INTERNAL ANATOMY OF INSECTS. 21 



spect to the internal structure of the ganglions and spinal 

 marrow of insects, we know little to build any theory 

 upon, except that the internal substance of the former is 

 filled with air-vessels ; at least so Lyonet, as has been 

 already observed, found in the goat-moth, while only 

 the tunics of the latter are covered by them. Taking 

 the above resemblance to the brain of vertebrates into 

 consideration, there appears ground for thinking that 

 the nervous system of insects, like some of their articu- 

 lations a , is of a mixed kind, combining in it both the ce- 

 rebro-spinal and the ganglionic systems ; and this will 

 appear further if we consider its functions. 



That learned arid acute physiologist Dr. Virey, as- 

 suming as an hypothesis, that the structure of the system 

 in question is simply ganglionic, and merely analogous to 

 the sympathetic system of vertebrate animals, has built 

 a theory upon the assumption, which appears evidently 

 contradicted by facts. Because, as he conceives after 

 Cuvier, insects are not gifted with a real brain and spinal 

 marrow, he would make it a necessary consequence that 

 they have no degree of intellect, no memory, judgement 

 or free will ; but are guided in every respect by instinct 

 and spontaneous impulses, that they are incapable of 

 instruction, and can superadd no acquired habits to those 

 which are instinctive and inbred b . This consequence 

 would certainly necessarily follow, was their nervous 

 system perfectly analogous to the sympathetic of warm- 

 blooded animals. But when we come to take into con- 

 sideration the functions that in insects this system con- 

 fessedly discharges, we are led to doubt very strongly 



a VOL. III. p. 663. 670. 



b N. Diet. d'Hist. Nat. ii. 47-. v. 592. xvi.308-. 



