The Facts of Sex in Relation to Metabolism. 265 
Even supposing Ryder’s conclusions to be justified, we 
cannot see that he has done more than add a morphological 
contrast to the physiological contrast between the sexes, as 
already indicated in the “ Evolution of Sex.” 
8. Hartoa’s, THEory.—In 1891, Prof. M. M. Hartog 
published, in the Quarterly Journal of Microscopical Science, 
a very important paper entitled, “Some Problems of Repro- 
duction: A Comparative Study of Gametogeny and Proto- 
plasmic Senescence and Rejuvenescence.” This paper is 
based on the author’s concrete researches, and though it 
seems to us to include an unduly large contingent of new 
terms, its orderly classifications, its trenchant criticisms, and 
its acute suggestions, are all important. 
It has for long been a favourite theory of fertilisation that 
the sperm brought to the ovum something which replaced 
what the ovum had parted with in forming polar bodies. 
Thus, according to Minot, Balfour, and van Beneden, the 
germinal vesicle lost in forming polar bodies some sexual 
substance, which was replaced by the sperm in fertilisa- 
tion; while according to Weismann, all that is lost and 
replaced is a certain quantum of nuclear substance. Now 
Hartog begins by pointing out that this theory, though 
based on facts occurring among numerous Metazoa, has 
been extended by an act of unwarranted faith (not uncom- 
monly illustrated in scientific theories) to all other cases of 
fertilisation. 
A study of the facts has led him to doubt all “ replacement 
theories,” and to come to the following conclusions :—(1) 
“That the most general, but not universal, feature under- 
lying the preparations for fertilisation, is the specialisation 
of gametes by rapidly repeated divisions of a cell—the 
gametogonium ; (2) that the alleged nuclear excretions in 
the Metazoan egg and the ciliate ‘gamete, etc., represent 
true gametes arrested in their development; (3) that the 
so-called ‘excretions’ of protoplasm in plants are of various 
kinds, many of which are homologous neither with the 
former processes nor with one another; (4) that the use of 
the rapid preliminary divisions is a purely physiological 
one; that is, to induce by exhaustion the same reproductive 
