348 DWIGHT E. MINNICH 



movements or tm-ns toward the injured side. Brundin ('13. p. 

 346) states that in positive specimens of Orchestia traskiana, cir- 

 cus movements will occur as often toward the blackened as 

 toward the normal eye, while Holmes and McGraw ('13, p. 370) 

 report the case of a positive skipper butterfly which almost inva- 

 riably circled toward the blackened eye. 



A very plausible explanation of these apparent anomalies, 

 however, has been offered by Dolley ('16, pp. 394-399), who has 

 shown that the contact stimulus afforded by the material cover- 

 ing the eye is sufficient to cause Vanessa, when in the dark, to 

 turn continuously toward the covered eye. This tendency, more- 

 over, exhibits little, if any, modification from day to day. The 

 effect of such a contact stimulus is continuous. But in the pres- 

 ence of photic stimulation of moderate or high intensity, it is quite 

 overwhelmed by the strong phototropism of the butterfly. In 

 the case of animals of less certain phototropic index, this contact 

 stimulus is, in all probability, frequently strong enough to over- 

 come the effect of light. An examination of the cases cited above 

 shows that the phototropism of these animals is not of the une- 

 quivocal kind exhibited by Vanessa. It seems likely, therefore, 

 that their apparently exceptional behavior was due to contact 

 and not to photic stimulation. 



Suppressions of photic circus movements by responses to other 

 stimuli are not surprising, when it is recalled with what facility 

 even the stereotyped circus movements produced through uni- 

 lateral lesions of the central nervous system may be altered in a 

 similar manner. Thus Bethe ('97 b, p. 507) states that the ten- 

 dency of bees to circle toward the normal side after the removal 

 of one half of the brain or the severance of one of the oesophageal 

 commissures, may be arrested, and the animal may even be com- 

 pelled to deviate toward the injured side by stimulating the legs 

 of the normal side. Moreover, in a general statement concern- 

 ing the several crustaceans and insects subjected to similar opera- 

 tions (p. 541), he says, '^ ... nach Aufhebung der Hem- 

 mung der gesunden Seite durch angebrachte Reize aber auch 

 spontan bei alien Versuchsthieren gerader Gang und Kreisgang 

 nach der operirten Seite eintritt." 



