34 



AN INTRODUCTION TO ZOOLOGY 



3. THE CELL THEORY 



Owing to the important place that cells have occupied in the 

 development of our fundamental biological ideas, it seems proper 

 to consider briefly the origin and growth of the cell theory. Cells 

 were first described by Hooke, an Englishman, in 1665. He 

 published a figure showing the minute structure of cork (Fig. 8). 



FIG. 8. Facsimile of a figure by Hooke representing cells of cork. (From 

 Farmer in Lankester's Zoology.) 



The regular arrangement of the compartments in this tissue 

 reminded him of the cells of the monks in a monastery. For this 

 reason they were given the name " cell," which they bear to this 

 day. Several later investigators observed cellular structures in 

 the tissues of plants and animals without realizing their impor- 

 tance. 



In 1833, Brown, an English botanist, described the nucleus as a 

 constant element of the cell. It was not, however, until the time 

 of Schleiden, a botanist, and Schwann, a zoologist, that the cell 

 theory was established. Schleiden, in 1838, published a small 

 pamphlet in which he advanced the idea that all plants are com- 

 posed of cells. A year later his colleague, Schwann. brought 

 forth a more pretentious work in which he made the same generali- 



