424 



SCIENCE. 



[N. S. Vol. V. No. 115. 



The bearing of these facts upon the current 

 theories of degeneration, panmixia, etc., 

 were indicated. 



The American eggs ranged in length from 

 18 mm. to 26 mm., wliile the shortest and 

 longest European eggs measured respec- 

 tively 18.5 mm. and 25 mm. The typical 

 American eggs, moreover, had an average 

 length of approximately 21 mm., while the 

 European eggs averaged af least 1 mm. 

 longer. 



The ratio of breadth to length, i. e., the 

 ratio of the lesser to the greater diameter, 

 showed much greater sphericity on the part 

 of the American eggs, though also in respect 

 to this feature the American eggs presented 

 a much greater amplitude of variation. 



The extremes of variation in shape and 

 color were determined by a process of ' dis- 

 interested selection.' After having placed 

 a secret mark upon each American egg, the 

 eggs of both countries (863 American and 

 863 British) were thoroughly mixed together 

 in a single tray. A disinterested person was 

 then requested to select from the mixture 

 100 eggs that appeared to him to present 

 extremes of shape variation. If eggs from 

 the two countries were equally variable, of 

 course approximately the same number 

 from each would be selected, and if the 

 American specimens were more variable, 

 more American eggs would be selected. The 

 result was in harmony with the evidence 

 derived from the comparison of length and 

 the ratios of breadth to length. Of the 

 selected eggs, eighty-one were American and 

 only nineteen were English, over four times 

 as many of the former as of the latter. 



The same method was adopted for the 

 determination of color variation and with 

 the result that eighty-two of the examples 

 of extreme color variation were found to 

 be American and only eighteen British. 

 It was pointed out that this large propor- 

 tion of extreme color variation on the part 

 of American eggs was not only interesting 



in itself, but that when the figures are com- 

 pared with those representing extreme vari- 

 ation in shape the sigpificance of both re- 

 sults is enhanced. Not only is the pre- 

 ponderance of variation among American 

 eggs very obvious, but in both cases, in 

 shape and in color, it is almost precisely 

 the same. 



It was concluded that the data, whether 

 gathered from comparisons of length, ratio 

 of breadth to length, shape or color, all 

 point in the direction of a general structural 

 modification. 



On the Plankton of Brackish Water. G. W. 



Field. 



Investigations of the Plankton are now 

 being carried on at the Marine Laboratory 

 of the Rhode Island Experiment Station at 

 the Great Salt Pond, near Point Judith, in 

 South Kingston, R. I. It is intended to 

 continue the observations, both summer 

 and winter, for a term of years. 



The pond is about five miles long and 

 comparatively narrow. Its area is esti- 

 mated at 1,500 acres. At the northern end, 

 where the river enters, the water at the sur- 

 face is quite fresh (specific gravity 1.000) ; 

 at the bottom it is slightly saline (specific 

 gravity 1.0055). The south end communi- 

 cates with the sea. The specific gravity of 

 the water at the outlet is 1.025. At points 

 between the north and south ends of the 

 pond are found all intermediate degrees of 

 salinity. 



Examination of the number of organisms 

 per litre shows that the number is greatest 

 in those areas where the specific gravity is 

 between 1.008 and 1.020 (i. e., the middle 

 portion of the pond), and that in passing 

 in either direction, southerly towards the 

 ocean, or northerly towards the river, the 

 number diminishes. 



The most important constituents of the 

 Plankton, named in order of the number of 

 individuals, are : diatoms and algal debris ; 



