Now the revelation of new facts, as startling as those which are now experimentally fully confirmed concerning flowing crystals, must inevitably cause searching reflection as to whether the magnificent geometrical work on the 230 homogeneous structures, and their development in actual fact in the 32 classes of crystals, is to stand or to be seriously affected. Again the author ventures to express the opinion, that just what happened in regard to the historic differences between the schools of Haüy and Mitscherlich, will in all probability again occur, namely, both extreme views will be shown to depend more or less on real facts, and other connecting facts will eventually be revealed which will completely reconcile the two series with each other. In the author’s opinion, the geometrical work will stand, as the grand generalisation it really is. But it will be interpreted in the future without the somewhat arbitrary assumptions which have more or less accompanied it. From these it will be freed, and then rise purified and elevated to its real dominating position in regard to crystal morphology. Lehmann, with the natural enthusiasm of the discoverer of one of the most remarkable facts for which the last few decades have been famous, may have carried his theory too far, and particularly in that part of his work, to which the author has not hitherto referred, in which he describes certain phenomena of flowing crystals as akin to the movement of living organisms such as bacteria, and thus brought even some of the sound facts under the criticism of the sceptic more than might otherwise have been the case. He may also have made his theory far more revolutionary than is essential. But the one incontrovertible thing stands out plainly, namely, that the “flowing crystals” with which he has made us acquainted are an indubitable experimental fact. Flowing crystals are produced, however, by a relatively few substances of very complex molecular constitution, involving a large number of atoms in the molecule; they are mostly compounds of carbon, and in number possibly not one per cent. of the innumerable substances known to produce ordinary solid crystals. That the theory of crystal structure can eventually be made to include these few remarkable substances is highly probable, when many more facts have been accumulated.