64 EDWIN G. CONKLIN 
IT. Nuclear size and cell size wn centrifuged eggs of Crepidula 
While the size relations of cells and of their various constituents 
may be readily observed in normal eggs, it is especially in eggs 
which have been centrifuged at various stages of development 
that the factors which determine these various size relations can 
be most satisfactorily studied. The various constituents of a 
cell may be moved by centrifugal force to one pole or another, 
according to their specific weights, and the axis of centrifuging. 
In this way the yolk, the cytoplasm, the nuclei and the centro- 
somes, may be caused to take very abnormal positions in the cell. 
Even the mitotic figure may be moved out of its ordinary position 
in the earliest stages of its formation, but after it has reached the 
metaphase it can be moved only with great difficulty; from this 
stage on it is anchored, probably to the cell membrane by the 
astral radiations, while the other constituents of the cell are free 
to move under the influence of centrifugal pressure. In this way 
it happens that the cytoplasm may be centrifuged away from the 
spindle and the latter left in a dense mass of yolk; or the normal 
relations of cytoplasm and yolk to the poles of the spindle may be 
completely. changed; or the normal size relations of the daughter 
cells may be quite reversed. As illustrating these changed rela- 
tions, due to centrifuging, a few eggs are shown in figs. 11-37, 
selected from a great number which are similar to these. 
These eggs were centrifuged on a centrifugal machine run by 
water pressure, at the rate of 2000 revolutions per minute; the 
radius of rotation was 6 cm., consequently the centrifugal pres- 
sure was nearly 270 times that of gravity. Eggs were centrifuged 
at this rate for varying lengths of time, after which they were 
removed from the machine and either fixed at once, or left for a 
longer or shorter time in sea water before fixation. All eggs were 
fixed in Kleinenberg picro-sulphuric mixture, were preserved in 
70 per cent alcohol only long enough to wash out the fixing fluid, 
and were then stained in my modification of Delafield’s haematoxy- 
lin and mounted entire in balsam, in the manner described in 
previous papers (Conklin, ’02 et seq.) 
