62 



THE CHAIN OF LIFE. 



i[ 



The most curious history in this group is that of the feather- 

 stars. In the Early Cambrian they are represented by a few 

 species known to us only in fragments, and these belong to a 

 humble group (Cystideans) resembling the larval or immature 

 condition of the higher Crinoids. Fig. 49 shows one of these 

 animals of somewhat later age. They have few or rudimentary 

 arms and short stalks, and want the beautiful radial symmetry 

 of the typical star-fishes. In the Silurian these creatures are 

 reinforced by a vast number of beautiful and perfect feather- 

 stars (Figs. 50, 51). These continue to increase in number 

 and beauty, and apparently culminate in the Mesozoic, where 

 gigantic forms exist, some of them probably having more 



Fio. 47. — Palo'aster Niagarensts 

 (Hall). One of the oldest star-fishes. 



Fig. ^%.—Palffchinwt clliptic7ts (McC'y). 

 One of the oldest types of sea-urchins. 



complicated skeletons, in so far as number of distinct parts is 

 concerned, than any other animals. Buckland has calculated 

 that in a crinoid similar to that in Fig. 52 there are no less 

 than 150,000 little bones, and 300,000 contractile bundles of 

 fibres to move them. In the modern seas the feather-stars 

 have somewhat dwindled both in numbers and complexity, 

 and are mostly confined to the depths of the ocean. On the 

 other hand, the various types of ordinary star-fishes and sea- 

 urchins have increased in number and importance. We thus 

 find in this group a certain advance and improvement from the 

 Cystideans of the Early Palaeozoic to the sea-urchins and their 

 allies. This advance is not, however, along one line, for the 



