218 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



cirri are developed, and in the further development and multiplication of the 

 cirri themselves. This segment, which now presents the aspect in miniature of 

 the centrodorsal of the adult Antedon, augments not only in absolute but in rela- 

 tive diameter, extending itself over the dorsal or outer surface of the basals, which, 

 at the time of the detachment of the body from the column, are almost entirely 

 concealed by it. The first-formed whorl of cirri now shows itself ready for pre- 

 hensile action, its terminal claws being hooked, the calcareous segments being bev- 

 eled off on their dorsal aspect so as to allow of the downward flexure of the cirri, 

 and a considerable amount of contractile fibrous structure being developed between 

 and around the extremities of the segments. A second whorl of cirri is now devel- 

 oped after the same manner as the first between the latter (with which it alternates 

 in position) and the base of the calyx, and a third whorl generally makes its appear- 

 ance before the detachment of the pentacrinoid, so that the young Antedon pos- 

 sesses 10 cirri in different stages of advanced development, and from one to five 

 still rudimentary. 



"The total length of the fully-grown pentacrinoid, from the base of the column 

 to the extremities of the arms when these are folded together may be about 0.7 

 inch, that of the column alone being 0.25 inch; the diameter of the circle formed 

 by the expanded arms may be 0.5 inch. At this period the body and arms usually 

 possess a decided color, which is sometimes sulphur yellow, sometimes light crimson, 

 sometimes an intermixture of both hues; this is usually more pronounced in the 

 arms than in the body, and is entirely due to the development of pigmentary matter 

 in the minute pyriform vesicles scattered through the sarcodic layer which still 

 forms, as in the earliest phase of embryonic life, the general envelope of the body 

 and its appendages. 



"The precise stage of development at which the body of the animal becomes 

 detached from the stem varies, but the detachment does not seem to occur nor- 

 mally until the dorsal cirri are sufficiently developed to enable them to take the 

 place of the stem functionally by giving the animal the means of attaching itself 

 to fixed objects." 



I can see no other way of deriving the columns of all the recent and most fossil 

 crinoids than by supposing them to be the potential homologue of the central plate 

 frequently developed in the later echinoids which has gradually become elongated 

 and resolved, either by non-physical morphological fracture or by simple reduplica- 

 tion (probably by the latter method), into a series of ossicles. The fact that when 

 viewed by polarized light the axis of crystallization is seen to follow the axis of the 

 column, while in the basals it passes at right angles to the plane of their surfaces and 

 therefore in the same direction toward the center of the calyx, would seem to indicate, 

 or at least to suggest, that the sum of the columnals was the potential equivalent of 

 a single calyx plate. 



Of course many animals, as, for instance, the stalked ascidians, attach them- 

 selves by a small portion of their external covering, which becomes pulled out into 

 a more or less slender stalk, as in Boltenia; this elongation of the external covering 

 would naturally carry with it any calcareous structures which happened to be 



