THE
PROBLEMS OF CANCER 101
of
neoplasms. They form, and this requires emphasis, only one set of many
degenerative and retrogressive phenomena encountered at all sorts of stages of
the cycle in comparative embryology. Truly, in dealing practically with
embryology, “in the midst of life we are in death.” “Das Werden” is ever
accompanied by” das Vergehen.”
The
whole doctrine of the tumours centres in the problems of identical twins. Than
these latter there is nothing more replete with interest in embryology. Of vast
import is the recognition of the existence of two kinds of these. There are
identical twins, which come as it were out of the same mould, and there is a
second and rarer kind—the “looking-glass-image” twins.* The occurrence of the
latter throws welcome light upon various zoological and anatomical questions—on
the right-handed and left-handed snails, fishes, etc.—as well as upon the
phenomena of reversed viscera. In other directions identical twins pass gradually
into double monsters, and these in their turn into the higher tumours or teratomata.
At the basis of the tumours is the fact that from one fertilized egg a
multiplicity of embryos may arise, just as from one such in a sea-polype a
legion of jellyfish may take their birth. As in the polar bodies of oögenesis
(egg-formation) we have rudimentary or abortive gametes (conjugating-cells),
so in the development of the higher animals we meet with rudimentary or
* These
looking-glass image twins are the greatest wonder in animate nature. Along with
Captain Lambelle and a former pupil, Dr. M. M. Morrison, a few years ago the
writer had a unique opportunity of examining and photographing two of these
(twin boys) in the south of Scotland. Both were very degenerate, and both
suffered from club-foot. The deformities in the right foot of the one were in
the left foot of the other, and so on. One of the two exhibited the phenomena
of reversed viscera, with right aortic arch, stomach and spleen transposed,
etc. The actual finds and photographs will be published elsewhere.