The Cytology of two Species of Characiopsis. 185 
kind, eight, sixteen and thirty-two small protoplasts are produced^ 
each containing a tiny nucleus and pyrenoid (Fig. 3, F, G and H). 
The small protoplasts round themselves off, and presumably 
become zoogonidia. In Fig. 3, H, the zoogonidia seem to have 
been swarming within the zoogonidangium at the time of fixation. 
Before accepting the characters of this species as typical 
of Characium it must first he compared with the only other species 
of the genus whose cytology has been investigated. It will he seen 
that the two species by no means agree in all respects. 
Smith (T6) found that in Ch. Sieboldii there was no definite 
chromatophore, the chlorophyll being diffuse. In this Ch. augustum 
and Ch. Sieboldii agree, hut in their cytological characters they 
have, beyond this, very little in common. For in the adult con¬ 
dition the latter species is multinucleate, containing usually thirty- 
two or sixty-four nuclei, and one or more pyrenoids, whereas 
Ch. augustum contains only one nucleus, and one pyrenoid previous 
to the beginning of cleavage. In the formation of zoogonidia the 
protoplast of Ch. Sieboldii undergoes progressive cleavage, 
forming first a number of multinucleate portions, and then by 
further division smaller uninucleate protoplasts. The original 
pyrenoids disappear during the process of cleavage, hut a new 
one reappears in each uninucleate protoplast before it rounds 
itself off and becomes a zoogonidium. This method contrasts 
strongly with the regular successive cleavage of the protoplast 
in Ch. augustum, where each cleavage is always preceded by the 
simultaneous division of both nucleus and pyrenoid. Thus in 
cytological characters Ch. augustum and Ch. Sieboldii only agree 
in the absence of a definite chromatophore and in the possession 
of pyrenoids and starch. 
On comparing now the structure of Characiopsis Ncegelii and 
Ch. saccata with these two species of Characium, it will he seen 
that the distinctions between the two genera are still very slight. 
Both species of Characiopsis are in the adult condition multi¬ 
nucleate, but this is also the case in Characium Sieboldii. In 
Characiopsis saccata the youngest individuals, those which have 
presumably just been formed from the coming to rest of the 
zoogonidia, contain only one nucleus, which divides by successive 
bipartitions as the individual increases in size, until in the adult 
condition there are sixteen or thirty-two. In Ch. Ncegelii the same 
thing probably occurs since specimens containing two and four 
nuclei were often observed (Fig. 1, F and G), hut owing to the 
much greater thickness of the cell in this species, and the more 
complicated nature of the cell-contents, the later stages in the 
increase in number of the nuclei are much more dfficult to follow. 
