IV. II — IV. 12. 129 



time it has a final cause, for it tells to their advantage by- 

 enabling them to guard against attacks from behind. For their 

 body, owing to its length and its want of feet, is ill-suited for 

 turning round and protecting the hinder parts ; and merely to 

 lift the head, without the power of turning it round, would be 

 of no use whatsoever. 



The ovipara with which we are dealing have, moreover, a part 

 which corresponds to the breast ; but neither here nor elsewhere 

 in their body have they any mammae, as neither has any bird 

 or fish. This is a consequence of their having no milk ; for 

 a mamma is a receptacle for milk and, as it were, a vessel to 

 contain it. This absence of milk is not peculiar to these animals, 

 but is common to all such as are not internally viviparous. 2* 

 For all such produce eggs, and the nutriment which corresponds 

 to the milk is in them formed in the egg. Of all this, however, 

 a clearer account will be given in the treatise on Generation and 

 Development.^^ As to the mode in which the joints bend, 

 a general account, in which all animals are considered, has 

 already been given in the dissertation on Progression. So also 

 the reasons for the presence or absence of a tail have been already 

 stated at large.^^ It suffices therefore to say that these animals 

 always have a tail of some sort, though the size which it attains 

 varies considerably. 



Of all the ovipara that live on land there is none so lean as 

 the Chartiaeleon.2'' For there is none that has so little blood. 

 The explanation of this is to be found in the psychical- 

 temperament of the creature. For it is of a timid nature, as 

 the frequent changes it undergoes in its outward aspect testify.^ 

 But fear is a refrigeration, and results from deficiency of natural 

 heat and scantiness of blood.^^ 



We have now done with the sanguineous animals, both such 

 as are quadrupedous and such as are apodous, and have stated 

 with sufficient completeness what external parts they possess, and 

 for what reasons they have them. 



(C/i. 12.^ The differences of birds ^ compared one with another 

 are differences of magnitude, and of the greater or smaller 

 development of parts. Thus some have long legs, others short 

 legs ; some have a broad tongue, others a narrow tongue ; and 

 so on with the other parts. There are very few of their parts 

 that present any greater differences than these, taking birds by 

 692 b. 9 



