266 Proceedings of the Royal Physical Socrety. 
incapacity that would otherwise require a long series of 
slowly repeated divisions.” 
According to Hartog, fertilisation is a process of rejuven- 
escence or constitutional invigoration. Cytoplasm and 
nucleus form, as it were, a firm, which in course of time— 
especially after repeated rapid divisions—ceases to be in a 
healthy state. The prolonged association of cell and nucleus 
has evil effects. In ciliate Infusorians which divide repeat- 
edly and are unable to conjugate, Maupas has shown that 
senescence sets in; so is it with other gametes, and fertilisa- 
tion is one of the remedies for the disease. In fertilisation 
a new cell-nucleus firm is constituted. 
In the absolutely asexual (agamous) Monadinee, rejuven- 
escence can be secured only by rest. In many apogamous 
and self-fertilising organisms, a change of the mode of life is 
the cure. In higher Monadinez and in the Myxomycetes, 
the migration of nuclei in plasmodium-formation serves the 
same end. In isogamy, plural or binary, there is nuclear 
union (karyogamy) as well as cytoplast-union (plastogamy). 
In most cases karyogamic rejuvenescence has become essential 
to the preservation of the species. 
“Rapidly repeated nuclear fissions, without sufficient 
interval for nutrition and recovery, may lower the vital 
energy or constitution of the cell, and accelerate reproductive 
incapacity; and this may be the physiological import of the 
fissions that so frequently differentiate the gamete, and 
determine its obligatory character.” “The constitutional 
weakness of the later terms of a cycle of fissions is largely 
due to the continuance of the association of nucleus and 
cytoplast unchanged.” 
“From considerations of (a) the known functions of the 
nucleus; (0) its chemical composition; (¢) the effects of 
rest, change of form, or change of habit (polymorphism 
and hetercecism) in effecting rejuvenescence, and often 
replacing karyogamy: it is suggested that the evil effects 
of the prolonged association of cell and nucleus are due (a) 
to the nucleus responding less actively to the stimuli from 
the cytoplasm; (b) its consequently inadequate directive- 
power; (c) to the resulting bad performance of its work 
