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Show 1903.] MEDUS.E FROM BRITISH COLUMBIA AND ALASKA. 177 although he thinks they may possibly be different; in this event he proposes that it should be called after Eschscholtz, Blainville (4) gives a description and coloured figure of the Melicertum penicillatum of Eschscholtz, but these are copied directly from Eschscholtz without further additions. So far as can be judged, the species figured by Eschscholtz was not based on immature specimens, considering the number and length of the gonads, the tentacles, and the height of bell. From the papers of Agassiz and Fewkes we are familiar with the young stages of the Pacific species of Polyorchis ; these are quite different in essential points from Eschscholtz's drawing of the form which he took off the coast of California (11, fig. 4, pi. viii.). The eight long tentacles, four radial and four interradial, are out of all comparison with the four rather large tentacles at the ends of the radial canals in the young stages figured by Fewkes. It is to Agassiz (2) that we owe the present name of Polyorchis, Haeckel (18) retaining this name and placing it under theLepto-medusee, family Cannotida?. Of the three species already known, by far the most interesting is P. campanulatus, originally described as Medusa campamdata, by Eysenhardt and Chamisso (12). Here the bell is much lower and more conical than in the other species. It is eight-sided, and the sides meet in angles. These characters, combined with the position and structure of the gonads as found in all Polyorchids, are remarkably like what is found in the Aglaurida?. For instance, the long finger-shaped gonads of Aglantha in position and structure are very strikingly similar to the gonads in Polyorchis, although they are more numerous. While there are never more than four radial canals in Polyorchis, as compared with the eight of the Aglaurida?, no great significance can always be attached to the number of radial canals. The possession of free " Horkolbchen " by the Aglaurida? would seem to separate them definitely from Polyorchis, although there are Leptomedusa?, such as Laodice, which possess the true endo-dermal sense-clubs of the Trachomedusa?. The most distinctive character between these two groups is the possession by Polyorchis of diverticula on the radial canals, but these undergo marked change during the growth of the animal. Hardly distinguishable in the young, they become apparent as the animal increases in age ; this points to their being a recent acquisition in the evolution of the race, probably within the limits of this particular group. Of the three species of Polyorchis at present known, two are from the Pacific, the third from the Adriatic. It has already been mentioned that Agassiz (2) found P. penicillata in the region of Puget Sound, while Fewkes (14) found it as far south as Santa Cruz on the southern coast of California; it would seem to be, therefore, one of the few Medusa-forms common to both the northern and southern fauna of the West Coast of N. America. P R O C . ZOOL. Soc.-1903, V O L . II. No. XII. 12 |