XXll THE MAIN GROUPS OF ANIMALS. 



honour, in whose soul there is still further the Intellectual faculty and 

 Reason." ' In proportion as the soul includes more or fewer of these 

 successive faculties will its possessor's place be higher or lower in the 

 scale of excellence. At the bottom will come organisms whose life is 

 ■confined to nutrition ; next, those that are also endowed with' sensation ; 

 jthen, such as besides feeling are also capable oMocomotion ; and, lastly, 

 jthose who add to these endowments the possession of^ reason. The 

 few groups thus obtained will again be divisible into smaller groups, 

 according to the degree in which each successive faculty is developed. 

 There are degree s of Nutritive power, of Sensibility, of Motility, of 

 Intelligence ; and the question next to be considered is, what were the 

 external characters by which Aristotle thought that he could determine 

 these degrees. 



(2). The Nutritive soul manifests itself, of course, in growth and 

 reproduction ; and the tests of its power are the bulk of the body,'' and 

 the duration of life, which is usually proportionate to the bulk. " For, 

 as a rule, big animals are long lived, though not invariably."' The 

 number of the progeny is not so good a measure as might be expected, 

 because the requirements of a large body on the nutritive material may 

 prevent an animal of great size from being prolific* The sensitive soul 

 is of course certainly present, if the organism have external organs of 

 sense. But a doubt may arise when, as in the sponge,* there are none 

 such. The test in such a case is to see whether the organism shrinks 

 when irritated. The degrees of ' sensibility must be judged of by the 

 number and perfection of the organs of sense, and especially of those 

 senses from which are* derived the perceptions, which conduce most to 

 knowledge. 



As to the Motor soul, and the Intellectual, the tests are self-evident ; 

 and may therefore be passed over. 



But besides these special tests, applicable to the several parts of the 

 soul, Aristotle had other more general ones, by which he gauged the 

 . . excellence of the soul as a whole. Foremost among these was the 

 temperature of the body. For though Aristotle would not allow,* with 

 Democritus, that heat was identical with the soul, that is, with life, yet 

 he admitted that heat was its necessary agent, so that the two were 

 inseparably conjoined, and the degree of the one became a measure of 

 the degree of the other. " The nobler an animal is, the greater is the 

 amount of heat it possesses. For with greater heat there must of neces- 

 sity be combined a nobler soul." ^ But how was the temperature to be 

 measured .'' As Aristotle had no thermometer, he could only form a 



' De An, ii. 3, i. "^ De Gen. ii. i, 7. ^ De Long, vitas 4, 3 ; De Gen. iv. 10, i. 



* De Gen. iv. 4, 20, and i, 8, 4. ' H. A. L i, 18. « D. P. ii. 7, 5. 



» De Resp. 13, 2. 



