. Catalogue of the Chaetopoda in the British Museum (Natural History). Oligochaeta; Polychaeta. 48 Arenicolidae the ecaudate species have, along one side, a narrow lamina (2 to 4 /x wide), which, however, soon breaks up into fine teeth (see the left proximal portion of Tig. 16 a). The opposite side of the chaeta bears longer spines. Towards the tip the shaft of the chaeta appears to be encircled by series of spines (Sageblatter), which can be resolved only with difficulty (Fig. 16 b). The only species of Arenicola in which the uotopodial chaetae present characters sufficiently striking and def
. Catalogue of the Chaetopoda in the British Museum (Natural History). Oligochaeta; Polychaeta. 48 Arenicolidae the ecaudate species have, along one side, a narrow lamina (2 to 4 /x wide), which, however, soon breaks up into fine teeth (see the left proximal portion of Tig. 16 a). The opposite side of the chaeta bears longer spines. Towards the tip the shaft of the chaeta appears to be encircled by series of spines (Sageblatter), which can be resolved only with difficulty (Fig. 16 b). The only species of Arenicola in which the uotopodial chaetae present characters sufficiently striking and definite to be of real service in systematic work is A. loveni, the chaetae of which are distinguished Ijy their well-developed Sageblatter, and the transverse striation of their distal portion. The notopodial chaetae in the case of a specimen of any other species would serve, at most, to indicate to which of three groups—marina-pitsilla-assimilis, cristata-glacialis, ccaudata-branchialis—the specimen belonged. Neuropodial Crotchets.—The successive generations of crotchets exhibit progressive changes which, although small, result in the end terms of the series being of markedly different form, that is, the crotchets of the larval and post-larval stages differ widely from those of the adult. A. marina.—The crotchets of a post-larval specimen oi A. marina, 5 mm. long, have the form shown in Fig. 17. The proximal end of the shaft is fixed to the bottom of the setal sac and the greater part of the length of the shaft, up to and including the well marked dilatation present upon it, is enclosed in the sac. The distal portion of the crotchet is bent almost at a right angle to the shaft and forms a beak-like structure—the rostrum. Immediately proximal to the rostrum, on the convex { ventral) side of the curvature of the crotchet,^ there are three (or four) teeth, of which that nearest the rostrum is the largest. On the shaft, just under the rostrum, there is generally visibl
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