ORGANS OF SENSATION. 81 



open to all sorts of crude fancies, so easy to form, but 

 so detrimental to correct inquiry. 



The Vision of insects is much better understood 

 than that of the other senses. As I have already 

 described the simple and compound eyes of insects, 

 so far as their outward structure is concerned, I shall 

 now call attention to the nerves of the eyes. (*) 



In insects which have large eyes, these nerves are 

 exceedingly large, bulging out after they go off from 

 the ganglionic brain into considerable knobs. In the 

 stag-beetle, in which these are pear-shaped, so many 

 minute branchlets go off to the eye, (one probably to 

 each facette,) that it is not possible to count them. 

 In the hive bee the knobs of these nerves are kidney- 

 shaped, and so much larger than the brain itself, that 

 they might lead an indifferent observer to suppose 

 they were actually the brain. 



The head nerves in the bee. a, the first nerve knot or gang- 

 lion, with its forked division below ; b, the small nerves of the 

 head ; c, c, the two large nerves of the eyes. 



It is remarkable that the eyes of insects are supplied 

 with large air pipes, arising from the main air pipe in 

 the head ; one rather large, surrounding the eye, and 

 many others going off from this and dividing into 



(1) In Latin, Nervi optici. 

 F 



