INDEPENDENT CELLS, ETC. 91 
brilliant confirmation of the correctness of the view, that the 
fibres of the crystalline lens are really cells, however much 
they may deviate from the fundamental type of the cellular 
form. 
There is no longer, therefore, any more difficulty in explain- 
ing the process of nutrition in the lens, than there is that of 
plants. The cells grow by their own independent force, and 
blood-vessels are unnecessary, as the nutrient fluid can be con- 
ducted from one cell into another. A morbid change of the 
cell-yitality, rendering the cell-contents opaque, is also possible. 
The structures included in this class, notwithstanding the 
strong general resemblance which they bear to each other, have 
furnished us with far more varied modifications of the cellular 
form than the previous class exhibited ; mdeed, these so-called 
unorganized tissues have already prefigured the type of all the 
changes by which the organized tissues are developed from sim- 
ple cells. Here, also, the fundamental form of the cells is that 
of a sphere, which, in consequence of their close contact, 
passes over, from mechanical causes, into a polyhedral figure. 
Two different modifications of this fundamental form occur, 
which cannot be explained mechanically ; they are the flatten- 
ing of the cells on two opposite sides to form tables, and their 
elongation in two directions into cylinders or fibres. We have 
already seen an instance of flattening of the cells in the blood- 
corpuscles of the previous class. It is not only more strongly 
marked here in the tabular epithelium, where the cell-cavity is 
quite obliterated, but a modification even of this form is pre- 
sented to us in the elongation of these tables on two sides into 
flat stripes, as seen in the epithelium of the internal coat of veins 
for example, and still more distinctly in the cortical substance 
of the shaft of the raven’s feather. The epithelium of many of 
the mucous membranes, that of the intestine for instance, which 
Henle describes as consisting of little palisade-like cylinders 
placed close to one another, furnishes us with a rudimentary 
form of the elongation of cells into cylinders and fibres. 
Sometimes these little cylinders become acuminated at their 
lower extremity, or they may diminish throughout their entire 
length from above downwards, and thus become small cones. 
