170 ESSAY ON CLASSIFICATION. 



in the Cyathophylloids. 1 None of the ancient Corals 

 form those large communities, composed of myriads of 

 united individuals, so characteristic of our coral reefs ; on 

 the contrary, the more isolated and more independent 

 character of the individual polyps of past ages presents a 

 striking resemblance to the isolation of young Corals, in 

 all the living types. In no class, however, is there so much 

 to learn still, as in the Polyps, before the correspondence 

 of then 1 embryonic growth, and their succession in time, 

 can be fully appreciated. In this connection I would 

 also remark, that, among the lower animals, it is rarely 

 observed that any one, even the highest type, represents 

 in its metamorphoses all the stages of the lower types, 

 either in their development, or in the order of their 

 succession ; and that frequently the knowledge of the 

 embryology of several types of different standing is 

 requisite to ascertain the connection of the whole series 

 in both spheres. 



No class, as yet, affords more complete and more 

 beautiful evidence of the correspondence of their embry- 

 onic changes with the successive appearance of their 

 representatives in past ages than the Echinoderms, thanks 

 to the extensive and patient investigations of J. Miiller 

 upon the metamorphoses of these animals. 2 Prior to the 

 publication of his papers, the metamorphosis of the Euro- 



1 Since I have ascertained that the their true affinity is rather with the 



Tabulata are Hydroids and not Po- Acalephs than with the Polyps, and 



lyps, I have had rny doubts respecting that the family of Lucernaria is a 



the real affinities of the Rugosa. The living representative of that type, 



tendency to a quadripartite arrange- but without hard parts. In this case 



rnent of their septa indicates uuques- the foot-secretion of the Actinoids 



tionably a nearer relation to Aca- would only indicate a typical resem- 



lephs than to Polyps. Moreover, blance between Polyps and Acalephs, 



their successive floors are different and not constitute an evidence of the 



from the interseptal floors of the true relative standing of the two types. 

 Polyps, and resemble those of the - MULLEK, (J.), Seven papers, q. a., 



Tabulata. It may be, therefore, that p. 105. 



