PROFESSOR DYER has already discovered one of the many new facts with which he has yet to become familiar, and hastens, in a straightforward manner, to acknowledge the circumstance; but I must again remind him that this, along with many other facts, was described in No. 129 of the Proceedings of the Royal Society. Professor Dyer further says: “Suppose the transverse septa separating these cells absorbed, as probably eventually they would have been, and the rows of cells become scalariform vessels.” But I can assure him, as a question of fact, that these cells do not become so changed; consequently his conclusion that the central cells and the investing vessels are but parts of “one central structure” becomes negatived. The separation of these two structures increases with age instead of diminishing.