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Show 940 DR. H. J. HANSEN ON CRUSTACEANS [Dec. 1, species. In the full treatment (" The Stalk-eyed Crustacea.-Rep. on an Explor. off the West Coast of Mexico . . .," M e m . of the Mus. of Compar. Zool. vol. xviii. 1895) he communicates extensive descriptions and a series of figures of the same 3 species, but he withdraws 2 of them as synonyms to earlier known forms; one of these, S. halla, must, however, be re-established. The result is that of Sergestes and Sergia, taken together, 59 species have been established, of Sciacaris 1-in all 60 species, of which 7 have been withdraAvn by various authors, but only 5 with good reason; so that we have the preliminary result: 55 species. The development of Sergestes was first and most fully elucidated by C. Claus. In 1863 (" Ueber einige Schizop. und niedere Malacostraken Messina's," Zeitschr. f. wiss. Zool. B. xiii. 1863) Claus describes a larva which he names Acanthosoma, without, however, being able to indicate its relations; but he (pp. 437- 439) correctly refers Mastigopus, Leuckart (1853), to a larva of Sergestes. In 1876 (Untersuch. zur Erforschung der Geneal. Grundlage des Crustaceen-Systems) he shows all the principal features of the metamorphosis : he has found a Protozoea-stage, and states the zoea described by Dohrn as Elaphocarls, Acanthosoma, and Mastigopus to be successive stages of the development. One point is of special interest, viz. his statement that the two posterior pairs of trunk-legs, which are well developed with long exopods in the Acanthosoma, are thrown off by the moulting to the Mastlgopus-stage, and then grow out again; they become " sichtbar als kurze Schlauche, die wir an grosseren und alteren Larven in verschiedenen Uebergangsstufen zu kleinen Fiissen sich entwickeln sehen " (Zeitschr. w. Zool. p. 438).-Some months before the " Untersuchungen " of Claus appeared v. Willemoes-Suhm published ("Prelim. Remarks on the Development of some Pelagic Crust.," Proc. Roy. Soc. Lond. vol. xxiv. 1876, and Ann. & Mag. Nat. Hist. ser. 4, vol. xvii.) a short paper, in which he states that Elaphocarls, Dohrn, is the zoea of Sergestes, and that the development passes through an Amphlon-stage &c.; but on the Mastigojms-stage and its want of the two posterior pair of trunk-legs he says nothing.-In Bate's ' Challenger' Report 30 pages and several plates are occupied by the representation of a series of Elaphocarls, Acanthosoma, Mastigopus, and considerations about the development. On p. 383 he says : " By tracing the several stages, we may safely conclude, from the direct structural affinities, that Mastigopus is a young Sergestes." This is correct, but when he really tries to establish any limit between Mastigopus and Sergestes he is not fortunate, nay, in the description of Serg. longlsplnus, Bate (pp. 417-18), he even writes : " Tbe fourth and fifth pairs are entirely absent," and later on he is " inclined to think that their absence is owing to the early stage of development"; thus his Serg. longlsplnus is a young Mastigopus with the legs referred to still less developed than in the form he in the earlier part (pp. 376- 77) describes as Mastlg. acetlformis, Bate. Thus the differences |