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.