NO. 1846. ON CERTAIN ELEUTHEROZOIC PELMATOZOA—KIRK. 115 



function as efficient ambulatory or s\nmming appendages. There 

 are so many factors indeed that might influence the crinoids that 

 there is small choice between them. The important fact after all is 

 that cementation did take place. 



Jaekel (1891) has combined these genera with the Eugeniacrinidse, 

 near which they unquestionably belong. It seems probable further- 

 more that different though closely related genetic lines may be repre- 

 sented. A tendency becoming effective in one line would be bound 

 to crop out among other related types. 



CONCLUSIONS. 



In the preceding portion of this paper an attempt has been made 

 rather toward the enumeration of specific instances of detachment of 

 the Pelmatozoa and the consequent modifications as shown by certain 

 types than toward the broader features as influencing the class as a 

 whole. It may be well to bring together the more pertinent facts 

 relative to the assumption of an eleutherozoic habit among the Pehna- 

 tozoa mdicating in a broad way the general tendencies to be observed. 

 This will of necessity include a comparative study of the manifesta- 

 tions of an eleutherozoic habit as shown in the various groups and by 

 the dift'erent classes of the Pelmatozoa. The probable proximal 

 causes for the assumption of this mode of life w^ll also be treated in a 

 general way. It was originally intended to discuss at length the 

 influence of the widespread acquisition of freedom on the symmetry 

 and distribution of the Pelmatozoa, but such topics though germane 

 to the subject matter of the present paper may perhaps best be treated 

 independently in separate articles. 



A review of the evidence relative to the maintenance of an eleuthe- 

 rozoic habit among the Pelmatozoa will show that such a form of 

 life has widely been assumed and maintained among the Cystidea, 

 Blastoidea, and Crinoidea throughout their history. In each class 

 highly specialized types have been evolved, the degree and nature 

 of the specialization being dependent in the mam on the structure of 

 the organisms involved. Among the stalked, erect forms detachment 

 from the bottom may be held as an almost universal attribute. At 

 times the period of detachment may be brief and succeeded by a period 

 of fixation. Again, there may be several alternating periods of at- 

 tachment and freedom. Such may be held to be the normal mode of 

 life of the majority of the stalked Pelmatozoa. 



It is obvious, I think, that those forms among wliich a detached 

 existence is largely maintamed are to be derived from types whose 

 periods of freedom were of short duration. Whether there ever 

 existed a stalked Pelmatozoan that was sedentary from the time of its 

 attachment is a question that must unfortunately be forever open. 

 One might argue that such should of necessity be the case in order to 



