No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 417 
this term any particular significance of these bodies. In eight 
individuals of Montagna which were sectioned, and which were 
of slightly different sizes, though the various growth stages of 
the ova were more or less the same in all, in only four were 
pseudonucleoli to be seen, and in only one of these four 
were they quite abundant, occurring in about 30 jo of the larger 
germinal vesicles. There are never more than from one to 
three in a nucleus. They are usually irregularly spherical and 
sometimes even angular in form ( Ps . n. in Figs. 72-77, 79). The 
largest attained about three-quarters the size of the true nucle¬ 
olus (of the same nucleus), though this size was attained by 
few, since they are, as a rule, but little larger than the nutritive 
globules which are observed in the caryolymph. Each pseudo¬ 
nucleolus consists of a denser, more deeply staining layer 
surrounding a less dense, more faintly staining core. The 
denser outer layer is homogeneous, somewhat refractive, and 
stains in the same manner as the ground substance of the true 
nucleolus. In smaller pseudonucleoli this outer portion appears 
on cross-section as a deeply staining ring, with regular out¬ 
lines, but in the larger ones small, irregular prominences may 
often be seen on its inner surface. The peripheral layer or 
ring, further, shows a double contour, but I am unable to deter¬ 
mine whether it is bounded by an outer membrane. It increases 
slightly in thickness with the growth of the pseudonucleolus, 
and in one case (Fig. 77) it was noticeably thickened at one pole, 
which gave to it somewhat the appearance of the tout ensemble 
of a true nucleolus. This peripheral layer surrounds a homo¬ 
geneous, non-refractive, probably fluid mass, which either stains 
not at all or else only faintly ; when it stains, it is either in the 
manner of the caryolymph or of the vacuoles of the true 
nucleolus. I have never noticed that the nutritive globules of 
the nuclear sap were apposed to these pseudonucleoli. What 
their origin is, and what their relation to the true nucleolus, I 
do not know. They are never found in contact with a true 
nucleolus and so are probably not buds from one. It is curious 
that they were frequent in the ova of only one mollusc, and in 
the same stages of the eggs of three other individuals were 
present in only a few cells, and in four other individuals were 
