84 ART. 3. — S. IKEDA : CONTRIBUTIONS 



the embryo has entirely recovered its normal condition by the 

 detachment of the right ex-ovate. 



Such a tendency we must regard as the result or sum of the 

 long course of selection, and is the reason of the great resisting 

 power which amphibian eggs offer to various disturbing circum- 

 stances. And there must be many such disturbances, sometimes 

 no doubt very slight, to which the frog's egg-masses must be 

 subjected in their natural environment in spite of their gelatinous 

 envelope. This probably accounts for the fact that individual 

 variations in the frog's egg in regard to the segmentation process 

 and the blastopore closure are so innumerable, that one is at a 

 loss to find out exactly which is the normal course. 



8). The greatest injury is done to the process of the blastopore 

 closure and to the formation of the embryonic body when an egg 

 is punctured at the region of the first appearance of the dorsal 

 blastopore lip, and the resulting embryo shows more or less im- 

 perfections. This has already been remarked by Assheton and 

 others. 



9). The least injury is done, when an egg is punctured at 

 either pole or on the future ventral side along the anti-blasto- 

 poric meridian. 



10). Not only a puncture, but various other causes such as 

 misplacement of eggs, insufficient supply of fresh water, unconscious 

 pressure of a blunt needle during an experiment etc., may disturb 

 the internal arrangement of the egg-contents and cause ab- 

 normalities in development, often greater than those produced by 

 a puncture. 



11). From what has been detailed, it seems evident to me 

 that the results obtained by puncturing eggs or by other similar 

 methods, can never be depended on to reveal the normal course 



