CELL SIZE AND NUCLEAR SIZE wo 
Figs. 35, 36, 37 represent eggs, from the same experiment, 
which were centrifuged thirty minutes during the first cleavage, 
and were fixed twelve hours later. The size of the micromeres of 
the first, second or third sets is but little influenced by the quan- 
tity of cytoplasm in the macromeres; the size regulation of the 
micromeres is here practically complete. In fig. 37 the cell 4c 
forms at the same time as 4d, though in normal eggs it does not 
form until much later; the precocious formation of this cell is 
probably due to the fact that the amount of cytoplasm in macro- 
mere C was larger than normal. 
III. General results of these experiments 
The results of these experiments, which have been described 
in the order of development from the earlier to the later stages 
without reference to a logical presentation of general questions, 
may now be classified and compared with the observations on 
cell size and nuclear size given in Part I of this paper. In gen- 
eral these experiments support in every detail the conclusions based 
upon the study of normal eggs and blastomeres. 
1. Nuclear size in centrifuged eggs. In centrifuged eggs, as in 
normal ones, the size of the nucleus is always dependent upon 
the quantity of cytoplasm surrounding the nucleus and upon the 
length of the resting period. Nuclei which are normally large 
may be caused to remain small, and nuclei which are normally 
small may be rendered large by merely changing the positions of 
the yolk and cytoplasm in the cell. 
In normal eggs of Crepidula the egg. nucleus lies in a protoplas- 
mic field near the animal pole of the egg, while the sperm nucleus 
enters the egg near the vegetal pole and moves up toward the 
animal pole through a field of yolk. As long as the sperm nucleus 
is in this yolk it remains very small, and only when it emerges 
into the protoplasmic field near the egg nucleus does it begin to 
grow rapidly. The egg nucleus on the other hand, grows rapidly 
and becomes much larger than the sperm nucleus. If now an 
egg is centrifuged during the formation of the second polar body 
so as to throw the yolk to the animal pole and the cytoplasm to 
