172 



MANUAL OF ZOOLOGY 

 Ap 



Int. ami 



Arrtb 



fnt.amb 



Fig. 95. — Corona of sea-urchin with the spines removed to show the arrangement 

 of the plates, lateral view. Amb, ambulacral zone with its perforated plates; 

 Ap, apical (aboral) pole; Int. amb, inter-ambuiacral zones. (From Bronn's 

 Thierreick.) ^ --. 



sharp tooth. The points of these five teeth can be seen 

 through the opening of the mouth. The enteric canal has 



no radiating cceca. The five 

 ducts of the reproductive or- 

 gans open on five ossicles, the 

 genital plates (Fig. 96, gen), 

 which with five smaller ocu- 

 lar plates (oc) each bearing 

 a rudimentary eye, form a 

 complete ring round the 

 space {peripr) at the anal 

 pole, in the middle of which 

 is the anus ; a madreporite 

 is amalgamated with one of 

 the genital plates. 



° c perifii 



inz.ami. 



Fig. 96. — Apical system of plates and 

 aboral extremities of zones of the shell 

 of a sea-urchin. amb, ambulacral 

 zones; gen, genital plates; int. amb, 

 inter-ambulacral zones; madr, madre- 

 porite; oc, ocular plates ; peripr, peri- 

 proct. (After Leuckart.) 



