The Facts of Sex in Relation to Metabolism. 275 
possible,” amphimixis became and continues to be necessary 
because of its deep and essential use. The periodicity of its 
appearance depends on adaptation, thus parthenogenesis is 
chiefly found in very prolific species. In short, amphimixis 
is no indispensable condition, no renewal of life or “ rejuven- 
escence,” nor inseparable from the continuance of vital 
processes; it is a mingling of hereditary qualities, and as such 
an essential advantage in the maintenance and modification 
of species. 
CRITICAL NOTES. 
No one who reads Weismann’s important essay with 
carefulness can fail to recognise that he has to deal with a 
thinker who will not fail to alter his positions whenever 
fresh facts appear to him to demand it. For with perfect 
frankness he now rejects his previous interpretation of the 
first polar body, his belief in the non-variability of par- 
thenogenetic animals, and his admission that in unicellular 
organisms external influences could directly call forth 
hereditary changes. Moreover, although his essay abounds 
in hypotheses, it cannot be denied that the entire theory is 
full of attractiveness; and there is some reason to justify 
hypothesis, as he says, on the ground that “future research 
will be more profitable if we endeavour to test some settled 
theory, instead of making observations with no end in view.” 
Such being Weismann’s scientific mood, we feel sure that 
he will appreciate the spirit of dissentients, who seek to 
maintain the old position as to fertilisation until that prove 
either untenable or stronger than he deems it. For in 
regard to these difficult problems, it is only by criticism 
and counter-criticism that we shall at length grasp what 
is true. 
First of all, we would notice, what Weismann himself 
recognises, that his “view as to the effect of amphimixis in 
originating variability may be perfectly correct, without the 
essence of fertilisation or of conjugation being thereby 
explained.” It is evident that we may accept Weismann’s 
positive conclusion that fertilisation is a mingling of two 
