The publication of the »Reports on the Scientific Results of the voyage of H. M. S. Challenger” undoubtedly will mark an era in the history of our knowledge of the Invertebrate Animals. Never before in any voyage such a bulk of wellpreserved material was collected and afterwards worked out by so many distinguished investigators. In the first place this can be stated about the Annelida Polychaeta, a group usually quite neglected in preceding voyages. Though in the last decennium the number of known species much increased owing to the careful investigations of Grube 1), Marenzeller 2), Hansen 3), Langerhans 4), Théel 5), a. o., by the Report of Mr. M’Intosh on the Challenger-Annelida, lately published, our systematical knowledge of this group is largely advanced, not only by the description of 220 species new to science, but also by his detailed descriptions and accurate figures of the essential parts of many little known species. He rightly states in his Introduction that little reliance can be placed on the description of bristles etc. without accurate representations; a good deal of the species of different authors cannot be identified on account of the vagueness of the figures or the total want of them. Though the Leyden Museum possesses only a small collection of Annelida, for the greatest part in an indifferent state of preservation, I think it not without interest to examine them carefully, as never has heen done before. I have begun to investigate the Amphinomidae, a family about which our knowledge is very scarce, notwithstanding Baird’s Monograph 1). Prof. A. A. W. Hubrecht favoured me also with the examination of the specimens of the Utrecht Museum.