iv. 5. 105 



themselves and can seize hold of their food, and that they are 

 sensible of objects which come in contact with tljem, they must 

 be considered to have an animal nature. The • like conclusion 

 follows from their using the roughness of their bodies ^^ as a 

 protection against their enemies. But on the other hand they 

 are closely allied to plants, firstly by the imperfection of their 

 structure, secondly by their being able to attach themselves to the 

 rocks with great rapidity, and lastly by their having no visible 

 residuum, notwithstanding that they possess a mouth. 



Very similar again to the Acalephae, are the Starfishes. For 

 these also seize hold of their prey, and suck out its juices, and 

 thus destroy a vast number of oysters.^' At "the same time 

 they present a certain resemblance to such animals as the 

 Cephalopods and Crustacea, inasmuch as they are free and un- 

 attached. The same may also be said of the Testacea. 



Such then is the structure of the parts that minister to nutrition, 

 and which every animal must necessarily possess. But besides 

 these organs it is quite plain that in every animal there must be 

 some part or other which shall be analogous to what in sanguineous 

 animals is the presiding seat of sensation. Whether an animal 

 has or has not blood, it cannot possibly be without this. In the 

 Cephalopods this part consists of a membrane, containing fluid, 

 through which runs the gullet on its way to the stomach. It 

 lies rather towards the dorsal surface of the animal, and is by 

 some called the mytis.^ Just such another organ is found in 

 the Crustacea, and is known in them also by the same name. 

 This part is formed by a combination of fluid and solid, and 

 is, as before said, traversed by the gullet. For had the gullet 

 been placed farther back, between the mytis and the dorsal 

 surface of the animal, the hardness of the back would have 

 interfered with its due dilatation in the act of deglutition. On 

 the outer surface of the mytis runs the intestine ; and in contact 

 with this latter is the ink-bag, which is thus removed as far as 

 possible from the mouth, while a considerable interval divides 

 its irritating fluid from the nobler and sovereign parts.^ The 

 position of the myiis shows that it corresponds to the heart 

 of sanguineous animals ; for it occupies the self-same place. 

 The same is proved by the sweetness of its fluid, which has the 

 character of concocted matter and resembles blood.^^ 



In the Testacea the presiding seat of sensation is in a cor- 

 681b. 



