DEFINITION OF THE TERM INSECT. 31 
SENSATION. 
Nervous System. A small bilobed brain crowning a 
double, knotty, medullary chord; nerves proceeding 
from the brain and other ganglions to all parts of 
the body. 
CIRCULATION. 
Heart unilocular, inaurite, with a system of circulation 
by arteries and veins; blood a cold white sanies. 
RESPIRATION. . 
Lungs replaced by internal gills receiving the air by 
spiracles. 
DicEstion. 
Liver, consisting of conglomerate glands, and enve- 
loping the intestines*; hepatic ducts. 
GENERATION. 
Genital organs double, ventral; more than one sexual 
union in the course of life. 
The external characters in this class are the same al- 
most in every respect as those which distinguish the 
Phalangide, the whole difference consisting almost in 
the systems of circulation, respiration, and digestion. 
Perhaps some future anatomist may discover in the tribe 
just mentioned, that there is a nearer agreement between 
them and the Arachnida in these systems than is at pre- 
sent suspected, which would prove them true Arachnida. 
I am inclined to think that Phrynus and Gonyleptes, &c. 
breathe by branchial spiracles; but having no oppor- 
@ What L. Dufour regards as the liver in Scorpio (N. Dict. d’ Hist. 
Nat. xxx. 421.) Treviranus looks upon as an Epiploon (Fetthorper) 
both in Scorpio and Aranea. 6. t. i. f. 6. A. A. t. ii. f. 24. dd. Hepatic 
ducts: #1. /. 6. ii. ¢. i, f. 24. B. B. @. B. 
