190 



HUBERT DANA GOODALE 



slight differences in the records. The units in table 1 are arbi- 

 trary. They nearly equal | mm. 



* Diameter of an egg from another set of 'large' eggs, which, being in a larger 

 dish were not affected by the high temperature prevailing. 



These measurements show, in addition to the results already 

 mentioned, that the eggs are largest during gastrulation. The fluid 

 filling the enlarged internal cavities of the egg appears to be de- 

 rived from, the peri vitelline space which does not share in the 

 increase in size, for the surface of the egg at this stage is separated 

 by a smaller distance from its membranes than was the case earlier. 



Changes in the shape of the blastopore and its fate 



The first appearance of the blastopore is a very shallow, narrow 

 cleft appearing among the yolk cells some 30-45° below the equa- 

 tor (fig, 22). It elongates rapidly and becomes crescentic (fig. 

 23). The concavity of the crescent is directed towards the lower 

 pole. The dorsal lip appears to be nearly stationaiy. The 

 elongation of the blastopore continues until it corresponds in 

 extreme cases to a little more than half a circumference (fig. 24) 

 though often it does not attain so great an extension. The 

 blastopore has not moved much, if any, from the point where it 

 originated towards the lower pole, differing in this respect from 

 the blastopore of the frog. 



