CONCRESCENCE IN EMBRYO OF CRYPTOBRANCHUS. 



251 



but a broad zone of cells occupying the lateral margin of the 

 yolk plug. 



Fig. ii represents the lower hemisphere of an egg stained in 

 the equatorial region of the late blastula. The stained areas 

 are elongated in a meridional direction. Figs. 12 and 13 show 

 the condition two days later. At the level of the early blastopore 

 there is a pronounced shifting of material from each side toward 

 the median line. 



12 



13 



16 



FIGS, ii TO 16. Each horizontal row of figures represents the history of an 

 individual egg of Cryptobranchus allegheniensis. The dotted areas indicate spots 

 produced with Nile blue sulphate. Fig. ii, lower hemisphere of an egg in a late 

 blastula stage, sketched immediately after marking in the equatorial region. Fig. 

 12, lower hemisphere of the same egg sketched in the early gastrula stage, two days 

 later. Fig. 13, same as the preceding, posterior view. Fig. 14, lower hemisphere 

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

 equatorial region. Fig. 15, lower hemisphere of the same egg, sketched a day 

 later. Fig. 16, lower hemisphere of the same egg sketched two days later than 

 the preceding. 



Fig. 14 represents the lower hemisphere of an egg stained in 

 the equatorial region of the early gastrula; some of the spots 

 extend in a meridional direction across the blastopore. Fig. 16, 

 sketched three days later, shows marked overgrowth and in- 



