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Show 134 MR. CYRIL CROSSLAND ON THE [June 16, finds in his specimen of this species from Naples that the setae described by Claparede as " incompletement comjjosees " end in a simple hook covered by a guard *, whereas in the ' Porcupine' specimen a second hook is present a short distance behind the terminal one. Also in the former the gill is borne on the fourth foot, in the latter on the fifth, and in both cases, simultaneously with its appearance, the ventral cirrus is thickened and shortened, presenting an intermediate stage between the normal pointed organ of the first feet and the secretory pad which represents it throughout the remainder of the body. This consensus in the variation of three characters seems a sufficient ground for the separation of the specimens as two distinct varieties. The question, however, now arises as to whether these characters always vary together and in the same direction, or whether their variations may not occur independently and sporadically. As regards the difference between the setae, Claparede mentions the occasional appearance of a second hook. Both in Prof. Mcintosh's specimens and in m y own we find that the young setae which do not yet project from the foot are always provided with the second tooth, which in m y Naples specimens may be present or absent in those setae which are exposed. This indicates that, in spite of the absence of a scar in some cases and the unbroken condition of the guard in nearly all, the lack of the ' proximal tooth is always accidental, and is owing to its brittleness and to the flexibility of the delicate guard. In the Zanzibar specimens a distinct scar is always to be seen in those rare cases where the somewhat stouter hook has been lost. In three specimens from Naples the first gill was borne on the fourth, in three others on the fifth foot, the total number of gills varying between 37 and 50. Out of nine examples from Zanzibar only two bear their first gill on the fifth foot, and the total number is between 46 and 59. The first gill is usually about half the length of the largest, but in two cases those borne by the fourth feet were only a quarter of that length. In the three Naples specimens, the fourth feet of which are devoid of gills, the same appendages bear hooked setae and ventral cirri of the normal form ; but in the three other examples, the fourth feet of which possess gills, they bear simple setae and possess ventral cirri which are knob-like in form. Of nine Zanzibar specimens, in five cases the change in the ventral cirrus takes place on the first, being deferred to the second branchiferous foot only in the remaining two, and in one of these cases the foot on which this change occurs is the sixth. Though I have not found a case of the extension of the hooked seta? to the first gill-bearing foot in any of the Naples specimens, I find such setae to be present on these feet in all those from Zanzibar, even in the two cases where this is the fifth foot. * As in the lower right-hand seta of those figured by Claparede. His other figures as noted above, are optical delusions. See Prof. Mcintosh's note on the ' Porcupine' specimen m the ' Annals and Magazine of Nat. History,' loc. cit. |