520 FISHES CHAP. X1X 
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. 
