228 HUBERT DANA GOODALE 



which remains noarly stationary, the cells above the lip reach it 

 first, then the cells of the lateral parts of the equator and finally 

 those from the opposite side of the egg. Judging from the light 

 color of the stain in the proximal ends of the ventral marks, only 

 a comparatively small amount of material from the equatorial 

 region reaches the blastopore, the rest having been distributed 

 along the way. While the daughter cells from the equatorial 

 region are moving blastopore-wards, the cells lying between them 

 and the blastopore are moving in the same direction with the 

 result that nearly all the lower hemisphere becomes invaginated. 

 Cell division appears to be less active among these last, since 

 stains made in this region usually move bodily into the blasto- 

 pore without extending into bands. 



The cells dorsal to the blastopore move into it along their respec- 

 tive meridians. Those lateral to it tend to enter from below, 

 hence their proximal ends swing ventrally, the result being a 

 curved mark. The marks opposite the blastopore move along 

 meridinal lines, generally speaking. 



Towards the end of gastrulation, certain changes concerned 

 with the development of the neural plate and dorsal parts of the 

 embryo affect the movements of the lateral marks. When the 

 cells of the neural plate begin to move up, the lateral marks, 

 which lie near the edges of the plate, move with them, thus revers- 

 ing the direction of their former movement. 



The question of concrescence is taken up in another place. 



Eggs marked in various 'places about the blastopore 



The typical changes in the shape of the blastopore have been 

 described. In marked eggs, the presence of stained places brings 

 to light certain remarkable shiftings of the blastopore, which 

 are dealt' with in the present section. 



A brief account of the matter in a few eggs will suffice to give 

 an idea of these movements. My data are not sufficient to deter- 

 mine the exact age at which the process begins, but there is con- 

 siderable evidence that it does not start until about thirty-six 

 hours after the commencement of gastrulation. 



