5 20 FISHES CHAP. XIX 



somewhat deceptive, and it seems improbable that the former 

 group stands in the direct line of Amphibian descent. In most 

 of their structural features not directly or remotely associated 

 with air-breathing the Dipneusti are true Fishes, and the 

 striking resemblances which they present to the Amphibians in 

 the vascular system and lungs seem to be rather the outcome of 

 physiological convergence, associated with adaptive and parallel 

 modifications in structure, and due to the influence of a similar 

 environment, than indicative of direct ancestral relations. With 

 more reason it may be inferred that both the Dipneusti and the 

 Amphibia have been derived from some primitive Crossopterygian 

 ancestor with Elasmobranch tendencies, and subsequently became 

 modified in certain respects on parallel lines. 



