4- INTERNAL ANATOMY OF INSECTS. 



Radiata, or star-fish and sea-urchins a . The third, the 

 glanglionic, is where the nervous system consists of a 

 series of ganglions connected by nervous threads or a me- 

 dullary chord, placed, except the first ganglion, below the 

 intestines, from which proceed nerves to the various parts 

 of the body. This system may be considered as divisi- 

 ble into two the proper ganglionic, in which it is gan- 

 glionic with the ganglions arranged in a series with a 

 double spinal chord. This prevails in the classes Insecta, 

 Crustacea, Arachnida, &c., and the improper ganglionic, 

 in which it is ganglionic with the ganglions dispersed 

 irregularly, but connected by nervous threads, as in the 

 Mollusca b . In the fourth, the cerebro-spinal, the ner- 

 vous tree may be said to be double, or to consist of two 

 systems the first taking its origin in a brain formed of 

 two hemispheres contained in the cavity of the head, 

 from which posteriorly proceeds a spinal marrow, in- 

 cluded in a dorsal vertebral column. These send forth 

 numerous nerves to the organs of the senses and the 

 muscles of the limbs. The second consists of two prin- 

 cipal ventral chords, which by their'ganglions, but with- 

 out any direct communication, anastomose with the spinal 

 nerves and some of those of the brain, and run one on 

 each side from the base of the skull to the extremity of 

 the sacrum. This system consists of an assemblage of 

 nervous filaments bearing numerous ganglions, from 

 which nervous threads are distributed to the organs of 

 nutrition and reproduction c . Its chords are called the 



a Cuv. Anat. Comp. ii. 360. MacLeay Hor. Ent. 201. 

 " N. Diet. d'Hist. Nat. xvi. 306. MacLeay Hor. Ent. 200. 

 c Ibid. 307- The great sympathetic nerves in fishes are said to 

 have no ganglions. Cuv. ubi. supr. 297. 



