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Must we not feel, with Darwin apparently, that the only intelligible explanation of use-inheritance is the hypothesis of Pangenesis, according to which each modified cell, or physiological unit, throws off similarly-modified gemmules or parts of itself, which ultimately reproduce the change in offspring? If we reject pangenesis, it becomes difficult to see how use-inheritance can be possible.
These bodies have no relation whatever with the production of the eggs or gemmules, as they are formed before the young polypi appear in the cells at the end of the growing branches; as they move independently of the polypi, and do not appear to be in any way connected with them; and as they differ in size on the outer and inner rows of cells, I have little doubt, that in their functions, they are related rather to the horny axis of the branches than to the polypi in the cells.
All these cases are intelligible on the hypothesis of pangenesis; for they depend on the gemmules of certain parts, although present in both sexes, becoming, through the influence of domestication, either dormant or developed in either sex.
Biology, with its protoplasmic elements, its plastids, gemmules, hypotheses on hereditary transmission by means of infinitesimal subdivisions; the theory of evolution, which speaks off-hand of periods of a hundred thousand years; and many other scientific theses that I omit, offer fine material for the numerical imagination.
"There is a growing skepticism on the part of biologists as to the extreme fierceness of the struggle for existence and of the consequent rigor of selection." Overproduction and shortage of space and food might sometime be a factor of importance, but has it been so in the past? Has it affected the human race? Darwin proposed the theory of gemmules. Prof.
Darwin's explanation of inherited mutilations which, as he notes, occur "especially or perhaps exclusively" when the injury has been followed by disease is that all the representative gemmules which would develop or repair or reproduce the injured part are attracted to the diseased surface during the reparative process and are there destroyed by the morbid action.
In the "Origin" Darwin throws out some suggestions as to the causes of variation, but he takes heredity, as it is manifested by individual organisms, for granted, as an ultimate fact; pangenesis is an attempt to account for the phenomena of heredity in the organism, on the assumption that the physiological units of which the organism is composed give off gemmules, which, in virtue of heredity, tend to reproduce the unit from which they are derived.
One cannot say what gemmules of thigh and proboscis may not have got into the neutral bees' stomachs, if they assimilate their food sufficiently, and thus into the larva. 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.
The gemmules with brilliant corpuscles had almost disappeared; we could see but very few, and those now consisted of the refractive bodies alone, the bulk of the vibrios accompanying them having undergone some process of re-absorption.
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