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 

 Protoplasm. , . ... 



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 

 4>ands, the material of which these are made being 

 called chromatin. This name, chromatin, is given be- 

 cause its substance takes a deeper 

 Chromatin. . , , , _ . . , 



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 



* For a discussion of this and other views more or less hy- 

 pothetical, see the essay on the Physical Basis of Heredity. 



