THE SEAT OF SMELL IN THE CRAYFISH. 157 



dent when the substance came in contact with the animal, it was 

 colored with eosin or carmine. It was found that stimulation 

 of various parts of the body would elicit a response. The animal 

 moved its mouth parts, became restless, moved the small cheli- 

 peds about and sooner or later attempted to go toward the source 

 of stimulus. The responses varied somewhat according to the 

 region to which the stimulus was applied, but there was a marked 

 tendency, as we have also found, for the first reaction to manifest 

 itself by a movement of the part most directly stimulated. The 

 antennules, antennae, mouth parts and tips of the large and small 

 chelipeds were found to be organs of especial sensitiveness. We 

 have repeated Bell's experiments with meat juice and verified in 

 the main his results. Bell, however, did not test his conclusions 

 by removal of certain organs or by operations on the nervous 

 system. One is never quite sure that by using chemicals which 

 diffuse through the water only the organ is stimulated to which 

 the stimulus is applied. It was thought desirable, not only for 

 this reason, but on account of determining more definitely the 

 role of certain organs in chemoreception to observe the reactions 

 of crayfish after the removal of the antennules and antennae, and 

 after the destruction of the brain or the division of the nerve 

 cord. 



The outer ramus of the antennules bears, in addition to the 

 kinds of setse found on the antennae and other parts of the body, 

 certain peculiar club-shaped organs which have generally been 

 considered the end organs of the sense of smell. These organs 

 are absent on the inner ramus, and on the antennae as well as 

 other parts of the body. Organs of a similar character are 

 common in other Crustacea, being in many cas'e, .oi*^'abundantly 

 developed in the male. This circumstance,!' l^I as the fact 

 that removal of the antennules diminishes the'k'^ponse to olfac- 

 tory stimuli, renders it quite probable that these club-shaped 

 organs perform the function which h?n so often been assigned to 

 them. In a series of experiments wt ave compared the reac- 

 tions of crayfish with the outer ram'' Ji the antennules removed 

 with the reactions of normal anim j and individuals otherwise 

 operated on. The rami were removed several days before the ani- 

 mals were experimented with in order to eliminate any effect of shock 



