24 EDWIN G. CONKLIN 
to make the measurements under a relatively low power, the 
8 mm. apochromat objective and the 1/1 micrometer eyepiece 
of Zeiss. Owing to the relatively low magnification the probable 
error is greater than in the measurements of the eggs of C. plana. 
With the exception of the cells 3A—-3C and 4A-4D the Kern- 
plasma-Relation is in this case practically constant, varying only 
from 1 :124 to 1:127. In view of the fact that I can find no. 
constant Kernplasma-Relation in the blastomeres of Crepidula 
this result in the case of Fulgur is unexpected. I am sure that 
my measurements in the case of Fulgur are not so accurate as in 
Crepidula, the number of eggs measured being relatively small 
and the magnification used low, so that each interval of the scale 
stood for 8u. The uniformity in the measurements of the differ- 
ent blastomeres and nuclei of Fulgur may be due in part to this 
fact; on the other hand this would only account for the lack of 
minor variations and would not explain the general uniformity. 
There is no doubt that the micromeres of Fulgur are more uni- 
form in size, than those of Crepidula; also the whole cleavage 
process is very much slower, and (with the exception of the macro- 
meres 3A-3C and 4A-—4D) the divisions are more nearly synchro- 
nous in the different cells than in Crepidula. It seems probable 
that these two facts are connected with the more uniform Kern- 
plasma-Relation of the different blastomeres of Fulgur. 
This conclusion is rendered still more probable by a consider- 
ation of the two generations of cells in which there is a wide de- 
parture from the usual Kernplasma-Relation, viz. 3A-3C and 
4A-4D. In these cases, as in the same cells in Crepidula the 
resting stage is particularly long, lasting in the case of 44—4D 
until all the organs of the embryo are outlined and more than one 
thousand cells are present; consequently the nuclei grow to an 
enormous size so that the Kernplasma-Relation falls in one case 
to 1 : 35.8 and in the other to 1 : 3.6. In the corresponding cells 
in Crepidula the ratio is 1 :1.6 and 1 : 0.37; the volume of the 
nucleus in the last named case being about three times that of the 
plasma. The Kernplasma-Relation of the cells 4a-4e is 1 : 0.58 
in Crepidula, the nuclei being about twice as voluminous as the 
plasma; in the corresponding cells of Fulgur this ratio cannot be 
