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 constructed the first efficient net which could be opened and shut at known depths, using a propeller mechanism (Bibl. Zool. vol. i.); and he improved his original pattern for the “National” and “Valdivia” expeditions. The present writer has devised a net, of which the opening and closing are effected from the deck by heavy weights; this has been used successfully on the “Siboga” expedition and in cruises of the “Research” (Proc. Zool. Soc., 1898). W. Garstang has constructed an ingenious net which is useful in comparatively shallow water, but is open to criticism as being too light for depths beyond 100 fathoms, and several other types are in use. The existence of a mesoplankton, that is, of a plankton living between 100 fathoms from the surface and the bottom, has been generally considered as definitely proved by these nets. On the other hand, A. Agassiz, using the Tanner tow-nets, contends that while a mixture of surface and bottom species may occur in a closed sea near land, there is no intermediate fauna in the open ocean between about 200 fathoms from the surface and the bottom; his conclusions, based on negative evidence, have not met with general acceptance. Animals captured below the first hundred fathoms in the open sea (the Mediterranean, for special physical reasons, is on a special footing) are divisible into at least three categories: (1) those which are eurythermal and eurybathic, e.g. Calanus finmarchicus, (2) those which, so far as we know, are purely mesoplanktonic and never come to the surface, for example, the Radiolarian family Tuscaroridae; (3) those which, like some Schizopoda, spend a larval period in the epiplankton, and seek deeper water when adult, rising to the surface, if at all, only at night. But until the publication of the results of expeditions provided with efficient mesoplankton nets, generalizations about this fauna had better be stated with all reserve There is, however, a certain amount of evidence to show that the mesoplankton includes different organisms in different latitudes, that surface animals of the north and south, unable to spread into the warmer surface water of lower latitudes, there sink into the cooler waters of the mesoplankton; the distributional area of such an organism will be in three dimensions bounded by isotherms (isobathytherms) and isothermobaths. As with the hypobenthos, there seems to be no theoretical reason against the universal distribution of the mesoplankton.

When a more systematic investigation of the various horizons has been carried out, many of the present cases of supposed discontinuous distribution will doubtless disappear. There are, however, undoubted cases of discontinuity where physical barriers have cut across a distributional area, an example of which may be cited here. The Isthmus of Panama was apparently only upraised about Miocene time, having been previously an archipelago through which a great circumequatorial current could pass, consequently the benthos of the Panama region shows marked alliance with the Caribbean, with which it was formerly continuous, but practically none with the Indo-Pacific. To the same cause is doubtless attributable the distribution of the five Decapoda which are characteristic of the Sargasso Sea, which are circumequatorial oceanic types, only occasionally littoral: three of these are known only from the Atlantic, one occurs in the Atlantic and Pacific, one in the Atlantic, Pacific and Indian Oceans. The damming of a great circumequatorial current by the Isthmus of Panama is probably also responsible for that dislocation of currents which resulted in the present relations of the Gulf Stream and North Atlantic Drift to the Labrador Current and cut the Atlantic Boreal fauna into two discontinuous districts (2 and 2′, fig. 3).

Under the head of discontinuous distribution, the alleged phenomenon known as bipolarity must be mentioned. In summarizing the work of the “Challenger,” Sir John Murray maintained on the basis of the reports that numerous species occurred in both polar and sub-polar areas which were absent from the tropic. He regarded them as the hardy survivors of a universal fauna which had withstood that polar cooling which set in towards the close of the Mesozoic period (Murray, Trans. Roy. Soc. Edin. vol. xxxviii., 1896; G. Pfeffer, Verh. deutsch. Zool. Gesellsch. ix. 1899) This view and the facts on which it was

based have been acutely contested, and the question is still far from settlement (for lists of the literature see A. E. Ortmann, Am. Nat. xxxiii. 583; and Miss E. M. Pratt, Mem. Manchester Soc. vol. xlv., 1901). As regards the purely epibenthic and sessile fauna, there are a few undoubted instances of actual specific identity; in some classes, however, such as the Echinoderms, this does not appear to hold (Hamburger Magalhaensche Sammelreise, and F. Römer and F. Schaudinn's Fauna arctica); but even in these the general composition of the fauna and the presence of certain identical and peculiar genera seem to point to something more than a mere “convergence” due to similar environment. As regards the plankton of the two polar regions and such epibenthic forms as extend also into deep water, the suggestion has been made that the Arctic and Antarctic benthos and plankton are really continuous by way of deep water in the main oceans, where the organisms can find a suitably low temperature. As an instance of this, C. Chun (Bezieh. zwischen dem arkt. und antarkt. Plankton, 1897) cites Krohnia hamata, a characteristic Arctic and sub-Arctic constituent of the epiplankton and mesoplankton, known only from the mesoplankton in the tropics, but rising to 38 fathoms at 40° S. 26° E. More exact information, such as may be expected from the various Antarctic expeditions, is required to settle this interesting question with its far-reaching corollaries. (G. H. Fo.)

See also : § Marine.  PLANQUETTE, ROBERT (1850-), French musical composer, was born in Paris on the 31st of July 1850, and educated at the Conservatoire. As a boy he wrote songs and operettas for café concerts, and sprang into fame as the composer of Les Cloches de Corneville (Paris, 1877; London, 1878). In this work he showed a fertile vein of melody, which won instant recognition. There is in his music a touch of pathos and romantic feeling, which, had he cared to cultivate it, would have placed him far above contemporary writers of opéra bouffe. Unfortunately, he did little but repeat the formula which originally brought him reputation. Le Chevalier Gaston was produced in 1879 with little success. In 1880 came Les Voltigeurs du 32me, which had a long run in London in 1887 as The Old Guard, and La Cantinière, which was translated into English as Nectarine, though never produced. In 1882 Rip van Winkle was produced in London, being subsequently given in Paris as Rip, in both cases with remarkable success. The libretto, an adaptation by H. B. Farnie of Washington Irving's famous tale, brought out what was best in Planquette's talent. In 1884 the phenomenon of an opera by a French composer being produced in London previously to being heard in Paris was repeated in Nell Gwynne, which was tolerably successful, but failed completely when produced in Paris as La Princesse Colombine. It was followed by La Crémaillère (Paris, 1885), Surcouf (Paris, 1887; London, as Paul Jones, 1889), Captain Thérèse (London, 1887), La Cocarde tricolore (Paris, 1892), Le Talisman (Paris, 1892), Panurge (Paris, 1895) and Mam'zette Quat'sous (Paris, 1897).  PLANTAGENET, a surname conveniently, but unhistorically, applied to the royal line descended from the union of Geoffrey, count of Anjou, with the empress Maud, who are now styled by historians the Angevin house. It was, historically, only a personal nickname of Geoffrey, as was “Beauclerc” of his father-in-law (Henry I.) and “Curtmantel” of his son (Henry II.), and was derived from his wearing in his cap a sprig of the broom (genet) plant, “which in early summer makes the open country of Anjou and Maine a blaze of living gold.” When the fashion of personal nicknames passed away, the members of the royal house were usually named from their birthplace, as Thomas “of Brotherton,” Thomas “of Woodstock,” Edmund “of Woodstock,” Edmund “of Langley,” Lionel “of Antwerp,” and so forth. But Edward I. and his younger brother, the founder of the house of Lancaster, had still nicknames respectively, as “Longshanks” and “Crouchback.” In the later days of the dynasty the surname of Beaufort was adopted by the legitimated issue of John of Gaunt by Katherine Swynford, but that of Plantagenet was bestowed on Arthur, natural son