risen from it.
Since then progress in these studies has been rapid, and the present
account, though bearing the same title, has been completely rewritten. A
number of illustrations have been added, and here I may acknowledge my
indebtedness to Miss Wheldale for the two coloured plates of sweet peas, to
the Hon. Walter Rothschild for the butterflies figured on Plate VI., to
Professor Wood for photographs of sheep, and to Dr. Drinkwater for the
figures of human hands. To my former publishers also, Messrs. Bowes and
Bowes, I wish to express my thanks for the courtesy with which they
acquiesced in my desire that the present edition should be published
elsewhere.

As the book is intended to appeal to a wide audience, I have not attempted
to give more experimental instances than were necessary to illustrate the
story, nor have I burdened it with bibliographical reference. The reader
who desires further information may be referred to Mr. Bateson's
indispensable Volume on _Mendel's {vi} Principles of Heredity_ (Cambridge,
1909), where a full account of these matters is readily accessible. Neither
have I alluded to recent cytological work in so far as it may bear upon our
problems. Many of the facts connected with the division of the chromosomes
are striking and suggestive, but while so much difference of opinion exists
as to their interpretation they are hardly suited for popular treatment.

In choosing typical examples to illustrate the growth of our ideas it was
natural that I should give the preference to those with which I was most
familiar. For this reason the book is in some measure a record of the work
accomplished by the Cambridge School of Genetics, and it is not unfair to
say that under the leadership of William Bateson the contributions of this
school have been second to none. But it should not be forgotten that
workers in other European countries, and especially in America, have
amassed a large and valuable body of evidence with which it is impossible
to deal in a small volume of this scope.

It is not long since the English language was enriched by two new
words--Eugenics and Genetics--and their similarity of origin has sometimes
led to confusion between them on the part of those who are innocent of
Greek. Genetics is the term applied to the experimental study of heredity
and variation in animals and plants, and the main concern of its students
is the establishing of law and order among the phenomena {vii} there