THE
EMBRYOLOGY AND ETIOLOGY OF TUMOURS 77
Matters
would appear to be complicated in some cases by the existence of two
well-marked portions in a normal life-cycle: the asexual one, represented by
the chorion (trophoblast); and the sexual one, taken up by an embryo, or
Metazoon. Some tumours—some ovarial teratomata, described by Wilms—exhibit
attempts to include the whole life-cycle, in that, along with a pathological
bizarre embryo, cancer, representing the asexual generation, is encountered. In
other tumours, again, there would appear to be nothing of the asexual generation;
and still others, the malignant cancers, confine themselves entirely to being
abnormal manifestations of the asexual portion—the first part of the life-cycle.
The
comparative embryology of tumours may now be considered more in detail. The
seed or seeds of tumours are unquestionably some or other of the vagrant (or if
in ovary or testis, persistent) primary germ-cells, treated of at greater
length in the writer’s works upon the germ-cells. So far (1911) they
have only been found from fishes to reptiles ; but from various considerations
it is not open to doubt that they occur even in the highest vertebrates, and in
man himself. Apparently they have been noted by Roux and Barfurth in the frog,
and by me in the salamander (S. maculosa). In all the embryos yet
studied by me under a certain age—i.e., within the limits during which
germ-cells are easily found in embryos— no single embryo examined has been devoid
of them.
The
mode of the development and the life-cycle, in practically all its details,
are the same in mammals as in fishes, and unquestionably the whole organization
and development of man follow closely along, but along higher lines than,
those of a fish. It is therefore concluded that, could one but hit upon some
easy method of distinguishing germ-cells during the early development of man
and