250 



BERTRAM G. SMITH. 



appearing entirely below the dorsal lip of the blastopore. They 

 have also moved toward the median line. . 



Fig. 7 represents the lower hemisphere of an early gastrula 

 stained in the equatorial region in such a way that one of the 

 spots extends in a meridional direction across the dorsal lip of 

 the blastopore. The results two days later (Fig. 8) demonstrate 

 overgrowth and convergence. 



.4. 6 8 10 



FIGS. 3 TO 10. Each vertical pair of figures represents the history of an indi- 

 vidual egg of Cryptobranchus alleghenicnsis. The dotted areas indicate spots 

 produced with Nile blue sulphate. Fig. 3, lower hemisphere of an egg in the first 

 cleavage stage, sketched immediately after marking in the equatorial region oppo- 

 site the ends of the cleavage furrow. The dotted line indicates the position of the 

 first cleavage furrow which is confined to the upper hemisphere. Fig. 4, lower 

 hemisphere of the same egg sketched a week later in the early gastrula stage. 

 Fig. 5, lower hemisphere of an egg in a late blastula stage sketched immediately 

 after marking in the equatorial region. Fig. 6, lower hemisphere of the same egg, 

 sketched in the early gastrula stage four days later. Fig. 7, lower hemisphere of 

 an egg in the early gastrula stage, sketched immediately after marking in the equa- 

 torial region. Fig. 8, lower hemisphere of the same egg sketched two days later. 

 Fig. 9, lower hemisphere of an egg in the early gastrula stage, sketched imme- 

 diately after marking in the equatorial region. Fig. 10, lower hemisphere of the 

 same egg sketched three days later. 



Fig. 9 represents an egg treated in approximately the same 

 manner as the one shown in Fig. 7. This egg sketched three days 

 later demonstrates the in-turning of a large area of the former 

 dorsal lip of the blastopore, and shows more clearly than the pre- 

 ceding thj phenomena of convergence. In addition it shows that 

 convergence involves, not merely the lips of the blastopore itself, 



