LETTER XXXIX. 
INTERNAL ANATOMY AND PHYSIOLOGY 
OF INSECTS, CONTINUED. 
CIRCULATION. 
WE learn from the highest authority, that the blood is 
the life of the animal? : 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— The fluid that visits and nourishes every part of 
a living body®. 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 znvert the process observable in 
the systems of sensation and respiration, where the ascent 
is from the most complex, to the most simple structure. 
In the lowest members of the animal creation, the blood 
seems the portion they imbibe of the fluid medium in which 
they reside, which when chylified, distributes new mole- 
cules to all parts of their frame‘. In others, as in insects, 
it is formed by the chyle that transpires through the intes- 
2 Genes. 1x. 4. > N. Dict. d’ Hist. Nat. xxx. 130. 
© Cuv. Anat. Comp. iv. 167. 
