364 WILLIAM L. DOLLEY, JR. 



this behavior. He says ('08, p. 486) : '' It is clear that the tropism 

 theory, with its assumption of local action of stimulus on the 

 side exposed to its effect, does not furnish a complete explanation 



of these reactions A 'pleasure-pain' reaction appears 



to inhibit and dominate a 'tropic' reaction." 



To Radl, circus movements are an evidence of inequality in 

 the tension of the muscles on opposite sides of the body, pro- 

 duced by the blackening of one eye. He says ('03, p. 63) : "Bei 

 einem Tier, dem ein Auge geschwarzt wurde, erschlaffen etwas 

 die Muskeln an der Korperseite, wo das Auge nicht sieht ; da sich 

 nun die Muskeln der anderen Seite kraftiger bewegen, so erfolgt 

 eine Bewegung in einer nach der Seite dieser starker arbeitenden 

 Muskeln gekriimmten Bahn." 



Parker ('03, p. 463), as has been previously stated, maintains 

 that the circus movements he observed in Vanessa antiopa are 

 in accordance with the view "that the orientation of an organism 

 in light is dependent upon the equal stimulation of symmetrical 

 points on its body." He says further: "Should the eyes be the 

 parts stimulated, any interference with one of these ought to 

 result in a disturbance of the direction of the butterfly's loco- 

 motion. Thus, if the cornea of one eye were blackened, the 

 insect in locomotion, being positively phototropic, ought to move 

 as though that eye were in shade, namely in a circle, with the 

 unaffected eye toward the center." 



To Barrows, who worked on the reactions of Drosophila to 

 odors, circus movements can only be explained by the 'tropism 

 theory.' He says ('07, p. 535): "It seems impossible to explain 

 the movements under these conditions in any other way than on 

 the basis of the tropism theory. This theory has been stated 

 in several ways. As applied to chemical stimulation, Verwom 

 ('99, p. 429) declares: 'The word chemotaxis is applied to that 

 property of organisms that are endowed with the capacity of 

 active movement by which, when under the influence of chemi- 

 cal stimuli acting unilaterally, they move toward or away from 

 the source of the stimulus.' " 



V. L. Kellogg ('07) and Bohn ('11) agree with Loeb, whose 

 views are given in the next paragraph, and Bohn even cites 

 circus movements as one of his criteria for tropisms. 



