The Facts of Sex in Relation to Metabolism. 279 
division” has hitherto escaped notice, and that the extremely 
unsatisfactory state of our knowledge in regard to ovum- 
maturation in reptiles, birds, and mammals should lead us 
to speak cautiously of “all the higher Metozoa.” It may be 
said, of course, that this is an argument ad ignorantiam 
again, but our contention is made in no polemical spirit nor 
with any prejudice against the probability of Weismann’s 
conclusion, merely with the desire of indicating a few of the 
gaps which remain in his demonstration. It can hardly be 
taken for granted that all his readers are as conscious of 
these as he himself is. 
(c) It will be remembered that Weismann inclines to the 
belief that the single polar division of normally partheno- 
genetic ova is a “reducing division,” preceded by a doubling 
of the idants. This, which is an important assumption, 
enabling Weismann to explain the variability of partheno- 
genetic organisms, is only “based upon probability.” When 
we turn to his discussion of exceptional cases of partheno- 
genesis, ¢.g., in the bee-eggs which become drones, or in 
Liparis dispar, in which the eggs exhibit two polar divisions, 
we are confronted with another ingenious hypothesis. As 
Weismann is convinced that a certain amount of germ-plasm 
must be present in the ovum if development is to proceed— 
which is also an assumption—he agrees with Strasburger 
that the germ-plasm of these exceptionally parthenogenetic 
ova “ possesses, In some unusual way, the power of increasing 
to double.” By such hypotheses any difficulty may be over- 
come; but one naturally looks for facts demonstrating that 
the doubling actually occurs, as Weismann may demand 
from us observations showing that it does not. Moreover, 
supposing that the increase of the germ-plasm to double do 
actually take place, it seems to us difficult to accept the 
opinion that “the difference between eggs which are capable 
of parthenogenetic development and those which are not, 
must be quantative and not qualitative.” One would 
naturally think that ova thus unusually endowed were 
entitled to be called qualitatively different from those which 
have no such power. 
