44 GENERAL ZOOLOGY 



rows (Fig. 12). Likening these to the rooms in monasteries 

 Hooke gave them the name, cells. 



Later workers found cells in various plants and animals, 

 but they were merely looked upon as. interesting features 

 without particular importance. It was in 1833 that 

 another Englishman, Brown, discovered the nucleus, which 

 he described in certain plant cells. Not until 1838-1839 

 was the Schleiden-Schwann Cell Theory brought before the 

 scientific world by the two Germans whose name it bears. 

 In 1838 Schleiden asserted that all plants were made up 

 of cells; and in the next year, Schwann published a great 

 work which convinced everyone that not only plants but 

 animals as well were made up wholly of cells. 



No generalization, unless it be Darwin's " Origin of 

 Species, " has so stimulated biological investigation as the 

 cell theory. A new field was opened up which led to the 

 discovery of the method of the fertilization of eggs and other 

 fundamental matters which had not been previously 

 understood. 



It is unfortunate that the name "cell" was given to pro- 

 toplasmic units. One thinks of a cell as a box or hollow 

 thing. A biological cell, however, is cytoplasm and nucleus. 

 The cell-wall, which originally gave the name, is not a con- 

 stant feature, and in animal cells is more often absent than 

 present. 



