Cell-life. 1 47 



and totality, consists only of cells and nothing else. 

 Skin, bone, cartilage, nerve, are very different to 

 the eye and touch; but they are all composed of 

 the self-same thing, cells. The cells, it appears, 

 are the same throughout in their origin and develop- 

 ment, till they become adult and perfect, when they 

 are all found specialized so as to discharge distinct 

 functions. In view of these distinct functions, the 

 anatomical form of the cells has become differenti- 

 ated, some taking one form, others another, cylin- 

 drical, hexagonal, polygonal, conical, pyramidal, len- 

 ticular, according to the place and work before them ; 

 whether it be that of the muscular tissue, cartilag- 

 inous, osseous, fibrous, vascular, or the like. Thus 

 the entire system, in its totality and individual unity, 

 is built up of many cells, and only cells: these go 

 to form all its organs. 



162. Each individual cell is first young and chen 

 old. In the same organism while some cells are 

 only beginning their development, while others are 

 carrying on theirs, another set are in full decrepitude, 

 and a number are being disintegrated as effete. In 

 the young state of cells, to which stage is to be re- 

 ferred also the earliest condition of an embryo, that 

 is, the germ of another complete organism, it is not 

 possible to distinguish the growing, moving matter 

 which is to evolve an oak, from that which is the 

 germ of a vertebrate animal. Nor, in the building 

 up of the same organism, can any difference be dis- 

 cerned between the germinal matter of the lowest, 



