BRADLEY M. PATTEN 



Methods. 



437 



The general external anatomy of the whip-tail scorpion and the 

 more important points concerning its experimental handling have 

 been taken up in a preliminary paper (1). For a detailed morpho- 

 logical consideration of the group to which Mastigoproctus giganteus 



Fig. 1. Plan of apparatus. About O as a center a circle 50 cm. in diameter 

 was described and graduated in degrees. This is termed the "observation circle". 

 The axis pp' is constructed parallel to the edge of the table and the axis yy' per- 

 pendicular to pp'. On the axis yy' two 15 watt Mazda lamps, A and B, were set 

 up, each distant 35 cm. from the center of the circle. On the axis pp' a similar 

 lamp was mounted on a movable frame, C. Affixed at right angles to the base of 

 the frame, C, was a scale, V, reading as a vernier against the scale, S, at the edge 

 of the table. Light-proof cases, s,s,s, enclosed each light except for diaphragms 

 3X3 cm. so placed that the beams of light transmitted each centered at 0. 



belongs reference should be made to Borner (2). The sketch of Masti- 

 goproctus reproduced in Fig. 2 will serve to give the location of the 

 photoreceptors considered in this paper. 



As has already been stated, the method mapped out for securing 

 data on the effectiveness of the various photoreceptors consisted in 

 comparing with the reactions of normal animals, the reactions of. ani- 



