MINUTE STRUCTURE OF PELOMYXA PALUSTRIS. 297 
The examination of sections under very high powers lent 
strong support to the views of Professor Biitschli as to the foam- 
like structure of protoplasm (‘ Mikroskopische Schaume,’ 1892). 
I was able to confirm the existence of the very fine vacuolisation 
described by him (loc. cit., pp. 200 and 216) for P. palustris, 
which probably occurs also in P. viridis, but, as he suggests, 
may have escaped Professor Bourne’s notice. The vesicles in P. 
palustris, which corresponded to the smallest seen by Professor 
Bourne in P. viridis, were easily known by their size as com- 
pared with that of the nuclei in both forms; and a foam-like 
structure, consisting of alveoli of infinitely smaller diameter 
(4—1 ) than these vesicles, was most distinct in many of the 
sections. Fig. 11 shows this fine alveolar structure with a 
nucleus and two vesicles for comparison; in fig. 10 it is seen 
on a larger scale. The strands of protoplasm bounding these 
smallest alveoli, and also some of the thin strands between the 
large vacuoles, appeared to me homogeneous, and comparable 
with the finest pseudopodia of Rhizopods and the finest strands 
of vegetable protoplasm described by Biitschli (loc. cit., pp. 
67, 79). The peripheral radiate alveolar border of Biitschli, 
said to be characteristic of froths, was clearly distinguishable 
in some sections (fig. 2), and the radiate alveolar layer de- 
scribed by him is seen in fig. 9, (2) round a nucleus, and (6) 
round a refringent body. 
Appearance of a Central Mass. 
In one individual of Pelomyxa, of which a consecutive 
series of sections had been cut, a very curious appearance was 
observable. The animal had been killed with osmic acid, and 
stained in bulk with carm-alum, a delicate protoplasmic stain. 
_ The sections presented a central, more deeply staining, irre- 
gularly oval ring of apparently denser protoplasm, which was 
traceable through many sections. ‘The ring diminished at 
each end of the series to a small central solid patch of denser 
protoplasm, and hence apparently represented a more or less 
spherical or oval mass, reminding one somewhat of a central 
