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Show 1905.] GEPIIV'REAN WORMS OF ZANZIBAR, ETC, hooks of the Physcosoma type that lie in the introvert. Generally the hooks in Phascolosoma are simple, slightly curved structures, and in only one other form, the Ph. papilliferum of Keferstein ( = Ph. dissors Sel. & de Man), do the hooks, so far as I know, acquire the features that are generally found in those of a Physcosoma, namely the greatly curved apex borne on a broad base, the more or less sharply differentiated clear central space, and often an accessory lobe. As regards the internal anatomy, the following are the most important features :-There are four retractors, of which the ventral arise fairly close to the nerve-cord and just behind, the dorsal just in front of, the middle of the body ; these unite very soon to enclose the oesophagus, above which lies the simple contractile vessel. The intestine is not much twisted, and the rectum, which is moderately long, opens a little in front of the origin of the dorsal retractors; a little in front of the anal opening again are the openings of the nephridia, which latter are short, rather broad, and unpigmented. The intestine is held to the hind end of the body by a fine muscle-strand, and two other somewhat stouter strands run («) from the left side of the nerve-cord to the commencement of the intestine, and (6) from near the anus, along the rectum, to the intestine. Two very distinct eye-spots may be seen just above the mouth. Externally the body is covered with numerous, conical, often brown-coloured papillae; in the middle, however, these are lower, less numerous, and more finger-shaped. These papillae, moreover, extend a little way up the introvert, gradually becoming fewer and lower, till they reach the rows of hooks (which reach more than halfway back along the introvert); in between the rows they appear as flattened elliptical bodies with a conspicuous central opening. IY. Genus CLOEosirHox. 14. C loeosiphon a sp erg il lum Quatrefages. Selenka, tom. cit. p. 126 (1883). Loc. Chwaka Bay, Zanzibar ; 2 specimens. British East Africa ; 1 specimen. Y. Genus A s p ie o s ip h o n . 15. AsproosrPHON e leg an s Cham. & Eysenh. Selenka, tom. cit. p. 124 (1883); Sluiter, Natuurk. Tijdschr. Ned. Ind. 1. p. 116 (1890), and Siboga-Exp. p. 19 (1902). Loc. Wasin, British East Africa. Hah. Among coral, at low tide. Several specimens. In Selenka's key to the species of this genus he includes A. elegans amongst those in which the anal shield is calcified. But there is certainly no calcification in the specimens I have seen, nor does Selenka mention the fact in his description. P roc. Z o o l . Soc.- 1905, Y o l . I. No. III. 3 |