mosaic encasing of the body with polygonal plates 

 took place, affording the much-needed protection 

 to the sessile creature. And it is now that the echin- 

 oderm may be said to be well on its way. 



As a matter of fact, fossils have been found that 

 bear a very close resemblance to this pictured pear- 

 shaped ancestor of the serpent-star. And it is partly 

 from this fact that full confidence in the likeness 

 of the portrait is possible. The further develop- 

 ment of the group presents a more serious problem; 

 it is unfortunately difficult to follow whether by 

 the road of embryology or paleontology. It may be 

 readily conceived, however, that the free-moving 

 modern forms originally departed from this primi- 

 tive type because of its eventual distribution to 

 the shallower areas near the shore. Here wave- 

 action would dislodge and tumble the individuals 

 about; the best fitted to survive in this newer en- 

 vironment were those types amenable to modifica- 

 tion; the rest became extinct. Some of these sur- 

 vivors, such as the holothurians, or sea-cucumbers, 

 adapted themselves by digging into the sub- 

 stratum, while others, like the asteroids and echi- 

 noids, that is, the starfishes and sea-urchins, de- 

 veloped devices for clinging fast to the bottom, 



[94] 



