34 EDWIN G. CONKLIN 
any stage, less the coefficient of the initial stage, viz. unity, gives 
the percentage of growth of that stage, as compared with the ini- 
tial stage. 
Since the ectoderm at the 24-cell stage is a plate of purely 
protoplasmic cells, nearly square, about 80 on each side and 36h 
thick its volume is about 230,400 cubic u; subtracting the volumes 
of the nuclei of the plate, 21,584 cubic p, leaves 208,816 cubic pz 
as the volume of the cytoplasm! of the ectodermal plate. Adding 
to this the volume of the protoplasm in the macromeres 3A-3D, 
viz. 22,185 cubic », we have as the total volume of the proto- 
plasm at the 24-cell stage 231,000 cubic ». This figure is 27,897 
cubic yu less than the volume of protoplasm at the 24-cell stage 
given in the table, which was calculated from the dimensions of 
each individual cell, rather than from those of the entire ecto- 
dermal plate. It is highly probable that the lower figure is nearer 
correct than the higher one, since minor errors in the measure- 
ments of individual cells are greatly magnified in determining 
the total volumes of these cells. ‘The same remark applies to the 
total volume of protoplasm in the 16-cell stage, which is probably 
actually less than the volume given in the table; and if the total 
volume of the protoplasm is less than the amount given in the 
table the total volume of the yolk in these stages is of course 
increased correspondingly. 
But assuming that the smaller number (in brackets) represents 
the actual volume of the protoplasm in the 24-cell stage of Crepi- 
dula plana we must admit that there has been a great growth in 
the plasma at the expense of the yolk during the cleavage. The 
coefficient of protoplasmic growth (i.e., the volume of protoplasm 
of any stage divided by the volume of protoplasm of the stage 
just before maturation) is given in the next to the last column of 
the table; and a glance at this shows that the protoplasm at the 
24-cell stage is at least 24 times as voluminous as in the maturation 
stage, while the yolk is correspondingly less voluminous. The 
volume of the entire egg, also, is considerably less in the 24-cell 
stage than at the beginning of development. Indeed there has 
been a gradual decrease in the volume of the entire egg during 
'The words ‘cytoplasm’ and ‘protoplasm’ are used synonomously throughout 
this paper. 
