MONTGOMERY. 
[Vol. XV. 
450 
It is probable that the two nucleoli of such nuclei have not 
arisen by division from a single nucleolus, but are nucleoli 
which have been developed at different points in the nucleus 
and which are destined to fuse together later and form a single 
one. This assumption was based upon the observation of 
nuclei where two nucleoli lie at opposite poles of a nucleus 
(Fig. 166) and each is apposed to the nuclear membrane, or 
where only one occupies such a peripheral position, the other 
being in the center of the nucleus (Fig. 164). In one figure 
(Fig. 165) we see a nucleus in which the two nucleoli lie near 
the center, close together, which might denote the beginning 
of such a fusion. On a little reflection this explanation of the 
presence of two nucleoli will appear quite allowable. In the 
more usual mode of development a larger nucleolus is formed 
at the periphery of the nucleus, wanders towards its center, and 
then much smaller masses of nucleolar substance are similarly 
formed and later fuse with the large nucleolus ; while in the 
cases under consideration two nucleoli of nearly equal size are 
produced, either simultaneously or in succession, and these 
afterwards fuse together. These two nucleoli of nearly equal 
size cannot be division products of a single primitive nucleolus, 
since two nucleoli are never found in the larger germinal 
vesicles. 
The nuclear sap of the smaller germinal vesicles does not 
stain at all ; in the larger ones (Figs. 168, 173—175, 177) it 
does, and the explanation for this staining may be given by the 
assumption that there is a dissolution of nucleolar substance 
throughout the whole nucleus, i.e., of that substance of the 
assimilated yolk balls which does not enter into the formation 
of the nucleoli. During the mitotic stages no constituents 
of the nucleus stain except the nucleolus and the chromatin 
filament, but these do not stain in the same manner. 
At first sight the heteronemertean Linens seems to differ 
markedly from all the metanemerteans here examined, in that 
it contains a single, enormous germinal spot. But in Linens , 
though a single large nucleolus is first formed, it nevertheless 
grows by the addition to it of much smaller nucleolar globules 
(Nut. 67 ., Figs. 168, 174, 177) which have the same method of 
