INTERNAL ANATOMY OF INSECTS. 3 
the Creator. Its pulpy substance is the visible medium 
by which the governing principle a transmits its com- 
mands to the various organs of the body, and they move 
instantaneously — yet this appears to be but the conduc- 
tor of some higher principle, which can be more imme- 
diately acted upon by the mind and by the will. This 
principle, however, whatever it be, whether we call it the 
nervous fluid, or the nervous power b , has not been de- 
tected, and is known only by its effects. The system of 
which we are speaking may therefore be deemed the 
foundation and root of the animal, the centre from which 
emanate all its powers and functions. 
Comparative anatomists have considered the nervous 
system of animals as formed upon four primary types, 
which may be called the molecidar, the filamentous, the 
ganglionic, and cerebrospinal c . The first is where in- 
visible nervous molecules are dispersed in a gelatinous 
body, the existence of which has only been ascertained 
by the nervous irritability of such bodies, their fine sense 
of touch, their perceiving the movements of the waters 
in which they reside, and from their perfect sense of the 
degrees of light and heat d . Of this description are the 
infusory animals, and the Polypi. The nervous mole- 
cules in these are conjectured to constitute so many gan- 
glions, or centres of sensation and vitality e . The second, 
the filamentous, is where the nervous system consists of 
nervous threads radiating from the mouth, as in the 
* To ' HyeftoviKou. 
b See Hooper's Medical Dictionary, under Nervous Fluid, and 
Mr. Sandwith's useful Introduction to Anatomy and Physiology, 83, 
c N. Diet. d'Hist. Nat. xvi. 305—. 
d Cuv. Anat. Comp. ii. 362. Compare MacLeay Hor. Entomolog. 
215.— e N. Diet. d'Hist. Nat. ubi. supr. 
B 2 
