72 THOS. H. MONTGOMERY, JR. 



they are disturbed by the removal of the eel grass, they all run 

 directly landward provided only the sun is shining from an angle. 

 Fifty or a hundred or more of these spiders may be set into 

 commotion by the lifting up of a bunch of the eel grass, and 

 under the conditions stated the large majority, sometimes all, 

 of them invariably run in a straight course right up the beach and 

 do not stop until they reach shelter beneath another mound of 

 the eel grass. This habit is the more striking because none of 

 the other species that live with them exhibit any such regular 

 landward migration. 



Direction and velocity of the wind have nothing to do with 

 determining this course of running, for the landward migration 

 occurs whether the wind blows upon the spiders from in front, 

 or behind or from the side, or when there is no wind. Further, 

 the spiders are not guided by any moisture sense, for (i) they do 

 not regularly run landward when the sun is obscured, and (2) if 

 the observer pours out sea water at a higher level and lets if 

 flow down towards the spiders, they nevertheless continue their 

 landward course. Again, this is not a geotropism, a tendency 

 of the spiders to run up hill, nor an orientation to the rolling of 

 sand grains. For the observer can dig a deep trench to land- 

 ward of the spiders, and they will go down its declivity and 

 up its opposite side without changing their course; or one 

 can implant a board vertically in the sand in front of them, when 

 they will climb up one surface of it and down the other without 

 changing their general direction of movement. 



Therefore the landward course of these spiders is not caused 

 by any influence of wind or moisture or slope of the beach, but 

 is probably a light reaction as the following observations would 

 show. 



When the sun is shining and when its rays come from an 

 angle, at any time but noon, the spiders regularly run up the 

 beach; this I have tested many times and on different beaches 

 facing different points of the compass. That is, the spiders run 

 up the beach whether the sun shines in front of, behind or to one 

 side of them. But at noon, when the sun is nearly vertical, 

 they run in all directions ; and that they do also when the observer 

 on a sunny day shades them with an umbrella. 



