388 



ZOOLOGY 



SECT. 



Projecting from the surface among the spines all the way from 

 the peristome to the periproct will be observed five double rows of 

 tube-feet or podia (Fig. 326), which in a living specimen will be found 

 to be capable of great extension. These are similar to the tube- 

 feet of the Starfish, and have similar functions : the sucker-like 

 extremity of each is supported by a plate of calcareous matter. 

 Each double row of tube-feet occupies a meridional zone of the 

 surface, termed the ambulacral area, corresponding to the ambulacral 

 groove of the Starfish : the intermediate zones are termed the 

 inter -ambulacra! areas. At the oral end of each ambulacral area 



7 



FIG. 327. Corona of Echinus esculentus, from the aboral surface, showing the arraiii;i - 

 ment of the plates of the corona. 1, the anus ; 2, periproct, with irregular plates ; 3. tlu- 

 madreporite ; 4, one of the other genital plates ; 5, an ocular plate ; 6, an inter-ambulacra] 

 plate ; 7, an ambulacral plate ; 8, pores for the protrusion of the tube-feet ; 9, tubercles. 

 (After MacBride.) 



on the peristome (Fig. 325, 4) is a pair of appendages similar to tube- 

 feet, but shorter, and termed oral tentacles. Ten shrub-like append- 

 ages, the dermal branckice (2), are situated in the peripheral part of 

 the peristome, a pair opposite each inter-ambulacra! area. 



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

 in a rigid globular shell, or corona (Fig. 327) as it is termed, 

 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 



