Page:Popular Science Monthly Volume 45.djvu/435

Rh announces that upon further investigation he believes that germ-plasm is universally unstable!

When this recantation occurred, Dr. Romanes considered for a while whether he should cancel the first two chapters of this book already prepared for publication. He concluded, however, to let them stand, justly observing: "It is open to question whether an author of any kind should suffer an elaborate system of theories to be published and translated at the very time when he is himself engaged in producing another work showing the untenable character of their basal premises. . . . At the least he should have added notes to his Polar Bodies and Amphimixis to let the reader know his change of doctrine."

It might be supposed when these leading features were stricken out from Prof. Weismann's theories of descent and evolution, the remainder would be characterless. But the fanciful mechanism of heredity was retained, the difference in mortality between the Metazoa and Protozoa was emphasized, and the instability of germ-plasm was confined to the least possible degree, still making amphimixis the main cause of variation. This disturbed Dr. Romanes more than all else. He chafed at "a germ-plasm that is both stable and unstable at the same time," and writes, "It is this half-turn to which I object, as unwarranted in logic and opposed to fact."

The subject of the inheritance of acquired characters, associated with the name of Weismann, is not taken up by the author of this dissertation, except incidentally, but is reserved for a future volume, when it will be discussed as a matter of fact. The major part of the book is devoted to a consideration of Weismann's theories in comparison with the hypotheses of Darwin and Galton.

According to Darwin the substance of heredity, gemmules, may be formed anew in each generation; is discontinuous, and proceeds from the somatic to the germ cells, i. e., centripetally, whence the inheritance of acquired characters is habitual.

With Galton the substance of heredity, stirp, is mainly continuous; proceeds from germ cells outward to somatic cells, or centrifugally. Acquired characters are rarely inherited.

Weismann taught that the substance of heredity, germ plasm, was perpetually continuous; proceeded from germ cells to somatic cells, centrifugally. Acquired characters can not be inherited.

With the modifications recently made, this theory substantially coincides with Galton's. Originally, Weismann held that the sphere of germ-plasm was entirely restricted and localized; that there was no reciprocal action between it and body substance; but afterward, upon being confronted with the botanic phenomena involved in cutting, budding, and graft-hybridization, he allowed that germplasm might be found in the nuclei of somatic cells, diffused in the cellular tissue of plants.

Wrapped up also in the tenet of unalterable stability was the origin of hereditary individual variation, which was thus referred to the Protozoa, amphimixis being the only possible cause of congenital variation among multicellular organisms.

In the germ-plasm these dogmas were molted as follows: "The cause of hereditary variation must lie deeper than this. It must be due to the direct effects of external influence on the biophores and determinants; . . . the origin of a variation is equally independent of selection and amphimixis, and is due to the constant occurrence of slight inequalities of nutrition in the germ-plasm."

These sentences, which undo so much of Weismann's distinctive theories, were, according to Dr. Romanes, unnoticed by most of his critics. It maybe added that the differentiation of doctrine is thus reduced to centripetal heredity, Galton and Weismann; centrifugal heredity, Darwin and Spencer.

Weismann's mechanism is extremely elaborate, including nine circles of germ-plasm: molecules, biophores, determinants, ids, idants, idioplasm, somatic idioplasm, morphoplasm, and apical plasm. Of these hypothetical divisions Dr. Romanes would adopt the ids and determinants, since it is a group of cells rather than a single cell that varies in descent.

Two appendices are added to the book. The first contains an argument as to whether a centrifugal theory, germ-plasm, is more conceivable than a centripetal one, pangenesis. Dr. Romanes concludes that one is no more imaginable than the other; "that, whatever the mechanism of heredity may be, it is at