From the Preface: The development of the frog's egg was first made known
through the studies of Swammerdam, Spallanzani, Rusconi,
and von Baer. Their work laid the basis for all later research. More recently the experiments of Pfluger and of Roux on this
egg have turned the attention of embryologists to the study
of development from an experimental standpoint. Owing to
the ease with which the frog's egg can be obtained, and its
tenacity of life in a confined space, as well as its suitability for
experimental work, it is an admirable subject with which to
begin the study of vertebrate development. In the following pages an attempt is made to bring together
the most important results of studies of the development of
the frog's egg. I have attempted to give a continuous account
of the development, as far as that is possible, from the time
when the egg is forming to the moment when the young tadpole
issues from the jelly-membranes. Especial weight has
been laid on the results of experimental work, in the belief
that the evidence from this source is the most instructive for
an interpretation of the development. The evidence from the
study of the normal development has, however, not been neglected,
and wherever it has been possible I have attempted to
combine the results of experiment and of observation, with the
hope of more fully elucidating the changes that take place.
Occasionally departures have been made from the immediate
subject in hand in order to consider the results of other work
having a close bearing on the problem under discussion. I
have done this in the hope of pointing out more definite conclusions
than could be drawn from the evidence of the frog's
egg alone.
