39G C. H. TURNER 



All insects did not respond in the same manner. Several beetles, 

 of- three different species, showed a tendency to turn toward 

 the blackened eye. A Jerusalem cricket, which is negatively 

 phototactic, when crossing from one side to the other, always 

 turned toward the left. In a series of trials, two species of the 

 Tachina fly and a specimen of the fly Eristalis tenax made 

 circus movements towards the normal eye. 



These same two investigators constructed a light-running 

 turntable of cardboard. An insect was held so that its feet 

 rested on this table and its head faced either the periphery or 

 the center. A light was placed near one side of the turntable. 

 Any movement on the part of the insect to escape from or to 

 approach the light would cause the table to revolve in the oppo- 

 site direction. Four species of butterflies (Picris raphae, Melitea 

 chalcedon' Eurymus eyrtheme, and Caenonymphia California) and 

 two species of flies caused the disc to rotate away from the light. 

 In the light of these two types of experiments, Holmes con- 

 cludes: ' It is not possible ,we believe, to construe phototaxis 

 entirely in terms of differential sensibility. Responses to the 

 shock of transition, whether in the direction of an increase or a 

 decrease of stimulus, may play a part in the orientation of many 

 forms, but the continuous stimulating influence of light appears 

 to be, in several cases at least, the factor of major importance." 



4. Rheotropism. — Based upon a study of Asellus communis, 

 Allee (2) has reached the following conclusions concerning the 

 responses of Isopods to currents of water: (1) In daily varia- 

 tions to currents the efficiency of the movements varies with 

 the per cent of positive reactions. (2) Large variations in 

 positive reactions are usually accompanied by similar variations 

 in efficiency. (3) Low efficiency is accompanied by a low per 

 cent of positive and a high per cent of indifferent responses. 

 (4) High efficiency is always accompanied by a low per cent of 

 indifferent responses, and usually by a low per cent of negative 

 and a high per cent of positive responses. (5) In exceptional 

 cases, high efficiency may be accompanied by either a low or 

 high per cent of positive reactions. In another communication 

 (1) the same author states that during moulting all currents 

 are disregarded by these animals. This effect persists for about 

 five hours after the complete casting of the skin. 



5. Thigmotropism. — According to Weiss (118), commencing 



