196 



HUBERT DANA GOODALE 



Fig. 30. The groove has deepened into a sht-Hke archenteron, 

 a, around whose inner ends are the elongated triangular cells. 

 The tongue, t, is larger, while the cells of the dorsal lip, d. I., 

 are smaller and more numerous. The blastopore has lowered to 

 an amount equal to the depth of the archenteron. As I shall 

 show bv means of artificial stained spots on the egg, the small 



3i 



Figs. 28-31 



cells now lying at the edge of the blastopore are derived by divi- 

 sion from cells which lay at the equator at an earlier stage. The 

 roof'' of the blastocoele is thinner, especially above the blasto])ore. 

 Numerous mitotic figures are present just above the blastopore. 

 The floor-cells of the blastocoele are migrating singly or in groups 

 towards the roof against which they place themselves. This 



^ The roof of the egg shown in fig. 30 is unusually thick. 



