COLE. — IMAGE-FOlimNG POWERS OF VARIOUS TYPES OF EYES. 413 



■and from the large light being equal in number, — its eyes have no 

 ability to form distinguishable images of objects which differ from each 

 other in size no more than did the two lights used. 



4. Onisciis asellus was found to be negative to light of the intensities 

 mentioned. Its responses to light are not so definite as those of 

 the larva of Tenebrio, but there is some evidence that it has a some- 

 what greater power of discriminating between the two lights acting 

 simultaneously. 



5. The cockroach (J^eriplaneta americana) is decidedly negative to 

 light from one side, but the reactions to the two lights used simultane- 

 ously showed an almost indifferent condition. The excess of 4.5 

 per cent of the reactions was on the side of motion toward the larger 

 light, whereas one would have expected that if there were any differ- 

 ence there would have been a predominance of reactions away from the 

 larger light. This is possibly to be explained as due to other 

 disturbing factors. 



6. The mourning-cloak butterfly {Vanessa antiopa^ is uniformly 

 positive in its -locomotor reactions to unilateral illumination. Exposed 

 to the simultaneous influence of both lights, it went in 87.2 per cent of 

 its responses toward the larger light, thus confirming Parker's con- 

 clusion that this insect responds to the size of the illuminated area 

 rather than to the intensity of the light received from it. 



7. Ranatra fusca varied in the character of its response to unilateral 

 illumination ; but, as far as possible, only positive individuals were 

 employed in the experiments with the two lights used simultaneously. 

 It was found that Ranatra gave a somewhat smaller proportion of 

 turnings to the larger light (70.6 per cent) than did Vanessa ; but 

 it is believed that this may be due to the inconstancy of the phototropic 

 states of Ranatra, rather than to less efficiency of the eyes in forming 

 images of the two lights. 



Individuals with the posterior half of the eyes blackened went 

 straight ahead, without hesitating, toward whichever light they chanced 

 to face ; when the anterior half of the eyes was blackened, they kept 

 turning from one light to the other, since the only one from which 

 light could enter the eyes was always the one behind the insect. 



8. The pomace fly {Dj-osnphila ampelophiki) gave only negative 

 results, owing, apparently, to technical difficulties in the experiments. 



9. Helix p>omatia did not prove to be a good form for the purpose 

 of these experiments, on account of the inconstancy of its phototropic 

 state. So far as the experiments went, they pointed to the conclusion 

 that the eyes are of little or no use in enabling this animal to discrimi- 

 nate between the sizes of the luminous areas employed. 



