PHYSIOLOGY OF DIGESTION IN BLATTIDAE 401 
6. The coecal epithelium has the same function and histological 
structure as that of the stomach. It exhibits somewhat more 
surface than the stomach, so that the digestive (enzymatic) power 
is somewhat greater than that of the stomach. The secretion 
appears as little spherical sacs released from the cells. 
7. The stomach and coeca absorb ‘ood in groups of absorbing 
cells. These groups are separated by groups of undifferentiated 
and immature cells which will later take the place of the older 
ones as they are cast at intervals. 
8. The tracheal end cells absorb fatty products from the lumen 
of the crop, and the peritracheal cells absorb them from the 
blood. The tracheae themselves never contain fat normally. 
The presence of fat and other substances in the lumina is due to 
imperfect methods of preparation. 
9. Certain tracheae of practically all animals contain a sticky 
substance whose origin is uncertain. Leucocytes are often 
present in this substance. 
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