EFFECTS OX EGGS OF FRESH WATER PULMOXATES 429 
Experiment 5. Lymnaea eggs were centrifuged for 10 min., 
generally after the disappearance of the germinal vesicle, but be- 
fore the formation of the first polar body. The three zones were 
quite distinct, the gray pole floated uppermost and the eggs 
oriented rapidly. In one or two eggs the germinal vesicle was 
still intact after centrifuging, lying in the clear zone, but border- 
ing on the gray. The first polar body formed 1 hr. and 25 min. 
after centrifuging; at this time the gray and yellow zones were 
still fairly distinct but the clear zone had largely diffused into 
the other two. In most cases the gra}- pole still floated up, and 
the yellow pole down. The first polar body was always on some 
portion of :he gray zone, but usually near the remains of the clear 
zone, consequently many eggs, after they had oriented, showed 
the polar body on the side. On the 4th day the embryos were 
normal except for the distribution of the gray and yellow mate- 
rials; on the 9th day normal little snails were present, but not 
yet hatched from the capsules: on the 16th day all had hatched 
as normal snails. 
Experiment 6. Lymnaea eggs, from a part of the same laying 
used in Exp. 1, were centrifuged 10 min. just as the first polar 
body was being extruded. The separation of the yellow, clear 
and gray substances was fairly complete. The first polar body 
always formed on the gray cap, though often eccentrically. The 
eggs did not orient as rapidly as in Exp. 1, but they still oriented 
in the same way. The gray substance was more coarsely gran- 
ular than in Exp. 1, and in general it was equally abundant with 
the clear and yellow substances, each constituting about one-third 
of the volume of the egg. On the 2d day few were normal, 
many abnormal or dead. The same was true on the 8tn and 
12th days. Almost all left alive on the 15th day were normal 
(The exact proportion of normal to abnormal forms was not noted.) 
Four eggs of this lot were isolated in the 2-cell or 4-cell stages, 
as follows : 
1. Two cells, one yellow the other gray (as in fig. 35). Sub- 
sequent cleavage stages were normal in form but not in distri- 
bution of colored materials; the same was true of the blastula, 
one-half of which was yellow and the other half gray. On the 
