544 



BERTRAM G. SMITH 



Fig. 203 Endoskeleton of the pectoral fin of Sauripterus taylori Hall, a cross- 

 opterygian from the upper Devonian. One-third natural size, linear reduction. 

 From a drawing by Dr. L. Hussakoff of the American Museum of Natural History. 



('96) as favoring a crossopterygian rather than a dipnoan ances- 

 try for the amphibia. 



It is upon embryological grounds that the strongest case has 

 been made out for the derivation of the amphibia from the dipnoi ; 

 the known facts of development indicate the common origin 

 and later separation of these two groups. In so far as this view 

 is based upon a study of the early stages, the evidence may be 

 dismissed with the remark that the early development of the 

 crossopterygian Polypterus (Kerr '07 a) resembles that of the 

 anura and the urodeles quite as much as does the early develop- 

 ment of the dipnoi (Semon '00 and '01 ; Budgett '01 ; Kerr '00, 

 '01 and '09) ; furthermore that these early stages are of very little 

 value in connecting up. the great groups of A^ertebrates. But 

 some marked resemblances between dipnoi and amphibia in 

 the later stages of development cannot be disregarded. Kellicott 

 ('05, a and b), on the basis of a detailed study of the circulatory 

 system of Ceratodus, came to the conclusion: ''The resemblance 

 in the vascular and respiratory systems between Ceratodus, the 



