CuAP. I. SUCCESSION AND DEVELOPMENT OF ANIMALS. 113 



a rcmarkaljle agreeuieiit with tlie ciiibnonic growth of aiiiiiials; though the state 

 of our knowledge in Embryology and Palaeontology justifies now such a conclusion. 

 The facts most important to a proper appreciation of this point, have already been 

 considered in the preceding paragraph, as far as they relate to the order of suc- 

 cession 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, 

 tliat the order of succession of their fossil rejjresentatives is sufficiently present 

 to the mind of the reader, to afford a satisfactory basis of comparison. Too 

 few Corals have been studied embryologicaUy, to afford extensive means of com- 

 parison ; yet so much is known, that the young polyp, when hatched, is an inde- 

 pendent, 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 Rngorn^ 

 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 w^hole life, as, for example, in the Cj-athophylloids. None of the 

 ancient Corals form those large communities, composed of myriads of united individ- 

 uals, 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 correspondence 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 

 any one, 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 differ- 

 ent standing, is required, to ascertain the connection of the whole series in both 

 spheres. 



No class affords, as 3-et, a more complete and more beautiful evidence of the 

 correspondence of their embryonic changes, Avith 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.^ Prior 

 to the publication of his papers, the metamorphosis of the European Comatula alone 

 was known. (See Sect. XV'III., p. 85.) This had already .shown, that the early stages 

 of growth of this Echinodenn exemplify the peduucated Crinoids of j^ast ages. I have 

 m}-self seen further, that the successive stages of the embryonic growth of Comatula 

 typify, as it were, the principal fonus of Crinoids which characterize the successive 



* Milxe-Edav.v.kds et IIaimi., i\. a., p. 31. " Mulleu, (.T..) SevcMi jmpors, q. 11., p. 71. 



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