ained in vogue
until superseded by that of Cuvier in the nineteenth century. It is
not to be supposed that all the terms of Aristotle's classification
originated with him. Some of the divisions are too patent to have
escaped the observation of his predecessors. Thus, for example, the
distinction between birds and fishes as separate classes of animals
is so obvious that it must appeal to a child or to a savage. But
the efforts of Aristotle extended, as we shall see, to less patent
generalizations. At the very outset, his grand division of the animal
kingdom into blood-bearing and bloodless animals implies a very broad
and philosophical conception of the entire animal kingdom. The modern
physiologist does not accept the classification, inasmuch as it is now
known that colorless fluids perform the functions of blood for all the
lower organisms. But the fact remains that Aristotle's grand divisions
correspond to the grand divisions of the Lamarckian system--vertebrates
and invertebrates--which every one now accepts. Aristotle, as we have
said, based his classification upon observation of the blood; Lamarck
was guided by a study of the skeleton. The fact that such diverse
points of view could direct the observer towards the same result gives,
inferentially, a suggestive lesson in what the modern physiologist calls
the homologies of parts of the organism.

Aristotle divides his so-called blood-bearing animals into five classes:
(1) Four-footed animals that bring forth their young alive; (2) birds;
(3) egg-laying four-footed animals (including what modern naturalists
call reptiles and amphibians); (4) whales and their allies; (5) fishes.
This classification, as will be observed, is not so very far afield
from the modern divisions into mammals, birds, reptiles, amphibians,
and fishes. That Aristotle should have recognized the fundamental
distinction between fishes and the fish-like whales, dolphins, and
porpoises proves the far from superficial character of his studies.
Aristotle knew that these animals breathe by means of lungs and that
they produce living young. He recognized, therefore, their affinity
with his first class of animals, even if he did not, like the modern
naturalist, consider these affinities close enough to justify bringing
the two types together into a single class.

The bloodless animals were also divided by Aristotle into five
classes--namely: (1) Cephalopoda (the octopus, cuttle-fish, etc.);
(2) weak-she