Page:Popular Science Monthly Volume 43.djvu/493

gate, no matter of what kind, inevitably end in a state of equilibrium. Suns and planets die, as well as organisms. The process of integration, which constitutes the fundamental trait of all evolution, continues until it has brought about a state which negatives further alterations, molar or molecular—a state of balance among the forces of the aggregate and the forces which oppose them.^[1] In so far, therefore, as Prof. Weismann's conclusions imply the non-necessity of death, they can not be sustained.

But now let us consider the above-described antithesis between the immortal Protozoa and the mortal Metazoa. An essential part of the theory is that the Protozoa can go on dividing and subdividing without limit, so long as the fit external conditions are maintained. But what is the evidence for this? Even by Prof. Weismann's own admission there is no proof. On page 285 he says:

"I could only consent to adopt the hypothesis of rejuvenescence [achieved by conjugation] if it were rendered absolutely certain that reproduction by division could never under any circumstances persist indefinitely. But this can not be proved with any greater certainty than the converse proposition, and hence, as far as direct proof is concerned, the facts are equally uncertain on both sides."

But this is an admission which seems to be entirely ignored when there is alleged the contrast between the immortal Protozoa and the mortal Metazoa. Following Prof. Weismann's method, it would be "easy to imagine" that occasional conjugation is in all cases essential; and this easily imagined conclusion might fitly be used to bar out his own. Indeed, considering how commonly conjugation is observed, it may be held difficult to imagine that it can in any cases be dispensed with. Apart from imaginations of either kind, however, here is an acknowledgment that the immortality of Protozoa is not proved; that the allegation has no better basis than the failure to observe cessation of fission; and that thus one term of the above antithesis is not a fact, it is only an assumption.

But now what about the other term of the antithesis—the alleged inherent mortality of the somatic cells? This we shall, I think, find is no more defensible than the other. Such plausibility as it possesses disappears when, instead of contemplating the vast assemblage of familiar cases which animals present, we contemplate certain less familiar and unfamiliar cases. By these we are shown that the usual ending of multiplication among somatic cells is due not to an intrinsic cause, but to extrinsic causes. Let us, however, first look at Prof. Weismann's own statements:

"I have endeavored to explain death as the result of restriction in the powers of reproduction possessed by the somatic cells, and I have suggested that such

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1. See First Principles, part ii, chap, xxii, Equilibration.