74 
Death and Individuality. 
[February, 
cells are homologous, all cycles are homologous ; hut individuals 
are not always homologous, since an individual may be either 
the whole or any fractional part of a cycle. This question 
I have discussed a little more fully in my article on “Growth 
as a Function of Cells ” (“ Proc. Boston. Soc. Nat. Hist.,” 
xx., igo — 201). Manifestly the death of the single cell is 
not necessarily identical with the termination of a cycle. 
Now, when a man, he being a cycle of cells, has lost the 
ability to continue the cycle, he (or it) dies. Further, it is 
inherent in his constitution to lose that ability gradually ; 
hence, when it is completely lost from internal causes, he 
dies, as we say, from old age. It is to this ending-off of the 
cycle, from causes resident in itself, I wish to restrict the 
term “ natural death.” 
We have now two questions to pose : i. Do all organisms 
belong to cell-cycles ? 2. If so, are all cycles self-limited ? 
In common language the second question would be, Is death 
always the natural and inevitable accompaniment of life ? — 
an inquiry which may appear singular, but is none the less 
perfectly sensible and legitimate. Weismann has answered 
it with a negative. 
1. I maintain the hypothesis that all organisms do deve- 
lope in cycles, and only in cycles ; which involves the 
assumption that all living species begin their life-history 
with an impregnated ovum or its equivalent. We come, 
therefore, at once to the question of how far sexual repro- 
duction extends downward in the scale of life. I deem it 
very probable that it extends to the lowest animated being, 
even though it be quite differently manifested in the lower 
forms from what we observe in ordinary bi-sexual reproduc- 
tion. This view is opposed to the opinions generally held; 
for botanists trace the evolution of sex within the vegetable 
kingdom, and zoologists trace it, though less definitely, 
within the animal kingdom. We are thus forced to assume 
that sex, one of the most fundamental and characteristic 
ohenomena of life, has arisen twice. This is to the last 
degree improbable. Such a coincidence would be the most 
extraordinary result of chance within human experience. It 
is more reasonable to suppose that, though we do not yet 
recognise it, the sexual function exists in the protobionts, 
which are neither animal nor vegetable, and that they also 
produce a body homologous with an impregnated ovum ; and 
to suppose, further, that out of this common commencement 
both animal and vegetable sex have been evolved. The 
essential property of the sexually produced ovum is its power 
of repeated division, producing a succession of cell-genera- 
tions, which; together with the original body {ovum), con- 
