358 WILLIAM L. DOLLEY, JR. 



This investigator found that these butterflies are highly positive 

 in their reactions to Ught, but that when they come to rest in 

 bright sunhght they ordinarily orient with the head directed 

 away from the source of light. He found, however, that when 

 one eye is painted black they do not orient, but continuously 

 creep or fly in curves with the functional eye toward the center. 

 Such reactions are usually called circus movements. This be- 

 havior, the author asserts (p. 463), is in accord with the view 

 ''that the orientation of an organism in light is dependent upon 

 the equal stimulation of symmetrical points on its body." 



A number of other investigators have, also, recorded experi- 

 ments with other organisms in which circus movements have 

 been observed. Reactions of this nature have been reported in 

 experiments of three sorts : those in which one eye has been pre- 

 vented from functioning, either by being blackened, or by being 

 injured; those in which one antenna has been removed; and those 

 in which certain parts of the brain or of the inner ear have been 

 destroyed. 



In these experiments it has been found that photo-positive 

 animals, usually turn continuously toward the functional eye, 

 while photo-negative animals usually turn in the opposite direc- 

 tion. This is especially true in those cases in which one eye 

 has been covered. Holmes ('01 and '05) and his students, 

 McGraw ('13) and Brundin ('13), maintain that they have 

 observed this behavior in the following organisms : Hyalella den- 

 tata, Talorchestia longicornis, Orchestia agilis, two species of 

 bees, the robber fly, Asilus, Tabinus, a Syrphid, Ranatra, Noto- 

 necta, several beetles, Stenopelmatus, three species of flies, a 

 number of species of butterflies, and the amphipod, Orchestia 

 pugettensis. In all these cases, positive animals turned toward 

 the functional eye, while negative animals turned toward the 

 covered eye. This, however, was not found to be true in all of 

 the species investigated. Holmes and McGraw ('11, p. 370) 

 state that several species of butterflies, among them Vanessa 

 antiopa, frequently went in circles toward the covered eye, while 

 Brundin ('13 p. 346) maintains that in positive specimens of the 

 amphipod, Orchestia traskiana, ''circus movements will occur 



