DEPARTMENT OF MARINE BIOLOGY. 165 



relative water-content remained unchanged during starvation, while 

 the nitrogen varies. 



A study of albino rats liberated by Professor Henry H. Donaldson 

 in July 1916, on East Key, Tortugas, showed that the animals had 

 bred upon the key and were feeding upon Ocypoda crabs and grass seed. 

 The weight of the brain and of the spinal cord has become relatively 

 heavier in these rats now living under the trying conditions imposed 

 by the small semi-desert islet East Key, which lacks a supply of fresh 

 water and provides only a limited range of food for the rats. 



Professor William H. Longley made much use of a submarine camera, 

 with which he photographed the reef fishes in their natural environ- 

 ment, demonstrating that the colors of these fishes blend with their 

 surroundings to a remarkable degree. These pictures often show 

 every scale and are in the best of focus, and yet the general shade of 

 color of the fish so closely matches that of its surroundings that it is 

 exceedingly difficult to discover the fish. Professor Longley has thus 

 demonstrated that the reef fishes of the West Indies are remarkable for 

 the many different ways in which they attain inconspicuousness. 

 Crabs also illustrate the same law. 



Professor J. F. McClendon carried out an extensive and interesting 

 series of observations upon the physiological properties and calcium 

 content of sea-water at Tortugas. Some of his conclusions have 

 already been referred to in this report and others will be found in the 

 Proceedings of the National Academy of Sciences and in his report 

 pubhshed herewith. He was enabled to discover some very interesting 

 facts, such as the diurnal change in CO2 content of the surface waters 

 of the ocean, the conditions under which calcium is precipitated in the 

 tropical ocean, and the respiratory quotient of animals which have 

 symbiotic plant-cells and can thus maintain their own oxygen supply 

 in sunlight, even oxygenating the surrounding sea- water. He also 

 found that when nerves of Cassiopea are stretched the rate of nerve- 

 conduction remains the same, and thus it takes a longer time to go 

 through a stretched nerve in proportion to the lengthening of the tissue. 



As a result of studies made at Tortugas, Alfred G. Mayer concludes 

 that death of certain corals from high temperature may be due to 

 the accumulation of acid in the tissues. He also attempted to deter- 

 mine the efficacy of holothurians as destroyers of sand over reef-flats, 

 and he determined the law of the rate of nerve-conduction in concen- 

 trated sea-water of the same degree of alkalinity as normal sea-water. 

 Experiments in ''shell shock" in invertebrates yielded negative results. 

 Accounts of these researches appear in the special reports pubhshed 

 herewith. 



Volume XI of Papers from the Department of Marine Biology, pub- 

 lished by the Carnegie Institution of Washington, appeared in July 

 and contains 360 pages, 21 plates, 69 text-figures, and 14 papers. 



