446 
EDWIN G. CONKLIN 
that each can give rise to only one organ or set of organs. In the 
normal development the clear and gray substances are largely 
contained in the micromeres, or ectomeres, the yellow substance 
in the mesomeres and entomeres. But in the centrifuged eggs 
the stratification of these substances may take place in any axis, 
thus locating the yellow material, for example, in the dorsal, the 
ventral, the anterior or posterior, the right or the left halves of 
the body, and yet the form of development may be perfectly 
normal in every case and young snails may hatch from such eggs 
and live indefinitely. Indeed the gray material may be thrown 
entirely out of the egg without interfering in the least with its 
normal development (figs. 27-30). 
In the study of these eggs one cannot avoid the impression that 
both the gray and the yellow substances are mere inclusions in the 
protoplasm and that neither are essential to development {vide 
Lillie 1906, 1909; Morgan 1908-1909.) The clear substance, on 
the other hand, seems to be the real protoplasm of the egg in which 
the heavier and lighter inclusions are contained, and when these 
inclusions are separated from the protoplasm by centrifugal 
force the latter is still capable of typical development. That the 
clear substance alone is protoplasm is indicated by the fact that it 
alone of the ooplasmic substances increases in quantity during 
development, and it alone contributes to the growth of the nucleus. 
The fact that the yellow substance decreases in quantity at the 
same time that the clear and gray increase is evidence that the 
former is converted into the latter; and in those centrifuged eggs 
in which almost all of the yellow material is contained in one of 
the first two blastomeres and the clear and gray substances in the 
other it may be seen that clear substance ultimately appears in 
the yellow cell. Evidently a small amount of clear substance 
may have been left in this cell, but just as evidently clear substance 
must be formed anew. This may take place in all cases in which 
a nucleus is left in a cell and consequently the nucleus must have 
power to form hyaline protoplasm or to transform yolk into 
protoplasm. 
But if the clear substance is protoplasm this work gives no evi- 
dence that it is so differentiated that certain portions of it are 
