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 1!). 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 ou 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 pheuomeuou 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 iu flocculent masses (tigs. 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. 

 1 regret that the subject of post-mortem change did not come up for consideration 

 when I was at the seashore. ' 



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 2x0 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 Bumpus writes me that Bellonci found something very 

 similar in the brain of Sqmlla, 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. 



