111. 7 — 111. 8. 79 



special character they are suited to serve in the excretion of the 

 fluid which collects in the bladder. In animals therefore where 

 this fluid is very abundantly formed, their presence enables the 

 bladder to perform its proper office with greater perfection.^^ 



Since then both kidneys and bladder exist in animals for one 

 and the same function, we must next treat of the bladder, 

 though in so doing we disregard the due order of succession ^^ 

 in which the parts should be enumerated. For not a word has 

 yet been said of the midriff", which, though not one of the viscera, 

 is yet one of the parts that environ them, and has to be considered 

 with them. 



(Ch. Z.) It is not every animal that has a bladder ; those 

 only being apparently intended by nature to have one, whose 

 lung contains blood. ^ To such it was but reasonable that she 

 should give this part. For the character of their lung with its 

 abundant blood causes them to be the thirstiest of animals, 

 and makes them require a more than ordinary quantity not 

 merely of solid but also of liquid nutriment. This increased 

 consumption necessarily entails the production of an increased 

 amount of residue ; which thus becomes too abundant to be 

 concocted by the stomach and excreted with its own residual 

 matter. The residual fluid must therefore of necessity have a 

 receptacle of its own ; and thus it comes to pass that all animals 

 whose lung contains blood are provided with a bladder. Those 

 animals on the other hand that are without a lung of this 

 character, and that either drink but sparingly owing to their 

 lung being of a spongy texture, or that never imbibe fluid at all 

 for drinking's sake but only as nutriment, insects for instance 

 and fishes, and that are moreover clad with feathers or scales 

 or scaly plates ^ — all these animals, owing to the small amount 

 of fluid which they imbibe, and owing also to such residue as 

 there may be being converted into feathers and the like, are 

 invariably without a bladder.^ The Tortoises,* which are com- 

 prised among animals with scaly plates, form the only exception ; 

 and this is merely due to the imperfect development of their 

 natural conformation ; the explanation of the matter being that 

 in the sea-tortoises the lung is flesh-like and contains blood, 

 resembling the lung of the ox, and that in the land-tortoises 

 it is of larger size in comparison with the bulk of the body 

 than in other animals of the same class.^ Moreover, inasmuch 

 671a. 



