212 CARNEGIE INSTITUTION OF WASHINGTON. 



if these species, others that may hereafter be taken with them, and such 

 surface-swimmers as Tylosurus, Hemiramphus, and Atherina, whose green 

 is a "water color," be excluded, no significant fraction of such a list may be 

 compiled from the whole fish fauna of the region. It is, therefore, con- 

 clusively proven that among these fishes the occurrence of this color is 

 correlated wiih its presence in their environment. 



It has now been determined that countershading is all but universal 

 among reef fishes. Their color changes are adaptive, and their colors corre- 

 lated with their habits in such a way that their conspicuousness is thereby 

 distinctly reduced. There is no correlation of bright colors with special 

 modes of defense, and no evidence that bright-colored types enjoy immunity 

 greater than that of their fellows. The hypotheses of warning and immu- 

 nity coloration, or signal and recognition marks, explain no such facts as 

 these. But it is to be noted that while this research leads one to reject 

 those hypotheses, it is consistent with the hypothesis of evolution through 

 natural selection. 



Nerve-Conduction in Cassiopea, hy Alfred Goldshorongh Mayer. 



Studies of the past three years have shown the importance of hydrogen-ion 

 concentration in determining the rate of nerve-conduction in Cassiopea. 

 Ordinary distilled water often remains acid, even though air freed from CO2 

 by means of soda-lime has been bubbled through it for 72 hours. Accord- 

 ingly, Professor George A. Hulett kindly arranged to have 144 liters of 

 distilled water prepared in accordance wdth his well-known method in his 

 laboratory at Princeton University. This water was sealed in 144 Pyrex 

 flasks and thus transported to Tortugas. The hydrogen-ion concentration 

 of each flask was tested separately, the range being 0.8X10"'^ to 1.0X10"^ 

 and the average being 0.9 XlO"*^, or 6.04 PH. 50 liters of this water were 

 placed in a green-glass carboy and air freed from CO2 was bubbled through 

 it at an active rate for 78 hours, after which the water in the carboy had a 

 hydrogen ion concentration of 10~^ which it maintained for 8 days while experi- 

 ments were being conducted with it. Its alkalinity was probably due to soda 

 derived from the glass carboy, the balance being maintained by a tendency of 

 the water itself to become acid. Professor J. F. McClendon determined the 

 PH of the Tortugas sea-water to be from 8.1 to 8.22, and dilution with this 

 PH 8 distilled water maintained a practically normal and constant hydrogen- 

 ion concentration in the solution, even when the sea-water was diluted with 

 its own volume of distilled water. 



It will be seen that the decline in rate of nerve-conduction with dilution 

 of the sea-water is apparently the same as that of the conductivity of the 

 sea-water when similarly diluted, the electrical conductivity of the sea-water 

 being determined by Kohlrausch's method. It should be said, however, 

 that the decline in concentration of the cations of sodium, calcium, and 

 potassium also follow nearly the same law and the rate of nerve-conduction 

 is proportional to the decline in concentration of these three cations and not 

 to that of the sea-water cations as a whole. 



Professor Pvalph S. Lillie is right in his recent paper in the Amencan Jour- 

 nal of Physiology (vol. 41, page 133) wherein he states his belief that the 

 rate of nerve-conduction in Cassiopea in diluted sea-water declines in a 

 similar ratio as the electrical conductivity of sea-water, and not in accordance 

 with the law of adsorption, as I had supposed. 



The distilled water used in my previous experiments was slightly acid 

 and therefore stimulating in weak and depressant in stronger concentration, 

 thus giving the seml)lance of an adsorption curve. The relation between 



