TWENTIETH CENTURY EMBRYOLOGICAL CONCEPTS
5
latter has penetrated beyond the horizons of the former through the
elaboration of special techniques. This contention may well hold true for
many fields of biology, but it is not adequate for the case of embryology.
In the first place, the application of the new experimental method to
embryology was initiated considerably earlier in the 19th century than is
commonly admitted. It is no secret (Schleip, 1929), though it is not
commonly bruited about, that in 1869 Haeckel himself, with whom Roux
was to start studying the following year, published the results of experimental division of siphonophore larvae, demonstrating that half-larvae
were able to form whole organisms. But if initiation of the experimental
method, so often said to be the special contribution of the innovators of
the changed embryology, was both possible and actual a third of the
way back into the 19th century, this is not the only example where the
specific chronology of events distorts our perspective. A further complication is that the methods used by experimental embryologists well
into the 20th century in their stark and beautiful simplicity were essentially 19th century methods. Roux killed the frog's blastomere by a
cautery needle in fact as brutal as the amputation iron of Paré; and what
were the first tools of Spemann but a lens, a dish, and a loop of hair?
If a clear division between the methods of 19th century and 20th
century embryology seems blurred by such considerations, it is possible
that a sharper line can be drawn between the two periods by considering
the nature of the problems investigated during the two periods. It might
be held that the 19th century was more single-minded; and viewed retrospectively this may be a greater significance of the 19th century germ
layer theory than that it was established by morphological techniques.
The investigators in the 19th century, sprung as they were from Naturphilosophie,
were inspirited with an idea which became the germ layer
theory, a concept recognizable as such even to those who have difficulty
in defining concepts in biology; and this doctrine, subject as it became
through the efforts of Haeckel to the unifying control of the evolutionary
concept of Unity of Descent, was a centralized and centralizing concept for the whole century, losing little of its sovereignty in 19th century
embryology even after the general acceptance of the cell theory and even
though much other embryological work of varied nature was completed.
The investigators at the turn into the 20th century, in contrast, no
longer centered their efforts on one focus. It is the essence of 20th
century embryology that it has not limited itself, until fairly recently,
to concentration on a single specific idea. Its earliest workers were
astonishing at the first for their widening curiosity. True, at the backs
of their minds lay the problem of progressive differentiation, but here
5
latter has penetrated beyond the horizons of the former through the
elaboration of special techniques. This contention may well hold true for
many fields of biology, but it is not adequate for the case of embryology.
In the first place, the application of the new experimental method to
embryology was initiated considerably earlier in the 19th century than is
commonly admitted. It is no secret (Schleip, 1929), though it is not
commonly bruited about, that in 1869 Haeckel himself, with whom Roux
was to start studying the following year, published the results of experimental division of siphonophore larvae, demonstrating that half-larvae
were able to form whole organisms. But if initiation of the experimental
method, so often said to be the special contribution of the innovators of
the changed embryology, was both possible and actual a third of the
way back into the 19th century, this is not the only example where the
specific chronology of events distorts our perspective. A further complication is that the methods used by experimental embryologists well
into the 20th century in their stark and beautiful simplicity were essentially 19th century methods. Roux killed the frog's blastomere by a
cautery needle in fact as brutal as the amputation iron of Paré; and what
were the first tools of Spemann but a lens, a dish, and a loop of hair?
If a clear division between the methods of 19th century and 20th
century embryology seems blurred by such considerations, it is possible
that a sharper line can be drawn between the two periods by considering
the nature of the problems investigated during the two periods. It might
be held that the 19th century was more single-minded; and viewed retrospectively this may be a greater significance of the 19th century germ
layer theory than that it was established by morphological techniques.
The investigators in the 19th century, sprung as they were from Naturphilosophie,
were inspirited with an idea which became the germ layer
theory, a concept recognizable as such even to those who have difficulty
in defining concepts in biology; and this doctrine, subject as it became
through the efforts of Haeckel to the unifying control of the evolutionary
concept of Unity of Descent, was a centralized and centralizing concept for the whole century, losing little of its sovereignty in 19th century
embryology even after the general acceptance of the cell theory and even
though much other embryological work of varied nature was completed.
The investigators at the turn into the 20th century, in contrast, no
longer centered their efforts on one focus. It is the essence of 20th
century embryology that it has not limited itself, until fairly recently,
to concentration on a single specific idea. Its earliest workers were
astonishing at the first for their widening curiosity. True, at the backs
of their minds lay the problem of progressive differentiation, but here