28 MUSCLES, ARMS AND FINS. 



Philonexis (Tremoctopus) they are cylindrical and extensible. 

 The sessile suckers are powerful means of prehension ; they act 

 like cupping-glasses by the withdrawal of a central plug. 



The pedunculated cupules of the decapods occupy alternately, 

 two lines in all the genera except Sepia, in which they are in 

 four lines. Always very oblique, raised on a narrow excentric 

 stalk, they are fleshy, marked externally by a thin margin which 

 confines a corneous ring, in the middle of which is an elevated 

 surface. The functions of these cupules compared to those of 

 the octopods appear to differ in this respect, that they cannot 

 hold by suction, being prevented by the thin border and corneous 

 ring, but in lieu of this means of prehension they have the ring 

 itself powerfully armed with recurred points, and greater facili- 

 ties of attachment on account of having the cupules pedunculated 

 and movable, instead of sessile as in the octopods. In a state 

 of repose these formidable rings are covered by their fleshy 

 borders, which are only contracted when their weapons are to be 

 used. 



Whilst the corneous circle or ring exists in all decapods, it is 

 modified nevertheless in the different genera, as will be shown in 

 the systematic portion of this work. Enoploteuthis, and the 

 fossil Belemnites offer a curious modification of structure of the 

 corneous ring, which 1ms disappeared apparently, and is replaced 

 by powerful recurved hooks, which are really the two sides of 

 the circle applied closely together. These hooks are retractile 

 or extensible at the will of the animal, and when retracted are 

 totally enveloped with flesh resembling the velvet cushion of 

 the paw of a cat. 



The tentacular arms or tentacles of the decapods, always 

 arising from sub-ocular sacks in the circle of sessile arms and 

 between the third and fourth pairs of the latter, are entirely 

 retractile in Sepia, in Sepiola and in llossia, but only partially 

 so in other geueni. Very long (in Ghirotettthis six times the 

 length of the body), they consist of a rounded or compressed 

 stalk, generally without cupules, and an expanded and thickened 

 extremity or dub, armed with cupules upon its internal face. 

 These cupules or hooks are very unequal in size and occupy four 

 lines upon the club in Loligo and Onimastrephcs, six in Hisfio- 

 teufhis Mud six or ten in Sepia, Sepiola and Kossia. Onycho- 



