702 THE AMERICAN NATURALIST. [Vor. XXXIX. 
region of protoplasm as in the Cyanophycex. There is of course 
no blue-green pigment (phycocyan) in the cells of bacteria and 
consequently no chromatophore but several sorts of inclusions 
may be present in the protoplasm. The nature of some of the 
inclusions is not clear and this subject has not been given as 
much attention as in the Cyanophycez. It is significant that 
this cell structure should be found so clearly in the Beggiatoa 
since this organism seems very close to Oscillatoria in its mor- 
phology. Some of the larger species of Beggiatoa may be 
expected to yield conclusions similar to those of Olive’s investi- 
gation on Oscillatoria if sectioned and critically stained, especi- 
ally as the cells are very large in some forms and there is 
probably less extraneous matter to complicate the interpretation 
of the preparations. 
As has been stated, investigations upon the smaller species of 
bacteria and especially upon pathogenic forms have met with 
great difficulties. These led at one time to the ingenious theory 
of Bütschli (’90), followed by Zettnow ('97) that possibly the 
entire protoplast had the value of a nucleus. That is to say, 
an outer peripheral region of. cytoplasm had either never been 
developed in these organisms or, if present, had become so 
closely associated with the chromatin that it could not be dis- 
tinguished as a special region of the cell. A peripheral region 
of cytoplasm is represented in some of the larger forms by the 
cilia and by accumulations of protoplasm at the ends of the cells, 
especially clearly shown in Spirillum (Bütschli, '96; Zettnow, 
97). Later Zettnow ('99) and Feinberg (:00) applying the 
staining method of Romanowski, followed by several later inves- 
tigators with improved technique (Nakanishi, :01, and others), 
succeeded in differentiating a minute body in the cells of smaller 
bacteria and pathogenic forms, which is regarded now as similar 
to the central body of the sulphur bacteria and a true nucleus. 
This structure is very minute since it occupies a portion of 
these exceedingly small cells. Naturally it will be very difficult 
to obtain any detailed knowledge of its structure and behavior 
during cell division. But enough seems to be known to justify 
the belief that differentiated nuclear structures are probably 
present even in the smallest types of bacteria. A recent paper 
