TO THE EMBRYOLOGY OF AMPHIBIA. 29 



four eggs during the spawning season of the present year, but 

 again all were failures. I ought to state also that I tried at first 

 to study the Bufo eggs in the basement-room before referred to, 

 but I found the constant low temperature of the room acted 

 injuriously on the Bufo eggs and I was therefore obliged to return 

 to the up- stairs laboratory which is kept warmed by hot- water 

 pipes. I will now proceed to describe the two eggs whose develop- 

 ment I followed, and in which I was able to make out the 

 relations between the first two cleavage-planes and the future 

 embryonic axis. 



The first egg was taken from a mass obtained from the pond 

 in our University grounds on the morning of March 16th. The 

 egg had not yet begun segmentation, when it was fixed on the 

 mirror at 10 a.m. The first cleavage line appeared at 2:50 p.m. on 

 the same day, and had nearly reached the lower pole by 5:30 p.m. 

 When the first cleavage line was placed approximately in the 

 middle vertical line of a side view of the egg the rotating dish 

 was at 175° (Fig. 44) or at 355°. At 6 p.m., the second cleavage 

 line appeared making right angles with the first (Fig. 43). When 

 this line was placed in the middle vertical line of the side view, 

 the dish stood at 85° (-175° -90) or at 265° ( = 175 + 90=355 

 — 90). Having made out the positions of these two cleavagv lines 

 on the scale, I was now able to identify the same positions by 

 simply turning the rotating dish to these several readings. 



At 8 a.m , ou the next morning, the egg had advanced to 

 a stage with 64 or more cells. The first dorsal blastoporic lip 

 appeared at 8:15 a.m., on the third day, about 30°-34° below the 

 equator. When the middle point of the dorsal lip was brought 

 on the middle vertical line of a side view, the rotating dish 

 stood at 85°, corresponding to the similar position of the second 



