84 DISTINCTION BETWEEN ANIMALS, 



Animals have some part at least of the sentient vital 

 principle, and are distinguished by being capable of sen 

 sation.* Some have all the senses, and others have certain 

 senses only, but all have the sense of touch,! so that their 

 life is denned by this. I 



It will thus be seen that an object which clearly con 

 tracted on being touched, or which moved bodily from place 

 to place, would be classed by Aristotle with animals. There 

 were also what may be called his border-line forms of life, 

 such as, for instance, his Holothouria, which showed some 

 features indicating that they were plants and also others 

 indicating that they were animals. Let us consider a few 

 of these forms of life and the way Aristotle proposed to 

 classify them. 



The fixed ascidians, Aristotle s Tethya, resembled plants 

 in always being attached to some object, but, since they had 

 a kind of fleshy substance, it must be assumed that they 

 had some degree of sensibility ; further, these animals did 

 not seem to have any distinct waste matters from their 

 nutriment, and, in this respect, they resembled plants. He 

 considered them to be animals which had a sense of smell 

 developed only to a very slight extent. || 



The forms of life to which he gave the name AJcalephai 

 included some of the Medusae, Actiniae, and other Coelen- 

 terata. He considered that they were animals, because 

 some of them became free and could capture their prey, but 

 that, like plants, they had no distinct waste matters. 11 



A satisfactory identification of Aristotle s Holothouria 

 does not seem to be possible. He says that they are free 

 forms of life incapable of moving from place to place,** and 

 that they are devoid of sensation and live like certain plants 

 which exist free from the soil, ft This is all the information 

 he gives about them, and it is not quite clear whether he 

 intended to class them with plants or animals. Some have 

 attempted to identify them with sea-cucumbers (Holothurice) , 

 but such identification is unsatisfactory, for sea-cucumbers 

 show marked signs of feeling. Prof. B. Forbes, after 

 describing the common holothurians of the eastern Medi 

 terranean, and expressing an opinion that they are not the 



* P. A. ii. c. 8, 6536 ; G. A. ii. c. 5, 14la. 

 f- H. A. i. c. 3 ; De Anima, ii. c. 2, 4136 and 414&. 

 I Ibid. iii. c. 13, 4356. P. A. iv. c. 5, 681a ; H. A. viii. c. 1, s. 3. 

 || H. A. iv. c. 8, s. 19. IF P. A.iv.c. 5,6816; H. A. iv. c. 6, ss.4-5. 

 ** H. A. i. c. 1, s. 8. ft P. A. iv. c. 5, 681rt. 



