. Catalogue of the Chaetopoda in the British Museum (Natural History). Oligochaeta; Polychaeta. Chaetae of Arenicola 41 those of the neuropodia in the greater length of its shaft, is present, but for a short time only, in a few of the last-formed notopodia of very young specimens. A notopodium never contains more than one crotchet, and after this has been cast out it is not replaced by a chaeta. Fig. 7.—A. cristata. Outline of a larva, about -7 mm. long, to show the chaetae. Pk. Prostoniiuni. of a similar kind, but henceforward capillary chaetae only are formed in the notopodium. The evidence
. Catalogue of the Chaetopoda in the British Museum (Natural History). Oligochaeta; Polychaeta. Chaetae of Arenicola 41 those of the neuropodia in the greater length of its shaft, is present, but for a short time only, in a few of the last-formed notopodia of very young specimens. A notopodium never contains more than one crotchet, and after this has been cast out it is not replaced by a chaeta. Fig. 7.—A. cristata. Outline of a larva, about -7 mm. long, to show the chaetae. Pk. Prostoniiuni. of a similar kind, but henceforward capillary chaetae only are formed in the notopodium. The evidence afforded by the young stages of A. cristata described above shows that, in this species, the crotchets are lost from the notopodium within a very short time of the attainment of the full number of chaetiferous segments. Probably this is also the case in other species, for in none of the notopodia of post-larval stages of A. marina (of which examples only 3"G mm. long have been examined) or of A. assimilis has the writer been able to find a crotchet. (^ NoTOPODiAL Capillary Chaetae of Young Speci- mens.—The capillary chaetae successively present in any one notopodium exhil)it a series of changes of form, the principal phases of w^hich, traced chiefly in A. 'pndlla, cridaia and marina, may be noticed here. Within twenty-four hours after hatcliing, the larva of A. pusilla or A. cristata acquires its first chaetae—a pair situated some distance ])ehiiid the middle of its length. There are no elevations of the body-wall, that is, no actual notojxidia, l)ut the two chaetae indicate the position of the first notopodia. The free end of the chaeta (Fig. 8 a) is almost spoon-shaped, the shaft being continued, but tapered, along the axis of the flat " bowl" of the " ; In older larvae, with three or four segments, each notopodium contains a chaeta similar to that just described, but in each of the anterior two or three segments there A Fig. S.—.1. puyi
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