The Facts of Sex in Relation to Metabolism. 263 
bodies, together with the great size of the egg, has rendered 
it passive. The recurrence of the minute flagellate condition 
as ‘male’ has rendered the male element active.” 
“The male and female elements became reciprocally attrac- 
tive to one another (sometimes through the production of 
certain chemical substances in the vicinity, Pfeffer), and in 
that their idioplasm is less different from one another than 
that of other cells there is no bar to their fusion, which is 
also favoured by the fact that in the male cell, with its pre- 
ponderant chromatin, there is now an attraction or need 
developed for more cytoplasm similar to its own diminished 
quantity, while conversely there is a similar need or attraction 
developed in the egg for additional chromatin, in consequence 
of its preponderating cytoplasm. This leads to the highest 
form of cumulative integration, through direct fusion of the 
male and female elements, or what I shall call reciprocal 
integration without loss of molecular identity, or, as it is 
commonly called, to ‘ fertilisation.’ ‘Fertilisation’ is a recip- 
rocal restoration of the equilibrium between the chromatin 
or nucleoplasm, and the cytoplasm of both ovum and sperma- 
tozoon ; this takes place, not with accompanying molecular 
disintegration, but by the actual fusion of both elements 
without the sacrifice of the molecular identity of either. 
Mutual digestion is not possible, for both elements are 
already composed of similar molecules. This molecular 
similarity constitutes the means through which the hereditary 
traits and tendencies of the male and female are transmitted.” 
The development which follows fertilisation “is rendered 
directly possible only in virtue of the fact that there is a 
large cytoplasmic field in which nuclear motion and growth 
can take place in three dimensions temporarily without 
access of nutriment, while the resulting segmentations 
are coherent, and tend to take place in such order and 
relation as to produce a being similar to the parent.” 
“The most important result of the evolution of sexuality 
is the physiological process of nuclear substitution through 
reciprocal integration or ‘fertilisation, thus blending and 
superposing matter and energy from two sources, and causing 
the latter to be potentially stored. Hunger has brought 
