190 ADAM SEDGWICK. 
called chromatin contained in the protoplasmic meshwork 
(both of nucleus and rest of ovum) behaves. In the nucleus it 
varies from a state of diffusion through the reticulum to a state 
in which it is condensed into the chromatin masses of forms a, 
c, and d. 
In the subsequent stages of segmentation the nucleus 
gradually becomes smaller until at the close of segmentation it 
has an oval form with a long diameter of 0°016 mm. It now 
presents the features described by Flemming and other obser- 
vers in the nuclei of the salamander and other animals. 
During segmentation the nucleus generally has the third 
form above described: I have never seen it in a spherical, and 
only once in a spindle form. I conclude that these forms if 
they occur are very rapidly passed through. 
2. The Female and Male Pronuclei—I include under this 
head the nucleus of the ovum after the formation of the first 
polar body. I have no observation on the nucleus of the 
uterine ovum before this event. 
a. Two Ova of Peripatus Balfouri with one polar 
body completely formed and no trace of the second.— 
In one the nucleus of the ovum had the spindle form and the 
two equatorial rows of chromatin bodies had already slightly 
separated from one another. It was placed near and with its 
long axis parallel to the surface of the ovum. The area of 
dense protoplasm in which it was placed was considerably 
smaller than in later ova which possessed the first segmenta- 
tion nucleus. The spindle had a length from pole to pole of 
‘(017 mm. _ It presented precisely the same features of structure 
as the larger spindle described above. 
In the other ovum the nucleus had the form of a number of 
closely aggregated masses of chromatin occupying an area of 
°0084mm. The protoplasm in which they were contained did 
not appear to differ in any way from the rest of the denser pro- 
toplasm of the animal pole. 
Male Pronucleus.—On the opposite side of the ovum, and 
nearly in the same transverse plane, was a small bold mass of 
chromatin having a diameter of ‘0042 mm. It was contained 
