Bell, Ri^actions of Crayfish. 313 



an arch, pushed the second and third pairs of walking legs back 

 to the pleopods, then brought them forward to the first pair which 

 in turn were carried to the mouth, just as if they were passing 

 forward a bit of meat. This process was continued four or five 

 times in each case. In three other cases the bowing up on the 

 chelae and telson was observed but not the pantomimic passing 

 of meat to the mouth. 



(10) The plates of the telson. Here there were nine failures 

 to respond. The response was usually a slight movement of the 

 abdomen. In two cases there was a downward stroke of the 

 pleopods and a quick, sharp flexion of the abdomen, w^hile in one 

 case the animal faced about to the source of the stimulus. 



(11) The back of the carapace. All the animals but three 

 reacted to this stimulus. The typical reaction was a movement 

 of some sort, sometimes taking the form of a restless moving 

 about and rubbing the chelae and chelipedes against each other. 



From the above experiments it will be seen that crayfish react 

 to the chemical stimulus of meat juice when applied to any part 

 of the body, and therefore we must conclude that there are organs 

 for the reception of chemical stimuli scattered all over the body. 

 These observations confirm the view that Gulland, in studying 

 the smooth hairs which, he says, are found on all the appendages, 

 had to do with chemical setae, and not, as he thought, with tac- 

 tile. His statement, however, that no such smooth hairs are 

 found on the carapace is not in accord with these results, and we 

 must assume that more careful observation would reveal some 

 kind of chemical sense organs there as well. That the stimuli 

 were received by organs on the carapace, and were localized by 

 the animal on a rather definite portion of the carapace, and that 

 the reactions were not due to diffusion to the appendages below, 

 will appear clearly in the later experiments with acids, etc. While 

 it must be said that the crayfish may respond to a chemical stim- 

 ulus on any portion of the body, it will be observed that the re- 

 sponses are more regular and more decided on the anterior appen- 

 dages, while the posterior walking legs and the telson are much 

 less sensitive. This agrees with the observation of Bethe and 

 Prentiss that the smooth hairs are more luxuriantly developed 

 on the anterior appendages. So far as vigor and regularity of 

 response are concerned, there is nothing in the present experiments 

 to indicate that the antennules are specially modified organs for 



