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Reviews.



controls the colour of a certain part of the body, and in the same

way there will be a biological molecule for other characters. Now

it is supposed that the atoms in the molecules of each individual

have a definite arrangement, which, as a ncle , is not altered in the

progeny when two individuals of the same species pair together,

but it is suggested that the arrangement may be altered and thus

give rise to a mutation.


The process is considered analogous to well known facts

of chemistry, in which connection alcohol and ether are instanced

as having the same formula C 2 Ho O, but entirely different pro¬

perties owing to the different arrangement of the atoms in their

molecules.


The authors allow that this idea is merely a suggestion (not

even a hypothesis), but it seems a pity to have introduced it

without calling up more facts to support it aud elaborating it

further, and we are surprised to find no mention of Weismann’s

biophors, ids, or determinants, as the last two seem to us to be

the molecules and atoms of the present work.


On the very debatable topic of sexual dimorphism, the

authors, after entering into the pros, and cons, of sexual selection,

suggest that sexual dimorphism arose as a mutation, and when

not detrimental to the species it was not eliminated by Natural

vSelection. With this view we cannot agree for the fact that it

was merely not detrimental would not be sufficient reason for its

development and perfection by Natural Selection. To persist

and swamp the original form it would have to be beneficial to the

race, and the author’s themselves allow that the percentage of

deaths among bright-coloured males is probably greater than

among their more soberly clad brothers, so that for it to have

survived, if it arose by mutation, the whole foundation of evolu¬

tion by Natural Selection would have to be abandoned.


Enough, however, has been said to show the main features

of the book, and, in conclusion, the authors are of opinion that

the line of future advance will lie in the study of the living rather

than the dead. With this idea we are entirely in accord ; avi-

culturists, breeders, and fanciers know only too well that most, if

not all, of their results are got by experimental breeding. There

is as yet no definite series of rules by which we can make sure of



