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Show 732 ON RESPIRATORY ORGANS OF LAMPREYS AND HAG. [Dec. 5, first gdl-perforation was seen to be wholly unrepresented; the area of its occurrence was crossed by the anterior of a recurrent series of vertical furrows (/) coincident in position with the branchial apertures, but these, together with a depression of the entire branchial region, appeared to be the mere effects of shrinkage during preservation. O n dissection (fig. 2 b), the ventral aorta was found to give off seven symmetrically disposed pairs of afferent branchial vessels ; but, this notwithstanding, the right anterior gill-sac (br. I) was a feebly de/eloped one, ending blindly some little distance from the integument, and, but for the possession of gill-folios, it recalled the condition of Huxley's vestigial "hyoidean cleft" as observed by subsequent investigators. The suppression of the parts was thus seen to be of the opposite order in the two examples, i. e. that possessed of the tegumental pit lacked the true gdl and vice versa; and the gills of the opposite side were in each case normal in every detail. The facts appeared to him to show that, although (in view of the well-known existence of more than five pairs of branchial arches and clefts in the living Sharks Notidanus and Chlamydoselachus \ of the paraal development of a sixth branchial cleft in Raja and Torpedo2, and of a sixth branchial arch in Protopterus, and of the alleged presence in Bdellostoma polytrema of 13 or 1 4 3 gill-apertures, and in B. bischofiii of 104) reduction of the branchial apparatus in both the Marsipobranchii and the true Pisces would appear to be the outcome of suppression postero-anteriorly, there was n o w before the Society evidence of a tendency on the part of the living Petrornyzontidse towards numerical reduction of the precisely opposite order-i. e. antero-posteriorl}. With respect to this, as to certain salient features in their organization5, the Marsipobranchii exhibit modification the precise converse of that of the gnathostomatous Vertebrata. Myxine glutinosa.-One specimen exhibited, for the discovery of which Prof. Howes was indebted to his pupd M r . H . B. Lacy. Externally it bore (fig. 3) two respiratory orifices on its left side, instead of one, viz. a smaller anterior one (br.s.) which gave exit to the collective series of branchial passages, and a larger posterior one (cl.ce.) alone related to the cesophago-cutaneous duct. This unique feature of the specimen was accompanied by tbe presence of a seventh gill (br.s.), as indicated in the accompanying figure; special interest attaches to this, on account of Parker's suggestion6 that the ductus cesophago-cutaneus is " a sort of abortive gill-cleft . . . the morphology of which is self-evident," and as it furnishes us with a variation in the C o m m o n H a g closely akin to that of the " Bdellostoma heterotrema " of Joh. Miiller (cf. Myxinoiden, pi. vii. fig. 3). 1 Cf. Grarman, Bull. Mus. Oomp. Zool. Oamb. Mass. vol. xii. no. i., and Giinther, ' Challenger' vols. ' Zoology', vol. xxii. p. 2. 2 W y m a n ; Beard, cf. Q. J. M . S. vol. xxvi. pp. 108, 109 (1886). 3 Cf. Giinther, Brit. Mus. Oat. Fishes, vol. viii. p. 512, and Schneider, Wiegmann's Archiv f. Naturgescb. Bd. xlvi. p. 115. 4 Schneider, loc. cit. 5 Cf. Trans. Liverpool Biol. Soc. vol. vi. p. 141. 6 Loc. cit. p. 384. |