ANIMALS THAT LIVE WITHOUT WATER 167 



greater than that in sea water (490 milliequivalents per 

 hter) and having about twice the maximal osmotic con- 

 centration of the urine. (The magnesium, calcium, and 

 sulfate of the sea water are apparently poorly absorbed 

 from the intestinal tract, and such of these divalent salts 

 as are absorbed are presumably excreted by the kid- 

 neys). The maximal rate of nasal secretion (ca. 0.2 cc. 

 per minute in a 1.5 kg. bird) was such that if continu- 

 ously maintained it would, together with the maximal 

 excretion of sodium chloride in the urine, suffice to re- 

 move all the sodium in the body in roughly 10 hours. 



Paired nasal glands are present in both terrestrial and 

 marine birds and have been known to anatomists for 

 many years. In the marine birds, however, each gland is 

 greatly enlarged and possesses a rich arterial supply and 

 a more highly developed glandular structure than in ter- 

 restrial forms. Invariably draining through the internal 

 nares, the gland may be located either in the supraorbital 

 groove of the frontal bone or in the orbital cavity close 

 to the interorbital septum. Hitherto the function of the 

 nasal gland has been incorrectly interpreted as protect- 

 ing the nasal mucosa from sea water by rinsing away 

 the latter when it penetrates into the nasal cavities. 



In the herring gull {Lams argentatus), in which the 

 anatomical structure is best known, the gland consists 

 of branched, secretory tubules radiating from a central 

 canal or duct; the tubules are made up of cylindrical 

 or polygonal cells characterized by striations or lamellae 

 extending lengthwise, apparently from one end of the 

 cell to the other. The blood supply is mainly from the 

 internal ophthalmic artery, and within the gland highly 

 branched capillaries with frequent anastomoses run ra- 

 dially from the central canal toward the surface, more 

 or less parallel with the tubules. The capillary blood 

 flows in a direction opposite to the secreted fluid in the 

 lumina of the tubules, but whether this 'counter-current' 

 flow is physiologically important is not known. The nerve 

 supply is from a parasympathetic ganghon in the an- 



