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PHYSIOLOGY OF DIGESTION IN BLATTIDAE 365 
are not glandular in function, but are adapted for efficient re- 
generation of cells. The membrane lining the wall of the epi- 
thelium is evidently cast at intervals, for it may be seen at 
various stages of disintegration. Such stages correspond to 
those described by Schroder. The spheres of secretion which 
appear on the surfaces of the cells will be discussed in a later 
section on the functions of the stomach. 
The structure of the epithelium of the coeca is the same as 
that of the stomach in every detail. This shows plainly in sec- 
tions which show the branching of the coeca from the stomach. 
In these cases it cannot be determined just where the coeca 
originate. I have seen practically no evidence of more secre- 
tion globules on the coeca epithelium, an observation which is 
surprising in view of the fact that several authors have de- 
scribed the coeca as preeminently secretory organs, capable of 
producing most of the secretion found in the stomach. Later I 
shall show that not only are the histological structures of the 
stomach and coeca alike, but also the digestive functions. 
At the hinder end of the stomach the epithelium makes a cir- 
cular fold which partially constricts the passage into the small 
intestine. This may be considered as a valve. Schroder sug- 
gests that the purpose of it is to help roll up boluses of food 
matter and pass these on to the small intestine, instead of a 
constant stream. Backflow is somewhat prevented, too. 
Small intestine. The small intestine is very short and has 
asmalllumen. Just behind the fold or valve at the hinder end of 
the stomach the high epithelium of this region gradually becomes 
lower and merges into the thin epithelium of the small intestine. 
At this point the Malphigian tubules enter in six great groups. 
The epithelium in this section consists of nearly cubical cells 
whose cell boundaries are hard to make out. The layer of cells 
is very much folded. The chitinous intima bears small swellings 
surmounted by very short spines. The cell structure resembles 
that of the oesophagus. Surrounding the epithelium is a thick 
layer of apparently confused muscular fibers. The function of 
the small intestine is not absorptive, and it has never been so 
considered except by Frenzel and Deegener. The explanation of 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 25, NO. 2 
