likened to the {352}notopodia and neuropodia of the Polychaetes; but it does not seem certain that this comparison is justifiable. It was at one time thought that the continuous circle of chaetae of the Perichaetidae was the primitive condition; but Professor Bourne has lately found that in _Perichaeta_ the young embryos have not got this continuous circle; it is only acquired later. BRANCHIAE.—The Oligochaeta were called by Cuvier the "Annélides abranches sétigères." But the epithet "abranches" is now known to be inaccurate. In fact it really was so when Cuvier wrote; for naturalists were at that time well acquainted, chiefly through the elaborate work of O. F. Müller, with the little fresh-water Naid _Dero_, the posterior extremity of which is provided with a varying number of branchial processes. These are furnished with looped blood-vessels and are covered externally by cilia, so that the water containing oxygen is constantly renovated. The second instance of a gilled Oligochaete was discovered in the very same family. Professor Bourne[408] of Madras found in "tanks" a Naid which he named _Chaetobranchus_, in which the head segments, to the number of fifty or so, are provided with long ciliated processes, which as a rule enclose the dorsal chaetae of their segments, and in addition a capillary loop. Curiously enough, this very same worm made its appearance in the _Victoria regia_ tank at the Botanical Gardens in the Regent's Park, whither it had in all probability been accidentally imported. Two members of the family Tubificidae were the next examples of gilled Oligochaeta made known to science; one of these, _Branchiura sowerbyi_,[409] appeared also in the Botanical Gardens, so that its native home is unknown. It differs from _Chaetobranchus_ in that the gills are at the posterior end of the body, and are contractile; during the life of the worm they are in continual motion. A species of the South American genus _Hesperodrilus_,[410] _H. branchiatus_, is also gilled, and, so far as can be made out from a spirit-preserved specimen, the gills are precisely of the same pattern and contractility as those of its ally _Branchiura_. Possibly _Branchiura_ ought to be included in the same genus with _Hesperodrilus_. A worm which was originally described by Grube as _Alma nilotica_, should really have been placed before the three last-mentioned {353}instances; but as this worm was only known from a fragment, and as the description was not by any means full, it was not thoroughly believed in; it was surmised that it might be a member of some marine genus, perhaps of the Capitellidae. Oddly enough, the same worm was independently described by a different name, _Digitibranchus niloticus_, a few years later by Levinsen. Quite recently Michaelsen has found by a reference to the original types that this worm is really gilled, and that it is specifically identical with a worm which had been given a totally different name, viz. _Siphonogaster_.