390 C. H. TURNER 



It seems to me that there is a difference between the behavior 

 just described and tropism in the strictest sense. In the narrow 

 sense mentioned a tropic response would be similar to the turning 

 of a magnetic needle towards the pole and would be subject 

 to like perturbations. It seems to me that the responses of these 

 bees towards light are more like those of a small bo}'- towards 

 the strains of an invisible brass band that has suddenly begun 

 to play. In the majority of cases the boy will make movements 

 that will take him in the direction of the source of sound ; but 

 he is not mechanically compelled to invariably make such move- 

 ments. Finding his way barred the boy may seek an indirect 

 path of exit. If intensely interested in a saucer of cream or 

 other occupation, his movements may bear no relation what- 

 soever to the sound stimulus. Occasionally a child may make 

 no response to the sound, although an onlooker can see no 

 reason for its passivity. The behavior of these parasitic bees 

 is quite parallel. When exposed to the direct rays of the sun 

 or other strong light, such a bee will usually fly in the direction 

 of the rays of light and towards their source. Failing to reach 

 freedom by that method, it may seek to escape by making move- 

 ments that bear no constant relation to the direction of the 

 rays of light. Intent on feeding or mating, it may make numer- 

 ous complex movements that bear no relation whatsoever to 

 the light stimulus. It may even remain outwardly inactive 

 in the presence of a strong light without the onlooker being able 

 to discern any reason for its passivity. I am anxious not to 

 be misunderstood. I do not consider these cases to be iden- 

 tical ; but they are similar. Without predicating either curiosity 

 or logical thinking to these parasitic bees and admitting that 

 the behavior of the boy is more flexible, it does seem that 

 the parallel between the light stimulated bee and the band- 

 excited boy is too marked for the two cases to be considered 

 different in kind. 



Bohn puts much stress upon what he calls " differential 

 sensibility " ( " sensibilite differentielle " ) , which is the ten- 

 dency of many animals to rotate through an angle of i8o de- 

 grees when confronted with a sudden change in the mechanical 

 or physical condition of the environment. These bees in their 

 movements did certain things that reminded me of this factor. 

 When a bee that was climbing up a sunlit wall came in contact 



