610 BIOLOGICAL EFFECTS OF RADIATION 



eye of Limulus comparable to that observed by Dolley in Eristalis after 

 it had been in darkness for several hours, but this may have been due to 

 insufficient time in darkness to induce the decrease in Limulus. 



MODIFICATION IN RESPONSE TO LIGHT 



Bees which are normally strongly photopositive can readily be trained 

 to go into totally dark places for food; they can be trained to go into or 

 out of either dark or highly illuminated hives, through long tortuous dark 

 passages, for example, an ordinary black garden hose 10 meters long, 

 with numerous sharp curves in it; and they can be trained to select, 

 regardless of brilliance, any one among a number of different colors or 

 patterns associated with food or with their hives (Lubbock, 129; Frisch, 

 74; Bertholf, 14; Baumgartner, 11; Opfinger, 181; Zerrahn, 235). 



VISION 



The behavior of many insects in the open clearly indicates that they 

 distinguish between objects at a distance. This is especially true of 

 robber flies and dragon flies in capturing prey; of the pupae of the 17-year 

 locust in selecting objects to ascend for the purpose of molting, and of 

 bees and butterflies in selecting flowers for the purpose of procuring food. 

 These phenomena may be due to difference in the brightness, difference 

 in the form or difference in the color of the objects distinguished. 



a. Brightness Vision. — Frisch (74) and Kiihn (118) in observations 

 on bees with the training methods, obtained results which indicate that 

 only great differences in brightness are distinguished; but Hess (103) 

 on the basis of results obtained in observations on the positive response to 

 light of different intensities, concluded that the ability to distinguish 

 brightness is very nearly as acute in bees as it is in man. Bertholf 

 (16) with a method somewhat similar to that used by Hess obtained 

 results which indicate that bees clearly distinguish between two surfaces 

 which differ in brightness by 30 per cent, whereas human beings clearly 

 distinguish between the same surfaces when they differ in brightness by 

 only 10 per cent. He concludes brightness vision is markedly less 

 acute in bees than it is in man. 



6. Form Vision. — Frisch (74), Baumgartner (11), Hertz (100 to 102), 

 Opfinger (181), Friedlaender (72), and Zerrahn (235) conclude on the 

 basis of results obtained in training experiments, that bees can distinguish 

 figures which differ only in form, but that their ability to discriminate 

 form is rather crude. They maintain, for example, that bees cannot 

 distinguish between circular, elliptical, triangular, and square figures of 

 the same size. Baumgartner concludes that bees have no true sense of 

 form comparable to that in man. Verlaine (205, 206) asserts, however, 

 that wasps are far more accomplished than bees in that they readily 

 distinguish between circles, triangles, and squares. 



