728 THE AMERICAN NATURALIST. 
very far toward a land-living or even an air-breathing type, 
although morphologically, z.e., especially in its organs of res- 
piration and circulation, it certainly presents the essential char- 
acters of the lower amphibia. They are feebly developed in 
some respects, but nevertheless include all the morpholog- 
ical and physiological potentialities of a higher vertebrate. On 
the other hand, in the possession of spiracles and in prim- 
itive skeletal characters, it strongly resembles the oldest fishes 
(Elasmobranchii). Several writers have recently contributed 
very convincing evidence that crossopterygians were lineal 
ancestors of the higher vertebrates, but judging from the 
conditions in Polypterus they were also sufficiently remote in 
the phylum of vertebrates to have given rise to both dipnoans 
and amphibians. 
DEPARTMENT OF ZOOLOGY, 
COLUMBIA UNIVERSITY, 
May 12, 1899. 
