[chthyopsida \(>\ 



Dipnoi. Taken all together, the. facts point to origin of amphibians 

 from crossopterygian fishes. 



It would seem that the modern perennibranch urodeles, with 

 their wholly aquatic mode of living, their permanent gills, poorly 

 developed lungs, long tail, feeble legs, and incompletely ossified skele- 

 ton, might reasonably be regarded as more "primitive" than amphib- 

 ians whose larvae undergo radical metamorphosis to become terrestrial 

 adults. If amphibians were derived from fishes, it is necessary to assume 

 that they acquired lungs and at least the beginnings of legs while living 

 in the water, because they could not have lived on land with gills and 

 ordinary fins. It is easy to imagine that our present perennibranchs 

 have come directly down from such pre-amphibious "amphibians" 

 along a line of descent in which, for unknown reasons, no further 

 progress toward terrestrial living was ever made. It would add much to 

 the scientific interest and importance of the perennibranchs if we could 

 feel confident that they are living and unchanged relics of Devonian 

 pre-amphibians. However, evidence from paleontology, admittedly 

 scanty, throws doubt on this view. It reveals, in the long history of 

 amphibians, a tendency to simplify structure by loss of parts. The 

 modern amphibian skull contains fewer bones and more cartilage than 

 the skull of old amphibians. The skeleton, in general, shows this tend- 

 ency, which may have extended to other organs, and it may have so 

 involved the metamorphic changes in some ancient amphibians which 

 had become terrestrial as adults that they ceased to complete their 

 metamorphosis and so reverted to aquatic adult life. It is a question, 

 therefore, whether such animals as Necturus come of a line of descent 

 along which, beyond the early acquisition of lungs and legs, no further 

 progress toward terrestrial life was ever made, or whether, at some 

 period in their ancestral line, terrestrial living had been achieved, only 

 to be abandoned later. Is Necturus merely a backward child of its race, 

 or is it a backsliding degenerate? If the latter, it is possible that the 

 degenerative process may have brought the animal down to a condition 

 resembling, at least in a general way if not in all particulars, a stage in 

 the early history of its race. However it may be, as we, from our hu- 

 man viewpoint, contrast the crawling, generally sluggish and retreat- 

 ing "mud puppy" with the sturdy, upsitting, dignified toad in our 

 garden, skillfully catching his daily ration of insects by lightning strokes 

 of an incredibly mobile tongue, we cannot help feeling that the mode of 

 existence of the toad savors rather more of "the higher life." 



