18 EDWIN G. CONKLIN 
Kernplasma-Relation may be the result of differentiations already 
present in the blastomeres. 
In table 3 only maximum nuclear and cell dimensions are given 
for the different blastomeres. Results would undoubtedly differ 
greatly if the minimum nuclear and cell dimensions were taken 
instead of the maximum. Accordingly in table 4 the minimum 
nuclear and cell dimensions for the various blastomeres of Cre- 
pidula plana are given, together with the Kernplasma-Relation 
of each. 
It is well known to cytologists that in cells undergoing regular 
division the minimum size of the nucleus is reached in the late 
anaphase, when the individual chromosomes have contracted to 
their smallest size and when they are most closely crowded 
together. A little earlier than this stage the chromatic plate is 
wider and the spaces between individual chromosomes greater; 
a little later the chromosomes begin to absorb achromatin and to 
swell up to form the chromosomal vesicles. At this stage of 
greatest nuclear contraction the chromosomal plate has approxi- 
mately the form of a disk or short cylinder, and although the polar 
ends of the chromosomes are closer together than the equatorial 
ends, the disk being like a truncated cone, rather than a cylinder, 
we shall not greatly err if we treat this chromosomal disk as a 
short cylinder, rather than as a truncated cone. In table 4, 
in the column giving the dimensions of the chromosomal disk the 
first number is the diameter of the disk, the second its thickness. 
Popoff (08) has found in Frontonia that immediately after 
cell-division there is a diminution of the nucleus, which is then 
followed by a slow growth (‘Funktionelles Wachstum’ of Hert- 
wig), and this by a much more rapid growth of the nucleus pre- 
ceding division (‘Teilungswachstum’ of Hertwig). Both the 
functional growth and the divisional growth occur in the cleavage 
of Crepidula, but there is no diminution of the nucleus following 
division as in Frontonia. On the other hand, the minimum nu- 
clear size is reached in the anaphase just before division of the 
cell body, as has been explained. 
In the early telophase the chromosomal plate is drawn close to, 
and moulded over, the centrosome, and consequently the shape 
