476 MISS B. MURIEL BRISTOI. ON A 
from a study of the alga stained in bulk, hence the material was imbedded in 
paraffin, and microtome sections were eut about 5 w in thickness. 
Sections stained with Delafield’s hematoxylin show that the cytoplasm has 
a somewhat reticulate structure, but that the reticulations have no definite 
radial arrangement; and in a few cases there can be seen an indication 
of a parietal chloroplast. In sections stained with Heidenhain’s iron-alum- 
hematoxylin the reticulate nature of the cytoplasm is not nearly so notice- 
able, and the spaces between the network are seen to be filled with a granular 
substance, Pyrenoids, with either spherical or polygonal pyrenocrystals and 
usually narrow starch-sheaths, are conspicuous, there being often many in 
the larger cells and at least one in even the smallest cells. The adult cells 
are hunet (PI. 18. figs. 18 & 19), the nuclei being situated at the angles 
of the retieulum, but they are so minute that they can only be clearly 
distinguished under a magnification of 1435. Then, each is seen to consist 
of a single small granule of chromatin, the karyosome, surrounded by 
a narrow but definite nuclear space which is bounded on the outside 
by an extremely thin nuclear membrane. The whole structure is not more 
than 1,4 in diameter, and even under a magnification of 2820 no further 
details are apparent. In very young cells there is a single nucleus exactly 
similar in size and structure to those of the mature cells, to which it evidently 
gives rise by repeated division; but the structures are so minute that it has 
been impossible, even in a single instance, to obtain any of the details of 
division, 
The division of the pyrenoids usually takes place by constriction, though 
multiplication by fragmentation has been observed ; and all the available 
evidence indicates that nuclear division and the division of the pyrenoids are 
entirely independent of one another. 
IV. MULTIPLICATION BY ZOOGONIDIA. 
Multiplieation by zoogonidia has been observed in cells of all sizes from 
about 20 win diameter upwards, Successive bipartition of the contents of 
the cell takes place, with the formation of 8, 16, or an indefinite number 
of small oval uninucleate bodies, according to the size of the cell. These 
acquire cilia and swarm about within the mother-cell until an aperture 
appears at some place in the mother-cell-wall, when they make their way 
through the aperture aud escape into the surrounding water. The zoogonidia 
Mi diinad in this way are extremely variable in size even from the same 
zoogonidangium, but this may be due to their being eultural forms produced 
lider ; slightly abnormal conditions. Most are about 8 p long with a breadth 
of about 4°5 u, but they seem to be somewhat contractile, and many are found 
which are about 13 long and not more than 25g broad. They have two 
equal cilia, and are usually oval or pear-shaped, while the longer ones are 
