152 PROFESSOR MARSHALL AND EDWARD J. BLES. 



the tubule itself the flagella, which are longer than the diameter of 

 the tubule, are directed inwards, and through the terminal aperture 

 of the tubule they project as a tuft some distance into the vein. In 

 all our sections of hardened kidneys the flagella are directed inwards; 

 but in separated portions of fresh kidneys, as noticed above, we have 

 found them pointing outwards. 



About the existence of these openings into the veins we have no 

 doubt whatever ; we have seen them with perfect distinctness in a 

 large number of specimens prepared in different ways, and from 

 different frogs. In specimens injected with carmine, after Nussbaum's 

 method, the particles of carmine may be seen in the nephrostomial 

 tubules, and passing through their open mouths into the veins, while 

 no carmine is found in any other portion of the urinary tubules ; but 

 sections prepared in the ordinary way show the communication 

 quite as clearly. When the blood corpuscles are numerous, the tuft 

 of flagella may be seen projecting from the mouth of the tubule, 

 between and among the corpuscles. 



In his first paper, Nussbaum speaks of the veins into which the 

 nephrostomial tubules open as the portal veins • but in his second 

 paper he calls them the branches of the posterior vena cava, i.e., the 

 renal veins. We have satisfied ourselves that the latter deter- 

 mination is the correct one. The veins into which the tubules open 

 lie along the ventral surface of the kidney, and can readily be traced 

 into the vena cava. 



In Fig. 3 we have drawn one of the nephrostomial tubules from 

 the kidney of a 40 mm. tadpole (cf. Figs. 1 and 9). The relations 

 are seen to be precisely the same as in the adult frog, except that 

 the tubule is rather shorter, and the lip round its peritoneal opening 

 less prominent. The tubule has no relation, except one of apposition, 

 with the urinary tubules, and opens by a conspicuous aperture, E B, 

 through which the tuft of flagella projects, into the renal vein, V R. 



Fig. 2 shows identical relations as seen in the kidney of a 21 mm. 

 tadpole (cf. Fig. 6). 



Earlier than 21 mm., our observations are less complete. In 

 17 mm. tadpoles the nephrostomial tubules are present, and open 

 into the body cavity at their outer ends. The inner ends of the 

 tubules appear to us to end blindly, but it is not easy to determine 

 the point satisfactorily. 



