310 'Journal of Comparative Neurology and Psychology. 



over the body, just as Herrick ^ has found that some fishes have 

 chemical sense organs all over the body. 



It is hoped that the following observations may throw some 

 light on this question from the physiological side. 



EXPERIMENTAL. 



The investigations of Graber and Nagel on the reactions of 

 Crustacea to chemical stimuli are open to the objection that no 

 details are given to indicate how the stimuli were applied. The 

 observations of Herrick on the lobster, while much more definite, 

 suffer from the highly abnormal position in w^hich the animals 

 were kept. In all of the following experiments upon the cray- 

 fish, Cambarus affinis, the animals were placed singly in a small, 

 white enameled pan in about four centimeters of water. This 

 water was changed and the pan rinsed out after every three or 

 four stimulations. To make the stimulation, a little of the chem- 

 ical substance to be tried was taken up in a fine pointed pipette 

 and was pressed out in the immediate vicinity of the part to be 

 stimulated. In order to follow its diffusion through the water, 

 the substance w^as colored with a little eosin, or in the case of 

 some substances with carmine. In this manner only a reaction 

 which took place immediately after the diffusion of the substance 

 to the part to be stimulated was counted as a reaction to the sub- 

 stance. Check tests were made on many of the animals with 

 pure water and with water colored w4th eosin and with carmine. 

 With pure water the only reaction ever obtained was from the 

 pleopods of the abdomen, and with care in pressing the bulb of 

 the pipette so that no current was set up in the water this was 

 avoided. With the colored water there were slight reactions in 

 many cases from the anterior portions of the animals. The re- 

 actions obtained with the various stimuli, however, were so decided 

 and characteristic that the slight effects of the coloring matter 

 could be discounted. 



I. Meat Juice.— A piece of fresh beef was left overnight in 

 just enough water to cover it and the juice then pressed out. To 

 this the animals reacted very decidedly and with a positive chem- 



'Herrick, C. J. Organ and Sense of Taste in Fishes. Bulletin U. S. Fish Commission, Vol. 2i. 

 pp. 237-272. 190-?. 



