When a function is ancillary to another, a like relation
manifestly obtains between the organs which discharge these functions;
and similarly, if one function is prior to and the end of another,
their respective organs will stand to each other in the same relation.
Thirdly, the existence of these parts involves that of other things as
their necessary consequents.
Instances of what I mean by functions and affections are
Reproduction, Growth, Copulation, Waking, Sleep, Locomotion, and other
similar vital actions. Instances of what I mean by parts are Nose,
Eye, Face, and other so-called members or limbs, and also the more
elementary parts of which these are made. So much for the method to be
pursued. Let us now try to set forth the causes of all vital
phenomena, whether universal or particular, and in so doing let us
follow that order of exposition which conforms, as we have
indicated, to the order of nature.
Book II
1
THE nature and the number of the parts of which animals are
severally composed are matters which have already been set forth in
detail in the book of Researches about Animals. We have now to inquire
what are the causes that in each case have determined this
composition, a subject quite distinct from that dealt with in the
Researches.
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