With the self-destruction of this criticism I am left without any other to answer; and I should not have occupied so much space in dealing with this one, were it not that the high estimation in which Mr. Wallace is so deservedly held by all other naturalists is calculated to render almost incredible the peculiar position to which he has eventually gravitated with reference to my views—professing hostility on the one hand, while reproducing them as original on the other. The misunderstanding of my ideas which this state of matters represents, might have led me to wonder whether I could possibly have rendered my meaning more clear in the first instance, were it not that this misunderstanding extends in an even greater measure to Mr. Gulick's paper than it does to mine. For seeing that the whole criticism is founded on the erroneous idea that our theory supposes physiological selection always to act alone, the misconception becomes positively ludicrous in its relation to Mr. Gulick's views; seeing that, as previously stated, Mr. Gulick not only agrees with me in holding that physiological selection must be greatly fortified by being associated with any other form of homogamy, but even goes so far as to agree with Mr. Wallace that, unless it is so fortified, it can never act at all. So that, as far as physiological selection is concerned, Mr. Gulick's theory is precisely identical with that of Mr. Wallace, and differs from his statement of it only in recognising a number of forms of homogamy, in addition to natural selection, sexual selection, etc., with which the principle of physiological selection may be associated. GEORGE J. ROMANES. THE IMMORTALITY OF INFUSORIA. The ingenious hypothesis that Weismann, the eminent Freiburg professor, promulgated several years ago regarding the vitality of all unicellular beings, but more especially of the Protozoans, is undoubtedly widely known. Weismann maintained that the Protozoans were distinguished from the Metazoans, or organisms composed of a number of cells, by the curious property they possessed of exemption from decay and death. The Protozoans exhibited, in the very words of the German savant, an instance of potential immortality;[8] that is to say, a natural physiological death did not exist for them; if they perished, it was by accident or chance, extraneous to the laws of their organisation. A great many authors have written upon this subject since Weismann, either in support of his opinion, or in refutation of it, and of them we may mention principally Goette,[9] Minot,[10] and M. Delboeuf.[11] [8] _Ueber die Dauer des Lebens._ Jena, 1882. [9] _Ueber den Ursprung des Todes_, 1883. [10] _La Mort et l'Individualité._ (_Bulletin Scientifique du Nord_, 1884-85.) [11] _La Matière Brute et la Matière Vivante._ Paris 1887.