TO THE EMBRYOLOGY OF AMPHIBIA. 31 



not be difficult, I think, to orientate the egg. The final point 

 of closure coincided nearly with the starting point of the dorsal 

 lip, showing that the egg did not rotate more than 55°-60°. 

 After this, the egg unfortunately became somewhat unstable by 

 the swelling up of the egg envelope. The egg seemed also to 

 show at times certain independent movements which I attributed 

 at the time to some accidental causes. 



The second Bufo egg that was studied was taken from a 

 mass that was obtained from the same pond on the morning of 

 March 21st. All the eggs had not yet begun segmentation. The 

 particular egg to be studied was soon fixed on the mirror at 10 

 a.m. The first cleavage line appeared about one hour later 

 (11 a.m.) and reached the lower pole at 12 m. when the second 

 cleavage line began to appear nearly at right angles to the first. 

 In this egg, the frontal view of the first cleavage plane was seen 

 at 115° and 295° of the rotating-dish, and the same view of the 

 second cleavage-plane at 20° ( = 115-95) and 200° ( = 295-95). 

 The dorsal blastoporic lip appeared first at 8 a.m., on the third 

 day, at about 28° or 29° below the equator. In this egg also, 

 the frontal view of the blastopore (the posterior view of the egg) 

 coincided with the frontal view of the second cleavage plane, 

 while the profile or side view of the dorsal lip was the same as 

 the frontal view of the first cleavage plane. 



The blastopore rim completed its circle when it had grown 

 downward to about 60° below the equator (2:30 p.m.). At this 

 stase, all the circumference of the rim was at the same level. 

 The same state of things still continued at 3:10 p.m., when 

 the lip had grown down to about 70° below the equator. At 

 3:30 p.m., the egg had just begun its rotation. At that time, 

 I noticed that the egg moved in an unexpected direction. Thus 



