158 FOOT-NOTES TO EVOLUTION. 
no attempt has been made even to indicate the many 
variations in detail which occur in different animals and 
plants. These are numerous, but do not affect the gen- 
eral plan nor the fundamental goal, which is always and 
invariably the same—viz., the equal, longitudinal divi- 
sion of the chromosomes or the chromatin band of the 
parent nucleus between the two daughter nuclei. 
Another method of cell division, formerly taken to 
be the universal one, has since been shown to occur 
solely as a stage in the degenerative 
changes of cells which are upon the 
downward road to disintegration, and in 
which the power of multiplication is about at an end. 
In this, the “direct ” or “amitotic”” form of cell divi- 
sion, the cell nucleus is simply constricted into two por- 
tions preceding the constriction of the cytoplasm. This 
method stands in marked contrast to the elaborate 
mechanism which insures the exact distribution of the 
nuclear substance in the karyokinetic or indirect method. 
‘* Direct ” 
division. 
Every multicellular organism arises by a process of 
division from a single cell, the fertilized germ or egg 
cell, which in turn has been cut off from the cells of a 
pre-existing individual. Out of the group of cells which 
result from the continued division of the germ cell and 
its descendants are differentiated the various tissues and 
organs of the body through which the vital functions are 
carried on. Those tissues and organs which perform 
functions pertaining directly to the existence of the indi- 
vidual have been termed “ somatic,” and 
their constituent cells the “somatic ” or 
body cells, in contradistinction to the 
reproductive tissues or cells whose func- 
tion concerns the continuance of the species. In some 
forms these two groups of cells, the somatic and the 
‘“Somatic ” and 
reproductive 
tissues. 
