138 E. R. HOSKINS AND M, M. HOSKINS 



SUMMARY AND CONCLUSIONS 



1. Digitiform gland 



The digitiform gland of Mustelus excretes about 1 cc. a day 

 of clear alkaline fluid containing urea. Certain injected solu- 

 tions, but no suspensions, were recovered in this excretion. 

 Injections of excretory toxins injure this gland. 



2. Kidney (mesonephros) 



The selachian kidney is a less efficient excretory organ than 

 the mammalian kidney (metanephros). The daily urine out- 

 put amounts to about 18 cc. per kg. body weight, with a urea 

 content o^ about 1 per cent (Baglioni, '06). The dogfish kidney 

 excretes injected solutions as rapidly as the mammalian kidney, 

 but only in small amounts, the solutions appearing in the urine 

 in eight minutes after intravenous injection and in fourteen 

 minutes after intramuscular injection. The dogfish kidney 

 does not excrete injected particulate matter and the tubules 

 are not noticeably stained by insoluble vital dyes, at least in 

 five days. Large amounts of renal toxins (potassium chromate, 

 tartaric acid, and uranium nitrate) are withstood by the dogfish 

 for long periods. These toxins produce nephritis in which three 

 different types of degeneration occur. These are hyaline, gran- 

 ular, and hydropic degeneration of the cytoplasm, especially of 

 the excretory tubules. The nuclei are destroyed after either 

 hyperchromatosis or hypochromatosis. Some of these cellular 

 changes are due to inanition. The blood-vessels in the glomeruli 

 and among the tubules are not seriously affected except after 

 severe necrosis. The capsules of the glomeruli are only slightly 

 injured. 



3. Liver 



The liver in dogfish is relatively a very efficient excretory 

 organ. The bile contains 1.7 per cent of urea (Van Slyke- 

 White, '11). The liver eliminates injected solutions and sus- 

 pensions readily and in great ^concentration. In a given timie 

 the liver excretes injected solutions in several times the amount 

 excreted by the kidney. The liver is the only organ in the 



