290 THE CEPHALOPODA 
The suckers are pedunculated in the Decapoda, the peduncles 
being axial or lateral, but they are sessile in the Octopoda 
(Fig. 256), They generally form a double series along the internal, 
that is to say, the ventral or buccal faces of the arms, but there is 
a single series in Hledone and Cirrhoteuthis (Fig. 260). In some 
cases, however, there are more than two rows, eg. Spirula (Fig. 
268, ar), Gonatus, Dosidicus, Tritaxeopus, Ctenopteryx (on the three 
dorsal pairs of arms), and Sepia (Fig. 299, c). In point of structure, 
each sucker consists of a globular or cylindrical projection, 
comprising an annular surface of application with a central cavity 
whose capacity can be augmented by the retraction of its floor. 
The floor is provided with perpendicular muscular fibres (Fig. 256, I), 
whose contraction causes the sucker to adhere to the prey or to 
the substratum. The surface of application of the sucker is 
Fic. 256. 
Axial section of a sucker of Argonauta. I, muscular fibres retracting the bottom of the 
sucker ; II, radiating muscular fibres ; III, annular muscular fibres ; IV, floor of the cavity of 
the sucker ; V, sphincter muscle ; VI, tooth on the margin of the sucker. (After Niemiec.) 
augmented by the action of radiating muscular fibres (Fig. 256, I), 
and its adherence is further assured by the cuticular rugosities of 
this surface. These cuticular structures are simply small projections 
in the Octopoda, but in the Decapoda there is a complete chitinous 
ring with denticulated edges which are often very prominent, and 
in some cases a single denticulation may become very large and 
preponderant and thus transform the sucker into a hook-bearing 
organ. In Onychoteuthis true functional suckers coexist with the 
hooks, but in the adult Veranya the suckers are nothing more than 
the bases of the hooks. In various species of Chevroteuthis the 
tentacular arms bear suckers in which the muscular system is feebly 
developed and there is neither a central piston nor a horny ring, 
but the bottom of the cupule is covered by a great number of 
anastomosed epithelial filaments which constitute an organ for fishing. 
In Cirrhoteuthis, in addition to the row of suckers, there are 
tentacular filaments on each arm alternating with the suckers. 
