isy3.] 



OEGANS OF LAMPllEYS ANJD HAU. 



731 



vidua] s of JL/x-ine glutinosa, aud it is well known that Johannes 

 Miiller's substitution ^ of the generic name Bdellostoma for DuuieriFs 

 '■' Heiitatrema '"' was directly expressive of numerical variation of the 

 branchiae. In knowledge of these facts he (Prof. Howes) had lost 

 no opportunity of seeking for additional evidence of variation of 

 the parts in question, aud the condition of the heads now exhibited 

 appeared to him sufficiently interesting to warrant the publication 

 of his results. 



Petromyzon jluviatilis. — He exhibited two specimens (both 

 " females ") ^. In the larger of them the fii'st branchial aperture of 

 the left side (fig. 1 a [which was visible only under a hand-lens]) 

 was but one-third the size of its fellows and longitudinally instead 

 of vertically disposed. Its free border was uniformly fimbriated and 

 bounded, not an orifice, but a shallow cutaneous depression {br. I, 



Fig. 1 f. Petromyzon fluviatUis, 2'r5 cetitim. total lengtli, showing vestigial 

 first gill on left side. Fig. 1 b. The same, dissected from beneath. Fig. 2 r/. 

 P. fliiviatiiis. 23"5 eentiiu., showing absence externally of first gill on 

 right side. Fig. 2 h. The same dissected from beneath. Fig. 3. Mi/xine 

 glutinosa, dissection from beneath of a specimen possessed of a super- 

 numerary gill on the left side. 



1 a, 2a, nat. size. 1 6, 2i X 1^-. 3 X \\. 



Heference letter^. — br., branchise ; br.s., supernumerary branchia ; cc, peri- 

 branchial blood- lymph sinuses ; d.O!., tt'sophago-cutancous duct; /., 

 tegumental furrows ; 7;/*., pharynx laid open from beneath ; s., inter- 

 branchial septum. 



fig. 1 h) which was closed internally. On dissection, the ventral 

 aorta was found to give off six branches on the left side and seven 

 on the right ; and, in accordance with this reduction, the gill 

 corresponding to the vestigial orifice was entirely absent, its place 

 being occupied by an extensive blood-lymph sinus (re.) homologous 

 with those of the normal poribrancliiai series. In the second 

 specimen, the opposite (right) side was somewhat similarly affected 

 in the corresponding region. View(;d externally (lig. 2 a) the 



' ("Myxinoidcn") Abiiandl. Akad. Wiss. IJerlin, 1834, p. 7".). 

 * Beard has recently diBCOVcrcd Ihepresenccof ovain the testis oi 1'. plaiicrU 

 Brit. Aaaoc. Eep., Edinburgh, 1802, p. 700, and Anat. Anz. vol. viii. p. 60. 



