Reaction to Light and other Points in Behavior of Starfish. 99 



CLIMBING OF VERTICAL WALLS. 



Most naturalists who have observed starfishes in their natural 

 habitat have seen them attached to the vertical walls of rocks, masonry, 

 or the piles supporting docks, and those who have studied these interest- 

 ing animals in the laboratory have been struck by what seems to be their 

 general tendency to climb up on the more or less vertical side of the 

 aquarium, often reaching the surface of the water and apparently at- 

 tempting even to crawl on this surface with the oral side uppermost. 

 It seems to me the " tendency of these animals to move upward" is more 

 evident in laboratory aquaria than under natural conditions. 



Preyer (1886-1887) was one of the first to call our attention to this 

 phenomenon and he saw in the behavior of starfish and brittle-stars a 

 strong tendency to move upward. Strange to say, he ruled out such 

 factors as lack of air, lack of food, changes in temperature or currents 

 of water, and desire for light, suggesting that parasites sometimes found 

 in the ambulacral furrows might be the cause of the upward movement. 



Loeb (1900) very justly pointed out the insufficiency of Preyer's 

 suggestion and also objected to the latter's generalization as to the factors 

 that do not influence the behavior. Loeb states that Asterina tenuispina 

 is attracted upward by the light ; on the other hand, he seems to be in- 

 clined to believe, from his study of Asterina gibbosa, that certain star- 

 fish move vertically upward on account "of the force of gravity"; that 

 they are "driven there by negative geotropism." 



Romanes (1885) makes no attempt to discover any factors that 

 might account for the upward movement of certain starfish, but simply 

 describes their behavior in a tank. He finds that they crawl in a determin- 

 ate direction and that when a starfish happens to touch a solid body it 

 may continue its direction unchanged or may turn toward the body which 

 it has touched. If while crawling along the floor of the tank a ray happens 

 to touch the perpendicular side of the tank, the starfish may continue 

 its direction of advance unchanged on the floor, feeling the perpendicular 

 side with the end of its rays, perhaps the whole way around the tank; 

 yet it may not ascend or it may go directly up the perpendicular wall. 1 



The starfish Echinaster crassispina, which I used in experiments, 

 has well-developed suckers on its tube feet and is able to ascend vertical 

 walls without any difficulty. It lives as a rule on rather level bottoms 

 and is migratory in its habits. When several healthy specimens of this 

 species are put in a medium-sized circular glass aquarium filled with 

 sea -water they begin to move after a short time, usually in a determinate 

 direction, and are soon seen climbing up the vertical sides of the aquarium 

 until they reach the surface. If, instead of the small aquarium, a large 

 one holding 200 or 300 gallons is used, some specimens will climb the 

 walls, others will move along the bottom with one or more rays in con- 

 tact with the walls; while the ascent of some individuals nearly always 

 occurs, the phenomenon is not so striking as when a small aquarium is used. 



1 Bohn's (1908) experiments show that light has much to do with "geotropic" 

 reactions; that the same lighting is sometimes followed by an ascent and sometimes 

 by a descent of a vertical surface. Assuming that there is a geotropic factor whose 

 action results in the ascent or descent of vertical surface by a starfish, his observa- 

 tions leave the impression that it is a very variable one. 



