732 ON BESPIEATOEY ORSAIfS OF lAMPEBXS AND HAG. [DeC. 5, 



first gill-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 bi'anchial region, appeared to be the mere effects of shrinkage 

 during p^'eservation. On dissection (fig. 2 h), 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 developed one, ending blindly some little 

 distance from the integument, and, but for the possessi6n of gUl- 

 f olios, 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 gill 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 Notklanus 

 and Chlamydoselachus ^, of the paraal development of a sixth bran- 

 chial cleft in Raja and Torpedo ^, and of a sixth branchial arch in 

 ProtopUrus, and of the alleged presence in BdeUostoma polytrema of 

 13 or 14^ gill-apertures, and in B. hisclioffii of 10*) 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 now before the Society evidence of a tendency on the 

 part of the living Petromyzontidse towards numerical reduction of 

 the precisely opposite order — i. e. antero-posteriorh . With respect 

 to this, as to certain salient features in their organization ^, the 

 Marsipobranchii exhibit modification the precise converse of that of 

 the gnathostomatous Vertebrata. 



O' 



Myxine glutinosa. — One specimen exhibited, for the discovery 

 of which Prof. Howes was indebted to his pupil Mr. H. B. Lacy. 

 Externally it bore (fig. 3) two respiratory orifices on its left side, 

 instead of one, viz. a smaller anterior one (5r.«.) which gave exit 

 to the collective series of branchial passages, and a larger posterior 

 one {d.oe.) alone related to the cesophago-cutaneous duct. This 

 unique feature of the specimen was accompanied by the presence 

 of a seventh gUl (br.s.), as indicated in the accompanying figure ; 

 special interest attaches to this, on account of Parker's suggestion ° 

 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 Common Hag closely akin to that of the 

 " BdeUostoma heterotrema " of Job. MiiUer (c/. Myxinoiden, pi. vii. 

 fig. 3). 



1 Cf. Gannan, Bull. Mu3. Comp. Zool. Camb. Mass. vol. xii. no. i., and Giiuther, 

 ' Challenger ' vols. ' Zoology', vol. xxii. p. 2. 



"^ Wyman ; Beard, cf. Q. J. M. S. vol. xxvi. pp. 108, 109 (1886). 



^ Cf. Giinther, Brit. Mus. Oat. Fishes, vol. viii. p. 512, and Schneider, 

 Wiegmann's Archiv f. Naturgesch. Bd. xlvi. p. 115. 



* Schneider, loc. cit. 



•' Cf. Trans. Liverpool Biol. Soc. vol, vi. p. 141. <= Loc, cU. p. 384. 



