Experiments on the Early Development of the Amphibian Embryo etc. 635 



time the organism is not as capable of witb-standing- adverse in- 

 fluences as when it is subjected to them before any development has 

 taken place. 



Experiment 6. Some Ambly stoma eggs in the 4 cell stage 

 were placed in the same dish with the Eana eggs of Experiment 3. 

 (In EiNGER solution.) This bunch was left with the jelly as it was 

 found, and was not changed in any way. 



The eggs developed very slowly for 17 days when the first 

 traces of the external gills began to appear. They were thus de- 

 layed more than the eggs in 0.6% salt solution since the latter in 

 the same time had produced embryos with the external gills fully 

 formed. A few of them had a very small yolk plug still protruding, 

 but the majority appeared perfectly normal. 



We have already stated that these 4 cell Amblystoma eggs were 

 put in the same dish with the 16 cell Rana eggs, so that the con- 

 ditions of development must have been exactly the same. The re- 

 sults, however, were very different, for while only 162/3% of the 

 Rana embryos lived to the 15*^ day, the Ambly stomas were all alive 

 on the 17*^ day. 



About one half of them were then preserved and the rest allowed 

 to develop. As soon as the stomodeum opened in both Ranas and 

 Amblystomas a marked change took place in their development. 



Hitherto the yolk cells had furnished the nourishment necessary 

 for the growth of the embryo, and everything had advanced steadily, 

 though slowly. Now the point was reached, where the digestive 

 canal begins to function and external food becomes necessary. 

 Ordinarily at this stage the embryo finds enough to eat in the 

 aquarium. These had to be kept in a clean dish for obvious reasons. 

 An attempt was made to feed them, but nothing proved acceptable, 

 and hence they soon began to die. Two of the Amblystoma however 

 lived until the 24*^ day. 



In comparing Amblystoma with Rana we must keep in mind 

 that the latter developed faster than the former, and so could not be 

 expected to live as long. But this does not explain the fact that 

 all the Amblystomas lived until after the opening of the stomodeum 

 while most of the Rana died before reaching that stage. 



Experiment 7. Amblystoma eggs in both the 16 and the 64 

 cell stages were placed in Ringer solution in the same dish. These 

 were also left in the original jelly untouched, but they developed 

 more slowly than those of Experiment 6. Here again we have eggs 



