Experiments on the Early Development of the Amphibian Embryo etc. 637 



Gastrulation was much delayed and the blastopore, when formed, 

 occupied fully one half the surface of the egg. iVs the embryo 

 began to elongate this yolk mass, which was out of all proportion 

 to the size of the embryo, was left free, and occupied the whole 

 of the ventral surface. In many cases the embryo was simply 

 coiled around the yolk and presented an appearance very similar 

 to that in the eggs of bony fishes. This free yolk became loose 

 and mealy and portions of it sloughed off from time to time. 



For this reason the embryos died rapidly, and none of them 

 reached the closure of the neural folds. For the same reason it 

 was found absolutely impossible to preserve any of the eggs so that 

 they could be sectioned, though many different methods w^ere at- 

 tempted. Accordingly it was determined to try these eggs in a 

 weaker solution, with the results given in Experiment 12. 



Experiment 10. Chorophilus eggs in the 4 cell stage were 

 placed in the same dish with the 16 cell Rana eggs of Experiment 3, 

 and the 4 cell Amblystoma eggs of Eperiment 6. These eggs had 

 all been taken from the same pool in close proximity to one another, 

 and by keeping them thus in the same dish it was possible to make 

 intelligent comparisons of the relative influence of the solution upon 

 them. The Amblystoma eggs were retarded most in their develop- 

 ment, and the Chorophilus eggs the least. The former remained 

 inactive for some time after being placed in the solution while the 

 latter seemed scarcely to stop at all. The Rana eggs were inactive 

 for a time, but not as long as the Amblystomas. 



On the other hand the ultimate effect of the solution was exactly 

 the reserve of this. The Amblystoma eggs recovered their activity 

 slowly, but seemed to recover it fully, and continued developing 

 until they became quite normal embryos with fully developed ex- 

 ternal gills. 



In strong contrast with these the Chorophilus eggs, which at 

 first were scarcely influenced by the solution, in later development 

 were so affected by it that none of them could be reared even to 

 the closing of the neural folds. 



In this particular, also, the Rana eggs occupied the middle ground. 

 They were more affected than the Amblystoma eggs, and not as 

 much as the Chorophilus. 



Ringer solution, therefore, retards most those eggs whose de- 

 velopment is least rapid, while its ultimate influence is greatest upon 

 those eggs which develop most rapidly. 



