138 JOURNAL OF SCIENCE 
the children of hybrids are more variable than the hybrids them- 
selves ; and that, from the evidence of the reciprocal crossing in 
the case of hybrids, variation is caused by the influence of the 
male. The evidence from variation is then considered, showing 
that variation is more common in sexual than in asexual repro- 
duction (in plants at least) ; that changed conditions cause varia- 
tion, not directly, but in subsequent generations ; that specific 
characters are more variable than generic ; that parts excessively 
developed in males are more variable then parts especially de- 
veloped in females. Professor Brooks next takes up the very 
complex subject of secondary sexual characters, and shows from 
various kinds of evidence that the male is more variable than the 
female, and that the male has led the way in evolution, while the 
female has followed. One of the most important aspects of the 
hypothesis the author considers to be the manner in which it 
removes objections to the theory of natural selection, by showing 
that large numbers of animals vary similarly and simultaneously, 
and so give an opportunity for natural selection to come into 
play. 
Now, how far can this ingenious and ably supported hypo- 
thesis be regarded as a permanently valuable contribution to 
science? One great objection is apparent at the very outset, 
—that the author has not gone to nature for his facts, but has 
taken them almost entirely from Darwin’s works, as he candidly 
says. This must necessarily impair the value of his conclusions. 
The whole work bears the stamp of being merely .an ingenious 
attempt to supplement Darwin’s hypothesis, and rearrange his 
facts, and might have been written by one whose knowledge of 
biology had been drawn almost entirely from Darwin’s books. 
The objection which Mr. Lewis made to pangenesis holds equally 
well against this hypothesis. “The hypothesis is thus seen to be 
one wholly constructed out of suppositions, each and all of which 
may be erroneous, every one of them being necessary to the 
integrity of the scheme.” Thus the existence of gemmules is a 
supposition ; that cells throw them off when disturbed is a sup- 
position ; that the male cell has acquired a special power of 
gathering and storing these germs is a supposition. Scarcely a 
single proposition of the hypothesis can be regarded as in any 
way proved. Then, again, some of the apparently simple as- 
sumptions really involve a number of others, equally without 
evidence. Thus, when it is said that the ovarian ova, being the 
direct descendants of the tertilized egg, inherit its peculiarities, 
we have no explanation offered for what is perhaps as great a 
mystery as the main problem itself. The ovarian ova are derived 
from the fertilised ovum through an immense number of inter- 
mediate cells, most of which become indifferent epithelium. We 
must, then, assume that the gemmules are all segregated together, 
and transmitted unchanged from cell to cell till they finally reach 
the ovarian ovum,—surely a very forced supposition. 
The evidence by which Professor Brooks endeavours to sup- 
port his hypothesis is by no means convincing: usually all that 
