THE SEAT OF SMELL IN THE CRAYFISH. 1 59 



Experiment V. 



(Specimens with eyes blackened over.) 

 Outer ramus removed 74 68 214 56 168 118 



Inner ramus removed 10 42 14 32 102 32 34 27 6 33 33.2 



The experiments show in a striking enough way that removal 

 of the outer branch of the antennules is followed by a much 

 greater loss of sensitiveness to olfactory stimuli than is caused by 

 removal of the inner ramus. But they also show that crayfish 

 with the inner ramus removed react less promptly than do normal 

 animals. We may conclude from these experiments that the part 

 most sensitive to olfactory stimuli is the outer ramus of the anten- 

 nules, but that the inner ramus is also to a certain extent sensitive to 

 the same kind of stimuli. Specimens with both rami removed re- 

 spond to meat juice or pieces of meat placed near the tip of the large 

 second antennae. It is scarcely possible that any chemical could 

 diffuse to other parts of the body before the reaction takes place 

 and hence the second antennae must have an olfactory function 

 also. Specimens in which both antennules and antennae were 

 removed showed a marked power of responding to bits of meat 

 or meat juice placed near the mouth parts or the tips of the 

 chelae. The small chelipeds were found especially sensitive to 

 substances placed near the tip. By very carefully applying the 

 tip of a pipette which had been drawn out into a long slender 

 tube near one of the small chelae and slowly forcing out a little 

 meat juice, one usually sees a slight grasping movement of the 

 chelae, often at first a small twitch of the dactyl, followed by 

 movements of reaching about. These movements are followed 

 by exploring movements of the other chelipeds, chewing move- 

 ments of the mouth parts, and by a turning of the body toward 

 the stimulus. 



Animals in which the brain was destroyed were also experi- 

 mented with. The crayfish was securely fastened to facilitate 

 working upon it. With a fine-pointed scalpel a piece of the cara- 

 pace about one fourth of an inch square was cut out just over 

 the brain. After destroying the brain the piece of the carapace 

 was carefully replaced and the edges sealed with asphalt varnish. 

 The animal was then kept out of water until the asphalt had dried 

 and the wound sealed. After a few days the animal was experi- 



