File:Chordate anatomy (1939) (20584894456).jpg

Title: Chordate anatomy
Identifier: chordateanatomy00neal (find matches)
Year: 1939 (1930s)
Authors: Neal, Herbert V. (Herbert Vincent), 1869-1940; Rand, Herbert W. (Herbert Wilbur), 1872-1960
Subjects: Chordata; Anatomy, Comparative
Publisher: Philadelphia : P. Blakiston's Son & Co.
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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296 CHORDATE ANATOMY to the original function of the coelomoducts from which, assuming an annelid ancestry, they are derived. (Fig. 266) Metanephros. The third kidney or metanephros appears not to be an amniote novelty, since transitional conditions between mesonephros and metanephros occur in some amphibians in the form of a combined meso- nephros-metanephros, the opisthonephros. The present ureter has been regarded also as an elongated renal tubule which secondarily acquires functional connexions with the numerous tubules of the metanephros.
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Fig. 266.—Diagrams of urogenital structures in (A) indifferent and female elasmobranchs and amphibians; (B) male elasmobranchs and amphibians; (C) male amniote (mammal); (D) female amniote (mammal), b, urinary bladder; c, cloaca; e, epididymis; /. Fallopian tube; g, gonad; h, "stalked hydatid"; k, kidney (meta- nephros); I, longitudinal tubule; m, Miillerian duct (oviduct), rudimetary in B and C; mn, mesonephros; o, ovary; ot, ostium tubae abdominale; pd, paradidymis; po, paro- ophoron; pv, parovarium; r, rectum; ti, testis; u, uterus; iia, urethra; tir, ureter; va. vas aberrans; vd, vas (ductus) deferens; ve, vasa efferentia; w, Wolffian duct, urinary in A, urogenital in B, genital in C and rudimentary in D. (From Kingsley's " Comparative Anatomy of Vertebrates.") In the female amniote, the mesonephros disappears except in the form of functionless rudiments, the epoophoron, the paroophoron, and the duct of Gartner. In the male, the primitive mesonephric duct is utilized as a ductus deferens. The anterior part of the mesonephros becomes the epididymis. Such relations are inherited from those of Anamnia. Rem- nants of the posterior portion of the mesonephros may persist in the adult as the rudimentary paradidymis and ductus aberrans. See Fig. 266. In vertebrates except most mammals, the excretions are poured into the cloaca. This is also true of monotremes. A bladder comparable to

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