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 % is of a mixed kind, combining in it both the ce- 
rebrospinal and the ganglionic systems ; and this will 
appear further if we consider its functions. 
That learned and acute physiologist Dr. Virev, 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 .V. Did. d'Hist. Nat. ii. 47-. v. 592. xvi.308— . 
