The Facts of Sex in Relation to Metabolism. 275 
equal and similar groups, or is a “reducing division,’ which 
has been preceded by a doubling of the number of idants, 
is uncertain; but Weismann regards the second possibility 
as the more likely. 
If it be a “reducing division,” there will be fresh com- 
binations of idants, so that “in parthenogenetic as well as in 
sexual eggs a change may take place in the constitution of 
the germ-plasm during successive generations.” 
And this conclusion, at least, has been experimentally 
confirmed by Weismann’s observations on Cypris reptans, 
in which he demonstrated parthenogenesis for no less than 
forty successive generations. Contrary te his former opinion 
that purely parthenogenetic species entirely lacked the 
capability of transformation by means of selection, he now 
recognises that “they do possess this power to a certain 
extent.” “In parthenogenesis individual variation exists, 
which, as in bi-sexual reproduction, has its foundation in 
the composition of the germ-plasm itself, and thus depends 
on heredity, and is itself inheritable.” 
When it is asked how parthenogenetic eggs may have 
arisen from those which require fertilisation, two answers 
seem to Weismann possible. (1) By the suppression of the 
second polar division the egg-cell would retain precisely as 
much nuclear material as it would have contained if 
fertilisation had followed the expulsion of a second polar 
body. It is in this way that Weismann believes that regular 
parthenogenesis has arisen. (2) But, as Blochmann observed, 
the egg of a hive-bee, which develops parthenogenetically 
into a drone, exhibits two polar divisions, and Platner has 
observed the same in the parthenogenetic eggs of Lipares 
dispar. In such cases of exceptional parthenogenesis, 
Weismann supposes that “the germ-plasm in the egg, after 
having been reduced to half its normal amount, possesses, 
in some unusual way, the power of increasing to double.” 
 (e) Amphimizis as the Significance of Conjugation and 
Fertilisation.—As the result of the investigations of Maupas, 
R. Hertwig, and others, we know that in the conjugation of 
two ciliate Infusorians, there is an exchange of equal amounts 
of nuclear substance. The micronucleus undergoes repeated 
