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MANUAL OF ZOOLOGY 



surface, in some forms (such as the worm-like Synapta and 

 its allies) tube-feet are entirely absent. 



Fig. 97. — Cucumaria planci. Entire animal seen from the ventral surface, with the 

 tentacles expanded, and the tube-feet projected outwards. (From Hertwig's 

 Lehrhuck, after Ludwig.) 



5. THE CRINOIDEA 



The Feather-stars and their allies constituting the class 

 Crinoidea, bear some superficial resemblances to the star- 

 fishes and brittle-stars, but with some important points of 

 difference. The body of a feather-star (Fig. 98) is star- 

 shaped, with a central disc and five arms which are bifurcate 



