THE AMERICAN LOBSTER. 
155 
dorsal side uppermost or in vertical suspension. This was repeated, and it invariably 
followed that the nucleolus fell from its own weight, to the lower side of the nucleus, 
like a shot within a tennis ball. This is well illustrated in cuts 18 and 19. The 
latter shows in section a part of the ovary hardened in its natural position, with the 
dorsal surface uppermost ; the nucleoli are here invariably on the lower side, in contact 
with the nuclear membrane. In 18, where the part of the ovary was turned bottom 
side up, the nucleoli are eccentric, but lie against the opposite side of the nucleus. 
Suspend the ovary and kill the tissue in any position you please, the nucleoli sink like 
shot in the karyolymph and lie against the lower side of the nucleus. This is true of 
all but the smallest ova, in which the nucleolus may or may not so readily respond. 
Such eggs sometimes possess two or more nucleoli (fig. 156). 
This phenomenon is a direct result of the structure of the nucleus and of the 
action of gravity, or else it is an artifact, the result of post-mortem changes. The 
nucleus consists of karyolymph, in which float granules of chromatin and other 
substances of but slightly less specific gravity, and a single large nucleolus of greater 
specific gravity than the surrounding fluids. The chromatophilous substance is 
distributed in floceulent masses (figs. 157, 158), which are commonly suspended in the 
nuclear fluid, but tend to “sink to the bottom” together with the nucleolus. There is 
no trace whatever of a nuclear network in the meshes of which bodies are suspended. 
The nucleolus stains very intensely, but is often highly vesiculated, in some cases 
forming a hollow shell, owing probably to the extraction of soluble matter by some of 
the reagents used. When the nuclear membrane is strongly contracted over any part 
of its area (as in fig. 152) it leaves between it and the rest of the egg a regularly 
defined space, which is partially filled with a coagulable liquid. This may come partly 
or wholly from the nucleus. 
I have never seen this phenomenon in the eggs of any other animal. If anyone 
have doubts about the facts, a very simple experiment like the one herein described 
will be convincing. The explanation which I have offered may, however, be questioned. 
I regret that the subject of post-mortem change did not come up for consideration 
when I was at the seashore. 1 
THE RIPE OVUM. 
The ripe unfertilized ovum is illustrated by figs. 119 and 141. Those which I have 
examined have been taken from the ovary or ducts a few hours or days after ovulation. 
The nucleus was in such cases found at or very near the surface of the egg. In 
fig. 161, as already mentioned, the nucleus was in karyokinesis. The plane of section 
passed through the equatorial plate, so that the poles lie, in reality, above and below 
the plane of the paper. This is apparently the division preliminary to the formation 
of the first polar body. The rest of the egg is composed of yolk disposed in spherules 
of fairly uniform size. A coagulable liquid is usually gathered at the surface, below 
the eggshell, where the yolk spheres are here apt to be smaller. There is a single 
egg membrane (about -gxo mm. in thickness), which is unaltered in the course of the 
passage of the egg through the oviduct. 
1 In regard to this question Professor Bump us writes me that Bellonci found something very 
similar in the brain of Squilla, and that this was afterwards explained by Mayer as the result of the 
action of reagents, the nucleoli migrating from the killing fluids. Here, however, the action of gravity 
certainly plays a part. 
