TYPE MOLLUSC A. 



341 



physiologically tlie dorsal, arid the posterior the ventral sur- 

 face. In the following description the surfaces will be con- 

 sidered in their morphological relations. 



The head is usually somewhat distinctly marked off from 

 the body proper by a neck constriction and bears two usually 

 remarkably-developed and highly-specialized eyes. A pecul- 

 iar feature of the Cephalopoda, and the one which has sug- 



coe 



FIG. 152. DIAGRAM TO SHOW GENERAL PLAN OF STRUCTURE OF A CEPHA- 



LOPOD (slightly modified from LANG). 



an anus. 



6 = bnccal mass. 

 cce = csecuin of stomach, 

 ct = ctenidium. 



e = eye. 

 go = reproductive organ. 



i = iuk-bag. 

 m = mantle. 



me = mantle-cavity. 

 ne = nephridium. 



ce = oesophagus. 



= stomach. 

 sh = shell. 



si = funnel. 

 t = tentacle. 



v = valve of funnel. 



gested the name applied to the class, is the fusion with the 

 head of a portion of the foot. The mouth thus becomes situ- 

 ated at the bottom of a funnel-like depression, formed by the 

 foot, whose margins are drawn out into a number of tentacle- 

 bearing lobes or into eight or ten long armlike processes 

 (Fig. 152, t) provided with suckers, and serving as powerful 



