254 



INVERTEBRATE PHYSIOLOGY 



into the kidney. The U/B inuhn ratios and the volume of urine formed 

 were determined for each of the intervals of different pressure. The results 

 are shown in Fig. 2, from Vv^hich it may be seen that, following a preliminary 

 equilibration phase, the volume of urine was inversely proportional to the 

 hydrostatic back pressure on the kidney. When the volume of fluid was 

 low, the U/B ratio tended to rise above one. This is suggestive evidence 

 that filtration continued but that the reabsorption of water was a normal 

 part of the kidney function under these circumstances. 





c ■^ 90 

 .5E 



o g eo 



O 



o o«o»o«°«o 



o O 



o 8*°' 



• o* 



• — Urine 

 O — Blood 



MINUTES 



Fig. 2. The effects of ureteral back pressure on the rate of urine formation in the 

 giant African snail. 



Similar experiments have been performed on the cephalopod Octopus 

 hongkongensis (Harrison, 1954; Harrison and Martin, 1955). In this 

 case inulin solution was perfused continuously into the closed vascular 

 system of the octopus. Urine samples were recovered as quantitatively as 

 possible at 15- to 30-minute intervals for many hours, and blood samples 

 were taken at corresponding but intermediate intervals. It was therefore 

 possible to follow the blood and urine concentrations in this marine form 

 for comparison with the terrestrial mollusc. The U/B ratio remained at 

 approximately one, indicating that the inulin was probably filtered from 

 the blood stream and excreted without change in the water content. 

 Filtration should be relatively independent of the actions of tissue poisons 

 and test showed that such was the case ; neither phlorizin, DNP, nor bene- 



