1885.] NATURAL SCIENCES OP 1'HILADELPHIA. 101 



would have been of no use to these ancient swimmers. The pos- 

 session of bony skeletons by all the Teleostei shows that this 

 adaptation is a valuable one. Modern Sharks and Ganoids, while 

 often cartilaginous, frequently possess completely ossified verte- 

 brae. Thus we have reason to believe that the absence of internal 

 bone in the most ancient fishes came from the fact that the con- 

 ditions for the secretion of such bone had not yet been devel- 

 oped. 



This leads to one further conclusion. Though a cartilaginous 

 basis of muscular attachment might suffice for large swimming 

 animals, it would not answer for large forms of terrestrial life. 

 In these a greater rigidity was necessary. Therefore land verte- 

 brates of large size could not appear until after the power of 

 forming a bony skeleton had been attained. And it is significant 

 that shortly after the appearance of bone in fish skeletons the 

 Batrachians make their appearance in the rocks. We know that 

 the land had been adapted for animal life for long ages before, 

 and peopled b}- insects and scorpions, and possibly by forms of 

 life of which we have no comprehension. It is very probable that 

 fishes had long used the land as a temporary place of residence 

 and feeding-ground. This we may safely infer from the existence 

 of fossil Dipnoi, with their powers of breathing air or water at 

 will. Yet it was impossible that large land vertebrates could 

 appear until the bone-making power was fully developed. Archee- 

 gosaurus one of the earliest air-breathers, possessed but a ring 

 of bone in its vertebra?, like the Carboniferous Ganoids. But in 

 all the remaining Carboniferous Batrachians a fully ossified skel- 

 eton appears, and this has been ever since an absolute requisite 

 of all land vertebral life, and of all ocean vertebrates except a few 

 survivals of the antique types. 



Thus we reach the general conclusions that fossilization of 

 animal forms was not possible until, after a long period of evolu- 

 tion, the power of secreting hard external coverings was gained ; 

 and that the existence of large land vertebrates was not possible 

 until, after a still longer period of evolution, the power of secret- 

 ing internal bony skeletons was developed. If these conclusions 

 be well founded, many of the conditions of early life must remain 

 forever unknown to us, and we cannot hope to recover more than 

 a fragment of the antique fauna. 



April 14. 



The President, Dr. Leidy, in the chair. 



Thirty-one persons present. 



A paper entitled " Notes on Mesozoic Cockroaches," by Samuel 

 H. Scudder, was presented for publication. 



