2S MUSCLES, ARMS AND FINS. 



Philoiiexis (Tremoctopiis) the}' are cylindrical and extensible. 

 The sessile suckers are powerful means of prehension ; they act 

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



The pedunculated cupules of the decapods occupj^ alternately, 

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

 four lines. Always ver^' 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 bj^the tliin border and corneous 

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

 itself i)Owerfnlly armed with recurred points, and greater facili- 

 ties of attacliment 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 ttesliy 

 borders, which are only contracted when tlieir wcnpous arc to Itc 

 used. 



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

 modified nevertheless in the different genei'a, as will be sliown in 

 the s^'stematic j)ortion of this work. Enoi)lot(uthis, and the 

 fossil JJelemnites offer a curious modification of structure of tlie 

 corneous ring, whicli has disappeared apparently', and is replaced 

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

 the circle applied closely togetlu'r. These liooks are retractile 

 or extensible at the Avill of the animal, and wlien retracted are 

 totally enveloped witli lU'sli — resembling tlie velvet cushion of 

 the paw of a cat. 



Tlie tentaculnr arms or tentacles of the decapods, always 

 arising from suli-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 Rossia, but only paitially 

 so in other genera. Very long (in Chiroteuthis 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 clnh^ armed with cupules upon its internal face. 

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

 lines upon the club in Loligo and Ommastrephes, six in Histio- 

 teuthis and six or ten in Sepia, Sei)iola and Rossia, Onycho- 



