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Show 1903.] PLANKTON OF TIIE FAEROE CHANNEL. 129 Once it occurred in enormous quantity in St. Andrew's Bay in company with Nyctiphanes norvegica, once at Redcar with a similar swarm of Euthemisto compressa, the latter being also an Arctic type-form \ In both these cases it is probable that the creatures had been driven down the North Sea by a strong southerly current, in the manner which I have alreadv •/ suDgogested2 for Parathemisto oblivia; and it has therefore no more l ight to be regarded as a " British " species than an occasional Velellci or Ianthinci brought up by the North Atlantic Drift to our shores. According to Ortmann (op. cit.), the ‘ National ' hauls gave no indication of the vertical distribution of this species. It will appear from the table (p. 119) that the 1 Research' was more fortunate, and the hauls point to its having a distinct preference for the mesoplankton in the Faeroe Channel. Like (at any rate some) other mesoplanktonic species, it rises to the surface at night. Specimens with adult characters were captured in 19 per cent, of epiplankton hauls, but in 66 per cent, of mesoplankton hauls. On the other hand, larval and post-larval stages, apparently referable to this species, were obtained in 38 per cent, of epiplankton hauls, but only in one mesoplankton haul, and that one terminating near the 100 fathoms. The species, therefore, appears to be epiplanktonic when young, mesoplanktonic when adult, so far as these observations go and in the Faeroe Channel at this time of year. In seeking deeper (colder) water in this locality, it follows what appears to be the practice of other Arctic type-forms when they meet the warmer water of the North Atlantic Drift. That this was not apparent from the results of the ‘ National ' is probably due to the fact that from the Hebrides almost up to the moment of coming into the Gulf-Stream the vessel was in far colder surface-water than that of the Faeroe Channel in summer. The larvae mentioned above ranged from an early Calyptopis stage up to the adult condition. It was not, of course, possible to derive them all with certainty from Thysanoessa longicaudata ; but the majority may be safely referred to this species, not only because the adults captured were far in excess of any other Euphausid, but also because the larvae could be traced gradually through successive stages back to the Calyptopis. The metamorphoses of this species follow the lines indicated by Sars 3 for Nyctiphanes, Euphausia, and Thysanopoda. As Paul Mayer4 has shown, the spination of the telson of Malacostracan larvae yields a character important both for phylo-geny and for diagnosis. It has not as yet, I think, been pointed out that the condition of the telson in Euphausiidae affords a further argument for the view maintained by Boas5 and others, 1 C. Cliun : ‘ Bezieliungen zwischen dem arktisclien und antarktisclien Plankton,' Stuttgart, 1897, 8vo, p. 30. 2 Proc. Zool. Soc. 1898, p. 583. 3 G. O. Sars : Chall. Rep. Zool. xiii. (Schizopoda). 4 P. Mayer: Jenaisclie Zeitschrift, xi. (1877), p. 246 et seqq. 5 J. E. V. Boas: Morphologisches Jahrbucli, viii. p. 485. P r o c . Z o o l . Soc.- 1903, V o l . I. No. IX. 9 |
