8 INTERNAL ANATOMY OF INSECTS. 
the most delicate and incloses the cortical and medullary 
parts, with the pia mater a . 
III. Parts. — The nervous system of insects consists 
of the brain ; the spinal marrow and its ganglions ; and 
the nerves. 
i. Brain b . Linne denied the existence of a brain in 
insects, and most modern physiologists seem to be of the 
same opinion. A part however, analogous to this impor- 
tant organ — at least in its situation, and in its emission of 
nerves to the principal organs of the senses, in which re- 
spect it certainly differs very materially from the upper 
cervical ganglion, which Dr. Virey regards as its ana- 
logue — is certainly to be found in them; and as Messrs. 
Cuvier and Lamarck distinguish this part by the name 
of brain, we may continue to call it by that name with- 
out impropriety. The brain of insects, then, is distin- 
guished from the succeeding ganglions of the spinal chord 
by its situation in the head, the middle of the internal 
cavity of which it occupies, and by being the only gan- 
glion above the oesophagus. It is usually small, though 
in some cases larger than they are A . It consists of two 
lobes, more or less distinct and generally of a spherical 
form. In Oryctes nasicornis and Pont i a Brassiccc the 
lobes are separated both before and behind e ; while in 
the larva of Dytiscus marginalis, but not in the imago, in 
which there are two large hemispheres separated by a 
furrow, the brane is undivided f . Cuvier mentions the 
3 Lyonet Anat. 100. /. iv.f. 6. Sand with Inlrod. 59 — . 
•» Plate XXI. Fig. 1. 7. 8. a. 
e N. Diet. d'Hist. Nat. xxii. 527- d Ibid. v. 591. 
c Cnv. Anat. Camp. ii. 318. Swamra. Bib/. Nat. /.xxix./. 7. He- 
rold Schmetterl. t. ii./. 1—10. a. f Cuv. Ibid. 322. 337. 
