■0. E. Gordon—Early Stages in Paleozoic Corals. 109 



Art. VII. — Studies on Early Stages in Paleozoic Corals ;* 

 by C. E. Gordon. 



The group of the Anthozoa has been the object of careful 

 and detailed study for many years. The discovery that these 

 organisms were really animals enlisted the attention of many 

 investigators during the latter years of the eighteenth century. 

 As first defined, the group included the Hydroid polyps, Bry- 

 ozoa and Sponges ; forms now known to be quite distinct. In 

 1828 Milne-Edwards showed that the " Sea-mat " and allied, 

 forms possessed a definite mouth and anus. Later the Sponges 

 were made a distinct class, and finally the Hydroid types were 

 firmly established as a distinct division of the Coelenterates. 

 "The anatomy and classification of the group thus purged of 

 intruders were placed on a firm basis by the classical works of 

 Dana and of Milne-Edwards and Haime (1857)." Since then 

 studies in the development, comparative anatomy, and histol- 

 ogy of the Anthozoa have contributed to a further and more 

 exact knowledge of the group, although much remains that is 

 yet doubtful and obscure. Especially is this true of the extinct 

 Anthozoa of Paleozoic time : the Rugosa of Milne-Edwards 

 and Haime, the Tetracoralla of Hseckel. 



Since with these extinct forms only the hard parts are pre- 

 served, the study of relationships and mode of development is 

 exceedingly difficult, and all conclusions on these points are 

 necessarily, to a greater or less degree, matters of conjecture 

 and inference. Several investigators, however, have endeav- 

 ored to show the relationship of these extinct types to modern 

 forms. How far .they have succeeded in doing this is still a 

 matter of dispute. 



In so far as the plan of structure, which should be under- 

 stood to mean the plan of growth from the earliest stages, can 

 be proved to be similar to that of modern forms, just so far 

 can relationships be assumed. Here we recognize that an 

 inference can be drawn from a study of the hard parts, for 

 example, the arrangement of the septa in corals. This arrange- 

 ment is such that a reasonable assumption may be made as to 

 their order of appearance. The difficulty must lie in securing 

 specimens well adapted to show primitive characters with 

 respect, to the plan of growth of these septa. 



With modern corals the order of appearance of the mesen- 

 teries is made of prime importance, and since the septa follow 

 the mesenteries, the endeavor to classify the fossil forms has 



* The studies embodied in this paper were carried on in the Paleonto- 

 logic Laboratory of Columbia University, New York City. 



