Embryological Concepts in the Twentieth Century
1
JANE M. OPPENHEIMER
Department of Biology, Bryn Mawr College, Bryn Mawr, Pennsylvania
Page
I. Introduction
1
II. The Whole Embryo
III. The Embryo as Constructed of Germ Layers
18
IV. The Embryo as Constructed of Cells
2
3
1. The Whole Cell
3
2. Cellular Components: Microscopic and Submicroscopic
26
V. Some Concluding Fancies
33
References
37
I. INTRODUCTION
It was an embryologist who wrote that "Die Madonna della Sedia
nimmt sich auf 1 cm Entfernung mit der Lupe betrachtet auch anders
aus, als auf 5 m Distanz. Das erste Mal sehen wir nur Klexe," and who
then raised the question: "Ist denn das Studium von Klexen wirklich die
einzige Aufgabe des Biologen?"
2 (Driesch, 1894, p. 163). An intellectual
historian concerned with the history of biology might well ask himself a
similar question with respect to the subject or object of his studies, substituting the parameter of time for that of space, and he might justifiably
regard as formidable the difficulties of establishing the interrelationships
of ideas evolving during the period which includes his own development.
If, however, there is any truth in the so frequently repeated truism that
the ideas of the present can properly be understood only in the light of
their precursors, in the same manner that an event in the development of
an embryo can be fully comprehended only in terms of the previous
events which have led up to it, there is no period to which it is more
desirable for the practising scientist to apply the techniques of intellectual history than the stage immediately preceding his own.
For embryology, at least, there has been no dearth of preliminary
attempts to trace sequences of ideas from the time of antiquity towards
1 An expansion of an address by the same title delivered as part of the Presidential
Symposium of the American Society of Zoologists at the meetings of the American
Institute of Biological Sciences in East Lansing, Michigan, in September, 1955.
2 The Madonna of the Chair examined with a lens at a distance of 1 cm shows
up quite differently than at 5 m away. The first time we see only blotches. Is then
the study of blotches really the only task of the biologist?
1
1
JANE M. OPPENHEIMER
Department of Biology, Bryn Mawr College, Bryn Mawr, Pennsylvania
Page
I. Introduction
1
II. The Whole Embryo
III. The Embryo as Constructed of Germ Layers
18
IV. The Embryo as Constructed of Cells
2
3
1. The Whole Cell
3
2. Cellular Components: Microscopic and Submicroscopic
26
V. Some Concluding Fancies
33
References
37
I. INTRODUCTION
It was an embryologist who wrote that "Die Madonna della Sedia
nimmt sich auf 1 cm Entfernung mit der Lupe betrachtet auch anders
aus, als auf 5 m Distanz. Das erste Mal sehen wir nur Klexe," and who
then raised the question: "Ist denn das Studium von Klexen wirklich die
einzige Aufgabe des Biologen?"
2 (Driesch, 1894, p. 163). An intellectual
historian concerned with the history of biology might well ask himself a
similar question with respect to the subject or object of his studies, substituting the parameter of time for that of space, and he might justifiably
regard as formidable the difficulties of establishing the interrelationships
of ideas evolving during the period which includes his own development.
If, however, there is any truth in the so frequently repeated truism that
the ideas of the present can properly be understood only in the light of
their precursors, in the same manner that an event in the development of
an embryo can be fully comprehended only in terms of the previous
events which have led up to it, there is no period to which it is more
desirable for the practising scientist to apply the techniques of intellectual history than the stage immediately preceding his own.
For embryology, at least, there has been no dearth of preliminary
attempts to trace sequences of ideas from the time of antiquity towards
1 An expansion of an address by the same title delivered as part of the Presidential
Symposium of the American Society of Zoologists at the meetings of the American
Institute of Biological Sciences in East Lansing, Michigan, in September, 1955.
2 The Madonna of the Chair examined with a lens at a distance of 1 cm shows
up quite differently than at 5 m away. The first time we see only blotches. Is then
the study of blotches really the only task of the biologist?
1