STRUCTURE OF TENTACLES. 



561 



Fig. 281. 



an additional pair is given, which, being prolonged considerably beyond 

 the rest, are not merely useful for seizing prey at a distance, but become 

 convertible to other purposes, and may be employed as cables whereby 

 the Cephalopods so furnished ride securely at anchor in a tempestuous 

 sea, the suckers being placed upon an expanded disk, situated (fig. 282) 

 at the extremity of the elongated tentacula, and thus rendered capable 

 of taking firm hold of the surface of a rock or other fit support. The 

 posterior extremity of the body is, in such forms, generally provided 

 with two broad muscular and fin-like expansions (fig. 282), evidently 

 adapted to assist in sculling the animal along. 



(1509.) Wonderful as are the provisions above described for ensuring 

 food and safety to these formidable inhabitants of the sea, it is only by 

 an attentive examination of the individual suckers, so numerously dis- 

 tributed over the tentacula, that the reader will fully appreciate the 

 mechanism we are so inadequately describing. Machines of human con- 

 struction admit of being variously esti- 

 mated, as they are found to be more or 

 less adapted to accomplish the object 

 of the contriver ; but in estimating the 

 works of the DEITY all degrees of com- 

 parison are merged in the superlative ; 

 everything is best, completest, perfect. 



(1510.) Examine any one of these 

 thousand suckers : it is an admirably 

 arranged pneumatic apparatus an 

 air-pump. The adhesive disk (fig. 

 281, A) is composed of a muscular 

 membrane, its circumference being 

 thick and fleshy, and in many species 

 supported by a cartilaginous circlet, so 

 that it can be applied most accurately 

 to any foreign body. In the centre 

 of the fleshy membrane is an aperture 

 leading into a deep cavity (B, 6), at the 

 bottom of which is placed a prominent 

 piston (c), that may be retracted by 

 muscular fibres provided for the pur- 

 pose. No sooner therefore is the cir- 

 cumference of the disk placed in close 

 and air-tight contact with the surface 

 of an object, than the muscular piston 

 is strongly drawn inwards, and, a vacuum being thus produced, the ad- 

 hesion of the sucker is rendered as firm as mechanism could make it. 



(1511.) Yet even this elaborate and wonderful system of prehensile 

 organs would seem, in some cases, to be insufficient for the purposes of 



2o 



Structure of the tentacular suckers 

 in the Cephalopoda. 



