316 



Mil. J. S. BUDGETT ON TEE STliUCTUEE 



Some authors have attempted to show that the Amphibia may have been directly 

 derived from some such Ibniis as the recent Crossopterygii, others derive them from 

 tlie Dipuoi : with both these views I venture to disagree. The Devonian Crosso- 

 pterygii no doubt merged into the Devonian Dipnoi, and it was from forms probably 

 intermediate between the Crossopterygii and the Dipnoi that the ancestral Amphibians 

 originated. In these times likewise the Crossopterygii merged into the Elasmu- 

 brancliii and thirdly into the Ganoidei, and it was from forms probably intermediate 

 between the Crossopterygii and the Ganoidei that the Teleostei originated. 



Thus the Amphibia appear to be related to the Elasmobranchii in two ways- 

 first through the Dipnoi, second through the Crossopterygii. In like manner, the 



Text-fig. 1. 



Diagram to illustrate the affinities of Vertebrata and their relative importance in Primary, 



Secondary, and Tertiary times. 



A. Amphibia and Amniota. 



C. Crossopterygii. 



D. Dipnoi. 



E. Elasmobranchii. 

 G. Ganoidei. 



H. Holocephali. 

 S. Stegocephali. 

 T. Teleostei. 



Primary. 



Secondary. 



Tertiary. 



Teleostei are related to the Elasmobranchii in two ways, the Crossopterygii and 

 the Ganoidei. 



To attempt to give a definite chart of the Ichthyopsida would be to assume a perfect 

 knowledge of the structure, development, and palseontology of the various groups 

 which I do not pretend to possess, I will therefore give a mere diagram (text-fig. 1) 

 in order to illustrate my meaning, and pass on to the facts of development as observed 



