IV 



PHYLUM CCELENTERATA 



197 



corresponds with a temporary stage m the development of one of 

 the more typical Sea-anemones, viz., the stage with eight mesen- 

 teries shown in Fig. 143, A ; it is probably to be looked upon as 



_..^-tv^ Y '''Vy s ,.;,Y 1 . 



the most primitive or generalised member 

 of the order. In Zoanthus (Fig. 144, B) 

 the dorsal directives (d.d.) do not reach 

 the gullet, and each lateral couple consists 

 of one perfect and one small and imperfect 

 mesentery. In Cerianthus, another bur- 

 rowing form, there are a couple of very 

 small ventral directives, and the remaining 

 mesenteries are very numerous, not 

 arranged in couples, and all directed 

 ventrally at their outer ends, so as to 



B 



*n& 



FIG. 148. Pennatula sulcata. A, entire colony ; B, portion of the same magnified- 



I. lateral branch; p. polype ; s. sjphonozooid. (After Koelliker.) 



FIG. 149. Tubipora musica. A, skeleton of entire colony ; B, transverse sections of polype. 



