Table Of ContentE. Hadorn
Experimental Studies
of Amphibian Development
Translated by D. Turner
With 45 Figures
Springer Verlag Berlin Heidelberg New York 1974
Professor Dr. Ernst Hadorn
Zoologisch-Vergl.
Anatomisches lnstitut der Universitiit Ziirich,
KiinstIergasse 16, CH-8006 Zurich
Translated from the German edition Verstandliche Wissen
schaft, Band 77, E. Hadorn "Experimentelle Entwicklungs
forschung, im besonderen an Amphibien", 2nd enlarged
Edition
ISBN-13: 978-3-540-06644-6 e-ISBN-13: 978-3-642-65812-9
DOl: 10.1007/978-3-642-65812-9
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Preface
Although this is basically a translation of the second German
edition published in 1970, more recent experimental findings have,
in several instances, been incorporated into the text. Furthermore,
we have tried to explain some of the experiments, and their possible
interpretations, in a more precise way. I am very grateful to
Dr. David Turner; in addition to translating the text, he was
able, thanks to his experience in developmental biology, to suggest
a number of improvements in the course of our collaborative
discussions.
Zurich, Spring 1974 ERNST HADORN
Preface to the Second German Edition
The guiding principle of the first edition remains in force. That
is, the methods and results of developmental research are intro
duced wherever possible with the aid of experiments on am
phibians.
However, the scope of the material has been substantially ex
panded in newly introduced chapters on the migrations and
affinities of somatic and germ cells as well as on the action of
genetic factors in early development. These are fields of study
which are at the center of today's research. In addition, numerous
new findings have been incorporated into the text.
The author hopes that this little book will continue to facilitate
understanding of exciting research problems, for the interested
layman as well as for the teacher and student of biology.
It was decided to omit literature citations once again. The reader
can find access to the specialized literature in the textbooks of
developmental biology listed at the end of the book. References
to the papers of those authors whose names appear in the figure
legends can also be found in these works. To my colleagues
P. S. Chen and P. Tardent, my heartfelt thanks for their helpful
counsel.
Zurich, Summer 1970 ERNST HADORN
Preface to the First German Edition
Our goal in this presentation is to introduce the reader to ex
perimental research on development. The discussion will be
limited almost exclusively to investigations carried out on the
eggs, embryos and larvae of the Amphibia. Other forms of life,
such as sea urchins, molluscs, worms, insects and birds, have, of
course, furnished vital insights into the fundamental principles
and regularities of the processes of development. Yet within the
framework of a small book it would be impossible to introduce
the characteristics of a number of different developing systems in
sufficient detail that the decisive experiments would be readily
comprehensible. We are, moreover, particularly justified in re
stricting ourselves to the Amphibia. For some eighty years now,
in many laboratories the world over, the embryos of these animals
have been worked on with unflagging enthusiasm. These efforts
have led to numerous fundamental discoveries that have validity
far beyond the world of the Amphibia; indeed, they apply to our
own human developmental processes as well. Accordingly, ex
periments on amphibians have long stood-and still stand to
day-at the center of research into the problems of development.
Of the vast wealth of experience from work on Amphibia we have
selected only a small and quite arbitrarily chosen sample. Some
of the most famous classical experiments are presented, but so
are many which are less well known. And, by presenting some
of the most recent experiments, we hope to lead the reader to the
forefront of today's research. We want him to experience for
himself how many are the secrets of life that remain unsolved
and how each new thrust forward discloses exciting new problems.
Very many researchers have contributed to the results described
in this book; only a few of them are mentioned by name. A proper
citation of sources would have overburdened our text. So I ask
forebearance of all those unnamed colleagues from whose work
I was able to glean new knowledge. The authors of the material
depicted in the figures are, however, indicated in the lengends.
For the artistic execution of the figures lowe sincere thanks to
my co-worker, Miss Maria Gandolla.
Zurich, Spring 1961 ERNST HADORN
Contents
Egg Laying and Provision for Posterity 1
A Hormone as Trigger of Egg Laying 4
The Egg Underway. . . . . . . 6
Fertilization of the Egg . . . . . . 8
Fatherless and Motherless Beings. . 14
Does the Nucleus Have a Monopoly on Inheritance? 19
Functions of the Genetic Material during Oocyte Maturation 23
From One Cell to Many. . . . . . . . . . 36
Formative Movements . . . . . . . . . . 44
Toward Order and Pattern: Cells on the Move 52
Experimental Production of Identical Twins 58
Exchanging Future Skin and Brain Cells. . 60
The "Organizer" . . . . . . . . . . .. . 63
On the Mechanism of Embryonic Induction 68
Lens Induction and Hierarchy of Inducers . 73
A Newt with a Frog's Mouth. . . . . . . 77
Double-headed Beings and Other Monsters. 80
Chimeras, Parabiosis and Sexual Development 84
The Male Toad as Mother. . . . . . . . . 92
On the Migration of the Primordial Germ Cells . 98
Color Pattern and Color Change . . . 104
On Wound Healing and Regeneration. 114
Hormones and Metamorphosis . 122
Suggestions for Further Reading 132
Subject Index . . . . . . . . 133
Egg Laying and Provision for Posterity
As early as the end of February or the beginning of March,
we can find the first egg masses (Fig. 1 a) of the common European
frog (Rana temporaria) in ponds and in the calmer waters near
the shores of lakes. A little later, the common toads (Bufo bufo)
deposit their eggs, embedded like pearls in long strings of jelly
(Fig. 1 b). The European newts (Triturus species) provide for each
egg individually. They grasp leaves and stalks of aquatic plants
with their hind legs and fold them around the egg as it is laid.
Fig. 1a - d. a Part of the egg mass of the common European frog. b Strings
of toad eggs stretched between plant stems. c Two newt eggs under leaves of
a water plant. d Larva removed from the oviduct of an alpine salamander, showing
the extreme development of the gills (G)
1
The outermost egg coat sticks to the inner surface of the folded
leaf, forming a concealed sanctuary for the development of egg
and embryo (Fig. 1 c). By contrast, European salamanders retain
the fertilized egg within the body of the mother. Only when early
development is complete and the larvae are ready for hatching
does the black-and-yellow spotted European (or "Fire") Sala
mander (Salamandra salamandra) seek an appropriate place in
the brook to set free as many as fifty offspring.
For the black alpine salamander (Salamandra atra) development
within the body of the mother actually requires some two to
three years. And what goes on during this time is highly astonishing.
First, each ovary releases into the oviduct anywhere from 30
to more than 100 eggs (see Fig. 2), depending on the habitat
(elevation) and the age of the female. Of these germ cells, only
one in each oviduct develops into an embryo and then into a
larva. The egg cells (oocytes) which receive this special privilege
are the ones which happen to be nearest to the cloaca in each
oviduct. Only these eggs become covered with a jelly coat of
the normal thickness, and as a rule only these become fertilized.
All of the other eggs usually remain unfertilized, and should one
become fertilized by way of exception, it will only manage to
get through the earliest developmental stages. While the two lowest
embryos are developing further, the rest of the oocytes unselfishly
degenerate, providing a kind of nutrient broth which is gradually
used up by the two privileged larvae. Part of this food is taken
up throught the surfaces of the giant gills (Fig. 1 d), much as
food passes through the wall of the intestine; the remainder is
eaten directly. The enormous gills also function in the uptake
of oxygen and in the resorption of oviduct secretions.
It is possible to remove such larvae by "Caesarian section" and
raise them in a glass dish. If a small worm is presented to such
a prematurely born animal, it is instantly snapped up and swal
lowed, that is, the animal does something which could never
be accomplished under normal circumstances at this developmen
tal stage. How are we to understand such behavior? Obviously
the inherited coordinated movements which are involved in the
feeding act of free-living larvae have not been impaired in the
course of those phylogenetic changes which have led to the evolu
tion of the alpine salamander. When removed from its mother's
2
Description:Although this is basically a translation of the second German edition published in 1970, more recent experimental findings have, in several instances, been incorporated into the text. Furthermore, we have tried to explain some of the experiments, and their possible interpretations, in a more precise
