670 



The paired fins of the Australian Ceratodus consists of a me- 

 dian cartilaginous segmented axis, with lateral cartilaginous rays on 

 both sides; the finrays are developed on both sides. In the African 

 Protopterus we have the same median axis, with lateral cartilages 

 and finrays on one side; or without lateral cartilages, but with fin 

 rays on one side (pectoral fins), and without lateral cartilages and 

 without any finrays whatsoever (pelvic fins). In the South American 

 Lepidosiren there is only the segmented axis. The paired fins 

 of Ceratodus are the least reduced, than follows Protopterus 

 and finally Lepidosiren, with the most simple form of fin imma- 

 ginable. 



I once believed that the Dipnoans are the ancestors of the Ba- 

 trachia and concluded that the stages of development where indicated 

 by the series Ceratodus, Protopterus, Lepidosiren, resulting in the total 

 disappearance of finrays and in a fin with a single cartilaginous axis; 

 that from this condition the cheiropterygium was developed by a pro- 

 cess of budding. This opinion was apparently confirmed by the fact 

 that specimens of Protopterus sometimes showed a bifid fin (Albrecht) ; 

 and later it was even shown that Protopterus was able to regenerate 

 its fins (Boulenger). But the Dipnoans can not be the ancestors of 

 the Batrachia, the nature of the ribs alone contradicts this view. We 

 can assume however that some of the Crossopterygii, the probable an- 

 cestors of the Amphibia, have undergone a similar reduction of the 

 fin rays as the Dipnoans, and that from such forms the Amphibia took 

 their origin. The devonian Crossopterygians , Glyptolaemus, 

 Osteolepis and especially Holoptychius have exceedingly 

 slender paired fins and in these forms also the median fins are much 

 reduced. It is quite evident that the median fins must also loose the 

 finrays in the ancestors of the Batrachia. 



We have examined the skeleton of the Stegocephali and have fol- 

 lowed its modifications in the higher and lower forms, in the Reptilia 

 and Fishes. We have seen that the Stegocephali form a central group, 

 the careful study of which explains many points in the morphology of 

 Vertebrates. It is very probable that we have to look for the an- 

 cestors of the Stegocephali among the Crossopterygians, which again 

 are closely related to the Dipnoi i). The Dipnoi really are modified 



1) All the resemblances between the Dipnoi and Batrachia are not 

 genetic resemblances, but parallelisms The following authors have ex- 

 pressed the opinion of the Crossopterygian ancestry of the Batrachia:. 

 Boas (1880), Pollaed (1891), Kingsley (1892) and Cope (1892). 



