600 
T. H. MORGAN 
Four females that had begun to lay (in water containing 
sperm) were centrifuged in the shell for 10 minutes. They were 
then put into water where they began to lay in a few minutes. All 
of the eggs were seen to have been well centrifuged. All sets pro- 
duced normal swimmers. In some cases the eggs were transferred 
to other dishes. These did not develop so well. About thirty- 
two other individuals gave similar results. In addition there were 
some sets that produced abnormal embryos. Comparison with 
lots composed of the same number of normal individuals showed 
that there were as many lots of the centrifuged eggs in which nor- 
mal development took place as of normal eggs. It is evident that 
the abnormal development so frequent in lots of eggs centrifuged 
after deposition has nothing to do with the effects of the centrifuged 
on the contents of the egg, hut is the result of the handling of the egg 
after contact vjith sea water. 
The localization of the visible materials of the egg 
Despite the fact that the yolk, pigment and oil are sometimes 
shifted before cleavage begins, the yolk remains in many cases 
either in place or, if shifted, moves as a mass (plate 1, figs. C, F, 
and plate 2, fig. P, Q). This holds also for the pigment and oil. 
When the egg divides the small cell may, to all external appear- 
ances, be made up almost entirely of the yolk (plate l,figH), 
since in size this cell corresponds approximately to the amount of 
yolk precipitated. Three eggs in the two-cell stage are shown in 
plate 1, figs. G, H, 1. It will be noticed that in all three cases the 
first cleavage passes through the pole where the polar bodies lie. 
In the first figure, the smaller cell is composed mainly of the oil 
cap ; in the second figure of the pigment (and the yolk within) ; 
in the third figure, the small cell contains oil, pigment, and 
yolk. Three four-cell stages corresponding to the last, are repre- 
sented in plate 1, J, K, L. In the first the smaller oil-bearing cell 
has divided into two equal parts, as in the normal egg; while a 
third small cell, containing pigment, is budded off from the larger 
cell. In the next figure these conditions are reversed. In the 
third figure L (turned over as compared with I) the small cell has 
