440 PHOTOREACTIONS OF WHIP-TAIL SCORPIONS 



and to chemicals, and the areas of extremely thin and unpigmented 

 chitin around the articulations of the appendages with the sides of 

 the cephalothorax. Careful searching of the feelers with the light 

 spot failed to elicit any reaction from the animal or movement of 

 the feelers. Furthermore when the feelers were cut off several 

 animals, some of which were otherwise normal and some of which 

 had both median and lateral eyes capped, the characteristic orienta- 

 tion to light was in neither case affected. 



Attention was then turned to the areas of thin chitin at the sides 

 of the cephalothorax. Searching these areas with the hght spot 

 caused the animals to turn away from the illuminated side. The 

 same areas were then rendered opaque by painting with asphaltum 

 varnish. 2 Animals with one side of the cephalothorax blackened, 

 when subjected to bilaterally balanced illumination, showed a very 

 marked deflection toward the blackened side. This deflection was 

 not attributable to mechanical interference with locomotion due to 

 the presence of the varnish, for when stimulated mechanically, the 

 animals did not move in curves. In another series of cases, scorpions 

 with all eyes capped and both sides of the cephalothorax blackened 

 were found to be insensitive to light. Methylene blue preparations 

 of the integument in this region made subsequently showed abundant 

 ganglion cells and nerve endings. 



These observations indicated that the analysis of the receptive 

 mechanism must deal with three elements: the median eyes, the lat- 

 eral eye groups, and the photosensitive areas at the sides of the 

 cephalothorax where the legs articulate with the body. With ef- 

 fective methods of preventing any receptor or group of receptors from 

 functioning, the work resolved itself into series of measurements in 

 wdiich all possible combinations of interference with the photorecep- 

 tors should be covered. 



^ The results of this treatment were at first somewhat unsatisfactory because 

 of the mucus thrown out when the areas in question were irritated by the varnish. 

 It was possible, however, by repeated paintings to get a nearly unbroken coat of 

 varnish to adhere. Animals treated in this way had to be used in the desired 

 experiments before the varnish had dried long enough to become brittle. 



