20 INTERNAL ANATOMY OF INSECTS. 



head two or three days 3 . The sensorium commune of in- 

 sects, therefore, does not, as in the warm-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 cerebro-spinal 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. 

 De Respiratione, c. 3. Reptiles have also this faculty. N. Diet. d'Hist. 

 Nat. xxix. 161. 



* Cuv. Anal. Comp. ii. 283. These are named " the upper and 

 lower cervical ganglions." 



c Lvonet Anal. t. ix. x. PLATE XXI. FIG. l.a.b. 



