THE ORGANIC CELL 
109 
ends of the original chromosomes being cast out into the 
cytoplasm. The next division repeats the same process — one 
cell retaining two complete chromosomes, the other having 
the reduced amount. This occurs for five successive divisions 
and then stops. From the one cell possessing the two complete 
chromosomes the reproductive tissues develop ; all the others 
with reduced chromatin form the somatic or body-cells. Thus 
‘ the original nuclear constitution of the fertilised egg is trans- 
mitted, as if by law of primogeniture, only to one daughter 
cell, and by this again to one, and so on ; while in the other 
daughter cells the chromatin in part degenerates, in part is 
transformed, so that all of the descendants of these side branches 
receive small reduced nuclei ’ (Boveri). It is evident from 
the above that there is a visible structural differentiation of 
the nuclei of the reproductive cells, which separates them off 
sharply from the somatic cells in the case of Ascaris. 
Further on convincing evidence will be brought to prove 
that the nucleus — i.e. the chromatin — is the carrier of here- 
ditary influences from one generation to another, also that the 
development and functional activity of every cell is dependent 
on the chromatin of its nucleus. 
In the higher forms of plants and animals there is a sharp 
line of differentiation between those cells which go to form 
the body tissues (somatic) and those which form the repro- 
ductive- or germ-cells. It must be remembered, however, that 
in many of the lower forms no such differentiation exists, and a 
series of forms may be taken which will clearly illustrate 
the different grades of evolutionary steps in what must have 
been a very gradual specialisation of function. A rapid survey 
of the phenomena of reproduction in the Protozoa will greatly 
assist us in gaining a clear conception of the more intricate 
processes peculiar to the Metazoa. These lowly forms consist 
of a single cell, and within the limits of these microscopic 
structures are carried on all the phenomena of growth, nutrition, 
assimilation, movement, reproduction, &c. In the Metazoa, or 
many-celled forms, there is a physiological division of labour, 
certain groups of cells carrying certain functions, other groups 
other functions. In the single-celled protozoan, the process 
of reproduction consists simply of a division of the nucleus 
VOL. IV.— No. 8. 
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