LETTER XXXIX. 
INTERNAL ANATOMY AND PHYSIOLOGY 
OF INSECTS, CONTINUED. 
CIRCULATION. 
Vv E learn from the highest authority, that the blood is 
the life of the animal a : every object of creation, there- 
fore, that is gifted with animal life, we may conclude, in 
some sense, has blood, which in this large sense may be 
defined — Tlie Jluid that visits and nourishes every part 
of a living body b . But the Great Author of nature 
has varied the machinery by which this nutritive fluid is 
formed and distributed, gradually proceeding from the 
most simple to the most complex structure ; in which he 
seems to have seen it fit to invert the process observable 
in the systems of sensation and respiration, where the 
ascent is from the most complex, to the most simple struc- 
ture. In the lowest members of the animal creation, 
the blood seems the portion they imbibe of the fluid me- 
dium in which they reside, which when chylified, distri- 
butes new molecules to all parts of their frame c . In 
others, as in insects, it is formed by the chyle that tran- 
' Genes, ix. 4. b N. Diet. a" Hist. Nat. xxx. 130. 
c Cuv. Anat. Comp. iv. 107. 
VOL. IV. G 
