THE CELL AND PROTOPLASM. 



73 



It was soon evident 



garded the other parts of the cell as of import- 

 ance. 



This conception, however, was quite tempo- 

 rary. It was much as if our hypothetical supra- 

 mundane observer looked upon the clothes of 

 his newly discovered human being as forming the 

 essential part of his nature. T ^ - 

 that this position could not 

 be maintained. It was 

 found that many bits of 

 living matter were entirely 

 destitute of cell wall. This 

 is especially true of animal 

 cells. While among plants 

 the cell wall is almost al- 

 ways well developed, it is 

 very common for animal 

 cells to be entirely lacking 

 in this external covering 

 as, for example, the white 

 blood-cells. Fig. 22 shows an 

 amoeba, a cell with very ac- 

 tive powers of motion and 

 assimilation, but with no 

 cell wall. Moreover, young 

 cells are always moreactive 

 than older ones, and they 

 commonly possess either 

 no cell wall or a very slight 

 one, this being deposited 

 as the cell becomes older and remaining long 

 after it is dead. Such facts soon disproved the 

 notion that the cell wall is a vital part of the cell, 

 and a new conception took its place which was to 

 have a more profound influence upon the study 

 of living things than any discovery hitherto 



m$mm<^ 



<<m$yr-- J 



*m/, 



.*-sf 1 1 



FIG. 22. An amoeba. A sin- 

 gle cell without cell wall. 

 n is the nucleus ; _/", a bit 

 of food which the cell has 

 absorbed. 



