Experiments on the Early Development of the Amphibian Embryo etc. 641 



even be compelled to lie dormant for a while. In this way diffe- 

 rences are produced which do not exist in normal development. 

 These differences increase rapidly, and in a short time become so 

 great as to result in the death of the embryo. 



The Amblystoma egg, therefore, possesses a bulwark of safety 

 in the more even distribution of its protoplasm, and is able thereby 

 to overcome influences which result disastrously to its more rapidly 

 growing relative. But at the same time the sluggish development, 

 which is the result of this more even distribution, increases the 

 period of exposure to danger, and a great many Amblystoma eggs 

 usually die in the jelly. 



Just subsequent to the experiments here given a dozen bunches 

 of Amblystoma eggs were found in a boggy field at the edge of 

 the woods. The water was nowhere more than 6 or 8 inches deep, 

 and was so thoroughly impregnated with iron as to tinge the soil 

 and herbage a deep rust color. 



It did not seem as if any eggs could develop in such a medium, 

 but subsequent examination proved that they actually did. Some of 

 the bunches were taken to the laboratory and produced perfectly 

 healthy embryos. A visit was made to the bog at about the right 

 time and the eggs were found hatching, apparently with no more 

 than the ordinary loss. No doubt they produced an average number 

 of adults provided the water did not dry up prematurely. This 

 furnishes a good example of the protection afforded against influences 

 which must arise quite frequently in natural development. 



Again we are able to infer that the amphibian embryo can 

 accommodate itself to adverse circumstances at the very beginning 

 of its development more readily than it can readjust its vital powers 

 after a sudden change during later growth. The older it gets, and 

 the farther it is developed normally the less becomes its ability to 

 change into something abnormal. 



This truth has been recognized for a long time as applying to 

 the adult life of an animal, and it seems to be even more applicable 

 to embryonic stages of development. According to the experiments 

 here recorded, eggs at stages as near together as the unsegmented 

 and the 64-cell stage show a difference in their ability to overcome 

 the influence of the solutions. This becomes very marked in com- 

 paring eggs subjected to the solutions at the beginning and at the 

 close of segmentation. We have here, perhaps, a stronger evidence 

 than that given by Hertwig, of the great delicacy with which 



