314 W. C. ALLEE 



in bunches when first placed in a solution containing chloretone. 

 Later they became acclimated and moved more normally but 

 would bunch again if more chloretone was added. As has been 

 previously stated, this reaction is also induced by a sudden in- 

 crease or decrease in temperature. 



The exposure to chloretone for the rheotactic experiments was 

 made in sealed glass jars, the solution being changed every twenty- 

 four hours. The results of one experiment only are shown, 

 (table 17) but these are entirely comparable to the reactions 

 given by a number of other tests. In this experiment the con- 

 trol animals remained strongly positive while the reaction of those 

 under the influence of chloretone was cut from 78 to 25 per cent 

 positive. Towards the end of the experiment the animals were 

 evidently becoming acclimated and hence gave a normal response. 



d. Potassium cyanide 



Potassium cyanide is known to decrease the amount of oxida- 

 tions by decreasing the ability of the tissues to take up oxygen. 

 (Geppert, '99, p. 208). Then weak solutions of this chemical 

 should show the same results upon isopod reactions as keeping 

 them in a low oxygen supply. Experiments prove this assump- 

 tion to be true. The results of two series of such experiments 

 are shown in table 18. These experiments were conducted in 

 every respect like those with chloretone. The amount of potas- 

 sium cyanide used gave only a faint odor to the water. 



In the first part of the table, isopods giving a positive pan 

 response of 82 per cent, were placed in N/100,000 KCN solution. 

 At the end of five days they gave a 30 per cent positive response. 

 For the next three days they were kept in N/125,000 solution and 

 during that time the response was practically the same. At the 

 end of eight days half of the original number were dead. The 

 remainder were put in tap water and showed a rapid recovery of 

 their normal response. The other trial shows the same results 

 except that when the experiment ended, all but two of the isopods 

 were dead. The lowering of the positive response in the control 

 is due to the fact that the control in these experiments was run 

 with verv little food. 



