400 W. C. ALLEE 



movement of the gills or for slight twitching of the anterior legs 

 gave the most satisfactory results. About the time of death the 

 pleopods which act as gill covers move out until they stand 

 almost at right angles with the body and the gills become more or 

 less swollen. As a check upon the supposed death-time, observa- 

 tions were carried on for an interval after the animals were appar- 

 ently dead. In doubtful cases or with very small isopods, the 

 animals were removed from the flask with a large pipette and 

 examined in a watch-glass under a dissecting microscope. This 

 was never done until movement had almost ceased and the stim- 

 ulation did not appreciably affect results. 



TESTING THE CYANIDE RESISTANCE METHOD 



If the resistance to potassium cyanide is a measure of the meta- 

 bolic condition of isopods, then, other things being equal, the 

 higher the temperature the greater the activity in the cyanide, 

 and the younger the animal the sooner it should die. Also the 

 greater the output of carbon dioxide, the shorter should be the 

 survival time. That all these requirements are fulfilled by the 

 cyanide method with isopods is shown by the tests recorded in 

 table 1. 



Raising the temperature of isopods during the survival period 

 gave a very marked decrease in the survival time. In making 

 the tests recorded in table 1, the isopods were placed in 0.001 

 molecular potassium cyanide solution at the same temperature as 

 the water in which they were tested for their rheotactic reaction 

 (18-21 °C.). As a control, other isopods as nearly similar as could 

 be selected were placed in an equal amount of water. Both lots 

 were then gradually heated to 30 to 32°. In all cases the isopods 

 in cyanide died in from thirty-five minutes to an hour and forty 

 minutes, a length of time much below the average survival-time 

 of similar isopods in cyanide of the usual temperature. Further- 

 more, in all instances the isopods in water survived the heating 

 process without being visibly affected by it. 



In other experiments an attempt was made to keep isopods at 

 about 25 °C. (5 to 8° above the temperature of the stock at that 



