As already stated in the Preface to the second edition of Darwin and after Darwin, Part I, severe and protracted illness has hitherto prevented me from proceeding to the publication of Part II. It is now more than a year since I had to suspend work of every kind, and therefore, although at that time Part II was almost ready for press, I have not yet been able to write its concluding chapters. Shortly before and during this interval Professor Weismann has produced his essays on Amphimixis and The Germ-plasm. These works present extensive additions to, and considerable modifications of, his previous theories as collected together in the English translation, under the title Essays on Heredity, Vol. I. Consequently, it has become necessary for me either to re-write the examination of his system which I had prepared for Part II of my own treatise, or else to leave that examination as it stood, and to add a further chapter dealing with those later developments of his system to which I have just alluded. After due reflection I have decided upon the latter course, because in this way we are most likely to obtain a clear view of the growth of Weismann’s elaborate structure of theories—a view which it is almost necessary, for the purposes of criticism, that we should obtain.

Having decided upon this point, it occurred to me that certain advantages would be gained by removing the whole criticism from the position which it was originally intended to occupy as a section of my forthcoming volume on the Post-Darwinian period. For, in consequence of the criticism having been written at successive intervals during the last six or eight years as Professor Weismann’s works successively appeared, it has now swelled to a bulk which would unduly encumber the volume just mentioned. Again, the growth of Professor Weismann’s system has of late become so rapid, that if the criticism is to keep pace with it in future, the best plan will doubtless be the one which it is now my intention to adopt—viz., to publish the criticism in a separate form, and in comparatively small editions, so that further chapters may be added with as much celerity as Professor Weismann may hereafter produce his successive works. Lastly, where so much elaborate speculation and so many changes of doctrine are concerned, it is inevitable that some misunderstandings on the part of a critic are likely to have arisen; and therefore, should Professor Weismann deem it worth his while to correct any such failings on my part, the plan of publication just alluded to will furnish me with the best opportunity of dealing with whatever he may have to say.

It must be understood, however, that under the term “Weismannism” I do not include any reference to the important question with which the name of Weismann has been mainly associated—i.e., the inheritance or non-inheritance of acquired characters. This is a question of fact, which stands to be answered by the inductive methods of observation and experiment: not by the deductive methods of general reasoning. Of course Professor Weismann is fully entitled to assume a negative answer as a basis whereon to construct his theory of the continuity of germ-plasm; but no amount of speculation as to what the mechanism of heredity is likely to be if once this assumption is granted, can even so much as tend to prove that the assumption itself is true. Therefore, in this “examination of Weismannism” I intend to restrict our attention to the elaborate system of theories which Weismann has reared upon his fundamental postulate of the non-inheritance of acquired characters, reserving for my next volume our consideration of this postulate itself.

Lest, however, it should be felt that “an examination of Weismannism” in which the question of the transmission of acquired characters is omitted must indeed prove a case of Hamlet without the Prince of Denmark, I may be allowed to make two observations. In the first place, this great question of fact is clearly quite distinct from that of any theories which may be framed upon either side of it. And, in the second place, the question was not raised by Weismann. It appears, indeed, from what he says, that he never caught a glimpse of it till about ten years ago, and that he then did so as a result of his own independent thought. Moreover, it is perfectly true that to him belongs the great merit of having been the first to call general attention to the subject, and so to arouse a world-wide interest with reference to it. But to suppose that the question was first propounded by Weismann is merely to display a want of acquaintance with the course of Darwinian thought in this country. As far back as 1874 I had long conversations with Darwin himself upon the matter, and under his guidance performed what I suppose are the only systematic experiments which have ever been undertaken with regard to it. These occupied more than five years of almost exclusive devotion; but, as they all proved failures, they were never published. Therefore I here mention them merely for the purpose of showing that the idea of what is now called a “continuity of germ-plasm” was present to Darwin’s mind as a logically possible alternative to the one which he adopted in his theory of pangenesis—an alternative, therefore, which he was anxious to exclude by way of experimental disproof. If it be said that no one could have been aware of this in the absence of publication, I reply that I think it may be perceived by any one who reads attentively his chapter on Pangenesis. Moreover, early in the seventies his cousin, Mr. Francis Galton, published a “Theory of Heredity,” which, as we shall see in the course of the following pages, presented as distinctly as could possibly be presented the question of the transmission of acquired characters, and answered it in almost exactly the same manner as Weismann did about ten years later. Lastly, as Weismann has himself been careful to point out, he was likewise anticipated in this matter by JÄger (1878), and Nussbaum and Rauber (1880).

For these reasons, then, I exclude this question from the following examination of what I think we ought to understand as distinctively “Weismannism.”

G. J. R.