Secondly, Weismann says that in parthenogenetic ova only one polar body is extruded. This he regards as equivalent to the first polar body of a fertilizable ovum (i.e., as composed of ovogenetic nuclear substance); and hence he argues that the second polar body of a fertilizable ovum must be regarded as composed of germ-plasm. But even supposing that he is right as to the fact that parthenogenetic ova invariably extrude but one polar body, his argument from this fact would only be available after we had already accepted his view touching the character of the second polar body. So long as this view is itself the subject of debate, he cannot prove it by the fact in question. In other words, unless we have already agreed that the second polar body has the function which Weismann assigns to it, we cannot accept the fact which he adduces as furnishing any evidence of his view touching the function of the second polar body. For these reasons I cannot see that the subordinate theory of polar bodies is required in the interests of the general theory of germ-plasm. The difficulties which it is adduced to meet do not appear to me to be any difficulties at all. Therefore, in now proceeding to consider what in my opinion are the real difficulties which lie against the major theory of germ-plasm, I shall not again allude to the minor—and, in this connexion, superfluous—theory of polar bodies. Such, then, is Professor Weismann’s theory of heredity in its original and strictly logical form. In the course of our examination of it which is to follow in Chapter III and IV, we shall find that in almost every one of its essential features, as above stated, the theory has had to undergo—or is demonstrably destined to undergo—some radical modification. But I have thought it best to begin by presenting the whole theory in its completely connected state, as it is in this way alone that we shall be able to disconnect what I regard as the untenable parts from the parts which still remain for investigation at the hands of biological science. Such, indeed, is the only object of my “Examination of Weismannism.” For, rightly or wrongly, it appears to me that the unquestionable value of his elaborate speculations is seriously discounted by certain oversights with regard to matters of fact, and not a few inconsistencies touching matters of theory. In displaying both these defects, I am not without hope that the result may be that of inducing Professor Weismann so to modify his system of theories as to strengthen the whole by removing its weaker parts. CHAPTER III. WEISMANN’S THEORY OF HEREDITY (1891). WE now proceed to examine Weismann’s theory of germ-plasm, and as this in its various developments has now become a highly complex theory, we had best begin by marking out the lines on which the examination will be conducted.