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 (l . It consists of two 

 lobes, more or less distinct and generally of a spherical 

 form. In Oryctcs nasicornis and Pontia Brassicce 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 



a Lyonet Anat. 100. t. iv./. 6. Sandwith Introd. 59. 

 f PLATE XXI. FIG. 1. 7. 8. a.- 



N. Diet. d'Hist. Nat. xxii. 527. d Ibid. v. 591. 



c Cuv. Anat. Comp. ii. 318. Swamiu. Bibl. Nat. /.xxix./. 7- He- 

 rold Schmetierl. t, ii./ 110. a. f Cuv. Ibid. 322. 337. 



