REACTIONS OF CRAYFISHES. 



tation was also definite. There seemed to be an acceleration of 

 all the reactions shown in the carbon dioxide experiments. Out 

 of fifteen trials fourteen (93.3 per cent.) showed turning at first 

 encounter of the high concentration, and of the fourteen, four 

 started toward the high end without first having invaded the low 

 or even a portion of it; 50 per cent, of the turnings were accom- 

 panied by backing. Only two individuals reached the screen in 

 the acetic acid end. Of these two one crossed after handling; 

 the other occurred in the lowest concentration of acetic acid 

 used. There was, after a certain period of time, a cessation of 

 invasions of the high acid concentration end; this period varied 

 inversely as the total concentration of the acid. Experiment 14 

 varies slightly from this rule. There was also periodicity of 

 invasions of the high concentration end (see Chart I., Expt. 14) 

 as described in the carbon dioxide experiments. 



(b) C. virilis. These experiments can be divided into three 

 groups, a low concentration, a high and a very high, i. e., experi- 

 ments 1 8 and 19 with a concentration of .0185 g. of acetic acid 

 per liter at the low end and .1145 to .228 g. per liter at the high 

 end; experiments 20 and 21 with .122 to 1.21 and .8 to* 1.67 g. ; 

 and experiment 35 with 2.88 and 28.99 g- P er n 'ter of acetic acid 

 in the low and high ends respectively. 



In the low concentration experiments at low temperature 

 there was a more definite orientation and a greater time prefer- 

 ence for the low end. This is shown by the ratings (see Table 

 III.). There was also a more or less periodicity of invasions of 

 the high end with a complete cessation of invasions in experiment 

 19 after 45 minutes. 



In the high concentration experiments at low temperature 

 there was less orientation except in turning at the first invasion 

 of the high end. There was but one individual (Expt. 20) 

 that showed periodicity of invasions of the high end. The 

 lack of orientation is shown by graph Expt. 21, Chart I. There 

 was an increased tendency to crawl on the sides of the tank and 

 out of the water. Thus there was a falling off of orientation and 

 a substitution of crawling out of the water. 



In experiment 30, in which the temperature was high and 

 specimens above medium size were used, there was better orienta- 



