I hope at this point a small digression is not out of place in order to introduce an aspect of Weismann’s work which is not usually appreciated. A child is aware of the great and lesser lights that rule the day and night, but for modern man these are not sufficient. Accordingly he has invented from immemorial times his oil lamps, rushlights, tallow and wax candles, gas and electric light for the illumination of his streets and houses. Prehistoric man did not seem to need them, as he thought. These useful examples of applied knowledge were obviously brought into use for showing man better where he was going and where to go, what he was doing and what he wished to see. I hope this trite remark may be pardoned, for there is another form of light which suits my purpose of illustrating the aspect of Weismannism referred to above, that is the light of a lighthouse. The ancients in their crude way saw the need for this and as far back as the days of Ptolemy II. a tower to give light was erected on the island of Pharus, off the Egyptian coast, and it was called a _pharos_. Man found it necessary, as navigation and seafaring advanced, to use this principle more and more, and on headland, sandbank and rugged coast has built noble structures to aid the sailor in his dangerous course. The oldest and finest of these in Great Britain is the Eddystone lighthouse, built first in 1695 by Winstanley and finally by Smeaton in 1756–9. For what reason is a lighthouse built and placed where it is? For the precisely opposite reason to that of the domestic candle. While this shows you where to go and how better to do your immediate business, a lighthouse is for the main purpose of showing a mariner where he should _not go_. It has no relation to adornment or pleasure. It does not invite you to come in your vessel and admire it. It tells you to go away and avoid the sunken rock or treacherous sands. I submit here the suggestion with all deference, that the final work of Weismann has lighthouse value of a high order, as to the _modus operandi_ of evolution. His greatness as a biologist, his candour and skill in dialectics, have built up a veritable lighthouse which may usefully warn the seeker after the path of evolution that he must turn elsewhere if he would not founder upon a reef of facts. The two great contributions to evolutionary thought that Weismann has made should be considered separately, the theory of germ-plasm and that of evolution, though the latter seems to be the necessary outcome of the former. But the truth of Weismann’s view of heredity does not of necessity require the error of his theory of evolution. Romanes on Weismann. For this study the examination of Weismannism by Romanes published in 1893 is of great value. I need only refer here to the main conclusions of that lucid and learned examination.