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, hut 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 /atent 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: “ Briicke’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 Briicke’s method of 
*C,O. Whitman. The Inadequacy of the Cell Theory of De- 
velopment. Biological Lectures, 1893. 
