Page:Popular Science Monthly Volume 85.djvu/40

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These are some of the facts of development—a very incomplete résumé of some of the stages through which a human being passes in the course of his development from the germ. What are the factors of development? By what processes is it possible to derive from a relatively simple germ cell the complexities of an adult animal? How can mind and consciousness develop out of the relatively simple psychical elements of the germ? These are some of the great problems of development—the greatest and most far-reaching theme which has ever occupied the minds of men.

Preformation.—When the mind is once lost in the mystery of this ever recurring miracle it is not surprising to find that there have been those who have refused to believe it possible and who have practically denied development altogether. The old doctrine of "evolution" as it was called by the scientists of the eighteenth century, or of preformation as we know it to-day held that all the organs or parts of the adult were present in the germ in a minute and transparent condition as the leaves and stem are present in a bud, or as the shoot and root of the little plant are present in the seed. In the case of animals it was generally impossible to see the parts of the future animal in the germ, but this was supposed to be due to the smaller size of the parts and to their greater transparency, and with poor microscopes and good imagination some observers thought they could see the little animals in the egg or sperm, and even the little man, or "homunculus," was described and figured as folded up in one or the other of the sex cells.