454 THE OCEAN WORLD. 



In the unarmed acetabulum, the mechanism for adhesion is well 

 described by Dr. Roget : " The circumference of the disk," says this 

 writer, " is raised by a soft and turned margin ; a series of long 

 slender folds of membrane covering corresponding fascicula of muscular 

 fibre converge from the circumference towards the centre of the 

 sucker, at a short distance from which they leave a circular aperture ; 

 this opens into a cavity which widens as it descends, and contains a 

 cona of soft substance rising from the bottom of the cavity, like the 

 piston of a syringe. When the sucker is applied to the surface, for 

 the purpose of adhesion, the piston, having previously been raised 

 so as to fill the cavity, is retracted, and a vacuum produced, which 

 may be still further increased by the retraction of the plicated portion 

 of the disk." Here we have an excellent description of the apparatus 

 for holding on. When the animal is disposed to let go his hold, 

 according to Professor Owen, " the muscular arrangement enables 

 the animal to push forward the piston, and thus in a moment destroy 

 the vacuum which retraction had produced." 



In the case of the armed Cephalopods (Onyclioteutliis), Professor 

 Owen remarks, "that there are circumstances in which even the 

 remarkable apparatus described by Dr. Eoget would be insufficient to 

 fulfil the offices in the economy of Nature for which the Cephalopod 

 was created, and that in species which have to contend with the agile 

 mucous-clad fishes more powerful organs of prehension are superadded 

 to the suckers, so that in the calamary the base of the piston is, he 

 remarks, enclosed in a horny hoop, the outer and anterior margin of 

 which is developed into a series of sharp curved teeth, which can be 

 firmly pressed into the flesh of a struggling prey by the contraction 

 of the surrounding transverse fibres, and can be withdrawn by the 

 action of the retracting fibres of the piston. " Let the reader," the 

 professor adds, " picture to himself the projecting weapon of the horny 

 hoop developed into a long, curved, sharp-pointed claw, and these 

 weapons clustered at the expanded terminations of the tentacles, and 

 arranged in a double alternate series along the internal surface of the 

 eight muscular feet, and he will have some idea of the formidable 

 nature of the carnivorous cephalopod." The professor notices another 

 structure which adds greatly to the prehensile powers of the 

 uncinated Cephalopods. " At the extremities of the long tentacles a 

 cluster of small, simple, unarmed suckers may be observed at the base 



