The Cytology of two Species of Characiopsis. 183 
and the dense cell contents. They are quite small, and usually 
show a distinct nucleolus (Fig. 1, H, I, J, L and O). 
Characiopsis saccata. 
Ch. saccata is quite different from Ch. Ncegelii in its internal 
structure. The cell-wall is of cellulose ; it is thin and delicate, 
and no attempt at the formation of the internal projections was 
observed. 
In the living condition it is usually very difficult to locate the 
chromatophores. The granular cell-contents appear faintly green, 
and on focussing on to the edge of the individuals it may be 
possible to distinguish a deeper green lining layer, with occasional 
paler interruptions (Fig. 2, A-G). After staining, the chroma¬ 
tophores are often still obscure, but can he seen in some 
individuals as very thin delicate plates closely adhering to the 
cell-wall (Fig. 2, M). Unlike the globular chromatophores of Ch. 
Ncegelii, which are so large and numerous as usually to fill the 
whole cell, in this species they occupy only a very insignificant part 
of the interior of the cell, and in transverse section are only to be 
distinguished as very thin plates bounding the protoplast (Fig. 2, 
O). In some very small individuals there is only one chroma- 
tophore which does not entirely cover the cell-wall (Fig. 2, N)* 
The remaining protoplasm is very homogenous, and appears 
to be coarsely granular. Neither vacuoles nor a definite network 
were ever noticed. The conspicuous granules are presumably 
only denser parts of the general mass of protoplasm, since they 
only assume a pale yellowish colour when treated with iodine, 
and do not give the characteristic reaction of any definite 
substance. 
The nuclei in this species are again very numerous, although 
they never reach such large numbers as in Ch. Ncegelii. In 
general the number of nuclei present is dependent on the size of 
the individual, and eight or sixteen are the usual numbers, 
although in one individual thirty-two were counted (Fig. 2, L). 
In many of the smallest specimens only one nucleus was present 
(Fig. 2, N), and the nuclei apparently divide by simultaneous 
bipartitions, since the commonest numbers of nuclei present are 
those of the progression 1, 2, 4, 8, 16, etc. (Fig. 2, H, I and K-M). 
In one case six nuclei were present, evidently owing to the more 
rapid division of two of the four nuclei which were previously 
present (Fig. 2, J). The nuclei very often take up a somewhat 
peripheral position, usually occupying the spaces between the 
chromatophores (Fig. 2, I and M). They are much larger than 
those of Ch. Ncegelii, and appear very conspicuous in stained 
