388 C. H. TURNER 



DISCUSSION OF THE EXPERIMENTS ON THE INFLUENCE OF LIGHT 



The above experiments show conclusively that, when con- 

 fined within a small cage and exposed to the direct rays of the 

 sun, the bees of the species studied make certain flying move- 

 ments that finally bring them in contact with that side of the 

 cage through which the direct raA^s of the sun are entering. 

 (Ex. I, 2, 4—7, 9, 12—14, 16, 17.) 



That this e fleet is produced, not by a bright patch, but by 

 the direction of the rays of light is evidenced by the fact that 

 a strong beam of light may be projected through the cage with- 

 out arousing any responses from the bees upon which the direct 

 ra^^s of the light do not impinge. (Ex. 10, 11, 19, 20.) 



It is also demonstrated that a shadow cast upon one of these 

 parasitic bees while it is basking in the sun usually causes the 

 bee to move. It may go to a light spot on the cage, or to the 

 bottom of the cage, or to the mud cell that is its home. (Ex. 

 3,8,17,18.) 



Do these experiments justify the conclusion that these para- 

 sitic bees are positively phototropic? If by tropism we mean 

 any diflerential response to a stimulus which result? in the 

 movement of that creature either to or from the source of the 

 stimulus then these bees are undoubtedly positively photo- 

 tropic or better positively phototactic; but if we limit the 

 word tropism to that form of behavior in which an animal is 

 mechanically forced by a stimulus to so adjust its body as to 

 have each side equally stimulated, and then to move, in a straight 

 line, either towards or away from the source of the stimulus, 

 then the above statement needs qualifying. Before copulation, 

 most males and females when exposed, while on the wing, to 

 strong rays of light flew in paths sufficiently parallel to the rays 

 to satisfy the most extreme form of the tropism theory; but, 

 even then, some of the bees flew about the cage, in every pos- 

 sible direction before alighting upon the netting of that side 

 of the cage through which the direct rays of the sun were enter- 

 ing (Ex. 13, 14), and, after feeding, for the first time, on honey 

 placed either on bits of paper or in watch-glasses, a bee always 

 made a short flight of orientation (Ex. 14). The males died soon 

 after copulation and I could secure no reliable data of their 

 behavior subsequent to mating. The females, however, lived 

 several days after copulating, thus permitting a careful study 



