546 BERTRAM G. SMITH 



the shape of the body. According to Moodie the caudata are 

 degenerate branchiosaurians and the changes which have taken 

 place in the exoskeleton are mostly brought about by the loss of 

 certain parts. The urodele skull is especially degenerate in the 

 occipital and temporal regions; it may be derived from the 

 skull of Branchiosaurus (for which see Credner '81 to '90) by the 

 loss of the dermoccipitals (supraoccipitals of Moodie '08; post- 

 parietals of Zittel '11), supratemporals (Zittel '11), postfrontals, 

 postorbitals, sclerotics, epiotics (tabulares of Zittel '11), jugals 

 and quadratojugals. The urodele skull has also in many cases 

 become narrow in connection with a general elongation of the 

 body — a degenerate feature. Hand in hand with the loss of 

 dermal elements in the skull has gone the loss of the exoskeleton 

 of the body. 



The paleontological history of the apoda is unknown; but exist- 

 ing members of the group are in certain respects more primitive 

 than the urodeles and more nearly allied to the stegocephali. 

 Thus the hyoid and branchial apparatus is more primitive than 

 that of any other recent amphibia; dermal scales are present 

 which are probably homologous with those of the stegocephali. 

 As in the urodeles, the skull shows degeneration in the loss of 

 certain bones; but the epiotics (tabulares) are retained, and occa- 

 sionally the postfrontals and the lacrimals. A second row of 

 teeth is sometimes present on the mandibles. Aside from some 

 very degenerate features, in other respects the apoda are highly 

 specialized, indicating, as in the case of the anura, a line of descent 

 separate from the urodeles. Yet there are some very suggestive 

 resemblances. Attention has already been directed (Smith '12) 

 to the marked similarity in structure of the egg envelopes of- 

 Ichthyophis to those of Cryptobranchus and Amphiuma, and 

 to the likeness in the brooding habits; but in Ichthyophis the 

 female protects the eggs, in Cryptobranchus the male. In their 

 embryological development the apoda show many points of sim- 

 ilarity to the reptiles. 



With this background, we now come to the question of the 

 interrelationships of the urodeles. In particular we are concerned 

 with the phylogenetic position of the aquatic urodeles (the peren- 



