216 
(!. ARNOLD. 
Occasionally, in even the earlier stages, some ingested 
bacteria are seen, but they are not numerous. But in the 
cells of two Planaria killed 118 hours after feeding they were 
extremely numerous (fig. 10, h. and c.), and also in the lumen 
of the intestine. 
At this stage the intestine is practically empty, except a 
few masses of blood-corpuscles and leucocytes, with numerous 
bacteria. That they appear in greater numbers only when 
the food, or what is left of it, has been in the intestine for a 
long period of time would suggest that the remainder of the 
free food is undergoing putrefaction. No great importance 
is to be attached to this isolated observation, but perhaps we 
have here the indication of the formation of a definite 
intestinal bacterial flora. 
Changes in the Nucleus. 
In all the columnar cells of the starved examples the 
nucleus contains only one nucleolus (figs. 11 and 13). At 
the most active state of digestion (fig’s. 7 and 10) there are 
two nucleoli, and sometimes even three. It is a question 
whether this multiplication of the nucleoli is to be inter- 
preted as an absorption of material from the cytoplasm to the 
nucleus, or as an expression of increased activity of the 
nucleus during digestion, with the consequent formation of 
waste products. 
Bxcketoey and I’igment- Gkanules. 
In all the columnar cells of the intestine certain granular 
masses are seen. They are highly refractive and preserve a 
yellow colour independently of the staining (fig. 15). Most 
of them are excretory products, but some can not be distin- 
guished from the pigment granules which form the greater 
part of the eyes of these animals. As digestion proceeds 
they increase in number, but always occur in groups, and are 
not evenly distributed through the cell. 
