290 



THE CEPHALOPODA 



The suckers are pedunculated in the Decapotla, the peduncles 

 being axial or lateral, but they are sessile in the Octopodu 

 (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 Eledone and Cirrhoteuthis (Fig. 260). In some 

 cases, however, there are more than two rows, e.g. 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 



Fio. 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, II), 

 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 Cheiroteuthis 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 Avith the suckers. 



