TRANSACTIONS OF SECTION K. 581 
in Zygnema there are two star-shaped chromatophores, each with a large pyrenoid 
in the middle, and between them a small very inconspicuous nucleus. 
In the Cyanophycee we are struck at once with the extraordinary prominence 
of the central body and the complete absence of pyrenoids. It seems to me that 
possibly this may be correlated with the presence of the assimilative colouring 
matters in the cell, and that in the absence of a differentiated pyrenoid the 
central body combines both the nuclear and the pyrenoid function. It is a 
perfectly well-known fact that the pyrenoid exhibits many of the characteristics 
of nuclein. It is not impossible, therefore, that it may be a derivative of the 
nucleus or of a body which may have been the precursor of the nucleus in the cells 
of primitive plants. There are many facts which indicate that the Cyanophyceve 
is not only a well-marked group, but one which is very rudimentary and possibly a 
very ancient group. It is, therefore, just in such a group that we should expect, 
to find a less highly differentiated protoplast than we have in the alge. We know 
that this is so as regards the chlorophyll-containing part of the cell, in that it contains 
no clearly differentiated chloroplast, and it may be that the central body itself is an 
undifferentiated region of the cell which includes both the function of a pyrenoid 
as well as that of a nucleus. This would explain its large size and chromatin 
characteristics, and also the absence of a differentiated pyrenoid and true nucleus 
such as we have in the higher alge. It is true that there is no pyrenoid in those 
cells of the higher plants which contain chlorophyll, whilst the nuclevs remains 
small proportionally to the size of the cell. In these plants, however, the 
chlorophyll corpuscles themselves give the phosphorus reaction. 
The hypothesis here put forward receives considerable support if we compare the 
cells of the Cyanophyce with those of various bacteria. In colourless forms, such 
as Beggiatoa alba, various Spirilla, Bacilli, &c., we tind very few chromatin granules ; 
but in the coloured forms, in which there is a process of assimilation comparable 
probably to that in chlorophyll-containing cells, we find, as both Butschli and Fischer 
have shown, that the chromatin granules are much more abundant. ‘They are not 
in the form of a definite central body, but they occur more abundantly in the centre 
of the cell than at the periphery. 
My view, then, is that the large size of the central body in the Cyanophycez may 
be connected with the development of the chlorophyll assimilation ; that it may be 
held to function both as a pyrenoid as well as a nucleus, and that this receives sup- 
port from what is observed in the coloured bacteria, in which the cytoplasm contains 
a more abundant supply of chromatin granules than do the colourless bacteria. 
Structure of the Bacterial Cell. 
Owing to the small size of the bacterial cells it is very difficult to arrive at a 
correct interpretation of the structures observed. The examination of the larger 
forms, such as the various species of Begyiatoa, Chromatium, Bacillus anthracis, 
Bacillus subtilis, &c., have, however, revealed a certain diflerentiation, which 
enables us to come to some conclusions as to their actual structure. Ernst has 
shown that the contents of these cells are not homogeneous, as was formerly 
thought to be the case, but show a differentiation into a less stainable substance, 
and embedded in it one or more deeply stained granules. 
Butschli has shown that the central portion of the contents of the cell exhibit 
a foam structure in which granules of a chromatin nature are embedded: this is 
surrounded by a thin layer of aless deeply stained substance, which sometimes 
accumulates more prominently at the ends of the cell. The central, more deeply 
stained, froth-like structure with its granules is the nucleus; the delicate peri- 
pheral layer is the cytoplasm: From a recent examination which I have made of 
Beggiatoa alba, Beggiatoa roseo-persicina, Bacillus subtilis, and other smaller 
species, I cannot agree with Butschli that there is a differentiation into a central 
body or nucleus, and peripheral cytoplasm. In the various species of Beggiatoa 
and Spirilla which I have examined the cell contents exhibit a reticulate or 
foam structure of the cytoplasm in which one or more deeply stained granules 
