VARIOUS THEORIES OF THE ORGANISM ii 



ing and retesting the supposed facts, adopting and discarding hy- 

 potheses, will continue to be the basis of our advance in knowledge. 



COEPUSCULAR THEORIES 



During the latter half of the nineteenth century, biology, and 

 particularly zoology, was to a large extent dominated by the cor- 

 puscular theories of heredity and organic constitution. These 

 theories postulate some sort of a material particle or corpuscle 

 consisting of more than one molecule as the ultimate basis of life. 

 The organism is built up in one way or another from a nmnber, 

 often very large, of such corpuscles, and the corpuscles are the 

 "bearers of heredity." The gemmules of Darwin, the pangenes 

 of DeVries, the physiological units of Spencer, the biophores and 

 determinants of Weismann, and various other hypothetical units 

 have played an important part in biological thought during almost 

 half a century. 



This group of theories may be called the morphological or 

 static group. They all postulate a complex morphological struc- 

 ture as the basis of inheritance and development, and they are all 

 attempts to answer the question as to how the characteristics of 

 the species are maintained from one generation to another. Among 

 them the theory of Weismaim has been more completely developed 

 and has influenced biological thought and investigation to a greater 

 extent than any other. 



All of these theories possess certain characteristic features in 

 common. The ultimate elements, whatever they may be called, 

 are not aUke, but each possesses certain definite characteristics and 

 plays a definite part in the development of the individual. The 

 organism is in short essentially a colony of such units. According 

 to Weismann, DeVries, and others, the ultimate units are each 

 capable of growth, and each reproduces its own kind. 



It is scarcely necessary to call attention to the fact that these 

 theories do not help us in any way to solve any of the fundamental 

 problems of biology; they merely serve to place these problems 

 beyond the reach of scientific investigation. The hypothetical 

 units are themselves organisms with all the essential characteristics 

 of the organisms that we know; they possess a definite constitution, 



