Geol.— Vol. I.] SMITH— PLACENTICERAS. 191 



complete, and whose stages of growth are almost exact 

 repetitions of successive antecedent genera, that it would 

 be impossible to find a student of the morphogeny of the 

 brachiopods, the marine molluscs, or the lower crustaceans, 

 that does not believe implicitly in the value of larval stages 

 of these groups as records of their family history. And this 

 is especially true of the paleobiologists, who regard it of 

 little importance whether the animal under investigation 

 died yesterday, during the Flood, or during the Paleozoic 

 era, whether it is preserved in alcohol or in a more perma- 

 nent museum in the bosom of Mother Earth; they recog- 

 nize the fact that the laws that govern the rise and decline 

 of organisms were just as true then as now, and that the 

 life-history of a Cambrian trilobite has as much bearing on 

 modern biology as does the history of the living cray-fish. 



Not all groups are equally useful to the student of mor- 

 phogeny, but in each of the lower subkingdoms there are 

 genera of which the ontogeny has been worked out and 

 correlated in no uncertain terms with the history of the 

 race. The testimony of these various groups is so uniform, 

 notwithstanding the fact of its having been gathered by men 

 of different beliefs, that its value can not be doubted. It 

 is also noteworthy that in the higher groups, such as ceph- 

 alopods and crustaceans, the evidence and the correlations 

 are much more decided. 



Ccelenterata. — It has been shown by Dr. C. E. Beecher 

 (1891) that the young stages of the Favositidas correspond 

 to Aulopora, or to some other similar unspeciahzed genus. 

 This same conclusion has been reached by Dr. G. H. Girty 

 (1895) based on a study of the ontogen}^ of Favosites, Syr- 

 ingopora, and other tabulate corals, all of which are shown 

 to go through an Aiilopora stage of growth. 



E chinoderniata . — The only crinoid of which the ontogeny 

 is known is Antedon, which has been shown by Sir Wyville 

 Thomson (1865) to go through successively stages corre- 

 sponding to the Ichthyocrinoidea of the Paleozoic, and Pen- 

 tacritms of the Mesozoic, before it becomes free swimming 

 and takes on the characters of Antedon. 



