218 
THEORIES OE HEREDITY. 
Nov., 1889. 
The fact that each germ-cell, placed under appropriate 
conditions, will develop somatic cells like those of the 
parent, is explained by the supposition that all the latter 
cells give off gemmules, which are stored up in the germ- 
cells. The gemmules are represented in Diagram I. by the 
small circles marked with the small letters h to u. The 
gemmules are seen to be traversing the space which separates 
them from the germ-cells, and also stored up in the latter. 
The space between the circle of somatic cells and the 
central germ-cells in the diagram is left for the sake of 
clearness : of course there is nothing corresponding to it in 
the body. The germ-cells are nevertheless localised, and the 
distance which the gemmules would be compelled to travel in 
order that, e.g., the change in a brain-cell may be registered 
in a germ-cell, would be far greater than that represented in 
Diagram I. 
With this hypothesis every somatic cell is a germ-cell, 
while the germ-cells proper are merely the meeting place for 
the germs of somatic cells. Because every part of the body is 
thus supposed to reproduce itself, Darwin called his hypo¬ 
thesis Pangenesis. Each germ-cell is supposed to be, as it 
were, an extract of the whole body; a microcosm, in which 
every cell that takes part in the composition of the organism 
is represented. 
The. first difficulty which this hypothesis encounters is 
the almost infinite complexity of a germ-cell which contains 
a material particle, a representative or gemmule, from every 
somatic cell of one of the higher animals. The countless 
number of cells in the human body may be imagined from 
the fact that it would require over ten million red blood 
corpuscles, lying flat, one deep, to cover an area one inch 
square. And yet every single blood corpuscle, although not 
exactly a cell itself, is the product of a single cell. 
But this is not all; for we must also suppose that each of 
the cells of every stage of development is also represented in 
each germ-cell, and is the material cause of the reappearance 
of such stages when the germ-cell itself undergoes development. 
Nor is this all; for we are also compelled to believe that 
gemmules from the cells of large numbers of generations of 
ancestors are present in many germ-cells, accounting for the 
facts of atavism or “ throwing back.” When an animal 
“ throws back ” to some remote ancestor, the gemmules must 
have been handed down in a dormant condition through all 
intermediate generations. 
There are also practical difficulties in the way of the 
acceptance of Darwin’s hypothesis. If it were true, we should 
