CHAPTER II 



THE CELL AND PROTOPLASM 



7. Cells. If we examine very carefully the different parts 

 of a squirrel under the high powers of the microscope 

 we find that they are composed of a multitude of small 

 structures which bear the same relations to the various 

 organs that bricks or stones do to a wall ; and if the inves- 

 tigation were continued it would be found that every or- 

 ganism is composed of one or more of these lesser elements 

 which bear the name of cells. In size they vary exceedingly, 

 and their shapes are most diverse, but, despite these differ- 

 ences, it will be seen that all exhibit a certain general re- 

 semblance one to the other. 



8. Shape of cells. In many of the simpler organisms 

 the component cells are jelly-like masses of a more or less 

 spherical form, but as we ascend the scale of life the condi- 

 tion of affairs becomes much more complex. In the squir- 

 rel, for example, we have already noted the presence of 

 various organs for carrying on different functions, such as 

 those of digestion, circulation, and respiration ; and, further, 

 the cells composing these various parts have been modified 

 in accordance with the duties they have to perform. In 

 the muscles the cells are long and slender (Fig. 4, D) ; 

 those forming the nerves and conveying sensations to and 

 from all parts of the body, like an extensive telegraph sys- 

 tem, are excessively delicate and thread-like ; in the skin, 

 and lining many cavities of the body, where the cells are 

 united into extensive sheets, they range in shape from high 

 and columnar to flat and scale-like forms (Fig. 4, E, F, G). 



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