598 MONTGOMERY— MORPHOLOGY OF THE [April 24, 



sheim (1890) ; for Aves, Sedgwick (1880), Felix (1891) ; and for 

 Mammals, Janosik (1887), Martin (1888), H. Meyer (1890). 



Metancphros {Kidney of Amniotes) . — This consists of the duct 

 or ureter, and the kidney proper, both developing behind the meso- 

 nephros. The ureter is a dorsal outgrowth from the segmental duct. 

 There are two views concerning the origin of the glandular kidney. 

 According to the first and older of these the kidney tubules arise 

 as evaginations from the anterior end of the ureter (Kolliker, 1861, 

 W'aldeyer, 1870). There is much more evidence for the second 

 view, origin independent of the ureter from mesoblastic tissue 

 (Emery, 1883, Hofifmann, 1889, Wiedersheim, 1890). The ureter 

 grows forward into an embryonic cell mass known as the kidney 

 blastema, of somewhat uncertain origin, but possibly homodynamous 

 with the anterior mesonephric anlage (Wiedersheim). According 

 to the description of Emery (1883) the so-called collective tubules 

 of the kidney arise as blind outgrowths of the ureter, and these join 

 with the secretory tubules that arise independently from the kidney 

 blastema. There is still much to be decided concerning the exact 

 method of formation of the kidney, but certainly a considerable 

 ])ortion of it arises independent from the ureter from somatic meso- 

 blast. Each tubule of the metanephros commences proximally with 

 a Malpighian corpuscle, that is, a vascular glomerulus enclosed in 

 a capsule of Bowman, a vascular relation like that of the meso- 

 . nephroi ; mctanephric tubules lack nephrostomes or other connec- 

 tions with the coelom.^^ 



Relations of these Nepliridial Systems. — That the pronephros 

 and mesonephros are homodynamic is the view of Balfour (1881), 

 Sedgwick (1881), Price (1897) and Brauer (1902). Field (1891) 

 argued that the two are differentiated parts of one ancestral organ, 

 that differ structurally because they develop at dift'erent periods. 

 But the majority of investigators hold them to be not homodynam- 

 ous, and here may be mentioned W. Miiller (1875), Fiirbringer 

 (1878), Van Wyhe (1889), Riickert (1892), Semon (1891), Rabl 

 (1896), Wheeler (1899), and Maas (1897). If we omit the con- 

 ditions in the Gymnophiones in which the relations of the pronephros 



"Adult mesonephric tubules may still maintain their nephrostomes, or 

 may lose them; cf. Spengel, 1876. 



