PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 27 



He said it was difficult for him to believe that the smallest Ptilometras, too young 

 to have assumed any of their characteristic generic or specific features, should be 

 the only ones that are breeding. 



He noted in conclusion that while he was perfectly sure these comatulids are 

 not Ptilometras, at the same time he was very much in doubt as to their real syste- 

 matic position. He thought it most unlikely that they are really Himerometras, but 

 he did feel reasonably sure that they belong in the family Himerometridae. 



In 1911 the author referred Ilimerometra paedophora to Ptilometra mulleri, of 

 which he stoutly maintained it was sunply a young form. He said that the straight 

 sides of the elements of the IBr series, the tapering cirri, and the uniformity of the 

 pro.ximal pinnules, together with the perisomic plating, especially on the pinnules, 

 seen in the larger specinaens, the distribution of the syzygies, and the abundance 

 and large size of the sacculi, as well as the very characteristic musculature, show 

 conclusively that these specimens can not be any species of Himerometra, young or 

 old, but that they must belong to the genus Ptilometra. He remarked that if one 

 can for the moment overlook the obsolescence or absence of carination on the outer 

 part of the arms and on the pinnules — a character always late in making its appear- 

 ance — the relationship is at once evident. 



In answering Dr. H. L. Clark's argimients the author said that it is rarely the 

 adults of any species which bear pentacrinoid young upon their pinnules or cirri, but 

 usually young ones. The free swimming young always drift to leeward of the parents 

 before settling down. At the next breeding season another brood drifts over to the 

 place occupied by the brood of the preceding season and settles down upon it. Thus 

 it is that while young comatulids often bear pentacrinoids, they are very rarely found 

 on the fully grown. He noted that there are some nice examples of this in the Museum 

 of Comparative Zoology at Cambridge, where the cirri of some young specimens of 

 Comactinia meridionalis bearing pentacrinoids are preserved, and he said he had seen 

 some scores of additional cases of the same thing. 



The author remarked that the comatulids change from their comparatively imde- 

 veloped post-pentacrinoid condition to the perfect form very quickly. This is accom- 

 panied by a rapid development of Pj and the pinnules immediately succeedmg; a 

 great increase in the width of the pinnulars and the brachials, so that the pinnules 

 appear much closer together and the brachials shorter; and, in species with long 

 cirri, by a rapid (distal) addition to the cirrus segments, the added segments as they 

 appear becoming progressively more and more developed. In the Thalassometridae 

 and in the Tropiometridae the carination of the brachials and pinnules is never present 

 in the very young, but is rather suddenly assumed at an early stage — a graphic re- 

 capitulation of this may be observed in any regenerating specimen. 



Dr. H. L. Clark, accordmg to the author, failed to mention a single character 

 by which his paedophora can be distinguished from the young of Ptilometra mUlleri 

 as predicated from the facts known in regard to the young of related species, and 

 as we have now been able to study a specimen exactly intermediate between the 

 paedophora stage and the adult condition there seems to be no escape from "the 

 conclusion I had arrived at, and communicated to him, when Dr. Clark fu-st showed 

 me his paedophora, namely, that paedophora is nothuig but the young of Ptilometra 

 mulleri, the sacculi, the broad IBr series and first two brachials, the syzygies, and 



556-022—67 i 



