104 FOOT-NOTES TO EVOLUTION. 



differentiation, repetition, and variation. These func- 

 tions are so co-ordinated that there can be no question 

 that the ultra-microscopical structure is an organization, 

 with part coadapted to part. The organization of the 

 cell, therefore, does not stop with what the microscope 

 reveals, but must be supposed to extend to the small- 

 est ultimate particles of living matter which manifest 

 specific functions. These are the vital units so gener- 

 ally postulated, the " smallest parts " of living matter, 

 as they were called by Briicke, who first demonstrated 

 that they must exist ; the " physiological units " of 

 Spencer, the " gemmules " of Darwin, the " micella 

 groups " of Nageli, the " pangenes " of De Vries, the 

 " plasomes " of Wiesner, the " idioblasts " of Hertwig, 

 the " biophores " of Weismann. Such ultimate units 

 have been found absolutely necessary to explain those 

 most fundamental of all vital phenomena, assimilation 

 and growth, while many other phenomena, especially 

 particulate inheritance, the independent variability of parts, 

 and the hereditary transmission of latent and patent char- 

 acters, can at present only be explained by referring them 

 to ultra-microscopical units of structure. To deny that 

 there are such units does not simplify the problem, as 

 some seem to suppose, but renders it impossible of ap- 

 proach. A corpuscular hypothesis of life, like that of 

 light, may be only a temporary makeshift, but it is 

 better than nothing. 



Whitman * well says : " Brucke's great merit consists 

 in this, that he taught us the necessity of assuming 

 structure as the basis of vital phenomena, in spite of 

 the negative testimony of our imperfect microscopes. 

 That function presupposes structure is now an accepted 

 axiom, and we need only extend Brucke's method of 



* C. O. Whitman. The Inadequacy of the Cell Theory of De- 

 velopment. Biological Lectures, 1893. 



