30 MAN, — THE ANIMAL 



of Students was centered on the larger organisms. 

 It was not until men saw that they could not ex- 

 plain the work of an animal in the terms of its 

 organs that they began to delve deeper. 



As soon as scientists recognized that all life was 

 built upon a plan and that definite units, the cells, 

 constituted the structural frame-work, a long step 

 in advance was made. Here was furnished a 

 starting point for all subsequent study. 



fe^'"; -i^^! ■ V:f iil^i^^i fe nucleus 



'^i^':'}:'':v^'-^?:^r^i0'^ cytoplasm 



membrane 



Figure 4. Partly diagrammatic sketch of a star-fish egg. In 

 shape and in relation of the various parts, this represents a 

 typical cell. 



From 1850 on to the present day, the progress 

 of our information on this aspect of life has been 

 rapid. Since this date we have come to realize 

 that the term cell, as originally applied, was a mis- 

 nomer. The vital part of the cell is what occurs 

 within the "little boxes." To this living sub- 

 stance is given the name protoplasm. It nearly 

 always consists of two easily recognized parts: 



