ii. 2. 23 



examples. The last of these points to a sub-division that may 

 be made in the class of homogeneous parts.^ For in some of them 

 the whole and a portion of the whole are synonymous. Thus a 

 portion of vessel is still called vessel. While in others there is 

 not this identity of name ; and so far these parts agree with the 

 heterogeneous parts ; for a portion of a face is never called face. 



The first question to be asked is what are the causes to which 

 these homogeneous parts owe their existence ? The causes are 

 various ; and this whether the parts be solid or fluid. Thus one 

 set of homogeneous parts represent the material out of which the 

 heterogeneous parts are formed ; for each separate organ is con- 

 structed of bones, sinews, flesh, and the like ; which are either 

 essential elements in its formation, or contribute to the proper 

 discharge of its function. A second set are the nutriment of the 

 first, and are invariably fluid, for all growth occurs at the expense 

 of fluid matter ; * while a third set are the residue of the second. 

 Such for instance are the faeces and, in animals that have a bladder, 

 the urine ; the former being the dregs of the solid nutriment, 

 the latter of the fluid. 



Even the individual homogeneous parts present variations, 

 which are intended in each case to render them more serviceable 

 for their purpose. The variations of the blood may be selected 

 to illustrate this. For different bloods differ in their degrees 

 of thinness or thickness, of clearness or turbidity, of coldness 

 or heat ; and this whether we compare the bloods from different 

 parts of the same individual or the bloods of different animals. 

 For, in the individual, all the differences just enumerated dis- 

 tinguish the blood of the upper and of the lower halves of the 

 body ; and, dealing with classes, one section of animals is 

 sanguineous, while the other has no blood, but only something 

 resembling it in its place. As regards the results of such dif- 

 ferences, the thicker and the hotter blood is, the more con- 

 ducive is it to strength, while in proportion to its thinness and 

 its coldness is its suitability for sensation and intelligence. A 

 like distinction exists also in the fluids which are analogous to 

 blood. This explains how it is that bees^ and other similar 

 creatures are of a more intelligent nature than many sanguineous 

 animals ; and that, of sanguineous animals, those are the most 

 intelligent whose blood is thin and cold. Noblest of all are those 

 whose blood is hot, and at the same time thin and clear. For 

 648 a. 



