GAS GLAXDS OF SOME TELEOSTEAN FISHES. 245 



EXPLANATION OF PLATES II.-IX. 



[All figures of sections drawn with tlie aid of the camera lucida. In figures 4,9, 13, 

 14, 15, 26, 38, 46, 49, 52 and 67, which, like most of the others, have been gi-eatly 

 reduced in size during the process of reproduction, the capillaries of the rete 

 mirabile have not been reduced to nearly the same extent as the other parts of 

 the figures, since, had this been done, they would have been invisible.] 



AnguiJIa vulgaris (PI. II. figs. 1-8). 



Fig. 1 (X 18). Semi-diagrammatic transverse section through the anterior end of 



gas bladder (A. B.) and pneumatic duct (P.D.). G.E., glandular 



epithelium ot bladder ; D.E., epithelium of duct ; A., artery, and V., 



yein supplj'ing bladder. 



2 (X 18). Similar section, more posterior. The artery and vein have each 



divided, each pair of vessels consisting of an artery and a vein. 

 3(X18). Still more posteriorly the ai-terj^ and vein of each pair have 

 subdivided so as to form a mass of intermingled arteries and veins. 



4 (X 18). Each mass of arteries and veins has, just before the pneumatic duct 



joins the bladder, subdivided to form a bunch of minute parallel 

 arterial and venous capillaries — the rete mirabile bipolare geminum 

 (Muller) here seen in transverse section. 



5 X 18). Where the duct joins the bladder, the minute capillaries of the rete 



mirabile have reunited to a considerable extent, arteries with 

 arteries and veins with veins, to form large vessels, which then 

 recapillarize in order to suppli^ the gas gland. P.D., pneumatic 

 duct which has now altered the character of its epithelium and 

 become part of the bladder, P.B. 



6 (X 18). Semi-diagrammatic transverse section through the posterior region 



of the bladder, P.B. 



7 (X 500). Transverse section through the lining epithelium of the pneumatic 



duct. Note the large capillaries and squamous epithelium 

 covering them. 



8 (X 500). Transverse section through the glandular epithelium of the bladder 



(gas gland). G.D., one of the gland ducts formed by the folding 

 of the epithelium. 



Opliichthys {Sphcegehranclms) imberbis (PI. II. fig. 9). 



Fig. 9 (X cir. 10). Semi-diagrammatic transverse section through "red body," 

 where the duct (P.D.) joins the bladder (B.). R.M., the single 

 rete mirabile, the long axis of which is situated transversely in the 

 ventral bladder wall. The capillaries of the rete are here seen in 

 longitudinal section. 



Syngnatlms acus (PL II. figs. 10-13 ; PL III. figs. 14-21). 



Fig. 10 (X 27). Semi-diagrammatic transverse section through the anterior 



attachment of the bladder. A. and V., arteries and veins which 



subdivide to form the rete mirabile ; Ves., vessels not taking part 



in the formation of the rete ; B.G., masses of the diff'use pancreas. 



11 (X 27). The arteries and veins are here subdividing to form the rete mirabile. 



Figs. 12, 13 (X 27). The formation of the rete mirabile (R.M.). 



Fig. 14 (X 27). The anterior end of the bladder (A.B.) has just appeared. The 

 i-ete mirabile (U.M.) is fully formed. 

 15 ( X 27). The arterial and venous capillaries of the rete mirabile have reunite<l 

 to form larger vessels which then recapillarize to supply the 

 bladder epithelium (G.E.). B., bladder cavity. 



Figs. 16-18 (X 27). The vessels of the rete mirabile gradually disappear in supplying 

 the bladder epithelium. 



Fig. 19 (X500). A fold of the "unthickened " bladder epithelium. B.L., gland 

 duct between folds of epithelium ; G.S., granular matter present in 

 only very minute quantity ; V.D., darkened zone of cytoplasm 

 round capillarj- wall. 



20 (X cir. 1000). Transverse section through rete mirabile. Venous capillaries 



indistinguishable from arterial, S.G., disintegration-products of 

 the erythrocytes. 



21 (X 1600). Stages in disintegration of the red blood corpuscles situated in the 



capillaries of the gas gland. S.G. as in fig. 20. 



Peoc. Zool. Soc— -1911, No. XVII. 17 



