INDEPENDENT CELLS, ETC. 91 



brilliant confirmation of the correctness of the view, that the 

 fibres of the crystalline lens arc 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-vitality, 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 ; indeed, 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. 



