252 



THE PROTOCHORDATA. 



From a morphological point of view a more striking- 

 resemblance between the two larvae than that furnished 

 by the longitudinal ciliated bands exists in connexion with 

 the anterior body-cavity or cntcroccei. In the Echinoderm 



Figs. 119 and 120. — Auricularia, lar\'a of Svnapta (after SemonI ; and 

 Tomaria, lar\'a of Balanoglossus. (After MORGAN.) 



a. Anus. a.p. Apical plate, bc^. Anterior bodv-cavitv, communicating with 

 exterior by the water-pore, be-, bc^. Second and third bodv-cavities of Tomaria. 

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

 and anterior body-cavity of Tornaria. ^^'■./. Gill-pouches, /i.e. Hydroccel of 

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

 /.e. Left enteroccel (body-cavity), w. Mouth, v. Lateral (paired) nerve-band 

 of Auiicularia. r.e. Right enteroccel. s/. Calcareous spicules, sf. Stomach. 

 wp. Water-pore. 



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

 band discovered by Semox. and known as the aJoral ciliated band. The poste- 

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

 cesophagus. 



larva this cavitv 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 3^et 



