821 



CHAPTER XLI. 



CLASS V. CEPHALOPODA. 



The members of the class Cephalopoda are bilaterally symmetrical 

 Molluscs, with a large head, and having the body enclosed in a 

 muscular mantle. The fore-part of the foot is split up i?ito eight or 

 more muscular processes or ' ; arms," which surround the mouth ; while 

 the epipodia are ivell developed, and give rise, by apposition or fusion, 

 to a muscular tube {"funnel") through which the effete water of res- 

 piration is expelled. One or two pairs of gills a?-e co?itai?ied within 

 the pallial sac, and the sexes are always distinct. 



The Cephalopoda, comprising the Cuttle-fishes, Pearly Nautilus, 

 8zc, constitute the most highly organised of the classes of the 

 Mollusca. They are all marine and carnivorous, and are possessed 

 of considerable locomotive powers. At the bottom of the sea they 

 can walk about, head downwards, by means of the arms which sur- 

 round the mouth, and which are usually provided with numerous 

 suckers or " acetabula." They are also enabled to swim, partly by 

 means of lateral expansions of the integument" or fins (not always 

 present), and partly by means of the forcible expulsion of water 

 through the tubular " funnel," the reaction of which causes the 

 animal to move in the opposite direction. 



The body in the Cephalopoda is bilaterally symmetrical, the 

 cephalic region being conspicuously marked out, and being sepa- 

 rated from the visceral region, which is enclosed in the mantle (fig. 

 736). The head bears a pair of large globular eyes, and has the 

 mouth placed in the centre of its anterior surface. The mouth is 

 surrounded by a circle of long muscular processes or " arms," 

 formed by the splitting up of the margins of the foot. In the 

 Cuttle-fishes there are always either eight or ten " arms," and 

 these are provided with muscular suckers, which can be used in 

 prehension. In the Pearly Nautilus, on the other hand, the arms 

 are numerous, and are not furnished with suckers. The lateral 

 margins of the foot ( ;; epipodia") are, again, either placed in 



