i6 



ECHINODERMA GENERAL DESCRIPTION 



FIG. XIV. 



Pluteus of Echinocyamus (after Theel). 

 About 75 times nat. size. 



Explanation of letters to Figs. 

 XIV. and XV. a.c, anterior coelom ; 

 a.d, anterior dorsal arm ; am, am- 

 niotic invagination ; a.v, anterior 

 ventral arm ; he, hydrocoel ; hp, 

 hydropore ; l.p.c, left posterior 

 coelom ; 0, mouth ; oe, oesophagus ; 

 p, podia ; pd, posterior dorsal arm ; 

 p.v, posterior ventral arm; r.p.c, 

 right posterior coelom ; s, spines of 

 Bchinoid ; sp, spicules of Pluteus ; 

 sp', the same being absorbed ; st, 

 stomach. 



am 



l.p.c/ 



FIG. XV. 



Development of Echinocyamus (after Theel). 1, portion of a Pluteus rather more developed 

 than in Fig. XIV. ; the ectodermic invagination has grown in towards the left coelom, which is 

 now separating into a posterior portion and a hydrocoel. 2, portion of a Pluteus about twelve 

 days old, showing the lobes of the hydrocoel growing into the amnion. 3, the same consider- 

 ably more advanced ; spines begin to develop and the amnion is connected with the exterior. 

 4, a Pluteus forty-five days old, with spines and podia of the young urchin protruding from the 

 amnion. 5, the young urchin, bearing on its back the remains of the Pluteus spicules and 

 integument ( x 100). 



