ZOOLOGY 



SECT. 



corresponding to the ambulacral groove of the Starfish : the inter- 

 mediate zones are termed the intcr-ambul acred areas. At the oral 

 end of each ambulacral area on the peristome is a pair of ap- 

 pendages similar to tube-feet, but without suckers and termed 

 tentacles. Ten shrub-like appendages, the dermal brancJiice, are 

 situated in the peripheral part of the peristome, a pair "opposite 

 each inter-ambulacral area. 



When the spines are removed, the body is found to be enclosed 

 in a rigid globular shell, or corona (Fig. 294) as it is termed, 



FIG. 293, Strongylocentrotus, entire animal with the tube-feet extended. (From Brehm's 



Thierleben.) 



formed of a system of plate-like ossicles, the edges of which fit 

 accurately and firmly together, and the surfaces of which are 

 ornamented with the rounded elevations or tubercles for the articu- 

 lation of the spines. These plates are arranged in ten zones, 

 each consisting of two rows, running in a meridional direction 

 from the edge of the peristome to the neighbourhood of the peri- 

 proct. Of the zones of plates there are two sets, each consisting 

 of five, the members of which alternate with one another. In 



