1885.] 
The Lesson of the Unnucleated Cell. 251 
or its equivalent.*; ^That sexual reproduction extends to the 
lowest animated being, although differently manifested in 
lower forms. This is not the general view. Botanists trace 
the evolution of sex within the vegetable kingdom, and 
zoologists less definitely within the animal kingdom : hence 
sex, the most fundamental and characteristic phenomenon of 
life, has arisen twice. It is more reasonable to suppose the 
sexual function exists in the protobionts, neither animal nor 
vegetable, and produces a body homologous with an impreg- 
nated ovum, and that out of this common commencement 
both the animal and vegetable sex has been evolved. The 
essential property of the sexually produced ovum is its power of 
repeated division, producing a succession of cell generations 
which together with the original body ( ovum J constitute the 
cycle (italics mine), even among the Protozoa of the Proto- 
phytes.f That all cycles of cells are self-limited (i.e., 
causes of natural death), our knowledge of which is solely 
derived from the higher animals. 
My experiments show that the growth, at least of the 
higher animals, gradually diminishes from the birth onwards 
— i.e., that the cells of a cycle continuously lose their power 
of division, so that the intervals between two successive 
divisions gradually increases, involving the ultimate termi- 
nation of the cycle, the losses going on, not until the cells 
can no longer divide, but until they exhaust themselves ; the 
series of changes is senescence, a continuous process covering 
the whole period of a cycle of cells. The question then 
arises whether the same phenomenon occurs with unicellular 
organisms. In the divisions of the Paramecium it is found, 
■ * Haeckel (“ Evolution of Man,” p. u i62, vol. i.) says “ All different kinds 
of cells originally proceeded by differentiation or specialisation from the simple 
egg cell, and from the homogenous descendants of that egg cell.” “ Schleiden 
and Schwann were the first to furnish experiential proofs that all organisms 
are either simple cells or accumulations (syntheses) of such cells” (‘‘History 
of Creation,” vol. i., p. 98). “ Every young ovum has the character of a 
simple cell formed from a mass of naked protoplasm ” (“ Embryology,” 
Balfour, vol. 1, p. 14). “ in its young condition is obviously nothing but a 
simple cell, and so remains until maturity” ( lb ., p. 16). “This is disputed 
by many biologists who ‘ hold the ovum to be a compound structure’ ” ( lb ., 
P- I 5) < 
t (Haeckel’s “Creation,” vol. ii. , p. 47.) — Protista cannot be assigned 
either to the pedigree of the vegetable or that of the animal kingdom. “ They 
show in their external form, in their inner structure, and in all their vital phe- 
nomena, such a remarkable mixture of animal and vegetable properties ” that 
they cannot be assigned to either. “ Many of these doubtful primary crea- 
tures botanists defined as animals, and zoologists as plants,” and so the oppo- 
site. “ All more recent investigations on the lowest organisms have completely 
effaced, or at the least destroyed, the sharp boundary between the animal and 
vegetable kingdoms ” (p. 48). At p. 49 the distinflive kingdom of the Protista 
is defined. 
