concentration of the chief nervous centres, and 

 by a great disproportion in the size of the various 

 bilateral branches. The only two important centres 

 are the cephalic ganglion (brain) and that in the 

 thorax, the latter being produced by a fusion of all 

 the larval ganglia, except the brain and suboesophageal 

 ganglion. The nerves, too, diflFer considerably in their 

 proportions, owing to the unequal development of the 

 organs and members to which they proceed. The 

 optic, which has already been described, is enormously 

 developed, to supply the numerous facets of the com- 

 pound eye. Next in size is that which proceeds to 

 the halteres, then that to the wings, whereby the 

 importance of these organs is sufficiently indicated ; 

 and the remaining nerves are of comparatively small 

 dimensions. 



We have thus dwelt upon the nervous system of 

 the Fly, not only for the purpose of showing its 

 analogy with that of the Worm, and the points of 

 difference between them, but also because the con- 

 sideration of this part of their anatomy, along with 

 that of the larva of the My, in reality comprises a 

 review of the nervous system of the whole series of 

 Articulated animals, all of which more or less nearly 



