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size as the protoplasmic disc the latter (if not already segmented) 
does not divide; if previously in the two- or four-cell-stage a few irre- 
gular divisions succeed but no embryo is produced. 
Comparing these results of loss of yolk with the preceding account 
of the loss of protoplasm we see that the egg of Fundulus has the 
ability to adapt itself to most unusual conditions and still produce an 
embryo that is distinctly that of Fundulus. Does not this point to 
the conclusion that while the egg during development adapts itself to 
the necessities of the occasion by utilizing the mechanical means placed 
at its disposal, that it is a mistake to suppose the external conditions 
determine the series of phenomena (however much they may modify the 
preliminary changes) for we see the same result follows even when the 
primary conditions are very much altered. 
The yolk may also be successfully removed at the time when the 
germ-ring just appears and the result is the same as when removed 
at an earlier stage. Similarly when the blastoderm has extended 
half over the yolk the latter may be reduced and the elastic blasto- 
derm will adapt itself to the new smaller sphere. A large number 
of embryos were partially deprived of their yolk during the early 
germ-ring period in order to see what effect would be produced upon 
the developing embryo. Briefly we find: that the blastopore closes 
in point of time much earlier than do the normal (check) embryos, 
and that as a consequence the embryo is exceedingly shortened in 
length. It corresponds in length to the length of the normal (check) 
embryo that has had the same time to develop, but in which the 
blastopore is still widely open. The embryo from the operated egg 
is therefore at the time of closure of its blastopore broader than the 
normal embryo that has closed its blastopore. Later the shortened 
embryo elongates but as yet I have not studied the process sufficiently 
to state how this is brought about. 
Other Experiments. 
The reverse experiment of adding yolk to the egg is not possible 
but a modification of this effect is produced by placing the eggs under 
compression. By doing this the blastodisc that lies between the yolk- 
sphere and the membrane is flattened to a half or a third of its pre- 
vious thickness. The blastodisc will still segment giving a flattened 
plate of cells. The plate later becomes several cells deep although 
all of its layers are much flattened. Whether the early blastoderm 
produces the normal number of vertical layers I can not say as such 
eges have not yet been cut. The compressed embryo forms a normal 
embryo. 
