A'otcs. iv. 13. 249 



10. The pectoral fins are, as rightly stated in the text, much more constant than the 

 ventral pair. Even in those elongated eels in which no pectorals are visible externally, 

 rudiments of them are to be found on dissection ; whereas not only are the ventral fins 

 more often externally wanting than the pectorals, but their absence is often complete, 

 no rudiment of them appearing on dissection, e.g. in Mursena, Muraenophis, Gymnotus, 

 etc. There are pectoral, but no ventral, fins in the eel, the conger, and the rest of the 

 so-called Apodal Physostomatous fishes. As to the Cestreus, it is impossible to say what 

 fish is here meant. Certainly it is not one of the Mugilidse, though these are the 

 fishes usually called Cestreus by Aristotle. 



11. The Smursena and the Mursena of A. are in all probability one and the same fish. 

 It is described as elongated ; without either ventral or pectoral fins (see last note) ; 

 marked with different colours ; having its branchiae less distinct than most fishes ; 

 depositing numerous ova ; living on flesh ; hiding itself under the ground in cold 

 weather ; occasionally leaving the water. It is moreover often mentioned in association 

 with the eel and conger. It seems most probable that the Muraena Helena is the species 

 meant. This is very common in the Greek seas, where, according to Erhard, it still 

 bears the name Smuma or Sphurna. 



12. The pectoral and ventral fins are not, as a rule, such important agents in the 

 propulsion of the fish as A. seems to think. Their chief uses are to give direction to the 

 motion generated by the lateral strokes of the tail, to check the progress when required, 

 to enable the fish to maintain its equilibrium and to keep itself at any level in the water. 

 They have also secondary uses as organs of touch, etc. 



In the elongated fishes the undulations of the body take a part in locomotion, but the 

 chief part still devolves, as in other fish, on the lateral strokes of the tail. These, 

 however, were apparently considered by A. as part of the undulatory movement. 



13. a. De Incessu, 8, l. The treatise on the Motion of Animals is unquestionably 

 spurious. Either therefore the words "and the motion" have been introduced by some 

 after-writer into the text ; or Aristotle uses a longer title than usual to designate his 

 treatise " on the progression of animals." 



At ii. 16, Note 11, the treatise on the Motion of Animals has been inadvertently quoted 

 as genuine. 



14. In the Hist. Anim. (i. 5, 15) it is said that serpents and finless fishes are yet 

 moved by four points of motion like other sanguineous animals, for "their flexures 

 are four." The only basis for this seems to have been the desire to bring all sanguineous 

 animals under one general law. 



15. That sanguineous animals can never have more than four motor organs is stated 

 over and over again by Aristotle. If it be asked why, the answer is that it is one of 

 those laws of type to which nature for some reason or other is bound to adhere. Cf. 

 Introd. p. X. 



16. See Note 10. 



17. A. correctly enough describes the manner of swimming of the rays ; but clearly 

 he had not the faintest suspicion that the lateral expansions which serve the office of 

 propulsion are in reality the pectoral fins themselves. Had his notion of the correspond- 

 ence of fins and limbs been founded on anatomical knowledge derived from dissection, 

 he would scarcely have made this oversight. As it is, not recognising the true pectorals, 

 he imagines that the dorsal fins, which in many rays are two in number and placed on 

 the tail, are the pectorals, placed far behind their normal position. 



18. In the fishing- frog the ventral fins are as stated in advance of the pectorals, and 

 are much smaller than the latter. It is quite true that when the ventral fins are advanced 



