TO THE EMBRYOLOGY OF AMPHIBIA. 33 



unfortunately I could not observe this, for the egg began at this 

 stage, to show some independent movements within the vitelline 

 membrane, which seemed to increase gradually. As the first Bufo 

 egg had showed similar movements at the corresponding stage, I 

 gave close attention to the matter. After examining the conditions 

 carefully, I came to the conclusion that such movements were not 

 natural but, were caused in some way by the strong sun-light 

 which was falling at the time directly on the mirror and the egg 

 — a conclusion which was soon proved to be false, as will be seen 

 further on. 



The third egg of Bufo was taken from a mass deposited in 

 the same pond early on the morning of March 27th. The eggs 

 had not yet begun segmentation, and one of them was fixed on 

 the mirror at 8:30. The first cleavage appeared at 9:45 a.m., 

 and the second cleavage at 11 a.m. I watched this egg at inter- 

 vals of time up to the fourth day, but unfortunately owing to 

 the clouding of the mirror, and to the unusual amount of pig- 

 ment in the egg, I am unable to give details about the exact 

 spot at which the dorsal blastopore lip appeared, or about the 

 mode of the blastopore closure. While, however, lookiug at the 

 egg at 12 m., on the fourth day when the blastopore had just 

 closed and the neural groove and folds had become clearly re- 

 cognizable, I noticed a curious behavior of the egg. As in the 

 last two cases, the egg began to show movements within the 

 vitelline membrane. The outer envelope was not swollen out as 

 in the first egg nor was the sun-light at the time falling on it, 

 as in the second egg. The movements were at first very slow 

 and seemed somewhat irregular so that they seemed somewhat 

 accidental, and due to some external stimulus. After a while, 

 however, the motion became more rapid and seemed to show 



