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HANDBOOK OF INVEIITEBKATE ZOOLOGY. 



spicule (d) of the post-oral arm (c). The spicules (f) of the 

 pre-oral arms (a f ) are now very long, and they reach nearly 

 to the posterior end of the body. 



A great fold or lip (Fig. 72, o I), now runs downwards 

 from the anterior end of the body towards the ventral 



FIG. 72. 



FIG. 72. Ventral view of the fully developed pluteus of Arbacia. 

 (Drawn from nature by Mr. H. Ganuan.) 

 For explanation see Fig. ":). 



