HEXAi'ODA : NERVOUS SYSTEM, ETC. 295 



and that the European Stag-beetle (Lucanus cervus) has 

 gnawed a hole an inch in diameter through the side of an 

 iron canister in which 1 it was confined ! 



Their nervous system, as already stated, consists of 

 a series of ganglions or knots of nervous matter con- 



FIG. 367. 



Nervous system of an Insect Beetle. 



nected by two longitudinal nervous cords or threads ; and 

 these are situated along the ventral side of the animal, 

 connected, however, with a nervous centre in the head. 

 From these ganglia arise the nerves of the body and 

 limbs (Figs. 358, 364, and 367). 



The organs of sight in Insects consist of ocelli and 

 eyes. Theoretically, the ocelli are the most anterior organs 

 of the head, but in the process of development they are 

 carried backward, so that in the adult insect they appear 

 on top of the head. The ocellus is the simplest form of 

 the eye. 







The ocellus consists of a "very convex, smooth, single cornea, 

 beneath which is a spherical crystalline lens, resting upon the plano- 

 convex surface of the expanded vitreous humor, the analogue of the 

 transparent cones of the compound eyes." 



