CLASSIFICATION OF ANIMALS. 11 



But the principles on which animals are now grouped together are 

 of a different and much higher kind : they are the fruits of the best 

 results of the researches of all the great comparative anatomists since 

 the time of Linnaeus. The characters of the classes of animals have 

 been rendered by the immortal Cuvier, the highest expressions of 

 the facts ascertained in the animal organisation. I know not any 

 thing more calculated to impress the stranger to anatomical science 

 with the immensity of the labour that has been gone through, and 

 with the vast number of careful and minute dissections that have 

 been made, than the propositions which now form the definitions of 

 the primary groups of the animal kingdom. 



The whole organisation of one species has been compared with that 

 of another, and this with a third, and so on, in order to ascertain in 

 what organ, or system of organs, the greatest number of animals w ould 

 be found to present the same condition : so that they might not be 

 arbitrarily, but naturally associated together. In the terms of logic, the 

 characters common to all animals having been ascertained, the ana- 

 tomist, in the next place, has sought to discover the difference, which, 

 added to the definition of animal, would form the most extended 

 species of that genus. 



Aristotle thought he had found this differential or primary character 

 in the blood, recognising as blood only the circulating fluid, which 

 was red coloured. His first division of animals was accordingly into 

 Enaima and the Atiaima, or the sanguineous and exsanguineous ani- 

 mals. For a long time no advance was made beyond this early step 

 in the primary arrangement of animals. It was at length discovered 

 that many of the exsanguineous animals of Aristotle did actually 

 possess blood, though differing in colour from that of the so-called 

 sanguineous species. This led, however, only to a nominal improve- 

 ment in the classification ; the Enaima were called " red-blooded," 

 the Anaima " white-blooded" animals. It was reserved for Cuvier to 

 discover, in the course of his minute dissections of the lower animals, 

 that an extensive class of worms had red blood circulating in a closed 

 system of arteries and veins ; and this discovery first materially affected 

 the value of the character applied by Aristotle to the primary groups 

 of the animal kingdom. 



The Annelides, or red-blooded vv^orms, could not, however, be com- 

 bined with birds, beasts, and fishes, in a natural system, since they 

 differed from them so widely in almost every other particular of their 

 organisation. 



Some other character was therefore sought for, since it became ob- 

 vious that the colour of the blood led to an artificial combination of 

 species. Lamarck thought he had discovered the desired character in 



