108 THE FAUNA OF THE DEEP SEA 



to these ancestral forms than the shallow-water 

 families ? 



The state of our knowledge at the present day 

 hardly allows us to answer this question very defi- 

 nitely. However nearly they are related to such 

 ancestral Echiuoderms in general form, they are 

 probably profoundly modified by a deep-sea life. 

 Nevertheless, in the simple shape of the calcareous 

 corpuscles of the skin, the simple form of the cal- 

 careous ring, the communication of the water- vascular 

 system with the exterior by one or several pores, and 

 in some other anatomical characters, they give evi- 

 dence of their primitive characters. 



