DIGESTION OF FOOD. 297 
discrimination; and it is also possible that some sort of digest- 
ive fluid may be secreted from the part of the body with which 
the food-particles come in contact. It has been shown, too, 
that there are differences in the digestive capacity of closely 
allied forms among Infusorians. 
The ciliated Infusorians have a permanent mouth, which 
may also serve as an anus; or, there may be an anus, though 
usually less distinct from the rest of the body than the mouth. 
Among the Celenterates inira-cellular digestion is found. 
Certain cells of the endoderm (as in Hydra) take up food-parti- 
Fie. 255.—A jelly-fish, the Medusa Limnocodium (after Allman). Note the long proboscis 
(mouth) leading up to the stomach, from which radiate the gastro-vascular canals. A 
portion of the bell has been removed, showing the generative arranged around the 
. digestive organs. Most of the.tentacles are turned up. 
cles Ameeba-like, digest them, and thus provide material for 
other cells as well as themselves, in a form suitable for assimi- 
lation. This is a beginning of that differentiation of function 
