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SOME NOTES ON DIGESTION AND THE CELL STRUC- 
TURE OF THE DIGESTIVE EPITHELIUM 
IN INSECTS. (Plate XLI.) 
By E. J. NEwcomer, Stanford University, California. 
The ultimate structure of the cell, as it is understood in 
animal and plant life, is still largely a matter of theory among 
biologists. A cell appears as a tangible unit, apparently 
definitely set off from its fellows, and easily discernible with 
low powers. Yet its exact constitution and its exact relation- 
ship to the surrounding cells are not known. So far, scientists 
have had to imagine how such a structure, with the known 
functions that it possesses, ought to be composed; it has not yet 
been possible by actual observation to prove this composition. . 
Many things enter into this difficulty. Cells are very small 
structures and cannot be viewed with the naked eye. The 
interposition of a lens or lenses increases the possibility of error. 
Especially when using lenses of high power is there very little 
certainty about what is seen. The difficulty of seeing cells in 
their natural state is great, and resort is had to material that is 
killed and fixed. Here, even though one is sure of what he 
sees, he cannot be certain that it is the same as in life. Again, 
the diversity of cells in different organs and organisms is il- 
limitable, and it is known that even in the same cell the cyto- 
plasm can change its appearance: so that the problem of getting 
at the typical and final structure and the behavior of this cyto- 
plasm is by no means an easy one. 
It was with the hope of possibly finding out some facts that 
might have a bearing on the general problem of animal cell 
structure and behavior that I have undertaken a special study 
of the make-up and behavior of the digestive epithelium in 
insects, which study permits me to offer the statements and 
illustrations embodied in the present paper. The digestive 
epithelium of insects is notable as a cell layer in which rapid 
changes occur, with a continual production and destruction 
of cells. Hence it may be presumed to be a tissue in which 
cell origin and growth may be advantageously studied. 
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