342 



A. W. BELLAMY. 



appears only under conditions of severe inhibition. In addition 

 to this secondary inturning, some overgrowth may take place; 

 in some cases the over growth is in the direction of the vegetal 

 pole as in normal gastrulation, while in other cases the over- 

 growth is toward the apical pole. In eggs where this upward 



bP 



FIG. 21. Some types of modification seen after the following treatment in 

 KNC: A, B (same egg). Eggs beginning two-cell at start of experiment; 24 hrs. 

 in w/i,ooo, 24 hrs. in m/20,ooo, ,12 hrs. in m/5O,ooo, 12 hrs. in w/ioo,ooo. C, 12 

 hrs. w/i,ooo, 12 hrs. w/5,ooo, 24 hrs. ?/io,ooo. (Experiment KNC A 3.) Note 

 the position of the blastopore which is nearer the equator than in control eggs. 



overgrowth is taking place over the secondary invagination, the 

 yolk cells below the original blastopore are usually overgrowing 

 the pigmented cells of the animal hemisphere, thus reversing the 

 usual process. 



This modification is similar to that described by Morgan 

 (1903), which he says is produced by a process in which "the 

 cells of the upper hemisphere . . . turn into the egg." It makes 

 little difference whether one refers to the process thus or whether 

 one calls it simply an invagination. I have used the latter term 

 because the process appears to me to be similar in many respects 

 to that of invagination and overgrowth seen in gastrulation. 



