GRAND DIVISIONS. 13 
larva to crysalis, from crysalis to the perfect in- 
sect. They are generally the most voracious 
while in the larva state. Some live long in the 
larva state, and but a short time in the state of 
the perfect insect. As the cicadia septendecim 
(American locust,) remains in the larva state sev- 
enteen years, and in the state of perfect insect 
but about a week, and eats nothing during that 
period. Others are in the larva state but a short 
time in proportion to their duration in the insect 
state ; as musca domestica, the common house-fly. 
which continues a long time and eats continually. 
Animals of this division were probably created 
before the vertebral. For it is said that the cast- 
off crusts of the crysalis of some species are found 
in older rocks than the bones of vertebral animals. 
[ have never found any such relics. Perhaps 
fish are found in formations about as old as any 
of this division. 
Examples. Angle-worm, leach, lobster, spi- 
der, beetle, cricket, bee, butterfly, gnat. 
IV. VERTEBRAL ANIMALS. 
dn this division the sentient principle is lodged 
ina medullary substance, the basis of which is in- 
closed in a bony tube, composed of a column of ver- 
tebre. : 
To the nervous axis enclosed in a bony tube, 
which is called the medulla spinalis, there is an 
appendage at one extremity, denominated the 
brain. ‘This is inclosed in a bony case, called the 
cranium. But animals of this division have an- 
other system of nerves, more analagous to the sys- 
tems found in the other three divisions, than the 
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