NO. 1846. ON CERTAIN ELEVTHEROZOIC PELMATOZOA—EIRK. 11 



It is not necessary, I think, to cite further cases of freedom in 

 adult stages among these primitive types. A sufficient number of 

 instances have been given clearly to mdicate that an eleutherozoic 

 habit was largely maintained among these many-plated, early Cys- 

 tidea. It may no doubt be safely assumed that this form of life may 

 be postulated for many such organisms. It may well be that in some 

 mstances fixation was effective throughout the life of the animals, but 

 it is probable that these form exceptions to the rule. 



It is evident that the members of this subgroup do not exactly fall 

 within the limits of Group I as defined. There is no column unless 

 one considers that such be potentially present. It is ui this sense 

 that the forms were classified as they are here found. They could not 

 be listed with Group II where the column had been differentiated and 

 subsequently lost, nor well with Group III; and it did not seem best 

 to create a new group for their reception. 



This subgroup is of great interest as containing the first variants 

 from an attached existence. As has been elsewhere noted, the 

 assumption of an eleutherozoic existence by these forms is less in the 

 nature of an abandonment of a statozoic habit as an imperfect 

 acqukement of such a form of life. For this reason these types may 

 be held as truly intermediate between the primitive eleutherozoic 

 stock and the primitive statozoic forms. It by no means follows 

 that these genera are the actual progenitors of the more typical 

 Pelmatozoa, but nevertheless they indicate the stages through which 

 such ancestral types may have passed. 



These forms are likewise of great interest as showing that even 

 when the tendency toward a statozoic existence had its inception, a 

 time the tendency should be perhaps in greatest force, reversion to an 

 eleutherozoic habit should have obtained. This shows how vitally 

 the eleutherozoic habit had impressed itself upon the pelmatozoan 

 stock. It is not surprising therefore that in the later forms, when the 

 force of this tendency toward fixation should have somewhat spent 

 its strength, that the assumption of a free existence should have 

 become almost universally effective. 



It is somewhat difficult to determine what form of life must have 

 been led by the Cystidea referred to this subgroup. As has been 

 shown in the cases cited above, there is apparently no indication of 

 the animals havmg rested upon or in contact with any extraneous 

 object. Such being the case we must postulate an existence of 

 such a nature as to render the organisms quite free from contact 

 with the bottom, or else to admit of free motion along the bottom 

 as among the bottom-crawlmg Holothurians. 



As has been argued above in the case of Ecliinosplisera, it seems 

 quite possible that this form at least was freely floating. It may be 

 that in such a case the brachial appendages, feeble though they are, 



