809. 
protoplasm and none of the yolk. Often the first cleavage plane 
of the normal egg divides the blastodisc into very unequal parts. In 
some cases the larger blastomere has been removed in others the 
smaller. The result is the same in either case as a perfect embryo 
is formed, but the embryo is smaller when the smaller 
blastosphere is left and larger when the larger blasto- 
mere remains. 
Removal of Yolk. 
The yolk may be removed from the egg of Fundulus at almost 
any stage of development and the embryo still forms. By sticking the 
egg at the pole opposite to the blastodisc and gently squeezing the 
egg between two needles the yolk will slowly flow out of the opening. 
The membrane collapses as the pressure is applied but subsequently 
fills out again as water passes into the space between egg and mem- 
brane. Usually a half or two thirds of the yolk was removed. If 
this is done an hour after fertilization or during the two- or four-cell- 
stage the method of cleavage is profoundly modified. The protoplasmic 
accumulation instead of forming a flattened disc heaps up into a cone 
or even into a nearly perfect sphere. Generally such a cone or sphere 
divides vertically into two then into four cells. The third division 
often comes in at right angles to the preceding two, i. e. in the third 
dimension of space, giving four cells distally and four proximally or 
next the yolk. From such eggs perfect embryos are produced. Many 
of these eggs divide irregularly so that one or two of the four cells 
may divide vertically and the remainder at right angles to this. These 
also give perfect embryos. 
_ Tn a few cases even the second cleavage came in horizontally but 
as these eggs!) were not isolated I cannot affirm that they have rise 
to perfect embryos. 
The shape of the blastoderm in these eggs with reduced amount 
of yolk is different from that of the normal eggs. It is at first much 
higher and contains apparently a greater number of cells vertically 
as seen in optical cross-section. Subsequently this dome-shaped blasto- 
derm flattens and produces a perfect embryo. 
The egg therefore can accommodate itself to the loss of at least 
half its yolk, the cleavage is modified, in consequence but a perfect 
embryo results. There is a point of reduction however beyond which 
it is impossible to go; for when the yolk is reduced to about the same 
1) Modified according to the amount of yolk removed as will be 
described later. 
