to higher and more specialized forms, such as are 

 to be found among the other groups. Their evolu- 

 tionary progression has been slow; and if we cite 

 the sea-cucumber as an example, which is worm- 

 like in even more ways than its appearance would 

 imply, this is one instance in which it seems there 

 has taken place actual regression. 



If abundance of fossils may be taken as a crite- 

 rion, the dominant echinoderm of ancient times 

 was the crinoid, or sea-lily. Reduced to the sim- 

 plest of terms, a description of the crinoid would 

 identify it as a starfish attached by its back to a 

 long, jointed calcareous stalk, and oftentimes 

 bearing slender many-branched arms. As the 

 crinoid is firmly fixed to the spot where it grows, 

 and as it has no weapons of offense or defense, it 

 relies only on its armor for protection ; its cup-like 

 body is composed of rigid plates, while the stalk 

 and the arms surmounting the cup are hard nearly 

 throughout. It acquires its nourishment by the 

 wave-like action of minute hair-like processes, or 

 cilia, arranged along a groove on the inner side of 

 each arm, these cilia sweeping the fine drifting 

 particles of suspended food material toward the 

 central mouth at the base of the arms. Its habits of 



[87] 



