78 iii. 7. 



All sanguineous animals, then, need these two parts ; and this 

 explains why these two viscera, and these two alone, are invariably 

 found in them all. In such of them, however, as breathe, there 

 is also as invariably a third, namely the lung. The spleen on 

 the other hand is not invariably present ; and, in those animals 

 that have it, is only present of necessity in the same sense as 

 the excretions of the belly and of the bladder are necessary, in 

 the sense that is of being an inevitable concomitant. Therefore 

 it is that in some animals the spleen is but scantily developed 

 as regards size. This for instance is the case in such feathered 

 animals as have a hot stomach. Such are the pigeon, the hawk, 

 and the kite.^* It is the case also in oviparous quadrupeds, where 

 the spleen is excessively minute, and in many of the scaly fishes. 

 These same animals are also without a bladder, because the loose 

 texture of their flesh allows the residual fluid to pass through and 

 to be converted into feathers and scales. For the spleen attracts 

 the residual humours from the stomach, and owing to its blood- 

 like character is enabled to assist in their concoction.^^ Should 

 however this residual fluid be too abundant, or the heat of the 

 spleen be too scanty, the body becomes sickly from over-repletion 

 with food. Often too, when the spleen is affected by disease, the 

 belly becomes hard ^^ owing to the reflux into it of the fluid ; 

 just as happens to those who form too much urine, for they also 

 are liable to a similar diversion of the fluids into the belly. But 

 in those animals that have but little superfluous fluid to excrete, 

 such as birds and fishes, the spleen is never large, and in some 

 exists no more than by way of token. So also in the oviparous 

 quadrupeds it is small, compact, and like a kidney. For their 

 lung is spongy, ^^ and they drink but little, and such superfluous 

 fluid as they have is diverted to the formation of feathers. 



On the other hand in such animals as have a bladder, and 

 whose lung contains blood, the spleen is watery, both for the 

 reason already mentioned, and also because the left side of the 

 body is more watery and colder than the right. For each of two 

 contraries has been so placed as to go together with that which 

 is akin to it in another pair of contraries. Thus right and left, 

 hot and cold, are pairs of contraries; and right is conjoined with 

 hot, after the manner described, and left with cold. 



The kidneys when they are present exist not of actual necessity, 

 but as matters of greater finish and perfection. For by their 

 670 b. 



