PARTS OF ANIMALS, II. viii. 



the medium of the sensation combined in one (com- 

 parable to the pupil plus the whole of the transparent 

 medium in the case of sic^ht). Now not only was it 

 pointless, it was impossible for Nature to make such 

 a combination in the case of the other senses ; with 

 touch, however, it was due to necessity, since its 

 sense-organ is the only one which is corporeal — 

 or at least it is definitely the most corporeal one." 

 It is also clear from our actual experience in sensation^ 

 that all the other parts exist for the sake of the organ 

 of touch (the flesh). In these I include the bones, the 

 skin, the sinews, the blood-vessels ; also the hair, nails 

 of every sort and kind, and the like. The bones, 

 for instance, which are hard in substance, have been 

 devised for the preservation of the soft parts. The 

 same is true of the counterpart ^ of the bones in other 

 creatures : two examples in species of fish are spine 

 and cartilage. 



Now with some animals this hard supporting 

 substance is situated inside the body, with others 

 (some of the bloodless ones) it is outside. It is out- 

 side in the case of all the Crustacea ^ {e.g. the Crabs 

 and the group of Crayfish), and the group of Testacea* 

 too, e.g. those that are known as Oysters. All these 

 have their fleshy part inside, and the earthy part 

 which holds it together and protects it is out- 

 side — outside, because it performs an additional 

 function as well : since these creatures are bloodless, 

 they possess but little heat, and the shell acts like 

 a couvre-feu ; it encloses the faintly burning heat 

 and protects it. Another quite different group of 

 creatures, the Turtles and the group of freshwater 



* Lit., "the shell-skinned creatures." "Testacea" is the 

 nearest modern term. See Introduction, p. 23. 



159' 



