280 RECENT CYTOLOGY 
character is represented by a paternal or a maternal 
determinant only, and not by both. Thus, not 
only are all immediate ancestors not represented 
in the germ-cells in respect of any particular 
character, but only one of the parents is so repre- 
sented—to the complete exclusion, so far as we can 
tell, of the other parent. In fact, we are led to 
believe that the germ-cells contain one set of de- 
terminants only—a single 7d—whilst the somatic cells 
contain two ids only. The Mendelian theory is thus 
seen to be considerably simpler than the germ-plasm 
theory, which it replaces. At the same time it must 
not be forgotten that many of the conceptions used in 
the Mendelian expression of the facts are borrowed 
from Weismann’s theory, and that but for Weismann’s 
work it would have been impossible for us to have got 
so far in the co-ordination of the facts derived from 
experiment and microscopic observation respectively. 
The preceding sketch may serve to show how Mendel’s 
observations have been found to throw light upon many 
of the facts of cytology the meaning of which was pre- 
viously obscure ; and how it affords at the same time 
a criterion by which may be tested the truth of theories 
based upon the interpretation of minute phenomena 
only made visible by the highest powers of the micro- 
scope. The disinterment of Mendel’s discovery took 
place only eleven years ago; and the rapid manner 
in which the facts of cytology have been found to 
fall into line with Mendelian conceptions augurs well 
for the future progress of discovery in these fields. 
