The sponge Suberites domuncula attracted the attention of the Italian naturalist Olivi almost a hundred years ago, but was on account of its firm india-rubber like consistency erroneously regarded as an Alcyonium. Beyond the general diagnosis of Nardo who erected the genus Suberites, the structure of the sponge has, I believe, remained virtually unknown. Not for this reason, however, but because the Monaxonia in general, of which Suberites is an example, are still for the most part but little known, Prof. F. E. Schulze of Berlin was good enough to ask me last winter to investigate the structure of this sponge. To him, therefore—perhaps the greatest living authority on the subject—I may be allowed to express my gratitude for the hospitable reception with which he welcomed a stranger to his laboratory, and for the constant interest and assistance with which he encouraged my work. That I have not succeeded in giving a perfect elucidation of the structure is largely due to the same cause which has kept it for so long almost wholly unknown. The crowded siliceous spicules, the compact consistence, the smallness of the ciliated chambers, make the histological analysis somewhat difficult. Such gaps as exist in my investigation I hope to be able to fill up by the study of related forms, and have with that end begun the study of Suberites mana.