FUNDAMENTAL RELATIONS OF ANIMALS III 



justifies now such a conclusion. The facts most important to a proper 

 appreciation of this point have already been considered in the pre- 

 ceding paragraph, as far as they relate to the order of succession of 

 animals, when compared with the relative rank of their living repre- 

 sentatives. In examining now the agreement between this succession 

 and the phases of the embryonic growth of living animals, we may 

 therefore take for granted that the order of succession of their fossil 

 representatives is sufficiently present to the mind of the reader to af- 

 ford a satisfactory basis of comparison. Too few Corals have been 

 studied embryologically to afford extensive means of comparison; 

 yet so much is known, that the young polyp when hatched is an in- 

 dependent, simple animal, that it is afterwards incased in a cup 

 secreted by the foot of the actinoid embryo, which may be compared 

 to the external wall of the Riigosa, and that the polyp gradually 

 widens until it has reached its maximum diameter, prior to budding 

 or dividing; while in ancient corals this stage of enlargement seems 

 to last during their whole life, as, for example, in the Cyathophyl- 

 loids.i"**^^ None of the ancient Corals form those large communities, 

 composed of myriads of united individuals, so characteristic of our 

 coral reefs; 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 is there, 

 however, so much to learn still as in Polypi, before the correspond- 

 ence of their 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 anyone, even the highest 

 type, represents in its metamorphoses all the stages of the lower types, 

 neither in their development nor in the order of their succession; 

 and that frequently the knowledge of the embryology of several types 

 of different standing is required, to ascertain the connection of the 

 whole series in both spheres. 



^"'' Since I have ascertained that the Tabulata are Hydroids and not Polyps, I have 

 had my doubts respecting the real affinities of the Rugosa. The tendency to a quad- 

 ripartite arrangement of their septa indicates unquestionably a nearer relation to 

 Acalephs than to Polyps. Moreover, their successive floors are different from the inter- 

 septal floors of the true Polyps, and resemble those of the Tabulata. It may be, 

 therefore, that their true affinity is rather with the Acalephs than with the Polyps, 

 and that the family of Lucernaria is a living representative of that type, but without 

 hard parts. In this case the foot-secretion of the Actinoids would only indicate a 

 typical resemblance between Polyps and Acalephs, and not constitute an evidence of the 

 relative standing of the two types. 



