CHAPTEE XIII. 

 ANIMAL MOTION. 



NUMEROUS passages relating to animal motion are to 

 be found in several of Aristotle s works, especially his 

 Progressive Motion of Animals, History of Animals, and 

 Parts of Animals. In these passages, many of which are 

 mere repetitions, he gives interesting information about the 

 locomotory parts and their movements, in walking, creeping, 

 flying, and swimming. His views on the causes of these 

 movements are, however, very incompletely expressed. 



According to him, every animal with feet has an even 

 number of these, and fishes either have no fins at all or two 

 or four fins, for he takes no account of fins other than the 

 pectoral and pelvic.* 



The number four seems to have had a special significance 

 in connection with his ideas about animals. He says that 

 they are moved by four or more awa t those with blood by 

 four only, and those without blood by more than four.t It 

 was sufficient, in fact, to count the aweia, whether fins or 

 other paired means of locomotion, to decide whether an 

 animal had or had not blood, e. g., speaking of fishes, he 

 says that they cannot have more than four fins, for if they 

 had they would necessarily be animals without blood. I 



The word OYIPEIOV (semeion), which means a sign or token 

 by which anything is known, is used in a special sense by 

 Aristotle to indicate the organs or means by the aid of 

 which animals moved from place to place. According to him, 

 legs, arms, wings, paired fins, and even the bendings of the 

 body of a grass-snake, eel, or caterpillar, when in progressive 

 motion, were semeia. 



Referring to the way in which they move, he says that 

 animals, whether they have four or more feet, move in the 

 same way, for their feet move in diagonal succession, but 



* H . A. i. c. 5, ss. 1 and 2. 



| H. A. i. c. 5, ss. 6 and 7 ; De Anim* Incessu, c. 10. 



| P. A. iv. c. 13, 696a. 



