1881.] NATURAL SCIENCES OF PHILADELPHIA. 211 



doner! , since it became known that the different parts of tlie column 

 in the same specimens are often widely dissimilar. 



In the growing animal, new columnar joints were continuallj- 

 introduced b}^ interpolation between the older segments, and these 

 younger joints, which are found throughout the column in all stages 

 of development, produce striking changes in the general aspect. 

 The column matured from the root upward, and the upper part 

 remained throughout the life of the crinoid in a kind of immature 

 state, wherein the intercalated joints did not attain the width of 

 the others. The uppermost joints, however, although they were 

 probabl}' among some of the earliest developed parts of the col- - 

 umn, are not separated b}" smaller joints. Gradually, sometimes 

 between the third and fourth joints, new plates make their appear- 

 ance ; the first one so thin as to be scarcely visible, the next which 

 lies between the succeeding joints much larger, the third probaltl}'. 

 reaching full size. Secondary intercalations follow between the 

 new pieces, the intervening spaces between the larger joints 

 increasing gradually to a maximum, from which point down tliQ 

 column seems to be mature, for all succeeding spaces have a like 

 number of intercalated joints. As a general rule, the column 

 decreases somewhat in thickness from the calyx for a certain dis- 

 tance down, after which it increases again towai'ds the root. In 

 some species the primary joints are only longer, but not of greater 

 diameter than the others. This is the case inPlatycrinus where 

 the new joints seem to have been formed directl}- beneath the 

 calyx, their number increasing in length gradually along the 

 stem, and not in sections as in the Actinocrinid* and the 

 Rhodocrinidte. 



Lateral cirrhi along the column have been rarely observed, and 

 in this famil}^ probablj' existed only toward the root. The form . 

 of the root is exceedingly variable, and depended evidently upon 

 the conditions of its place of attachment. When living in a soft 

 or sandy soil, it seems to have been provided with a great number 

 of small rootlets which are given off both vertically and horizon- 

 tally ; but when it was attached to a rock or other hard substance, 

 the lower surface grew entirel}- flat and was often deeplj- grooved. 

 The grooves pass out from the root, and apparently took the 

 place of the vertical rootlets. The central passage extends to the 

 smallest rootlets and is often of considerable size. "We have 

 already noted this fact in Part I, and suggested that probably the 



