20 INTERNAL ANATOMY OF INSECTS. 
head two or three days 3 . The sensorium commune of in- 
sects, therefore, does not, as in the wvrm-blooded ani- 
mals, reside in the brain alone, but in the spinal marrow 
also. It was on this account probably that Linne denied 
the existence of a brain in insects, regarding it merely 
as the first ganglion of the spine. 
Cuvier and other modern physiologists, from the gan- 
glionic structure of this organ, are of opinion that it is 
not the analogue of the cerebrospinal system of verte- 
brate animals, but rather of their great sympathetic nerves. 
Indeed, considering solely the external structure of the 
nervous system of insects, a great resemblance strikes us 
between it and these nerves ; for besides its general gan- 
glionic structure, there is also in them an upper ganglion 
in the neck, seemingly corresponding with what we have 
named the brain of insects, from which the nervous chord 
dips to the lower part of the neck, where it forms a se- 
cond ganglion, which appears to correspond with what 
we have considered as their second ganglion b . We may 
observe, however, that at least in one respect there is 
even an external resemblance between the brain of in- 
sects and that of vertebrate animals: — it most commonly 
consists, as has been stated, like them, of two lobes, often 
very distinct ; a circumstance which not unfrequently 
distinguishes the other ganglions c , and is not borrowed 
from the ganglions of the great sympathetics. With re- 
a Linn. Trans, ii. 8. Aristotle had observed this vitality of insects, 
and that that of the myriapods is greatest. Hist. Animal. I. iv. c. 7. 
T)e Respiratione, c. 3. Reptiles have also this faculty. N. Diet, a" Hist. 
Nat. xxix. 161. 
b Cuv. Anat. Comp. ii. 283—. These are named " the upper and 
lower cervical ganglions." 
c Lyonet Anat. t. ix. x. Platk XXI. Fig. 1. a. b. 
