AND THEIR FUNCTIONS. 163 



but wider than the oesophagus, extends backwards towards 

 the mouth.* 



This description apphes very well to the alimentary 

 canal of a sepia or loligo (calamary), except that Aristotle 

 mistakes for a crop what is the stomach, and the stomach 

 for an intestinal caecum. He also states correctly that the 

 sepia and calamary differ in the form of the above-mentioned 

 parts, but adds incorrectly that the parts about the stomach 

 are the same in the sepia and octopus, t for the octopus has 

 a well-marked crop. He states correctly that the ink bag 

 of the cephalopods serves as a means of defence, that its 

 duct opens close to the terminal end of the intestine, and that 

 it is largest in the sepia and situated lower down than in 

 the octopus and calamary, t 



Aristotle's statements about the gastric teeth of crusta- 

 ceans have been discussed in Chapter x. With respect to 

 the general characters of the alimentary canal in crustaceans, 

 he states substantially correctly that the oesophagus is 

 short and opens into a membranous stomach, whence 

 extends a simple intestine of uniform diameter. § 



His descriptions of the alimentary canal in that section 

 of his Ostrakoderma which consists of molluscs are full 

 of difficulties. He mentions some species of Buccinum 

 {Keryx), Murex or perhaps Purpura (Porphura), and other 

 gastropods in his descriptions, but does not describe all the 

 chief parts of the alimentary canal for any one of these. 

 He gives a concise general description of the alimentary 

 canal of a gastropod in P. A. iv. c. 5, 6796, where he states 

 that next to the mouth is a crop, like that of a bird, then a 

 stomachos, and next to this a coelia or stomach in which is 

 the mecon (liver), whence the intestine takes its origin. 

 Aristotle seems to be referring to the crop, which occurs, it 

 is true, in snails and many other gastropods, but not close 

 to the mouth in the way which he seems to suggest. 

 It is less likely that Aristotle refers to the buccal cavity. 

 The relations between the stomach, intestine, and mecon 

 or liver he did not understand. The stomach requires to be 

 carefully dissected out from the enveloping mass of the 

 liver ; he does not seem to have done this, but took the 

 whole mass for the stomach, which he says contained the 

 mecon. 



- H. A. iv. c. 1, s. 10; P. A. iv. c. 5, 6786. 

 f P. A. iv. c. 5, 6786. \ Ibid. iv. c. 5, 6786 and 679a. 



§ H. A. iv. c. 2. ss. 10-12 ; P. A. iv. c. 5, 679(T, 



