REACTIONS OF CRAYFISHES. l8l 



reactions which were made as the crayfishes entered the higher 

 concentration. Such reactions were waving the antennae, moving 

 the appendages, backing and walking with the legs extended. 

 The waving and moving of the appendages were especially noted 

 in the reactions of propinquus, virilis and diogenes, in the carbon 

 dioxide experiments in which the concentrations of carbon dioxide 

 in the two ends were 40 to 60 and 80 to 100 c.c. per liter respec- 

 tively. The animal would also crouch down in the corner of 

 the tank. This tendency to wave the antennae and move the 

 appendages was present in virilis in the acetic acid also. The 

 backing reaction was not so common in the carbon dioxide 

 experiments but was marked in the hydrochloric and acetic 

 acid experiments. 



IV. THE EFFECT OF CARBON DIOXIDE AND ACETIC AND HYDRO- 

 CHLORIC ACIDS. 



i. The Effect on Reflex of the Crayfishes. 



The crayfishes not only detected the presence of the acids 

 but were intoxicated or anaesthetized by them in the low tem- 

 perature experiments, possibly due to the less regular movements 

 of the animal. This is shown in graphs (Chart I.) by the longer 

 periods of time required to cross the tank in the experiment 

 than that required in the control. The effect was greatest in 

 the experiments with high concentrations. The first effect of 

 the carbon dioxide was to interfere with the correlation of move- 

 ments and to cause the animal to carry the body high with legs 

 extended. Progressively locomotion became slower and slower 

 until it ceased, but the appendages were still moved one after 

 the other. The crayfish would finally fall upon its back and 

 continue to move its appendages for a short time, after which 

 it would remain motionless as if dead. It would recover rapidly 

 if placed in fresh water and after a short time move about 

 normally. The acetic acid produced this same effect upon virilis 

 but propinquus, diogenes and immunis were either not intoxicated 

 by the acetic and hydrochloric acids or acted rapidly enough to 

 get out of the high concentration before being greatly affected, 

 (see Charts I. and II.). The movements of virilis were always 

 more or less irregular. One of the individuals in experiment 21 



