Vol.. 8, 1922 
ZOOLOGY: S. 0. MAST 
243 
and that the series set up varies in character and in extent with every point ; 
so that if the point stimulated is located at the posterior edge of the retina 
the series of reflexes carries him through a large angle, the degree of turn- 
ing in every case depending upon the location of the stimulus. Thus in 
the fire-fly orientation is the result of series of reflexes, the nature and ex- 
tent of which is specifically related to the location of the stimulus. There 
is much evidence indicating that similar factors are involved in the process 
of orientation in other insects. 
If in Kristalis or Krax with one eye covered the stimulus is localized 
at the posterior edge of the retina, the feet on one side move forward while 
those on the other move backward, the two front feet deflecting toward 
the side stimulated, the two hind feet from this side. If it is localized in 
the lateral portion both front feet move laterally toward the light, as do 
also the middle feet but to a less extent. If it is localized in the central 
part of the anterior surface of the eye the feet on both sides move forward 
and the insect does not turn. If it is localized at the antero-median edge 
it turns toward the covered eye. 
This indicates that stimulation of a given region of the retina in one eye 
induces certain definite reactions in all of the legs on both sides, of such 
a nature as to tend to turn the insect toward the point stimulated just as 
it does in the fire-fly. But if there is only a momentary illumination 
Kristalis and Erax turn thru only a very small angle regardless of the loca- 
tion of the stimulus, whereas the fire-fly turns until it faces the source of 
fight. However, if the illumination continues, then, as Kristalis or Krax 
turns, the image of the source of fight on the retina travels forward and 
a continuous series of points extending forward in the eye become suc- 
cessively stimulated and the stimulation of each successive point induces 
reactions of such a nature as to produce turning toward the region stimu- 
lated and the result is continuous turning until the image reaches the an- 
terior portion of the eye and the insect faces the light. Orientation is 
brought about by a series of reflexes (differential responses to localized 
stimulation) similar to the scratch reflexes in higher forms induced by 
stimulation of various points on the surface of the body. In photic orien- 
tation the nature of each series of reflexes depends upon the localization 
of the stimulus in the eye just as the nature of the scratch reflexes depends 
upon the localization of the stimulus on the surface of the body. This 
is what occurs if the stimulation is confined to one eye. If both eyes are 
simultaneously stimulated other processes are involved as is indicated 
in the following paragraphs. 
If Kristalis is exposed to light from two sources at the same distance 
and equal in size and intensity and so arranged that the rays cross ap- 
proximately at right angles at the place of exposure, it will turn until it 
faces a point half way between the two sources and then proceed toward 
