186 ADAM SEDGWICK. 
doubt represent different phases in the life-history of the 
nucleus. It has been impossible for me with the small 
number (ten) of unsegmented ova at my disposal to determine 
their sequence. I have, however, seen it in four conditions, 
which differ from one another sufficiently to merit a special 
description; three of these were found before the beginning 
of segmentation, and one in an ovum of two segments. 
a. A spherical structure (diameter, 0:04 mm.) bounded by 
a membrane, which is slightly indented at one point, where it 
sends in a prolongation of itself, which passes through the 
nucleus to become continuous with the membrane of the 
opposite side (Pl. XII, fig. 8). The prolongation of the 
membrane across the nucleus is also connected with the mem- 
brane at another point (on the lower side of the figure), and, 
in addition, sends off processes which ramify in the substance 
of the nucleus. The nucleus is made up of a fine spongework 
of very pale fibrils, which are continuous with the 
nuclear membrane and with the septum and its pro- 
cesses just mentioned. In this spongework are a number 
of deeply-staining more or less spherical bodies. 
The membrane, septum, and its processes stain about as 
deeply as the strands of the extra-nuclear reticulum, and 
they appear to be continuous with the fine, pale, 
little staining strands, which constitute the main 
mass of the nuclear spongework. The pale spongework 
further possesses, as I have already said, a number of bodies— 
some elongated and branched, others globular—which are, I 
think, stained rather more deeply than the membrane and its 
offshoots, and which are likewise continued into the strands 
of the pale nuclear network. This latter fact is quite easy 
to see in the elongated branched staining fibrils, and the 
deeply-staining globular bodies, when carefully examined with 
a high power, present in many cases an angular appearance, 
the angles being continued into the pale reticulum. 
As already stated, the nuclear membrane and septum appear 
precisely similar in structure to the strands of the external 
protoplasmic reticulum, and the latter are continued 
