THE CELL IN GENERAL. 2Q 



as for convenience of study, and not as expressing 

 any absolute and fully established truth. 



Cells are variously classified according to their 

 nature and relations to adjacent parts : thus we have 

 epithelial cells, which cover the skin and mucous 

 membranes, and occur in certain parts of the gland- 

 ular organs ; connective-tissue cells, which lie scat- 

 tered throughout the substance of the structures, 

 presently to be described as connective tissue, and 

 in certain parts undergoing modification of form 

 and relation to neighboring parts, and called endo- 

 thelial cells ; gland cells are those which, possessing 

 peculiar functional or morphological characters, 

 make up the parenchyma of certain glands and or- 

 gans. The special characters of these classes of 

 cells, together with those of other classes not here 

 mentioned, will be considered in our systematic 

 study of the tissues. 



TECHNIQUE. 



Many of the above-described general characters of 

 cells may be seen by studying the epithelial cells of the 

 bladder, the pigmented cells of the retina, and the living 

 ciliated cells from the mucous membrane of the frog's 

 mouth. 



Epithelial Cells from the Rabbit's Bladder. The blad- 

 der is removed from a recently killed rabbit, laid open, 

 care being taken not to touch the surface, and pinned 

 out on a piece of sheet cork, mucous-membrane side up, 

 and then floated, specimen side downward, on Miiller's 



