l/a FROM FISH TO PHILOSOPHER 



tresses brought to the States in April, 1958, have sur- 

 vived captivity for 15 months and are now in the Na- 

 tional Zoological Park, Washington, D.C. One bird died 

 of heat prostration after one month in Washington. 



The discovery of the salt gland in marine birds immedi- 

 ately raised the question whether an homologous struc- 

 ture existed in the marine reptiles. Unlike the bird kid- 

 ney, the reptilian kidney cannot concentrate the urine 

 at all above the osmotic pressure of the blood, and con- 

 sequently such reptiles as do not have a source of water 

 available to them are in an even more precarious posi- 

 tion with respect to salt and water balance than are the 

 birds. 



Reptiles with a marine habitat occur in four di£Ferent 

 orders: turtles, crocodiles, snakes and lizards. Five 

 species of turtles are strictly marine, returning to land 

 only to lay their eggs. At sea they subsist on fish, which 

 have a relatively low salt content, and on invertebrates 

 and seaweed, which are isosmotic with sea water. The 

 salt-water crocodile Crocodylus porosus is generally es- 

 tuarine, but it wanders far out into the Indian and 

 Pacific Oceans, hving mainly on fish. The sea-snakes, 

 Hydrophidae, which inhabit the Indian Ocean, are also 

 fish eaters; the primitive Lacticauda lay their eggs on 

 land, but the more specialized sea-snakes are ovovi- 

 viparous. From the present point of view the most in- 

 teresting of the marine reptiles is the Galapagos sea 

 iguana (Amblyrhynchus cristatus) which Hves in the 

 surf-splashed rocks of the Galapagos Islands and sub- 

 sists on seaweed, with a large salt excess and water 

 deficit. 



Schmidt-Nielsen and Fange have demonstrated the 

 nasal secretion of a concentrated sodiimi chloride solu- 

 tion after the injection of hypertonic salt solution in the 

 brackish-water terrapin {Malacolemys terrapin) and the 

 completely marine loggerhead turtle (Caretta caretta), 

 and from the anatomy of the nasal gland infer that the 



