“I am still of opinion that the origin of sexual reproduction depends on the advantage which it affords to the operation of natural selection.... Sexual reproduction has arisen by and for natural selection as the sole means by which individual variations can be united and combined in every possible proportion.”—Nature, vol. xli. p. 322.
How such contradictory statements can be reconciled I do not perceive; but they furnish a good example of the extreme laxity with which the term “natural selection” is used by ultra-Darwinians.
[6] The meaning of this term, however, as originally used by Nägeli, he so greatly changes to suit the requirements of his own theory, that I think it would have been better had he coined some new one.
[7] I think it is to be regretted that for this other kind of idio-plasm (i.e., idio-plasm-B) Weismann has not coined some distinctive name, or some distinctive prefix, such as that which he sometimes employs when speaking of the other kind (i.e., idio-plasm-A)—viz., “somatic-idioplasm.” Also, the interchangeable manner in which he uses his term “idio-plasm” with the term “ nucleo-plasm,” is somewhat confusing (e.g., pp. 217, 219, 220, 250, 251, &c.). I may add that the word “plasm” in all its combinations appears to me an unfortunate one, since it seems to betoken a substance that can be seen, instead of merely inferred. But, be this as it may, the following table of terms employed may be useful for ready reference:—
| Nucleo-plasm | = the whole contents of the nucleus of any cell. |
| Cytoplasm | = all the other contents of any cell. |
| Idio-plasm-A | = that portion of nucleo-plasm which “controls” a single cell. |
| Idio-plasm-B | = that portion of nucleo-plasm which is destined to construct future cells. |
| Germ-plasm | = undifferentiated idio-plasm-B. |
| Somato-plasm | = idio-plasm-A + cytoplasm. |
[8] See close of Appendix.
[9] See Part I, figs. 36, 37, and 38. The substance of this thread, in the various phases of its segmentation, is the “chromatin,” as there depicted, and so called because it takes a stain better than other parts of the nucleus—thus showing some distinctive character.
[10] For an account of the formation and expulsion of these bodies, see Part I, pp. 125-6. There is now no longer any doubt touching the statement there made as to the male-cell likewise parting with some of its nuclear substance prior to fertilizing the female.
[11] In the case of identical twins, both are probably always produced from the same ovum.
[12] We have no means of estimating exactly the proportional number of cases in which this is possible, either among the lower or the higher plants; but it is certainly much greater than Weismann supposes. “How is it that all plants cannot be reproduced in this way?” he asks, and then adds,—“No one has ever grown a tree from the leaf of a lime or an oak, or a flowering plant from a leaf of the tulip or the convolvulus.” But I am told by botanists that the only reason why the phenomenon thus appears to be a rare one, is because it is not worth anybody’s while to grow plants in this way at a necessarily unsuitable season of the year. Thus, the Rev. George Henslow writes me:—“The fact is that any plant will reproduce itself by its leaves, provided that the cells be ‘embryonic,’ (i.e., the leaf not too near its complete development), and that it be not too thin, so as to provide enough nutriment for the bud to form till it has roots.”