CRINOIDEA ; PENTACRINUS. 471 



has never been obtained, the mode by which the Pentacrinus 

 attaches itself to solid bodies has never been clearly made out ; 

 but there is reason to believe, from the circumstances under 

 which fossil remains are sometimes met with, that the animals 

 of this genus are not permanently adherent to solid masses, but 

 have the power of occasionally detaching themselves. 



1 1 10. In some of the fossil species, the subdivision and rami- 

 fication of the arms is carried to a much greater extent than 

 in any of the recent forms of this tribe. The number of pieces 

 in the skeleton thus becomes very large. In the Pentacrinus 

 Briar eus, it has been calculated that at least 100,000 exist, 

 exclusively of the joints of the lateral appendages, which are 

 probably more than 50,000 additional. As each joint was fur- 

 nished with at least two bundles of muscular fibre, one for its 

 contraction, the other for its extension, we have 300,000 such in 

 the body of a single Pentacrinus an amount of muscular appa- 

 ratus far exceeding any that has been elsewhere observed in the 

 Animal Creation. But it will be remarked that these parts are 

 but repetitions of one another in structure, and that consequently 

 their variety of actions must be very small ; and, accordingly, 

 we find that the movements of this complex piece of mechanism 

 are far less capable of being combined and adapted to a specific 

 purpose, than those of a prehensile structure of higher organi- 

 sation the hand of Man with its twenty-seven bones and 

 thirty-nine muscles. A repetition of similar parts always 

 implies a low degree of organisation, as it indicates a very 

 small amount of variety in the functions to be performed ; 

 and the approach towards a higher character is marked 

 by the modification of some of these for particular purposes 

 a specialisation, or setting apart, for some object of a more im- 

 portant nature than those general functions to which they all 

 contribute. But the simple actions, which alone can be per- 

 formed by the arms of the Pentacrinus, are all that it needs for 

 the grasp of its food. . 



1111. The general structure of the Encrinus, of which no 

 recent species exist, bears a close affinity with that of the 



