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Show 1890.] WORMS OF THE GENUS PERICH.ETA. 57 (5) Genus HOPLOCH^ETA, gen. nov. Setae forming a continuous row round each segment; atria tubular, two pairs opening on to segments 17 and 19. (For P. stuarti, Bourne.) Distribution. India. PERICHCETA INDICA (Horst). 'Eine Perichceta von Java,' Horst, Nederl. Arch. f. Zool. iv. p. 3. Megascolex indicus, Horst, Notes Leyden Mus. vol. v. p. 186. Perichceta indica, Beddard, Proc. Zool. Soc. 1886, p. 298; Horst, Midden-Sumatra, Vermes, p. 4. This species is already pretty well known, and I have not much to add to our knowledge of it beyond the appearance of the living worm, which has been already described (p. 52) and which is illustrated in the accompanying coloured drawing (Plate IV. fig. 1). Horst remarks (15. p. 189) that probably some of the specimens of P. cingulata described by Vaillant (22) are identical with this species ; Perrier has suggested that several species are included under the name of P. cingulata. In view of these difficulties it seems to be reasonable to adopt Horst's name of P. indica and to drop the name of P. cingulata altogether. On the first few segments of the body there are two specially large and distinct pairs of setae, situated at almost equidistant intervals on the ventral side of the body. I did not refer to them in m y earlier paper upon P. indica; the condition of the setae is a step in the direction of those very remarkable Perichaetous worms described by Mr. Fletcher, which I have ventured to include in a distinct genus. These facts have an important bearing upon the general question of The Distribution of the Setce in Chcetopods. The paired setae of Lumbricus and other Oligochaeta are usually compared to the parapodia of the marine Chaetopods ; and it has been supposed that four distinct parapodia and four pairs of setae represent the typical arrangement of the locomotor organs of these two divisions of the Chaetopoda. Deviations from this arrangement, the extremes of which are shown in the Capitellidae and in the genera Perichceta and Perionyx, are regarded by perhaps the majority of naturalists as secondary modifications. There is, however, a certain amount of evidence which seems to point the other way, indicating that the complete circle of setae, which characterizes the family Perichaetidae, is the primitive arrangement; in this case the paired setae of Lumbricus, Acanthodrilus, &c, will be due to reduction, and the comparison with the four seta-bundles of Poly-chaeta will fall to the ground. Among Polychaeta the nearest approach to the Perichaetous condition is found in the Capitellidae ; but Eisig (13) argues with considerable force against regarding the almost continuous circle of setae found in some Capitellids as the primitive |