602 BIOLOGICAL EFFECTS OF RADIATION 



flash of light produced by a male has been formed on the retina of a 

 female, she, in total darkness, directs the ventral surface of the abdomen 

 toward any point in space, depending upon where the male chances to 

 be when he glows. The image obviously starts a series of reflexes, the 

 nature of which is specifically correlated with the location of the image 

 in the eye. 



The males very rarely if ever respond to the glow of other males. In 

 some way they are able to distinguish between the flashes of light pro- 

 duced by the two sexes (Mast, 141). 



Some insects, after they have assumed a definite axial position in 

 relation to a source of light, tend to retain this position. This phenom- 

 enon is particularly prominent in a complex field of light, e.g., in direct 

 sunlight in an open field and in insects on a turntable. The insects 

 apparently tend to take such a course that the location of the images in 

 the eye remains constant. It has been observed in the beetle Coccinella 

 by Radl (189), in ants by Santschi (194); in bees by Wolf (224, 225), 

 and in a considerable number of other insects by Buddenbrock (22, 23, 

 26, 27), Niemczyk (177), Fraenkel (68), Willrich (222), Schulz (199), and 

 Buddenbrock and Schulz (29). 



Loeb (126), Bohn (20), Garrey (75), and many others hold that photic 

 orientation in insects is the result of quantitative difference in the activity 

 of the locomotor appendages on opposite sides, that this difference in 

 activity, e.g., length of steps, is due to difference in the tonus of the 

 muscles in the appendages on opposite sides, that the difference in tonus 

 is directly proportional to the difference in the amount of light received 

 by the eyes on opposite sides, in accord with the Bunsen-Roscoe law, that 

 light acts continuously, not intermittently, that after orientation the 

 two eyes receive the same amount of light, and that this results in equal 

 muscle tonus and equal activity in the locomotor appendages on opposite 

 sides. 



These conceptions concerning orientation do not account for many of 

 the facts presented above, for example : (a) orientation in insects with one 

 eye covered; (h) orientation in insects with legs on one side removed; (c) 

 turning upward or downward toward the light, while the two eyes are 

 continuously equally illuminated; (d) turning toward the side on which 

 the legs are more extended; (e) orientation in a field of light consisting of 

 two beams unequal in intensity crossing at right angles, in which the two 

 eyes do not receive equal quantities of light after the insect is oriented; 

 (/) shock-reactions in one-eyed insects; (g) decrease in deflection in circus 

 movement, with increase in light intensity; (h) orientation in insects 

 which tend to maintain an axial direction such that the images in the 

 eyes remain constant in position; (i) orientation of the male firefly in 

 response to a flash of light produced by the female. 



