PARTS OF ANIMALS, IV. ix. 



them do so to some extent, but most markedly 

 those conical Testacea which have a spiral shell, 

 since both these classes have this natural struc- 

 ture * ; and therefore they walk with an even gait, 

 and not as is the case with quadrupeds and man.^ 

 Now man has his mouth placed in his head, viz. in the 

 upper pari of the body, and after that the gullet, then 

 the stomach, and after that the intestine which 

 reaches as far as the vent where the residue is dis- 

 charged. This is the arrangement in the blooded 

 animals, i.e., after the head comes what is known as 

 the trunk, and the parts adjoining. The remaining 

 parts {e.g. the hmbs at front and back) have been 

 added by Nature for the sake of those which I have 

 just mentioned and also to make movement possible. 

 Now in the Crustacea too and in the Insects the 

 internal parts tend to be in a straight alignment of 

 this kind ; though with regard to the external parts 

 which subserve locomotion their arrangement diifers 

 from that of the blooded animals. The Cephalopods 

 and the conical-shelled Testacea have the same 



" The passage which follows has been badly corrupted by 

 references to a diagram which have ousted the text. The 

 words in itaHcs have been translated from the Arabic version, 

 of which Michael Scot's Latin translation is given opposite, in 

 default of the original Greek. See supplementary note on 

 p. 432. 



* This refers to their uneven progression by moving first 

 one side of the body and then the other. The Testacea, how- 

 ever, " have no right and left" {De incessu an. 714 b 9), and 

 their movement was evidently an awkward problem for 

 Aristotle. He reserves them until the very end of the De 

 incessu, and he has to admit that they move, although they 

 ought not to do so ! They move Trapa <^volv. The mechan- 

 ism of their motion can be detected by the microscope, and is 

 known as ciliary. See also De incessu^ 706 a 13, 33, Hist. 

 An. 528 b 9. 



' 357 



