252 



THE PROTOCHOKDATA. 



From a morphological point of view a more striking 

 resemblance between the two larvas than that furnished 

 by the longitudinal ciliated bands exists in connexion with 

 the anterior body-cavity or enteroccel. In the Echinoderm 



c.c 



Figs. 119 and 120. Auricularia, larva of Synapta (after SEMON) ; and 

 Tornaria, larva of Balanoglossus. (After MORGAN.) 



a. Anus. a.p. Apical plate, be 1 . Anterior body-cavity, communicating with 

 exterior by the water-pore. 6c 2 , tc 3 . Second and third body-cavities of Tornaria. 

 c.b. Circular ciliated band of Tornaria. c.c. Contractile cord between apical plate 

 and anterior body-cavity of Tornaria. g.p. Gill-pouches, h.c. Hydrocoel of 

 Auricularia (anterior body-cavity), l.c.b. Longitudinal (circumoral) ciliated band. 

 I.e. Left enterocoel (body-cavity), m. Mouth, n. Lateral (paired) nerve-band 

 of Auricularia. r.e. Right enterocoel. sp. Calcareous spicules. st. Stomach. 

 wp. Water-pore. 



N.B. In Auricularia, the margin of the mouth is surrounded by a ciliated 

 band discovered by SEMON, and known as the adoral ciliated band. The poste- 

 rior, V-shaped portion of this band lies inside on the ventral floor of the larval 

 oesophagus. 



larva this cavity arises as a median pouch of the archen- 

 teron, and there is every reason to suppose that it has a 

 similar origin in Tornaria, although this point has not yet 



