DEPARTMENT OF MARINE BIOLOGY. 177 



five days during the middle of June at Boca Grande Cay for that purpose. 

 Here the fish are to be found in large numbers, 23 being counted at one 

 time, 33 at another. They come out of the deeper water to bask in the 

 sunshine and play in the shallows on the south side of the island, and are 

 fearless of man. Several times I drifted over groups of two to five of them, 

 they making no movement until the keel of the boat touched their dorsals. 

 As the breeding-season was only just beginning, it was impossible to collect 

 any material for the embryology of the fish. 



At Tortugas and at Key West I was fortunate in obtaining specimens of 

 Hypoprion brevirostris and of Galeocerdo tigrinus (the tiger shark). The 

 data obtained from these, in addition to that secured last season, will make 

 it possible to write careful descriptions of these two sharks. This is desir- 

 able, since the descriptions now available are very brief and imperfect. 

 The largest tiger shark was 113^ feet long and was estimated to weigh from 

 600 to 800 pounds. 



In addition to the above, a specimen of the dusky shark (Carcharhinus 

 ohscurus) 8 feet long was captured at Key West. It and several others of 

 these sharks were females, but unfortunately none of them carried embryos. 

 Thus the opportunity was lost of settling the interesting question of the 

 method of gestation in these sharks. 



Further observations were made on the structures and habits of the sting- 

 ray (Dasyatis hastata), but no embryos were obtained. Four specimens of 

 the beautiful spotted eagle-ray, Aeiobatus narinari, were obtained at Key 

 West, and sufficient data obtained to finish my history of this fish. This 

 paper will appear in volume 6 of Papers from the Tortugas Laboratory 

 (Carn. Inst. Wash. Pub. 183). 



Considerable numbers of teleostean fishes were collected and dissected, 

 and careful notes made of their habits and structures. There is now at 

 hand a considerable volume of data on the natural history of these fishes. 

 During this season several were taken which are new to the fauna of the 

 Tortugas, and at least one, Diplodus sargiis, which (so far as I know) has not 

 before been recorded from the waters of the United States. 



Report of Investigation of Color of Gulf-weed Fauna and of Reef Fishes, 

 by W. H. Longley, Goucher College, Baltimore. 



During the month of June, I continued the investigation of the ecological 

 relations of the gulf-weed fauna begun two years before. The point toward 

 which inquiry was particularly directed concerns the significance of the color 

 combination which appears so commonly upon the animals occurring in the 

 floating Sargassum. Not less^than 12 species (4 fishes, 2 crabs, 2 shrimps, 

 3 gastropods, and a planarian) are marked with the gulf -weed colors, chiefly 

 shades of brown and yellow. Moreover, some of these animals possess ex- 

 ternal organs whose likeness to the leaf-like divisions of the plant-body 

 seems to be thoroughly objective. Since these species appear to be confined 

 to the floating algse, it is strongly suggested that their uniformity in color as 

 well as their convergence in structure toward that of the plant is in some 

 essential way related with the lack of variety, the comparative simplicity, or 

 poverty, of the environment in color and form elements. We seem, there- 

 fore, to have here an impressive series of instances of "concealing colora- 

 tion" coupled with structural modifications tending likewise to protect 

 their possessors by rendering them invisible in their normal environment. 



As an example of a group of animals in which some principle other than 

 that of protective coloration has been said to be operative, a preliminary 

 study of the colors, color-patterns, and color-changes of 30 species of reef 



