266 INVERTEBRATE PHYSIOLOGY 



In the octopus, Mayer and Rathery ( 1907) concluded that reabsorption 

 of glucose and urea was possible. Their experiments are not as physio- 

 logical as might be desired, since they injected glucose or urea solutions 

 into the renal sacs, ligated the urinary papillae, and left the animal un- 

 disturbed for 24 hours. At the end of this time either glucose or urea was 

 present in the renal sac only in a trace. From our experiments (Harrison 

 and Martin, 1955) and the report of von Furth (1900), it would be an- 

 ticipated that the renal sacs would be highly distended with the urine 

 secreted by a healthy octopus during this period of time, and that dilution 

 as well as reabsorption would have taken place. There is no reason to 

 doubt, however, that the glucose was reabsorbed and deposited in the body 

 tissues, and that the urea diffused into the blood and was excreted through 

 the gills in the form of ammonia. 



Harrison and Martin have performed experiments on glucose injected 

 intravascularly and found that, as in the giant African snail, the filtered 

 glucose is normally reabsorbed, but that in the presence of phlorizin the 

 urinary glucose concentration rises until it reaches the level of the blood. 



Arthropods 



Because of their wide diversity of form and great success in invading 

 every major habitat, a considerable variation in excretory function among 

 the arthropods is to be expected ; but members of this group appear to 

 have developed sites of absorption other than the kidney which are so 

 effective in handling the osmotic problem that reabsorptive processes by 

 the kidney tissue may be rendered unessential. 



The striking ability of the palaemonid shrimps to maintain their blood salt 

 at a high level even in dilute media has already been noted. Parry (1955) 

 continued his physiological investigations on this group by determining 

 the rates of urine formation at the extremes of the osmotic range. A mini- 

 mum output was found at a salinity equivalent of 50% sea water. Output 

 increased almost linearly at lower concentrations with a maximum output 

 at a salinity equivalent of 5% sea water, at which point the rate of urine 

 production had increased tenfold. There was also an increased output at 

 salt concentrations above 50%, reaching rates of about four times the mini- 

 mum level when the salinity equivalents reached 100 and 120% of sea 

 water. These observations were made on another species than Palaemon 

 serratiis, for which it was shown that the blood and urine remained isotonic 

 over a considerable range of environmental salt concentration. It is clear 

 that, if the blood salt were to be maintained at a high level while the animal 

 was in 5% sea water, and the urine were to remain isotonic with the blood, 

 and at the same time a very large volume of urine were to be formed, an 

 enormous load would be thrown onto the salt-absorbing mechanisms. 



