298 J. E. S. MOORE. 
capacity which its premises exhibit of being logically worked 
up into harmony with what has been actually observed. Thus, 
according to Weismann,! the phenomena of heredity depend 
ultimately on the existence of innumerable little unities in the 
“germplasm,” or “ ids,”’ and these are in reality the hypothe- 
tical doers of everything that is done. ‘They are capable of 
influencing the protoplasm which surrounds them in different 
ways, and by coming into action successively during develop- 
ment, they produce the structural differentiation of a complex 
form. Representatives of all the different kinds of “ ids,” 
actual or potential, which exist in any given animal or plant, 
are continually being locked up for future use in every ovum 
or spermatozoon formed, and in consequence of the indefinite 
multiplication of the “ids,” which must occur after every act 
of fertilisation, it appears, according to Weismann, a logical 
necessity from the premises of his theory, that the reproductive 
cells, before fertilisation, must each get rid of half their here- 
ditary substance (i.e. “ must each get rid of half their nuclear 
rods”’). ‘This is supposed to be accomplished by there being 
two kinds of division among cells. In the first of these (the 
ordinary somatic division) the chromosomes split in half, there 
being consequently the same number in each daughter-cell, 
and this method of division has consequently been termed 
“ Kquationstheilung,” to distinguish it from the second or 
“ Reductionstheilung,” which is apparently introduced only 
during the final stages of the development of the reproductive 
elements, and is brought about by half of the entire number of 
chromosomes formed during a mitosis passing unsplit into one 
daughter-cell, and half into the other. 
The value of these hypothetical speculations touching the 
nature of the phenomena immediately antecedent to fertilisa- 
tion, appeared to be enormously enhanced by O. Hertwig’s 
description of a process answering to the Reductionstheilung 
in the final stage of the spermatogenesis of Ascaris, because 
if this process should turn out to be universal, as at one time 
seemed probable, it would give to the “id” theory an actual 
> 
1 «The Germplasm,’ English trans. 
