Isolated Blastomeres of the Frog’s Egg. 429 
and are not all on the same side. There is some displaced pigment 
in the center of the lens, and the cells of the optic cup have not 
preserved their normal arrangement. An examination of the 
ectoderm showed more or less disintegration, and the defects 
observed may be explained by the fact that the specimen was 
dying when it was taken out of the water to be preserved. 
These differences in the two eyes of the eighty-day embryo 
from one blastomere, are the most striking differences between 
the right and left sides. The ear vesicles are almost identical on 
the two sides, and the same is true of the other paired organs. 
Furthermore, no general defect of the anterior, posterior, dorsal 
or ventral regions of the body could be found. The study of the 
five other embryos developed from operated eggs, and cut in 
serial sections also revealed complete forms. 
Roux described right and left ‘‘hemiembryones iaterales’”’ and 
also “‘hemiembryones anteriores”? developed from one blasto- 
mere in the experiments mentioned above. 
Since the anterior end of the neural folds lies on one side of the 
egg between the equator and the animal pole, i. e., about the 
region in which the gray crescent appeared, and the dorsal side 
of the embryo is formed chiefly on this side, it is probable that in 
case the first cleavage plane were transverse to the plane of sym- 
metry, it would divide the egg into the halves that would form 
the dorsal and ventral parts of the embryo respectively. There- 
fore the ““hemiembryones anteriores” might better be described 
as “‘dorsales” as indicated by Przibram. Roux obtained no 
‘“posteriores” (‘‘ventrales” of Przibram) and since a number of 
the eggs died, it is probable that those blastomeres which corre- 
spond to the ventral part of the embryo, and therefore contain no 
part of the gray crescent, are not so well adapted to independent 
development. In my experiments the position of the grey crescent 
as marking the future dorso-anterior region of the embryo was 
not recorded, but it seems probable from the results of Roux’s 
experiment, that those isolated blastomeres containing no part of 
the grey crescent did not develop. 
As noted above, Roux found that half-embryos sometimes be- 
came complete embryos by post-generation. 
