6 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



it advisable to approach them in a somewhat different way from that which has 

 usually been adopted, in order the more strongly to bring out many points which 

 are obvious enough if the crinoids are considered as recent animals, but which are 

 greatly obscured if one attempts to consider both the recent and the fossil forms 

 together. 



This somewhat radical treatment emphasizes some very interesting facts in a 

 way not possible by any other method, and sheds an entirely new light upon many 

 complex problems. Moreover, the results are strictly comparable with the results 

 deduced from the data gathered from a study of other recent groups; a line of 

 investigation may be followed up with the certainty that one is not liable to mistake a 

 very highly specialized for a very primitive structure or type. Comparative 

 anatomy may be employed as an aid in systematic work, so that conclusions do not 

 have to be based upon the skeletal system alone; and, most of important of ah 1 , the 

 crinoids in their relations to the other echinoderms and to other marine organisms 

 stand forth in their true light, quite devoid of the false prestige which has hitherto 

 been theirs as a natural result of their magnificent palseontological record, a record 

 which is not surpassed by that of any other marine organisms, and is approached 

 only by one or two restricted groups. 



The strongest argument which can be made against this method of treatment 

 is that questions of phylogeny are entirely divorced from any possible solution by 

 the study of chronogenesis, but it seems to me that a phylogeny grafted upon a 

 chronogeny is a very unsatisfactory structure unless one is certain that the chrono- 

 genesis represents, as of course it should, the true phylogenetic development. 



When any group of a class of animals adopts a mode of life entirely different 

 from that of all of the other members of the same class we must be prepared to 

 encounter and to discount extraordinary, sudden, and unexpected changes' in the 

 organization which are not connected with the ancestral type of organization by any 

 intermediate stages. Among such animals we almost always find the group char- 

 acters developed in a most erratic manner. Some structures will be very highly 

 specialized, sometime specialized far beyond what is seen in any other member of 

 the class, while others will be in a very rudimentary or primitive state of develop- 

 ment, or perhaps even absent altogether. 



The echinoderms differ very abruptly from the crustacean line of descent from 

 which they took their origin, and similarly each of the echinoderm groups differs 

 abruptly from each of the others. 



We see in the echinoderms to-day most perplexing combinations of primitive 

 and highly specialized characters associated in all sorts of ways, and this leads 

 naturally to the assumption that there was no definite intergrading form between 

 the echinoderms and the barnacles, which, of all the Crustacea, approach them most 

 closely, but that the former sprang from the phylogenetic line, which may by easy 

 stages be traced to the latter, by a broad saltation in which the assumption of the 

 free habit (subsequently modified in the Pelmatozoa) and the correlated assumption 

 of pentamerous symmetry combined to make the existence of intergrading forms 

 impossible, while at the same time it resulted in the formation at the very moment 

 of their origin of two diverse stocks, the heteroradiate (including the Pelmatozoa, 



