640 
T. H. MORGAN 
the sphere. When the mature egg is set free in the water the 
protoplasm moves to one pole to form there the blastodisc. 
The blastodisc lies immediately below the micropyle, which is 
the only point in the membrane through which the spermatozoon 
can enter. The protoplasm is transparent, and almost entirely 
fre from granules, which are so characteristic a feature of the 
eggs of other animals. 
A cursor}'- study of the effect of centrifuging sufficed to show 
that the blastodisc can be produced at once w^hen the eggs are 
centrifuged, instead of taking an hour to form as in the normal egg. 
The blastodisc appears on that part of the egg that is turned 
outwards on the machine. It is clear and transparent as in the 
normal egg, and shows no stratification of its substance. Its loca- 
tion bears no relation to the micropyle, which raises at once the 
question whether the blastodisc is produced at any point on the 
surface of the egg that happens to lie outermost, or whether the 
egg proper orients within its membranes in response to the cen- 
trifugal force. Simple as these alternatives appear, no small 
amount of labor has been neccessary to settle this point. The 
solution of this question seemed the more desirable because it 
not only involves certain important problems in the egg of the 
fish, but bears on certain possibilities in the eggs of other animals. 
Another point of interest appeared when it was found, that, 
beneath the micropyle, a minute blastodisc also appeared after 
fertilization, that segmented and produced a rounded blasto- 
derm. The relation of this blastoderm to the larger one, its ori- 
gin, and is fate have also been examined. 
The work had progressed this far in the summer of 1908, but 
wishing to settle more conclusively certain essential questions, I 
repeated and extended the experiments during part of the summer 
of 1909, and am now in a position to give an answer to the main 
problems outlined above. 
The orientation of the egg in the machine 
- An examination of unfertilized eggs placed at once on the 
machine and turned 150 times shows that the blastodisc artifici- 
