1887] The Significance of Sex. 29 
tissues for the good of the whole. Even some of the generative 
cells had to serve their more fortunate brethren by giving origin 
to the accessory parts of the generative tissues that a few cells 
might be successfully prepared to perpetuate the species. All 
the tissues, including the generative, are based on a stroma of 
undifferentiated, “ embryonic” cells, capable of dividing as they 
have in the past, and differentiating into their proper tissue when 
they have the chance, as in regeneration of lost parts. These cells 
are all the descendants of the original egg, and homodynamous 
with it and each other as if they were separate amcebe. But 
after a certain number of divisions they lose the power of di- 
viding further without fertilization and then they differentiate. 
Only the cells differentiated in the direction fitting them for 
fecundation ever get a chance to be fertilized. ae 
Possibly this want of fertilization, more and more increasingly 
felt by the embryonic cells as they continue their final divisions, 
may explain senescence ; but so long as we do not understand the | 
nature of senescence in the Protozoa we cannot understand it in ~ 
the Metazoa. 
Growth is due in the Metazoa to the double process of cell- 
multiplication and cell-growth. May we not say that cell-growth 
is also partly a result of a reproductive process, and that the cell 
is a living unit by virtue of being organized? There can now no 
longer be a doubt of this. We can no longer speak of animals 
as “evolved from a homogeneous bit of jelly.” Cells and the 
Protozoa and Protophyta in general, may be considered as illus- 
trating as wide a diversity of differentiation and gradation of 
organization as we see exemplified in the larger units or in the 
social units (societies and states). We cannot conceive of life 
without organization. The homogeneous cannot be called living. 
The cell-wall at first was thought of importance, but soon it 
was seen that this was a secreted product, and so its gelatinous 
contents, called protoplasm, next became the definition of a cell. 
But most cells had one or more “nuclei” in them, and this was 
conceived as a differentiated product of the protoplasm. Con- 
tinued study of the zucleus raised its importance more and more, 
until at present some eminent cytologists are ready to make it 
the essential part, and the surrounding plasma almost as secondary 
as the cell-wall itself. Believing this to be the true view, we are 
ready to consider,— 
