254 BRADLEY M. PATTEN 



Thelyphonids ^\^th which he worked, although he speaks of them 

 as being present in others of the Pedipalpi. 



Unhke the true scorpions, the Thelyphonids have an attenu- 

 ated, many-jointed tail with little muscular development and no 

 terminal sting. Although the tail vibrates spasmodically when 

 the animal becomes excited, it appear to be in no wise a weapon 

 of defense. 



The position of the median and lateral eyes is shown in figure 

 1. The median eyes are black, bead-like elevations rising out of 

 small depressions dorsally situated on either side of the mid-line 

 at the anterior end of the head. The lateral eyes, of which 

 there are three pairs, are located considerably more caudad on 

 the dorsolateral margins of the cephalo-thorax. The three lat- 

 eral eyes of each side are clustered, close together, in a minute 

 triangle. When a small beam of light is focused on them, they 

 reflect the light so that they appear like a single brilliant spot. 

 There is no visible reflection of light when the median eyes are 

 thus illuminated. 



While these scorpions were very sensitive to light, at no time 

 during the experiments did I observe any reactions which might 

 be interpreted as visual responses. As often as animals were 

 approached with forceps in handling them, they never made any 

 movement which would indicate that they could see. A par- 

 ticularly striking failure to demonstrate a visual response was 

 given by the following procedure. Animals were thrown into a 

 state of alertness by scratching the table near them. An ob- 

 ject could even then be waved back and forth directly in front 

 of the eyes, between the opened jaws, without their making any 

 attempt to strike at it. Pinch one of their spines, however, 

 and they throw themselves entirely clear of the table in a fren- 

 zied attack on the forceps. Repeated many times and in many 

 different ways, experiments with moving objects never elicited 

 any activity. While these results, being entirely negative, are 

 not conclusive as to complete lack of vision, there is no reason 

 to doubt that vision in distinction from photosensitiveness, is, 

 at least, very poorly developed. 



