GRAY CRESCENT MATERIAL IN FROG EGG. 257 



at the margin between the yolk and pigmented hemispheres. 

 I injected the stain into ten of these blastulas, inserting my needle 

 at right angles to the axis of the egg through the gray crescent 

 material in such a way as to destroy nearly all of the material 

 in that region. In eight other eggs I made a similar injection 

 on the opposite side of the yolk field. Examination of the 

 uninjured control eggs on the afternoon of April 3 showed them 

 to have developed into embryos with external gills appearing. 

 Except in two cases where there were structures which might 

 possibly have been incomplete transverse cerebral commissures, 

 there was no evidence of anything like a neural plate in any of 

 the ten eggs having all or most of the gray crescent material 

 destroyed. Closure of the blastopore was interfered with in 

 these eggs, but apparently little if any more so than in those eggs 

 in which the injection was made on the side of the yolk hemisphere 

 opposite the gray crescent and from which I obtained seven 

 neurulas out of a lot of eight eggs. The eggs with the gray 

 crescent material destroyed were kept until the afternoon of 

 April 4th when they were preserved, no neural plate or folds 

 having been formed in any of them. 



EXPERIMENTS WITH EGGS OF Rana pipiens. 



The morning of April 5 I collected eggs of R. pipiens and 

 brought them into the laboratory as they were passing into the 

 two-cell stage. In forty-six of these eggs in which the first 

 cleavage plane was anterior-posterior I injected one of the first 

 two lateral cells. Of eight eggs in which the first cleavage plane 

 was transverse to the anterior-posterior axis I injected the 

 anterior cell in four eggs and the posterior cell in the other four. 

 On account of the moribund condition resulting from injection 

 none of the eggs injected at the two-cell stage developed far 

 enough to give any information in regard to the fate of the gray 

 crescent. I shall not therefore give their history here. 



From eggs injected at the four-cell stage I obtained more 

 definite results. From fourteen eggs having one of the two 

 posterior cells of the four-cell stage injected I later obtained 

 ten embryos defective on one side of the blastopore but having 

 complete neural tubes. 



