556 BERTRAM G. SMITH 



The important features of the later stages of the cleavage 

 have to do with processes that are not well expressed in the 

 superficial cleavage pattern: migration of cells and the various 

 processes of differentiation that lead up to gastrulation and early 

 embryo-formation. 



The occurrence of a septal furrow in the gastrula stages of two 

 such widely-separated forms as Cryptobranchus andPetromyzon 

 is a remarkable case of convergence in purely embryonic charac- 

 ters. The septal furrow and fenestra are the mechanical product 

 of gastrulation by invagination and epiboly in a heavily yolk- 

 laden egg with a very thin roof to the blastocoele. So far as known 

 these features of gastrulation in Cryptobranchus are unique 

 among urodeles; but there is evidently an approach to this con- 

 dition in Spelerpes, since the egg is heavily yolk-laden and during 

 gastrulation the blastocoele roof becomes quite thin (Goodale '11). 



The study of the later embryonic and larval stages is as yet too 

 superficial to furnish much data for phylogenetic generalization; 

 yet for this purpose the late stages will probably prove of greater 

 value than the earlier ones (Wilson '98, p. 23). It should be par- 

 ticularly noted that the larval Cryptobranchus reaches an age 

 of two years before transforming — evidence of a retarded meta- 

 morphososis. Reasons have already been given for believing that 

 • the metamorphosis is incomplete. 



The study of the breeding habits, the organization of the eggs, 

 and the early course of development lead us to look among the 

 land-living salamanders for affinities to Cryptobranchus — more 

 particularly to forms like Desmognathus, Spelerpes andPlethodon. 

 Considerable evidence from comparative anatomy, particularly 

 with regard to skull structure, will be found to harmonize with 

 this view. Desmognathus in particular is suggestive; according 

 to Kingsbury ('02) it is semi-aquatic in its habits, living at the 

 edges of swiftly running brooks. It conceals itself under stones 

 at the edge of the stream or in its immediate vicinity, and here 

 its unpigmented and heavily yolk-laden eggs are laid. There 

 is a brooding habit, though in this case the female guards the 

 eggs; we have noted some marked similarities to Cryptobranchus 

 in the early development. Yet we are hardly warranted in con- 



