SUCCESSION AND DEVELOPMENT OF ANIMALS. 169 



now living and the fossil representatives of the same 

 families in earlier periods. 1 But these comparisons have, 

 thus far, been traced only in isolated cases, and have not 

 yet led to a conviction, that the character of the suc- 

 cession of organized beings in past ages is such, in 

 general, as to show a remarkable agreement with the 

 embryonic growth of animals ; though the state of our 

 knowledge in Embryology and Palaeontology now jus- 

 tifies 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 succession of animals, when com- 

 pared with the relative rank of their living representatives. 

 In now examining 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 suc- 

 cession of their fossil representatives is sufficiently present 

 to the mind of the reader to afford a satisfactory basis of 

 comparison. Too few Corals have been studied ernbryo- 

 logically to furnish extensive means of comparison ; yet 

 so much is known, 2 that the young polyp, when hatched, 

 is an independent, 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 Rugosa? 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 enlarge- 

 ment seems to last during their whole life, as, for example, 



1 AGASSIZ (L.), Poiss. foss., q. a., 3 I have ascertained these facts 



p. 81. Embryonic Types, q. a., p. 14. from the investigation of several 



Twelve Lect., etc., p. 8. EDWARDS corals of the reef of Florida, especi- 



(H. MILNE,) Considerations sur quel- ally of the genera Porites, Astraea 



ques principes relatifs a la Classifica- and Manicina. 



tion naturelle des Animaux, Ann. Sc. 3 MILNE-EDWAKDS et HAIME, q. a., 



Nat., 3e ser., 1844, 1 vol., p. 65. p. 44. 



