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of irregular methods of cleavage were noted. This third furrow of the 
half egg corresponds to the fourth furrow of the normal egg. The 
fourth furrow of the normal egg at right angles to the third cut off 
four central cells and twelve peripheral cells. In the half egg this 
cannot happen if the furrow is at right angles to the last division 
(as it is in fact) because all four cells of the preceding stage are 
quadrants. A discussion of this problem will be taken up when the 
points can be illustrated by figures. Embryos normal in all respects 
except as to size result from these eggs. The embryo is larger 
than half of the normal embryo and not so large as the 
whole embryo. In point of size they seem to be between 
a half and two thirds of the normal embryo. 
The problem that such an egg solves is an interesting and diffi- 
cult one. A single blastomere has (after cleavage) to grow over a 
sphere of yolk that bas the same size that two such blastomeres cover 
under normal circumstances. A single nucleus (through its products) 
has to do the work of two. Whether this is accomplished by a fewer 
number of smaller nuclei or by the same (normal) number 
of smaller nuclei (or in some other way), I am unable to say. 
This point will be determined by sectioning such embryos. 
The reason that the embryo resulting from one of the first two 
blastomeres is larger than half a normal embryo I believe to be due 
to this: the blastodisc is formed as is well known, by a slow concen- 
tration of the peripheral protoplasm of the surface of the yolk. This 
flowing continues under normal circumstances up to the eight-, sixteen- 
cell-stages, etc., for there is a steady increase in size of the early 
blastoderm. Presumably the same process takes place in the operated 
egg so that the half blastomere increases in size by the protoplasm 
that it would receive had it remained in connection with the one re- 
moved but also must receive the additional protoplasm that 
would normally have gone into the other blastomere. Hence a blasto- 
derm larger than half is formed and from this an embryo larger than 
half an embryo. The conditions are peculiar. There remains in 
the operated egg half the segmentation nucleus, more 
than half of the protoplasm, and the whole of the yolk. 
There results a perfect embryo of nearly two-thirds size. 
The conclusion seems to follow that the size of the 
embryo is determined by the amount of protoplasm 
present and not by the quantity of nuclear matter. The 
problem involves more than that of the half holoblastic egg, for here 
as there we-remove half of the segmentation nucleus but not half the 
