338 



the periphery, the smaller toward the axis ; it also commonly happens 

 that the nucleoli of all eggs are eccentric, and that all lie on the same 

 side of the nucleus ^). 



It seemed estremely probable that this was due to gravity, acting 

 directly upon the nucleolus, which was free to move in every part of 

 the nucleus. A few simple experiments immediately proved that this 

 was the case. The ovary of a lobster which had recently hatched 

 a brood was selected, and cut into several parts. The latter were 

 hardened in different positions — with ventral or dorsal side upper- 

 most, 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 Figs. 3 and 4. 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 con- 

 tact with the nuclear membrane. In Fig. 3 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 caryolymph, 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. 



This phenomenon is a direct result of the structure of the nucleus, 

 which is illustrated in Figs. 1 and 2, and the action of gravity. The 

 nucleus consists of caryolymph 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 flocculent masses, 

 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 employed. 



1) This eccentricity of the nucleolus was noticed by Bumptjs in 

 1891, but no explanation of the phenomenon was offered. Journal of 

 Morphology, Vol. V, p. 225. 



