208 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



It has already been suggested that the relation of the posterior portion of the 

 digestive tube to the anal area, and especially to the right posterior ray, is such as to 

 result in the retardation in this region of any developmental changes along the lines 

 of a reduction in the number of the elements in the calyx and its consequent simpli- 

 fication. 



Thus if the radianal really is, as seems at least possible, the first element of a 

 pair of exactly similar plates of which the right posterior radial is the second, and 

 if this condition was originally found in all the radial areas, it is easy to under- 

 stand why in the crinoids as we Imow them, both fossil and recent, the radianal has 

 been greatly reduced and confined to the right posterior radial region or elimi- 

 nated altogether. 



If at the stage in which the radianal and the right posterior radial, both of the 

 same size and to all appearances just alike, are present, this pair of plates is as- 

 siuned to be reduplicated in all the radial areas, an assumption which is by no 

 means without justification, there would result an organism from which a broad 

 series of echinodermal homologies could be worked out; for from such a pair of 

 plates in each radial area additional pairs would be added either proximally or 

 distally, according to whether the development of the body took place proximally 

 or distally in reference to the zone or belt in which they occur ; and if we add the 

 possibility of larval development in the crinoids without the rupture of the vesti- 

 bule, a logical connection between the recent types, the Camerata, the blastoids, and 

 the cystids becomes easily traceable. 



ORNAMENTATION. 



Ornamentation is the exponent of, or the resultant from, a superabundance of 

 vitality or excess of ontogenetic energy over the immediate needs of the individual. 

 It is limited in its manifestations by considerations of vital economy, which as a 

 rule operate to confine it within narrow bounds. 



The fixed habit of the crinoids would appear to be conducive to the development 

 of ornamentation, but their enormous specialization, intimately connected with their 

 body form, and their curiously specialized method of feeding, have resulted in such 

 a delicate adjustment to their environment that only a slight departure from a 

 generalized type is possible. 



The ornamentation of the recent crinoids is confined to comparatively slight 

 modifications of the edges or exposed surfaces of the ossicles and much of it, 

 though undoubtedly ornamental in origin, has come to possess a secondarily eco- 

 nomic function exactly as has happened in the case of many other animals. 



Comatulid ornamentation appears to be (exclusive of the very distinct inter- 

 articular ornamentation) divisible into three general types, one including all the 

 productions of the free edges of the ossicles, another the lateral compression and 

 carination of the median line of the ossicles, and the third the general modification 

 of the exposed surfaces ; but all three types intergrade more or less. 



The first type appears to be the most primitive and appears earliest in the 

 ontogeny, while the last is the most specialized and is the latest to become evident; 

 it is only found in highly specialized genera. 



