62 ZOOLOGICAL PHILOSOPHY 



This primary division of animals into two main groups was fairly 

 good, but the character taken by Aristotle for discrimination was 

 bad. That philosopher gave the name of blood to the chief fluid in 

 animals which has a red colour. He imagined that all animals which 

 he placed in his second class only possessed white or whitish fluids ; 

 and he thereupon regarded them as having no blood. 



Such apparently was the first outUne of a classification of animals ; 

 it is at any rate the oldest of which we have any knowledge. But 

 this classification also furnishes the earUest example of an arrange- 

 ment, though in the opposite direction from the order of nature ; since 

 we may notice in it a progression, though a very imperfect one, from 

 the most complex to the simplest. 



That erroneous direction has been generally followed ever since 

 in the arrangement of animals ; and this has clearly retarded our 

 knowledge of nature's procedure. 



Modern naturahsts have endeavoured to improve upon Aristotle's 

 division by giving to the animals in the first class the name of red- 

 blooded animals, and to those in his second class that of white-blooded 

 animals. It is now well known how defective is this character ; since 

 there are some invertebrate animals (many annelids) which have 

 red blood. 



In my opinion the essential fluids of animals do not deserve the name 

 of blood, except when they circulate in arteries and veins ; for the 

 other fluids are so degraded, and the combination of their principles 

 so imperfect, that it would be wrong to assimilate them to fluids which 

 have a true circulation. One might as well attribute blood to a plant 

 as to a radiarian or polyp. 



In order to avoid ambiguity and hypothesis, I divided the entire 

 known animal world in my first course of lectures at the Museum 

 in the spring of 1794 (the year II. of the repubUc) into two perfectly 

 distinct groups, viz. : 



Animals that have vertebrae. 

 Animals without vertebrae. 



I called the attention of my pupils to the fact that the vertebral 

 column, among animals provided with it, indicates the possession 

 of a more or less perfect skeleton and of a plan of organisation on the 

 same plane ; whereas its absence among other animals not only 

 distinguishes them sharply from the first, but shows that their whole 

 plan of organisation is very diff'erent from those of vertebrate animals. 



From Aristotle to Linnseus nothing of note appeared with regard 

 to the general arrangement of animals ; but in the course of last 

 century naturalists of the highest distinction made a large number 

 of special observations on animals, and especially on many inverte- 



