ACTIVATION OF UNFERTILIZED STARFISH EGGS. 



103 



as the rectangular vessel and connecting the latter with the 

 electrode dishes. These bridges were made as follows : A concen- 

 trated solution of agar-agar in sea-water was allowed to solidify in 

 a large beaker; the mass of jelly was then removed and cut into 

 two blocks of the general shape indicated in the figure; one end of 

 each block stood in the ZnSO 4 solution and the other in the sea- 

 water, as shown diagrammatically in the longitudinal section 

 (Fig. i). By means of this arrangement strong currents (up to 2 



FIG. i. 



or more amperes) could be passed through the sea-water. Ex- 

 periment showed that the composition of the sea-water was not 

 appreciably affected during the flow of the current for the period 

 of an experiment. The temperature, however, rose rapidly unless 

 controlled. In part of our experiments the control of temperature 

 was effected by setting the whole system in a pan of ice water; 

 this method proved satisfactory with currents of moderate in- 

 tensity (up to 150 ma. /cm.). 1 In a number of experiments with 

 stronger currents another method was used, to be described below. 

 The strength of the current was regulated by two rheostats and 

 measured directly by a Weston voltmeter provided with shunts so 

 as to read as a milliammeter over the several ranges required. 

 Intensities as high as 3 or 4 amperes were used for a brief period in 

 some of the experiments with running sea-water described below 

 (densities up to ca. 800 ma. /cm.). 



The usual procedure was as follows : A somewhat small quantity 

 of eggs was placed with a pipette in the rectangular dish midway 

 between the agar bridges (2 to 4 cm. from each). When the eggs 

 had settled the circuit was closed, and at stated intervals, usually 

 2, 4, 8 and 12 minutes, successive portions of eggs were transferred 

 to small dishes (usually Syracuse watch glasses or stender dishes) 



1 Milliamperes per square centimeter of sectional area. The commonly used 

 unit of current-density, 5 (microampere, i.e., .001 milliampere, per sqium- milli- 

 meter), is one tenth of this unit. 



