256 W. C. GEORGE. 



ical injury did not prevent further segmentation. I observed, 

 however, that the presence of the stain induces a moribund 

 condition which results sooner or later in the death of the cell 

 injected or of the cells arising from it. I therefore used this 

 method in the following experiments to kill certain regions of the 

 egg, considering it preferable, since it can be better controlled, 

 to the usual method of pricking with a hot needle. 



EXPERIMENTS WITH EGGS OF Rana sylvatica. 



On the morning of March 26 I brought into the laboratory a 

 quantity of R. sylvatica eggs in the gray crescent stage. In 

 nineteen of these eggs I injected one of the cells of the two-cell 

 stage. In sixteen of the nineteen the first cleavage had come in 

 along the median plane of bilateral symmetry, dividing the egg 

 into right and left halves. In eight of these eggs I injected the 

 right-hand cell and in eight the left. In one egg the first cleavage 

 plane was oblique to the anterior-posterior axis. Whether or 

 not the injected cell in this case contained the greater or the less 

 amount of the gray crescent was not noted. In the other two 

 eggs of the nineteen the first cleavage plane was transverse to 

 the median axis, thus dividing the egg into anterior and posterior 

 halves. In one of these two eggs I injected the anterior cell, 

 which contained the gray crescent material, and in the other I 

 injected the posterior cell leaving the cell containing the gray 

 crescent material uninjured. The morning of March 28, two 

 days after the injections had been made, I found in the egg in 

 which the posterior cell had been killed by injection, that the 

 anterior cell containing the gray crescent material remained 

 uninjured and had developed into an embryo with neural folds 

 uplifted and lying alongside the dead material resulting from 

 the injected cell. None of the other eggs either at this time or 

 later showed any thing resembling a neural plate. They formed 

 a cap of live cells on a mass of dead material but developed no 

 further. 



On the morning of April i I collected eggs of R. sylvatica in the 

 early blastula stage. The gray crescent material could still be 

 distinguished by the characteristic pigmentation and by the 

 smaller size of the cells there as compared with other regions 



