TELEOLOGY AND PHYSIOLOGY. 47 
how all these facts comprised under Morphology, Physi- 
ology, and Chorology have come to be what they are; 
and the attempt to solve this problem leads us to the 
crown of Biological effort, Aitiology. When it supplies 
answers to all the questions which fall under these four 
heads, the Zoology of Crayfish will have said its last 
word. 
As it matters little in what order we take the’first three 
questions, in expanding Natural History into Zoology, 
we may as well follow that which accords with the history 
of science. After men acquired a rough and general 
knowledge of the animals about them, the next thing which 
engaged their interest was the discovery in these animals 
of arrangements by which results, of a kind similar to 
those which their own ingenuity effects through mechanical 
contrivances, are brought about. They observed that 
animals perform various actions ; and, when they looked 
into the disposition and the powers of the parts by which 
these actions are performed, they found that these parts: 
presented the characters of an apparatus, or piece of: 
mechanism, the action of which could be deduced from: 
the properties and connections of its constituents, just 
as the striking of a clock can be deduced from the 
properties and connections of its weights and wheels. 
Under one aspect, the result of the search after the 
rationale of animal structure thus set afoot is Teleology ; 
or the doctrine of adaptation to purpose. Under another 
