CHAPTER X.

PANGENESIS.

A "provisional hypothesis" supplementing "Natural Selection."-Statement of the hypothesis.-Difficulty as to multitude of gemmules—as to certain modes of reproduction—as to formations without the requisite gemmules.—Mr. Lewes and Professor Delpino. -Difficulty as to developmental force of gemmules as to their spontaneous fission.Pangenesis and Vitalism.-Paradoxical reality.-Pangenesis scarcely superior to anterior hypotheses.-Buffon.-Owen.-Herbert Spencer. "Gemmules" as mysterious as “physiological units.”—Conclusion.

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In addition to the theory of "Natural Selection," by which it has been attempted to account for the origin of species, Mr. Darwin has also put forward what he modestly terms a provisional hypothesis" (that of Pangenesis), by which to account for the origin of each and every individual form.

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Now, though the hypothesis of Pangenesis is no necessary part of "Natural Selection," still any treatise on specific origination would be incomplete if it did not take into consideration this last speculation of Mr. Darwin's. The hypothesis in question may be stated as follows: That each living organism is ultimately made up of an almost infinite number of minute particles, or organic atoms, termed "gemmules," each of which has the power of reproducing its kind. Moreover, these particles are sup

posed to circulate freely about the organism (which is made up of them), and to be derived from all the parts of all the organs of the less remote ancestors of each such organism during all the states and stages of such several ancestors' existence; and therefore of the several states of each of such ancestors' organs. It is further supposed that such a complete collection of gemmules is aggregated in each ovum and spermatozoon in most animals, and in each part capable of reproducing by gemmation (budding) in the lowest animals and in plants.

In many of such lower organisms, therefore, such a congeries of ancestral gemmules must exist in every part of their bodies, since in them every part is capable of reproducing by gemmation. Mr. Darwin must evidently admit this, since he says: "It has often been said by naturalists that each cell of a plant has the actual or potential capacity of reproducing the whole plant; but it has this power only in virtue of containing gemmules derived from every part." 1

Moreover, these gemmules are supposed to tend to aggregate themselves, and to reproduce in certain definite relations to other gemmules. Thus, when the foot of an eft is cut off, its reproduction is explained by Mr. Darwin as resulting from the aggregation of those floating gemmules which come next in order to those of the cut surface, and the successive aggregations of the other kinds of gemmules which come after in regular order. Also, the most ordinary processes of repair are similarly accounted for, and the successive development of similar parts and organs in creatures in which such complex evolutions occur is explained in the same way, by the independent action of separate gemmules.

1 " Animals and Plants under Domestication," vol. ii. p. 403.

1

In order that every living creature may be thus furnished, the number of such gemmules in each must be inconceivably great. Mr. Darwin says: "In a highly organized and complex animal the gemmules thrown off from each different cell or unit throughout the body must be inconceivably numerous and minute. Each unit of each part, as it changes during development-and we know that some insects undergo at least twenty metamorphoses -must throw off its gemmules. All organic beings, moreover, include many dormant gemmules derived from their grandparents and more remote progenitors, but not from all their progenitors. These almost infinitely numerous and minute gemmules must be included in each bud, ovule, spermatozoon, and pollen grain." We have seen also that in certain cases a similar multitude of gemmules must be included in every considerable part of the whole body of each organism; but where are we to stop? There must be gemmules not only from every organ, but from every component part of such organ, from every subdivision of such component part, and from every cell, thread or fibre entering into the composition of such subdivision. Moreover, not only from all these, but from each and every single stage of the evolution and development of such successively more and more elementary parts. At the first glance this new atomic theory has charms from its apparent simplicity, but the attempt thus to follow it out into its ultimate limits and extreme consequences seems to indicate that it is at once insufficient and cumbrous.

Mr. Darwin himself is, of course, fully aware that there must be some limit to this aggregation of gemmules. He

1 "Animals and Plants under Domestication," vol. ii, p. 366.

says:1

Excessively minute and numerous as they are believed to be, an infinite number derived, during a long course of modification and descent, from each cell of each progenitor, could not be supported and nourished by the organism."

But apart from these matters, which will be more fully considered further on, the hypothesis not only does not appear to account for certain phenomena which, in order to be a valid theory, it ought to account for; but it seems absolutely to conflict with patent and notorious facts.

How, for example, does it explain the peculiar reproduction which is found to take place in certain marine worms --certain annelids ?

In such creatures we see that, from time to time, one of the segments of the body gradually becomes modified till it assumes the condition of a head, and this remarkable phenomenon is repeated again and again, the body of the worm thus multiplying serially into new individuals which successively detach themselves from the older portion. The development of such a mode of reproduction by "Natural Selection" seems not less inexplicable than does its continued performance through the aid of "pangenesis.' For how can gemmules attach themselves to others to which they do not normally or generally succeed? Scarcely less difficult to understand is the process of the stomach-carrying-off mode of metamorphosis before spoken of as existing in the Echinoderms. Next, as to certain patent and notorious facts: On the bypothesis of pangenesis, no creature can develop an organ unless it possesses the component gemmules which serve for its formation. No creature can possess such gemmules unless 1 "Animals and Plants under Domestication," vol. ii. p. 402.

it inherits them from its parents, grandparents, or its less remote ancestors. Now, the Jews are remarkably scrupulous as to marriage, and rarely contract such a union with individuals not of their own race. This practice has gone on for thousands of years; and similarly also for

AN ANNELID DIVIDING SPONTANEOUSLY

(A new head having been formed towards the hinder end of the body of the parent).

thousands of years the rite of circumcision has been unfailingly and carefully performed. If then the hypothesis of pangenesis is well founded, that rite ought to be now absolutely or nearly superfluous from the necessarily

R