Experiments on the Early Development of the Amphibian Embryo etc. 633 



Experiment 4. A fourtli lot of Rana eggs in advanced seg- 

 mentation (64 cells onward) were placed in Ringer solution at the 

 same time with those of Experiment 3, and were kept under the 

 same conditions. The influence of the solution was more marked 

 than in the previous cases, development was slower, and a much 

 larger proportion died. The period of rest was nearly three hours 

 (2 hrs. 50 mins.) and the eggs did not appear to recover as fully 

 as in. Experiment 3. There was also another significant difference. 

 These eggs were farther advanced when placed in the solution, 

 and yet their subsequent development was slower than that of the 

 16 cell eggs. 



Although both were subjected to the solution at the same time, 

 the 16 cell eggs reached gastrulation considerably in advance of 

 the 64 cell ones. 



Here again individual pecularities may partially explain this 

 difference in rapidity of development, but is does not seem probable 

 that this alone could occasion so great a discrepancy. None of 

 these embryos could be reared to the formation of the external 

 gills although every effort was made to secure that result. They 

 died off very rapidly during early development and none lived beyond 

 the twelfth day. 



Experiment 5. A bunch of Rana eggs in which the blasto- 

 pore was fully developed was obtained March 25*^. A portion of 

 these were placed at once in a 0.6% salt solution. These lay dor- 

 mant for nearly 10 hours without showing any signs of further 

 development. They then advanced very slowly. Although the 

 blastopore was fully developed and had begun to contract in size 

 before the eggs were placed in the solution, this action ceased, and 

 there was no further diminution for several days. 



That this was not the result of a complete cessation of activity 

 was proved by the fact that the embryos showed the usual amount 

 of development elsewhere. 



They elongated, the neural folds appeared and gradually fused, 

 and the head was differentiated. Sections also showed that internal 

 development was going forward slowly. The activity of the yolk 

 cells alone seemed temporarily paralyzed. There was the same 

 migration of material from the sides of the blastopore to the center 

 of the dorsal lip, and the latter began to elongate and grow out into 

 the tail. The failure of the borders of the blastopore to contract 

 could not have been due, therefore, to any lack of activity in the 



