MINUTE STRUCTURE OF THE NERVOUS TISSUES 23 



are only 3^7 inch across their circular faces. If there can 

 be said to be a standard of form for the cell, it is the 

 sphere. But this primitive form is merely the point of 

 departure for the widest variations. The units in con- 

 tractile tissues are always greatly elongated, those of epi- 

 thelia are flattened, cubic, or prismatic, those of connective 

 tissue are irregular and often quite freely branched. The 



Fig. 2. Drawings like the above are almost always made from 

 tissues which have been prepared and colored by special means to 

 make clear, minute features, a represents an ovum or egg-cell, 

 the typical cell may be assumed to tend toward this spheric form; 

 b is a cell from a compact tissue, to show how mutual pressure pro- 

 duces a faceted or polyhedral form; c is a contractile element such 

 as occurs in the walls of the alimentary canal, it illustrates an elon- 

 gated cell; d is an epithelial or lining cell of the order found on the 

 inner surface of blood-vessels; this is an example of extreme fatten- 

 ing; '% from the nervous system, exhibits the possibility of a branch- 

 ing development. 



cells in nervous tissues are most peculiar of all, and must 

 presently be described at some length (Fig. 2). 



When such diversity of form is considered the student is 

 disposed to ask: What have these differing packets of 

 organized substance in common that the same name 

 should be applied to them all? It is hard to say that 

 any single feature is always to be found in them. One 



