^Ehh, Reactions of Crayfish. 315 



four showing marked avoidance by retreating or removing the 

 member. In one case the animal pushed outw^ard with the chelae 

 as though fending off the substance, and in another there were 

 movements of the mouth parts but more as if cleaning off an offend- 

 ing substance than as if feeding, while the cheliped stimulated 

 was brought to the mouth, the forceps closed, the member pushed 

 outward to its fullest extent, and the forceps opened, precisely as 

 if casting something away. (6) The reactions from the second 

 chelipedes of all five animals were of the same sort as those from 

 the first chelipedes, and seemingly were about as vigorous. (7 

 and 8) Only two animals out of the five reacted to stimulation 

 of the third and fourth chelipedes, and that by a slight movement 

 of avoidance. (9 and 10) Stimulation of the abdominal pleopods 

 affected only two of the animals, causing a flexion of the abdomen, 

 while three responded in the same manner to stimulation of the 

 dorsal surface of the telson. (11) On the carapace only two ani- 

 mals reacted, and that merely with a slight movement. 



The striking feature in these experiments with lavender water 

 is the uniform avoidance of the stimulus on the part of all the ani- 

 mals that responded. Again we find the first and second cheli- 

 pedes apparently the most sensitive, and the reactions from these 

 and the mouth parts especially vigorous and characteristic. Note- 

 worthy is the absence of chewing movements when the mouth parts 

 are stimulated. 



J. Acetic Acid. — The same five animals were tested in like man- 

 ner with a 10 per cent, solution of acetic acid. Owing to precipita- 

 tion of the eosin in this solution carmine was used as a coloring 

 substance. Here the reactions were more constant and striking 

 than with lavender water, (i) All the animals responded to stim- 

 ulation on the antennae, four by moving the organ stimulated, one 

 by a quick jump backward. (2) Stimulation of the chelae pro- 

 duced vip-orous and striking reactions in every case. As soon as 

 the acid diffused to the member violent chewmg movements were 

 set up, the limb was drawn in and rubbed vigorously by the first 

 and second chelipedes and the maxillipedes. After the rubbing 

 the chelipedes were also brought to the mouth and rubbed by the 

 maxillipedes. All the while chewing movements were kept up. 

 (3) When the antennules were stimulated three animals jumped 

 back, one of these and the two others dropped the antennule, 

 and one animal rubbed the antennule with the maxillipedes. (4) 



