106 
THE ORGANIC CELL 
rubber bands are attached to two small rings, which simulate 
the centrosomes, and these two small rings are fastened 
together. Should the fastening of the centrosomes be severed, 
they are at once separated forcibly, until they reach a new 
position of equilibrium, when it will be seen that the rays are 
arranged in two asters exactly as occurs in the cell. (See 
diagram.) To whatever cause Mitosis is due, the result is 
Heidenhain’s Model of Mitosis. 
Dotted lines show position of the rays on severing the connection between 
the small rings (Centrosomes). 
that there is an equal division of the chromatin of the mother- 
cell, and an equal distribution of the same to the nuclei of the 
daughter cells. 
Origin of the Germ-Cells 
The germ-cells arise from what are called primordial germ- 
cells, which can easily be differentiated from the 4 somatic-’ 
or body-cells at a very early stage in development. It is 
interesting to note that at this early stage the cells are exactly 
alike for the two sexes. With very few exceptions it would 
appear that the primordial germ-cells are indifferent as regards 
sex, and what determines their final development into sper- 
matozoon or ovum merely depends on external causes. The 
