ECHINODERMATA 79 



a growth of small algae to a dead fish, or even the skin of 

 one of their relatives, the heart urchins scoop up, by 

 means of the projecting lip on the under side of the test, 

 large quantities of sand and mud, for the sake of what 

 organic matter may be mixed with it. 



A spangus, opened, will appear to any person not trained 

 to see and trace its anatomy simply a case filled with shell 



A B 



Fig. 33 

 A. Cucumaria niger. f Natural size 



gravel, sand, and mud. We now reach the final division 

 of the Echinoderms. 



The Holothuroidea. Of these the common " Sea- 

 cucumber " (I wince each time I have to write these 

 silly and misleading popular names) however, the " Sea- 

 cucumber " (Cucumaria vulgaris) is the type. As its name 

 implies, it is shaped like a small cucumber, with a row of 

 retractile tentacles, which takes the place of rays, around 



