10 THE STORY OF THE BACTERIA. 



perfect way, while others have remained in a 

 condition of comparatively low organization. 



Let us look at two examples of these two 

 types of cells from the adult body first at 

 certain muscle cells. These in the very young 

 animal look just like many other cells ; they 

 are individuals, they are alive and their life 

 finds expression, just as the amoeba's does, in 

 certain activities nutrition, growth, function, 

 and reproduction. Presently they become 

 longer than their neighbors, little striations 

 appear along their sides, they grow long and 

 narrow until at last they are little thread-like 

 bodies with a very complicated internal struct- 

 ure, anJ are grouped in bundles to form the 

 muscles as we see them with the naked eye. 

 The peculiarities of structure of these muscle 

 fibres are necessary for the performance of the 

 work which they have specially to do namely, 

 the accomplishment of rapid and powerful 

 movements. Now the capacity of the muscle 

 cells for doing this work has been acquired, if 

 I may say so, at the expense of some of the 

 other capacities which they originally possessed 

 in common with other cells. Thus the power 



