338 



CHAPTER XV. 

 OF THE CLASS OF CEPHALOPODA. 



949. THE Cephalopoda unquestionably constitute the group 

 of highest organisation in the Molluscous sub-kingdom. They 

 are characterised by the possession of feet, or locomotive organs, 

 around the head ; whence their name is derived. But these feet 

 have no analogy either with the fleshy disc of the Gasteropods, 

 or with the feet of Articulata or Vertebrata. They are, in fact, 

 prolonged tentacula, or lips. In the Nautilus (Fig. 648), which 

 approaches the nearest to Gasteropoda, they are very numerous, 

 and are evidently feeble as instruments of prehension ; whilst 

 they would seem, from the distribution of their nerves, to be 

 more concerned in sensation. In some of the Cephalopoda the 

 feet are much prolonged, and of great power ; and are evidently 

 very important organs both of locomotion and prehension (Fig. 

 643). But in those forms which approach most nearly to 

 Fishes, we find them again greatly reduced in size, in propor- 

 tion to the elongation of the body ; and it is by the latter, and 



the fin-like expansions with 

 which it is provided, that 

 progression is then chiefly 

 accomplished (Fig. 640). 



FIG. 640.-CALAKAKY. 



possess tentacular prolong- 



ations of the lips, evidently analogous to the arms of the Cepha- 

 lopoda ; and this is one of the many interesting points by which 

 a transition is effected between these two classes. In many 

 species of this class one of the arms of the male is singularly 

 modified and rendered subordinate to the business of reproduc- 

 tion ; in the Argonaut and Tremoctopus, this arm is even thrown 

 off by its owner, when it attaches itself to the female, and exhi- 

 bits so much vitality that it was until recently described as a 

 parasitic worm, under the name of Hectocotylus. The Nautilus is 

 the only one amongst existing Cephalopoda, in which the prin- 



