XXIV THE MAIN GROUPS OF ANIMALS. 



were built was that it was the inherent_£ropertj of heat, and therefore 

 \ of everything possessing heat, to motint upwa_rd&. He fancied that 

 varying indications of such a tendency were to be traced in the ordinary 

 attitudes of animals. At the bottom of the scale came those humble 

 creatures in whom there was so little elevating heat that their bodies 

 lay prostrate on the ground/ or were even, like plants, actually attached 

 to it ; while at the other end came man of all animals alone erect and 

 of all the one with most heat; while between these two extremes came 

 animals in intervening gradations of heat and corresponding differences 

 ) of bodily attiliide. 



Such were Aristotle's tests of vital heat. The relative warmth of 

 animals was not, however, his only, though his main, guide in judging 

 of the soul's excellence. Another, to which he not unfrequently refers, 

 was the dj ggree of complexity of the organism. The nobler the soul 

 the more varied its activities, and the more numerous the instruments 

 it requires. " For when the functions are but few, few also are the 

 organs required to effect them. For this reason animals present a 

 greater complexity of structure than plants ; and this complexity is 

 again more marked in some animals than in others, being most varied 

 in those to whose share has fallen not mere life but life of high degree."' 

 Nature might, of course, use one organ for many purposes, and so 

 endow a simple organism with complex activities. Sometimes, indeed, 

 she does so.^ But as in handicrafts so in the body ; it is better to have 

 special instruments for special operations, than single instruments for 

 multiple uses. Nature never, therefore, when she can help it, acts like 

 \ the artisan, who for cheapness makes "a spit and lamp-holder" in 

 ikone.* In the more perfect animals, then, there are numerous organs, 

 V V reach with its separate office; whereas in less perfect ones such division 

 of labour is much less complete, and in some is so slight that, when 

 the body is cut into bits, each separate fragment can continue to live 

 independently for a short time ; there being scarcely more unity between 

 them than if the animal had been a plant or an aggregation of distinct 

 animals into a single mass.* " But in animals of the most perfect con- 

 formation no such phenomena as these are observable, because their 

 nature has attained to the highest possible degree of unity." ^ Thus 

 ^ - centralisation of vitality^ becomes a test of excellence as well as com- 



plexity of structure, the one like the other implying division of labour. 



(3). These tesls we may now proceed to apply. But it is important 

 to bear in mind that no one of them was supposed by Aristotle to be 

 sufficient by itself. The true nature of any group is not to be defined 



' D. P. iv. 10, 16, and iii. 6, 9. ' D. P. ii. lo, 3. » D. P. iii. i, 11, and ii. 16, 6. 



* D. P. iv. 6, 13. » De Resp. 17, 4 ; D. P. iii. 5, 3. ^ De Juvent. 2. 



