602 
T. H. MORGAN 
This result meets a criticism that might be made of mass results 
in the absence of isolation experiments, namely, that only those 
embryos develop normally in which the direction of centrifuging 
coincides with the poles of the egg. Since in most sets there are 
some, often many abnormal embryos, in addition to those due to 
polyspermy etc., it might be claimed that only those segregations 
of materials that correspond with the normal location of oil, 
yolk, pigment etc., might give normal results. The figures of the 
living embryo show that the pigment and the yolk, that have prac- 
tically the same distribution, and the oil may have all possible 
positions in the egg in relation to the axis. A study of the normal 
distribution of pigment and yolk shows in fact how little ground 
exists for supposing them to be formative materials. 
The location of the visible materials of the normal eggs, and the effects 
of centrifuging 
The eggs, en masse, have a distinct red color; the depth of color 
varying in different individuals. Not infrequently lots are met 
with that are quite colorless. The color is due to a red pigment in 
the egg. When seen under the microscope the egg appears faintly 
reddish or brownish-red (plate 1, fig. A). At one pole there is a 
large clear area free from pigment that is the animal pole of the 
egg. The opposite pole, too, is often seen to be lighter in color. 
Across the egg in the animal" hemisphere there is a lighter band, 
(fig. A), that may be connected with the presence there of the polar 
spindle, that has already formed when the eggs leave the ovary. 
A section of the normal egg (plate 2, fig. M) shows that the 
yolk lies near the surface of the egg. The yolk placques are very 
large compared with the size of the egg. The interior of the egg 
is filled w4th a finely granular, stainable protoplasm in which lies 
the large, well-developed karyokinetic spindle of the first polar 
body. The oil and the pigment are dissolved by the reagents and 
do not appear in the sections. 
When the egg is centrifuged the pigment and yolk are carried 
-to the outer pole, the oil to the inner (fig. N). Between the two 
lies a band of clear protoplasm. An optical section of a well- 
