File:Comparative anatomy (1936) (20661115702).jpg

Title: Comparative anatomy
Identifier: comparativeanato00neal (find matches)
Year: 1936 (1930s)
Authors: Neal, Herbert V. (Herbert Vincent), 1869-1940; Rand, Herbert W. (Herbert Wilbur), 1872-1960
Subjects: Anatomy, Comparative
Publisher: Philadelphia : P. Blakiston's Son
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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4o6 COMPARATIVE ANATOMY nephric tubules also in the fact that they acquire connexions with glomeruli and thus are enabled to eliminate liquid wastes directly from the blood vessels and not indirectly by way of the body cavity. In the male the anterior portion of the mesonephros changes its function from that of an excretory organ to that of a reproductive organ. In other words, the tubules of the anterior part of the mesonephros
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Fig. 335.-—Diagrams of urogenital structures in (.4) indifferent and in female elasmobranchs and amphibians; (B) male elasmobranchs and amphibians; (C) male amniote (mammal); (Z?) femal'e amniote (mammal), b, urinary bladder; c, cloaca; e, epididymis;/, Fallopian tube; g, gonad;/?, " stalked hydatid "; ^, kidney (metanephros); I, longitudinal tubule; m, Müllerian duct (oviduct), rudimentary in B and C; mn, mesonephros; o, ovary; ot, ostium tubae abdominale; pd, paradidymis; po, paroophoron; pv, parovarium; r, rectum; ti, testis; u, uterus; iia, urethra; nr, 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.") return to the original function of the coelomoducts from which, assuming an annelid ancestry, they are derived. (Fig. 335) Metanephros. The third kidney or metanephros appears not to be an amniote novelty, since transitional conditions between mesonephros and metanephros occur in some amphibia in the form of a combined meso- nephros-metanephros, the opisthonephros. In the amniote embryo, the nephrogenic tissue from which the excretory tubules of the metanephric kidney arise resembles that which forms the mesonephros. The tubules . of the metanephros, like those of the posterior portion of the mesonephros, arise from the nephrotome and are non-metameric in origin.

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