amj). 



•perist. 



Fig. 422. Echinus miliaris from the oral side. amb. ambulacrum; gill, gill 

 inter, interambulacrum ; perist. peristome. 



-g.plt. 



amb.. 



Fig. 423. A diagram of an aboral view of the dried shell of an Echinus. The 

 spines, pedicellariae and tube feet have been removed. From Shipley and 

 MacBride. amh. ambulacrum; ^n. anus; 60. bosses w^hich bear the spines; 

 g.plt. genital plate with genital pore; jun. line of junction of ambulacral and 

 interambulacral plates ; mad. madreporic plate ; oc.plt. ocular plate ; por. pores 

 through which tube feet protrude ; ppr. periproct (leathery skin around anus). 



