Page:Popular Science Monthly Volume 43.djvu/181

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169
THE INADEQUACY OF "NATURAL SELECTION."

stration that the somewhat different units of a foreign germ-plasm permeating the organism, permeate also the subsequently-formed reproductive cells, and affect the structures of the individuals arising from them, the implication is that the like happens with those native units which have been made somewhat different by modified functions: there must be a tendency to inheritance of acquired characters.

One more step only has to be taken. It remains to ask what is the flaw in the assumption with which Weismann's theory sets out. If, as we see, the conclusions drawn from it do not correspond to the facts, then, either the reasoning is invalid, or the original postulate is untrue. Leaving aside all questions concerning the reasoning, it will suffice here to show the untruth of the postulate. Had his work been written during the early years of the cell-doctrine, the supposition that the multiplying cells of which the Metazoa and the Metaphyta are composed, become completely separate, could not have been met by a reasonable skepticism; but now, not only is skepticism justifiable, but denial is called for. Some dozen years ago it was discovered that in many cases vegetal cells are connected with one another by threads of protoplasm—threads which unite the internal protoplasm of one cell with the internal protoplasms of cells around. It is as though the pseudopodia of imprisoned rhizopods were fused with the pseudopodia of adjacent imprisoned rhizopods. We can not reasonably suppose that the continuous network of protoplasm thus constituted has been produced after the cells have become adult. These protoplasmic connections must have survived the process of fission. The implication is that the cells forming the embryo-plant retained their protoplasmic connections while they multiplied, and that such connections continued throughout all subsequent multiplications—an implication which has, I believe, been established by researches upon germinating palm-seeds. But now we come to a verifying series of facts which the cell-structures of animals in their early stages present. In his Monograph of the Development of Peripatus Capensis, Mr. Adam Sedgwick, F. R. S., Reader in Animal Morphology at Cambridge, writes as follows:—

"All the cells of the ovum, ectodermal as well as endodermal, are connected together by a fine protoplasmic reticulum" (p. 41).

"The continuity of the various cells of the segmenting ovum is primary, and not secondary; i.e., in the cleavage the segments do not completely separate from one another. But are we justified in speaking of cells at all in this case? The fully segmented ovum is a syncytium, and there are not and have not been at any stage cell limits"(p. 41).

"It is becoming more and more clear every day that the cells composing the tissues of animals are not isolated units, but that they are connected with one