NO. 7 SEA-LILIES AND FEATHER-STARS — CLARK 5 



columnals, progressively increasing in width with the growth of the 

 crown, are formed before a fixed attachment occurs. In the group 

 including the pentacrinites (fig. 41) and the feather-stars (figs. 43- 

 50) two widely different extremes are found. The pentacrinite 

 column is extremely precocious. It reaches the mature stage and 

 forms the definite topmost columnal when the crown is still extremely 

 immature and, so to speak, as yet lacks the instinct to attach itself to 

 the column. The column therefore continues to grow and forms a 

 second topmost columnal as in Bathycrinus, though in this case the 

 two are separated from each other by a number of intercalated 

 columnals. The second, like the first, fails to become attached to the 

 crown and, the rapidity of stem growth increasing, a continuous series 

 of these topmost columnals is formed each of which immediately 

 after its appearance is pushed away from the crown by the formation 

 of another one above it, the column becoming so enormously over- 

 developed that the animal cannot nourish it all and so it dies away at 

 the distal end as rapidly as new segments are added beneath the crown. 

 As they are pushed backwards the numerous elements which nature 

 intended for topmost columnals become separated by a definite num- 

 ber of intercalated segments from which they are always to be dis- 

 tinguished by their larger size and the presence of a whorl of five long 

 jointed processes ending in a strong hook, the so-called cirri. In the 

 feather-stars the column is just as precocious as in the pentacrinites, 

 reaching maturity and forming the definite topmost columnal at a 

 very early stage (fig. 55). But in this group attachment occurs. The 

 column, being mature, has ceased its development ; the crown is as yet 

 very small and young; the topmost columnal has become attached to 

 the latter and now forms an integral part of it, and it continues to 

 develop with it regardless of the conditions in the column of which it 

 was once a part. The crown becoming too large and heavy for the 

 column, the latter breaks away just beneath the enormously enlarged 

 topmost columnal, now called the centrodorsal, and the animal be- 

 comes free. The further development of the soft structures of the 

 column takes place entirely within the centrodorsal (fig. 7) from 

 which the numerous cirri, here crowded together instead of spaced in 

 whorls of five as in the pentacrinites, are extruded (fig. 10). 



Feather-stars mostly attach themselves to foreign objects by means 

 of their usually stout and hook-like cirri which are most commonly 

 from one-fourth to one-third the length of the arms (figs. 33, 34), 

 though in a few species they are longer than the arms (figs. 32, 46). 

 In some the cirri are very numerous, long, slender and nearly straight, 

 forming collectively a sort of disc which, on the principle of a snow- 



