DEVELOPMENT OF KIDNEYS AND FAT-BODIES IN THE FROG. 151 



Nussbaum's method of proceeding is as follows : He first kills the 

 frog with chloroform, then injects into the body cavity carmine 

 rubbed up finely in normal salt solution ; the wound is closed at 

 once, which is conveniently effected by twisting a ligature round a 

 couple of needles passed through the body wall close to the lips of 

 the wound, and the frog is at once placed in Muller's fluid. After 

 about three hours the body cavity is cut open so as to allow the 

 Muller's fluid free access to the kidneys, and the frog is then left 

 in the fluid for twelve to twenty-four hours longer, when the kidneys 

 are removed and examined either by teasing or by sections. The 

 flagella lining the nephrostomial tubules continue their movements 

 for some time after death of the frog, and in this way the carmine is 

 drawn through the nephrostomes. In sections or teased prepara- 

 tions, the carmine particles are found in the nephrostomial tubules, 

 and also in the blood vessels around them, but in no part of the 

 urinary tubules. 



We have repeated Nussbaum's experiments with complete success, 

 and have also been able by examination of sections of kidneys 

 prepared in the ordinary way to demonstrate conclusively the 

 correctness of his description. 



In Fig. 7, the middle one of the three nephrostomes figured is 

 shown ending with an open mouth into the renal veins ; and in 

 Fig. 4, one of the nephrostomial tubules of an adult frog is drawn 

 on a larger scale. The tubule commences with an open, somewhat 

 funnel-shaped mouth, E A ; the tubule itself runs inwards, not 

 vertically to the surface of the kidney, but almost parallel to it, a 

 condition we have found to be almost invariable (cf. Fig. 6). The 

 tubule is somewhat conical in shape ; its inner end is narrow, but 

 opens by a distinct aperture into the vein surrounding the tubule. 

 The wall of the tubule consists of a single layer of epithelial cells, 

 columnar round the peritoneal mouth or nephrostome, cubical or 

 slightly flattened along the rest of its length. Eound the peritoneal 

 opening, the columnar or cubical cells of the tubule extend outwards 

 a short distance, forming a lip to the nephrostome, and then pass 

 suddenly into the squamous cells of the peritoneum. Each of the 

 epithelial cells of the tubule bears a single long flagellum ; round 

 the lip of the nephrostome these flagella project into the body 

 cavity, but their direction is inwards towards the nephrostome. In 



