THE MAIN GROUPS OF ANIMALS. XXXI 



fifth class. First, however, he divided his Sanguineous group into two 

 subdivisions, the v ivipara and the Ovipara. Of these the Vivipara, 

 including the biped Man, the quadrupedous Beasts, and the apodous 



I Cetacea, were manifestly superior to the Ovipara ; for their more perfect 



o rgans of respiration, and the more mature condition of their young 

 at birth testified indisputably to their greater heat. 



The Ovipara include the Birds, the Reptiles, and the Fishes. Of 

 these the Fishes were clearly at the bottom. The stunted character of 

 their external form,' the absence of lungs and the substitution for them 



I of an inferior organ of refrigeration, were unmistakable signs of inferiority. 



But more than all was this shown by their ovum being deposited in an 

 imperfect condition. It was true that in one great subdivision of Fishes 

 the ovum was not so deposited. These fishes were ovoviviparous, that is, 

 the ovum was hatched inside the body, and in some cases the embryo 

 even formed a kind of '^ placental attachment to the mother. But, says 

 Aristotle, such ovoviviparity is not to be taken like viviparity for a sign 

 of heat. On the contrary, it is a sign of cold. These fishes are of 

 so cold ^ a nature, that they have not enough heat to harden the outside 

 of their ovum into a shell. Their egg remains soft ; and if extruded in 

 this condition would soon be destroyed. It is therefore retained in the 

 parent's body for security. », 



There remain the Reptiles and the Birds. It is not easy to decide | . 

 off"hand which of these was held by Aristotle to be the higher in the ! 

 scale. One would have thought that the manifest warmth of the one to 

 the touch, and equally manifest coldness of the other, would at once 

 have decided the matter. But, strange as it seems, there is no passage, 

 so far as I can ascertain, in which Aristotle recognizes this difference. 

 Yet he had most certainly laid his hand on a living chameleon, and on a 

 living tortoise, for he describes* their vivisection ; and it is impossible 

 to imagine that he had never touched a living bird. The explanation, I 

 think, is to be found in the fact, already stated, that Aristotle drew a wide 

 distinction between ordinary heat and vital heat; and would not allow that 

 touch was any measure of the latter. Tried by his main vital standards the 

 two groups were on a par. Each had red blood ; each breathed b.y a lung, 

 and in each this lung was of a bladdery and therefore an inferior character.* 

 In each the sexes were invariably separate. Each was oviparous, and in 

 each the ovum was a perfect one, that is, had attained its full size at the 

 time of deposition. The similarity between the ova went moreover still 

 farther. For in each it consisted of a white part and a yellow part ; 



1 D. P. iv. 13, 1. 



' D. G. iii. 3, 9. This statement of Aristotle regarding the smooth galeus (Mustelus 

 Isevis) has been shown by Miiller to be true. 



' D. G. i. 10 and 11. * H. A. ii. 11, 11 ; D. Resp. 17, 4. 



* Aristotle mistook the bladder-like air-sacs of Birds for their lungs, cf. iii. 6, note 10. 



