A treatise on zoology . ^ duct. Degenerate as this organ is,it is better developed in the Cyclostomes than in any known adultCraniate, excepting perhaps some aberrant Teleostei (p. 364). The permanent functional kidney, or mesonephros, is repre-sented by a single longitudinal duct on each side, into which opena number of tubules leading from closed renal capsules withglomeruli (Fig. 32). In all cases the tubules have lost their pi-imi-tive openings into the abdominal coelom ; in Petnmvizon they do. Petromi/zon moniiKs, L. Left-side view of the tnuik region near the base of the dorsal tin ;the
A treatise on zoology . ^ duct. Degenerate as this organ is,it is better developed in the Cyclostomes than in any known adultCraniate, excepting perhaps some aberrant Teleostei (p. 364). The permanent functional kidney, or mesonephros, is repre-sented by a single longitudinal duct on each side, into which opena number of tubules leading from closed renal capsules withglomeruli (Fig. 32). In all cases the tubules have lost their pi-imi-tive openings into the abdominal coelom ; in Petnmvizon they do. Petromi/zon moniiKs, L. Left-side view of the tnuik region near the base of the dorsal tin ;the shin and muscles have been partially removed, a, anus ; ao, dorsal aorta ; , cartilagerays snppoiting fin ; , dorsal tin ; yo, left genital aperture into urinogenital sinus; i, intestine ;/,, mesonephros, and kd, its duct; my, myotome ; , neural arch ; nt, notochord ; , posteriorcardinal vein ; , radial muscles of tin ; , urinogenital opening on papilla. not appear even during development (Wheeler [480]). While in theLampreys the elongated kidney consists of crowded coiled tubulesmuch more numerous than the segments of the body they occupy,in the Myxinoidea the tubules preserve their original metamericorder (Midler [306]). In this character the Myxinoids appear to bemore primitive than any other known Craniate (p. 82, where themorphology of the excretory organs is dealt with). The right and left kidney ducts of the adult end behind in acommon urinary sinus, Avhich opens b
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