No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 417 



this term any particular significance of these bodies. In eight 

 individuals of Montagiia 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^ 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. yy) 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 



