122 FOOT-NOTES TO EVOLUTION. 
The germ cell, male or female—and the two are alike 
in all characters essential to this discussion—is one of 
the vital units or body cells set apart for a special pur- 
pose. It is not essentially different from other cells, 
either in structure or in.origin. But in its growth it is 
capable of repeating the whole organism from which it 
came, “ with the precision of a work of art.” 
The germ cell is made up of protoplasm, a jelly-like 
substance, less simple than it appears, not a “ sub- 
stance” at all, in fact, but a structure 
as complex as any in Nature. In con- 
nection with this structure all known phenomena of life 
are shown. Inside the germ cell, or in any other cell, is 
a smaller cellule called the nucleus. In connection 
with the nucleus appear most of the phenomena of 
hereditary transmission. Its structure in the higher 
animals is a complicated arrangement of loops and 
bands, the material of which these are made being 
called chromatin. This name, chromatin, is given be- 
cause its substance takes a deeper 
stain or colour (chroma in Greek) than 
ordinary protoplasm or other cell materials. In the 
chromatin are the determinants of heredity, and these 
preside in some way over all movements and all changes 
of the protoplasm. In the fertilized egg, the mixed 
chromatin * of the two cells which have been fused into 
one may be said to contain the architect’s plan by which 
the coming animal is to be built up. In the mixed 
chromatin of the cell which is to grow and to divide, to 
separate and integrate, till it forms Richard Roe, the 
potentialities of Richard Roe all lie in some way hidden. 
How this is we can not tell. We know that the struc- 
ture of a single cell is a highly complex matter, more 
Protoplasm. 
Chromatin. 
* For a discussion of this and other views more or less hy- 
pothetical, see the essay on the Physical Basis of Heredity. 
