4 6 EVOLUTION IN THE PAST 



were now appearing with the arms strengthened on all sides 

 with small plates as is the rule with modern forms (Euo- 

 phiurea). This development, no doubt, deprived the limbs 

 of some flexibility ; but it considerably improved the 

 ambulatory powers of the animals. 



STARFISHES Starfishes of Cambrian form were still in the seas ; but 

 were now in a failing condition, and before the close of the 

 Period they became extinct (Palceasterina). Other forms, of 

 later evolution, but with archaic features notably in the 

 construction of the arm-grooves continued in some force 

 (Palaaster). Several of the new Devonian forms seem to have 

 been closely related to starfishes of our own time ; but their 

 sensitive skins were probably not so well protected (Astro- 

 pecten, Echinasterella). 



BLASTOIDS Blastoids, confined, so far as is known, during the preceding 

 Period to the " new " world, had now discovered the " old," 

 and were in some force in European waters. The peculiar 

 breathing apparatus, for which these bud-like animals were 

 remarkable, had undergone some modifications (Pentremitidce, 

 Eleacrinus). The tubes or hydrospires had been brought into 

 closer co-operation, resulting, no doubt, in easier breathing 

 and a consequent saving of energy. 



SEA-LILIES Crinoids or " sea-lilies " seem to have been scarcely so 

 prosperous as in the Silurian seas, but they still greatly out- 

 numbered all other members of the " spiny-skinned " fra- 

 ternity. 



The sanitary reformers do not appear to have been making 

 great progress. But in some localities they were fairly 

 numerous ; and certain forms had the long tube on an 

 exaggerated scale (Eucalyptocrinus). The apparatus was 

 probably efficient in working, but it may have required more 

 protection against hostile attack than crinoids were able to 

 supply. 



There is no doubt that in the Devonian Period crinoids 

 were being seriously affected by their foes; among which 

 fishes, no doubt, were to be numbered. To meet dangers and 

 difficulties, a few forms were appearing in which the cup or 

 body-covering was protected by movable spines, resembling 

 those of sea-urchins (Arthrocantha). As this device never came 



