606 



COMPARATIVE ANATOMY. 



to a MuUeriaHj and a secondary archinephric duct (Fig. 348). The 

 latter serves as the efferent duct of the kidney, or ureter, in the 

 Ccecilia3, Urodela, and female Anura, while in the males of many 

 of these latter the primary archinephric duct appears to retain its 

 original function. They open independently into the cloaca. 



Muller, W., Das Urogenitalsystem der Cyclostomen. Jen. Zeitschr. IX.— 

 Semper, C, Das Urogenitalsystem der Plagiostomen. Arbeiten aus deni 

 zool. Institut zu Wiirzburg, II.— Spengel, J. W., Das Urogenitalsystem der 

 Amphibien. Ibid. III. 



[Balfour, F. M., A Monograph of the Development of the Elasmobranch Fishes. 

 London, 1878.] 



§ 449. 



The primitive kidney is likewise developed in the Amniota. 

 For some time in development it extends through the ccelom, and 



projects into it from the dorsal 

 wall of this cavity. The archi- 

 nephric duct is again (Fig. 346,ng) 

 the first part to be developed. 

 The urinary canaliculi (u), which 

 form the glandular portion of the 

 organ, open into it. 



The hinder portion of the 

 primitive kidney, which has 

 always the same function, is well 

 developed even in the Selachii, 

 but still more so in some of the 

 Amphibia ; this is effected by 

 the increase in the number of 

 the urinary canals, and by the 

 formation of special efferent 

 ducts. These processes indicate 

 prophetically the relations of 

 these parts in the Amniota. In 

 the Reptilia the additional por- 

 tion of the urinary canals is 

 directly connected with the 

 hinder portion of the primitive 

 kidney (Lacerta), but it is not 

 connected with it to form the same, but a new organ — the per- 

 manent kidney. For a long time it is present in company with 

 the primitive kidney, but it has its own ducts (ureters), and it takes 

 on the function of the primitive kidney, in proportion as the latter 

 is atrophied, or converted to the purposes of the generative system. 

 In Birds the rudiment of the permanent kidney appears to be 

 formed independently ; and this is still more the case in the Mam- 

 malia. We see, therefore, that the so-called permanent kidney of 

 the Amniota is at first an organ which is connected with and forms 

 part of the primitive kidney, and that it is gradually separated from 



Fig. 346. Section through the embyro 

 of a Bird (Fowl). A Amniotic cavity. 

 am Amnion. ch Notochord. a Aorta. 

 v Cardinal veins. u Primitive kidney. 

 ug Archinephric duct. e Germinal 

 epithelium. P Pleuroperitoneal cavity 

 D Enteric groove. 



