CONCRESCENCE IN EMBRYO OF CRYPTOBRANCHUS. 



253 



such movements occur, can they be explained as a mechanical 

 necessity in the process of invagination and epiboly? My earlier 

 observations (Smith, '12) gave no clue to the occurrence of con- 

 fluence in this region, so that I approached the experimental 



27 28 



FIGS. 19 TO 30. Each horizontal row of figures represents the history of an 

 individual egg of Cryptobranchus alleghcniensis. The dotted areas indicate spots 

 produced with Nile blue sulphate. Fig. 19, lower hemisphere of an early gastrula 

 sketched immediately after marking in the equatorial region, especially above the 

 blastopcre. Fig. 20, the same, posterior view. Fig. 21, a posterior view of the 

 same egg, sketched a day later. Fig. 22, posterior view of the same egg sketched 

 a day later than the preceding. Fig. 23, lower hemisphere of an early gastrula 

 sketched immediately after marking in the equatorial region. Fig. 24, a similar 

 view of the same egg sketched a day later. Fig. 25, the same as the preceding, 

 posterior view. Fig. 26, the lower hemisphere of the same egg sketched a day later 

 than the preceding. Fig. 27, lower hemisphere of an early gastrula sketched imme- 

 diately after marking in the equatorial region. Fig. 28, the same, posterior view. 

 Fig. 29, posterior view of the same egg, sketched a day later than the preceding. 

 Fig. 30, posterior view of the same egg, sketched a day later than the preceding. 



study of the subject in a skeptical frame of mind that made the 



results the more impressive, since they were entirely unexpected. 



Figs. 19 and 20 represent an egg stained in the equatorial 



