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not quite abreast of the anatomical knowledge of his time, since, correct as Harvey's main conclusions were, the observations upon which he based them had already been superseded. Chiefly, however, Maupertuis rests his case upon the facts of double heredity and hybridism. If the embryo be truly 'predelineated' in the ovum or in the 'zoosperm,' how, he asks, can it come about that it inherits the specific or individual characters of now one and now the other parent, and often of both? The preformationists had, of course, their devices for explaining away this pretty obvious difficulty; but Maupertuis finds it easy to show that the explanations are altogether inadequate when they are compared with even the common and easily observable facts of heredity. His reasoning is especially effective when he cites his own investigation of the transmission of hexadactylism (sexdigitisme) through several generations of a certain German family whose records he had examined, and points out how little the preformation hypothesis could account for the transmission of such a peculiarity through male and female parents alike, its progressive disappearance as succeeding generations more and more intermarried with persons having the normal number of digits, and its occasional atavistic reappearance in remote descendants. In view of these classes of facts, he declares, the encasement theory must be abandoned, and the conclusion must be accepted that the embryo is no ready-made article, preexistent from the creation of the world, but a new birth, the product of a true genesis;—not, indeed, a genesis of life itself, but of a new and unique combination and intermingling of already-living elements contributed by both parents alike. These arguments and this conclusion, it should be remembered, were advanced by Maupertuis more than a decade before the publication of the great work of Kaspar Friedrich Wolff,[1] from which the modern revival of the doctrine of epigenesis is usually dated. The conception of epigenesis held by Maupertuis, was, moreover, far more complete and accurate than that which Harvey had put forward a century earlier. For although Harvey had asserted marem et foeminam pariter efficientes causas esse generationis, he had denied that there can be any physical interpenetration of ovum and spermatozoon, and had declared that fecundation consists in the communication of a purely immaterial force. It was in order to make this a little more intelligible that Harvey had worked out his famous analogy between the conception of the embryo in the uterus, and the conception of an idea in the brain.[2] All this, Maupertuis remarks, is an idée étrange; where we have double

  1. 'Theoria Generationis,' 1759.
  2. Harvey's reason for this opinion lay in his failure to discover any traces of the spermatozoon in the uterus. His own words are 'Quoniam nihil sensibile in utero post coitum reperitur; et tamen necesse est ut aliquid adsit, quod foeminam foecundam reddat; atque illud, ut probabile est, corporeum esse nequeat: superest ut ad mcrum conceptum, specierumque sine materia receptionem, confugiamus,' i. e., the ovum is fertilized by being impregnated with a general concept! ('De generatione animalium,' 33).