38 THE SMALLEST LIVING THINGS 



structive, characteristic of life, which we group under the 

 comprehensive term metabolism. 



It thus happens that the protoplasmic organization of a liv- 

 ing form is constantly changing in its active state with or without 

 the formation of structures not previously present. If new struc- 

 tures are thus formed, such activity leads to successive states of 

 complexity of organization which we include under the terms 

 development and differentiation. With differentiation or devel- 

 opment of new parts, a division of labor is set up among these 

 parts; hence at each stage of its growth the organism has a 

 slightly different organization accompanied by slightly different 

 functions of its parts. Finally, when the possibility of further 

 structural change is exhausted the individual is said to be fully 

 developed. 



Derived Organization 



We can distinguish, therefore, between the fundamental or 

 initial organization of the protoplasm of an individual and the 

 derived organization resulting from development. Encysted uni- 

 cellular organisms and the fertilized egg-cells of all animals 

 and plants represent protoplasm having the fundamental organi- 

 zation of the species in each case, no two of them being exactly 

 alike. We must not consider the protoplasm of the adult to be 

 identical with the protoplasm of its one-celled stage for it decid- 

 edly is not. Similarly, the millions of species of animals and 

 plants represent protoplasm with its particular ultimate derived 

 organization in each case, and no two of them are identical. 



The higher many-celled plants, like animals, all start as single- 

 celled fertilized eggs. The protoplasm in one such cell has the 

 fundamental organization to develop into an adult, in which the 

 protoplasm of the various cells, through specilization and differ- 

 entiation, changes in organization — thus becoming the derived 

 organization. In fact with the various delicate tests at the com- 

 mand of biologists, minute differences between individuals of the 

 same species can be demonstrated. 



The classification of animals and of plants, as given today, 

 is based upon studies and comparisons of the final or derived 

 organizations of the species. With increased knowledge it is 

 hoped and highly probable that more attention will be given to 



