GENERATION OF ANIMALS, II. i. 



does not lie in any of the organs of locomotion. 

 No ; those animals are W^iparous which are more 

 perfect in their nature, which partake of a purer 

 " principle " ; in other words, no aninial is internally 

 vixiparous unless it draws in breath — respires. The 

 more perfect animals are those which are by their 

 nature hotter and more fluid and are not earthy. 

 (The test of natural heat is the presence of the lung, 

 provided it has blood in it. Speaking generally, 

 animals which have a lung are hotter than those 

 that have none, and of the former those are hotter 

 w'hose lung is not spongv nor compact nor poorly sup- 

 plied M"ith blood, but well supplied with blood and 

 soft.) And since an actual animal is something per- 

 fect whereas larvae and eggs are something imperfect, 

 Nature's rule is that the perfect offspring shall be 

 produced by the more perfect sort of parent. Those 

 animals which are hotter (as their having a lung indi- 

 cates), though of a more solid" consistency, or are 

 colder but more fluid, either (o) are oviparous and 

 lay a perfect egg, or (b) first lay an egg and then are 

 viviparous internally. Thus, birds and the animals 

 with horny scales, on account of their heat, produce 

 something perfect, but on account of their solidity 

 it is an egg only '' ; the Selachia are less hot than 

 these are, but more fluid ; hence they share in the 

 characteristics of both — they are oviparous because 

 they are cold creatures, and internally viviparous 

 because they are fluid (the reason being that fluid 

 matter is conducive to life, whereas solid matter and 

 the living organism are at opposite poles) ; and as 

 they have neither feathers nor horny plates nor 

 scales, which are signs of a constitution that tends to 

 be solid and earthy, the egg which they produce is 



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