PREFACE.
The following paper stands in close relation to a series of short essays which I have published from time to time since the year 1881. The first of these treated of ‘The Duration of Life,’ and the last of ‘The Significance of Sexual Reproduction.’ The present essay is most intimately connected with that upon ‘The Continuity of the Germ-plasm,’ and has, in fact, grown out of the explanation of the meaning of polar bodies in the animal egg, brought forward in that essay. The explanation rested upon a trustworthy and solid foundation, as I am now able to maintain with even greater confidence than at that time. It rested upon the idea that in the egg-cell, a cell with a high degree of histological differentiation, two different kinds of nuclear substance exert their influence, one after the other. But continued investigation has shown me that the explanation built upon this idea is only correct in part, and that it does not exhaust the full meaning of the formation of polar bodies. In the present essay I hope to complete the explanation by the addition of essential elements, and I trust that, at the same time, I shall succeed in throwing new light upon the mysterious problems of sexual reproduction and parthenogenesis.
It is obvious that this essay can only contain an attempt at an explanation, an hypothesis, and not a solution which is above criticism, like the results of mathematical calculation. But no biological theory of the present day can escape a similar fate, for the mathematical key which opens the door leading to the secrets of life has not yet been found, and a considerable period of time must elapse before its discovery. But although I can only offer an hypothesis, I hope to be able to show that it has not been rashly adopted, but that it has grown in a natural manner from the secure foundation of ascertained facts.
Nothing impresses the stamp of truth upon an hypothesis more than the fact that its light renders intelligible not only those facts for the explanation of which it has been framed, but also other and more distantly related groups of phenomena. This seems to me to be the case with my hypothesis, since the interpretation of polar bodies and the ideas derived from it unite from very different points of view, the facts of reproduction, heredity and even the transformation of species, into a comprehensive system, which although by no means complete, is nevertheless harmonious, and therefore satisfactory.
Only the most essential elements of the new facts which form the foundation of the views developed in this essay will be briefly mentioned. My object is to show all the theoretical bearings of these new facts, not to describe them in technical detail. Such a description accompanied by the necessary figures will shortly be given in another place[[234]].
A. W.
Freiburg I. Br., May 30, 1887.