260 THE ENZYME TREATMENT OF CANCER
strated in 1883, the germ-cells arise in and upon an asexual stock—the hydroid polype or colony of such— and thence they migrate into the rnedusa or its equivalent. This is not termed a metamorphosis, but an alternation of generations. In such an animal as the skate the phenomena are exactly comparable. Within a living structure—the blastoderm—there arise germ-cells, which upon the appearance of an embryo wander into it. Is it at all remarkable that, as the blastoderm and its appendages never become “metamorphosed” into the skate, one should also describe this as an alternation of generations?
By looking at the phenomena in this light, one immense advantage is gained, in that thereby it becomes possible to compare together, so as to show their essential identity, the phenomena in the life-cycles of a hydrozoon, a worm, a mollusc, an insect, a fish, a mammal, and a man. And to these must be added the higher plants or Metaphyta. In other words, it reveals the unity of organic nature! What other view of development possesses this enormous advantage? What upholder of direct development, or of epigenesis, can produce a diagram of the life-cycle of a higher animal from egg to egg, corresponding to and including all the known facts of the development, and confirming to the hilt his view of the process? There is no ring of uncertainty in the answer. Apart from that drawn up by the writer, there exists no other complete diagram of the life-cycle.* For no metazoon has it been established beyond cavil and doubt that the development is direct. H there be any such thing as direct development, where under it do the germ-cells arise, and what is their cell-lineage from the fertilized egg ? It is easy to ask these questions, but the difficulties in the way of answering them are so great that they never will, or can, receive convincing replies in the sense of a direct development.
On the other hand, it may be stated confidently and
* This was true nearly ten years ago, when it was first written, and it holds equally to-day (1911).