DEPARTMENT OF MARINE BIOLOGY. 189 



Effect of Stretching on the Rate of Nerve-Conduction in Cassiopea. 



Stretching has no effect on the rate of nerve-conduction in Cassiopea; that 

 is to say, if it requires 1 second for the nei"ve-impulse to traverse a strip of 

 umbrella of unit length, 2 seconds are required if the length is doubled by 

 stretching. Owing to hysteresis, time must be given for adjustment to new 

 conditions after change in length. The rate of the nerve-impulse corresponds 

 to about 400 mm. of subumbrella tissue per second at 30°. 



The Equilibrium Between Sea-Water and Calcite or Aragonite Crystals. 



The solubility of CaCOs in salt water depends chiefly on the total CO2 

 content, but this is difficult to measure directly. The total CO2 affects the 

 hydrogen-ion concentration, Ph, and this may be determined colorimetrically. 

 In order to simplify nomenclature, sea-water is regarded as a mixture of water, 

 neutral salts, CaO, and CO2. The CaO may be titrated while boiling to re- 

 move the CO2 liberated by the acid used in titration. Sea-water was shaken 

 with calcite crystals at 30° until equilibrium was reached and the Ph and CaO 

 (as carbonate and bicarbonate) were determined. A curve was plotted show- 

 ing the relation of Ph to CaO. Aragonite gave the same curve within the 

 limits of error. Sea- water is supersaturated as regards calcite and aragonite. 

 No equilibrium was obtained by shaking the precipitated calcareous mud of 

 Tortugas with sea-water. 



Local and Diurnal Changes in Sea-Water. 



Sea-water was studied at various locations at Tortugas and between Tortugas 

 and New York. Determinations were made of temperature, CI, CaO, CO2, 

 CO2 tension, O2, and Ph. The only diurnal change detected in the axis of the 

 Gulf Stream was 1° in temperature. Marked diurnal changes were noted at 

 Tortugas in water of 6 fathoms or less depth over populated bottoms. All 

 shallow water of considerable area had some portions of the bottom populated, 

 and the only shallow water not showing marked diurnal changes was associ- 

 ated with a tidal current flowing from deep water near at hand. Extremes 

 were noted in the water between dawn and about 3 p. m. local time, the tem- 

 perature and O2 content being lowest at dawn and the CO2 content being lowest 

 at about 3 p. m. At about 3 p. m. the Ph is most favorable for the precipita- 

 tion of CaCOs, and a precipitate was noted in very shallow water, especially 

 in the lagoon at Marquesas. A precipitate was coming down in the water and 

 a calcareous crust was forming on the blades of eel-grass. 



