84 THE ENZYME TREATMENT OF CANCER
In the comparative account of the tumours I shall follow the lines laid down by Wilms, and, therefore, it is his summary of them, not mine. His account of their comparative anatomy appears to me to be logical and convincing; and in giving his results in tabular form I should like to say with what intense interest and instruction I have studied his writings. As elsewhere stated, the highest and most complicated tumours—the cystic embryomata of ovary and testis (Wilms)—are at the basis instances of identical twins with one abnormal embryo, the embryoma. If nothing else would account for their pathological development, the circumstance that neither they nor any of the less complicated tumours can, from their mode of origin, contain sexual organs might suffice. They are, therefore, sterile embryos; and in other directions my researches have convinced me that embryonic sterility may be the source of pathological changes.
From the facts established concerning the tumours by pathologists, it is clear to the comparative anatomist and embryologist that in certain respects they present certain analogies to instances of parasitism among animals. They differ, however, markedly in being, from the mode of their development, sterile organisms, even in the best-developed cases. The resemblances between tumours and parasitic Metazoa or higher animals may be exemplified by a short account of certain snails parasitic upon Echinoderms (starfish and the like). The series is derivable from free-living Eulima species. It may be taken as beginning with Mucronalia eburnea, which is an external parasite, and possesses the full organization of a snail. Stylifer linckiae is also an ecto-parasite, but it is partially encapsulated upon the host. In this case the foot is rudimentary, and the radula is absent.