TO THE EMBRYOLOGY OF AMPHIBIA. 9 



a slight noteli may be noticed at the middle point of the dorsal 

 blastopore-lip. But such eggs can not be perfectly normal, I think, 

 for they show sooner or later some abnormalities. In eggs which 

 develop normally, the dorsal lip is always entire and the blasto- 

 pore is a perfect circle in shape, until it is completely closed. 



Up to this stage, the egg always rests on about the middle 

 point of the blastoporic area with the translucent area of the 

 segmentation cavity on the exact top. As the closure of the 

 blastopore progresses, the resting-point of the egg is gradually 

 shifted toward the ventral face of the future embryo. Thus, 

 when we look at an qq-o- a t about the end of the srastrulation 

 process, the now much reduced blastopore may be seen on the 

 dorsal side of the embryo, nearer the equator of the egg than 

 before, (Fig. 12-14). At the same time the greatly reduced 

 translucent area of the segmentation cavity will be seen to have 

 shifted anteriorly, in front of the future embryo. 



Such a change in the position of the blastopore may lie 

 considered as due to the overgrowth of the ventral blastopore lip 

 being greater than that of the dorsal lip, and to the eccentric 

 closure of the blastopore thus brought about. But careful observa- 

 tions have convinced me that here there is a real rotation of the egg- 

 as a whole on its horizontal axis. In this, I find myself in agree- 

 ment with many of my predecessors. But I am unable to follow 

 Pflugee ('83), Koux ('88a), Morgan (97), et al, when they state 

 that the dorsal lip of the blastopore grows over the lower yolk 

 hemisphere about 170° or 180° from the spot of its first appear- 

 ance before the rotation of the egg takes place. Observations 

 which I shall record in the sequel incline me strongly to the 

 view that in normal eggs, the dorsal lip does not grow over the 

 yolk hemisphere beyond its middle point, (the yolk pole in the 



