ii. 8— ii. 9. 39 



this being the most advantageous condition, so far as strength 

 is concerned. These animals have also a part inside them 

 corresponding to the spinous bones of fishes. For instance in 

 the Cuttle-fishes there is what is known as the os sepiae, and in 

 the Calamaries there is the so-called gladius. In the Poulps 

 on the other hand there is no such internal part, because the 

 body or, as it is termed in them, the head,^ forms but a short 

 sac, whereas it is of considerable length in the other two ; and 

 it was this length which led nature to assign to them their 

 hard support, so as to ensure their straightness and inflexibility ; 

 just as she has assigned to sanguineous animals their bones or 

 their fish-spines as the case may be. To come now to Insects. 

 In these the arrangement is quite different from that of the. 

 Cephalopods ; quite different also from that which obtains in 

 sanguineous animals, as indeed has been already stated. For 

 in an insect there is no distinction into soft and hard parts, 

 but the whole body is hard, the hardness however being of 

 such a character as to be more flesh-like than bone, and more 

 earthy and bone-like than flesh. The purpose of this is to 

 make the body of the insect less liable to get broken into 

 pieces.' 



(Ch. g.) There is a resemblance between the osseous and the 

 vascular systems ; for each has a central part in which it begins, 

 and each forms a continuous whole. For no bone in the body 

 exists as a separate individuality in itself, but each is either a 

 portion of what may be considered a continuous whole, or at 

 any rate is linked with the rest by contact and by attachments ; 

 so that nature may use adjoining bones either as though they 

 were actually continuous and formed a single bone, or, for purposes 

 of flexure, as though they were two and distinct. And similarly 

 no blood-vessel has in itself a separate individuality; but they 

 all form parts of one whole. For an isolated bone, if such there 

 were, would in the first place be unable to perform the office, 

 for the sake of which bones exist ; for, were it discontinuous 

 and separated from the rest by a gap, it would be perfectly 

 unable to produce either flexure or extension ; nor only so, but 

 it would actually be injurious, acting like a thorn or an arrow 

 lodged in the flesh. Similarly if a vessel were isolated, and not 

 continuous with the vascular centre, it would be unable to retain 

 the blood within it in a proper state. For it is the warmth 

 654b. 



