WHEN this little work first appeared, it was put for-
ward as a Part I, to be followed by other Parts. That
plan was however soon abandoned. Nevertheless the
volume seemed to have a place of its own; and my dear
lost friend undertook to prepare a second edition, in-
tending to add some account of the development of
the Mammal with a view of making the work an
elementary introduction to vertebrate embryology more
particularly suited for medical students. He was occu-
pied with the task at the time of his sad death; and
indeed a melancholy interest is attached to some of the
sheets, by the fact that he had taken them to Switzer-
land with him, on that fatal journey.
All the first part up to p. 160 he had passed for
press; and he had further revised up to about p. 202.
The whole of the rest of the volume has been under-


vl PREFACE.
taken by Mr Adam Sedgwick and Mr Walter Heape.
They have attempted to carry out as far as possible
what we believe to have been Balfour’s views, and
trust that the public will judge leniently of their
efforts to perform a difficult task. I have myself been
able to do no more than offer general advice from time
to time; and though it has not been thought advisable
to change the title, the merits as well as the responsi-
bilities of the latter part of the work must rest with
them.
M. FOSTER.
Trinity CoLLEcs,
CaMBRIDGE,
March, 1883.
TABLE OF CONTENTS.
PART I. THE HISTORY OF THE CHICK.
CHAPTER I.
Tur SrRucTtuRE oF THE HeEn’s Eae, AND THE CHANGES WHICH TAKE
PLACE UP TO THE BEGINNING oF INCUBATION + pp. 1—24.
