114 POTERIOCKINID.E PENTACRINUS. 



of such reproduced members in the genera Platycriinis, Poteriocrhius, Actinocrinus, &c.; 

 and it is beyond dispute that animals low in the scale of organic life possess powers of 

 reproduction which are unknown among those of superior organization. This may be 

 considered as a compensating power to the lower animals, whose liability to injury 

 must be greater, owing to their habits and conditions of life exposing them to dangers 

 which the more perfectly endowed creatures evade through superior intelligence or 

 instinct. 



The power of reproduction possessed by crinoids is paralleled in crustaceans. Crabs 

 and lobsters it is well known can reproduce both claws and legs ; the lobes of star- 

 fishes also when broken off by casual mischance or dismembered by their own contor- 

 tions are readily reproduced. 



The rays are thickly set with round and jointed tentacula. 



The pouch containing the organs of digestion is protected and covered in with a 

 plated integument, in the centre of which is the mouth. The construction of this 

 organ renders it incapable of being elongated into a proboscis, but the lips of the 

 orifice can doubtless be protruded to a small extent for the purpose of taking up, or 

 sucking in the food designed for its support. This portion of the animal is but 

 imperfectly known as in the few specimens which enrich the European museums the 

 integument is so shrivelled or even destroyed that a satisfactory examination is rendered 

 impossible. Besides being strengthened and protected by small angular plates, the 

 tentacula on the lower rays in some measure guard this part from the aggressions of 

 the smaller predaceous animals. 



The ventral portion of the pentacrinus probably predominates over the dorsal side as 

 it does in the Extracrinus, but of this we have no positive evidence. 



The column is pentangular and composed of alternate thick and thin joints, with a 

 small central perforation throughout its whole length, and communicating with the 

 cup in which the digestive organs are situated, in the same manner as in other crinoids. 

 The way in which the column is lengthened by the introduction of new joints is clearly 

 visible in the recent species, and agrees with the description given under the head of 

 Extracrinus Briareus. The secretion of calcareous matter first commences round the 

 central canal, then by a regular and continual deposit the process of enlargement still 

 proceeds until the new joint has acquired a size and thickness consistent with the 

 position it is designed to occupy in the column. By the renewal of this operation 

 from time to time, the column becomes lengthened, and as the new joints are interposed, 

 others of an older growth towards the base become thicker and more indurated. 



As the columns of the specimens hitherto brought to Europe are broken off in such 

 a manner as to preclude the possibility of correctly ascertaining the exact form of the 



