ORIGIN AND DEVELOPMENT 41 



which may be the beginning of psychical 

 states. These activities are all more or less 

 controlled and regulated by the nucleus. If a 

 cell be divided artificially so that one portion of 

 the protoplasm contains the nucleus, while 

 the other has no nucleus, the latter portion 

 soon dies, but the other portion remains alive, 

 and may grow and perform its functions as 

 before. Cells apparently secrete certain mat- 

 ters which collect outside the cells, forming 

 intercellular matter, so as to form a tissue, 

 such as cartilage or gristle ; in other cases, 

 this intercellular matter may form a fibrous 

 structure impregnated with earthy matter, 

 as in bone ; or the cells themselves may 

 be modified so as to form more complicated 

 tissues, such as muscle ; or the cells may cover 

 such surfaces as the skin, or, as secreting cells, 

 line the pouches of glands. All tissues are 

 primarily formed of cells, and the activities of 

 these tissues are the sum of the activities of 

 the cells. All cells arise from cells. Omnis 

 cellula e cellula. 



15. The formation of the body is the result 

 of the union of two primitive cells, an ovum, 



