EXPERIMENTS ON ECHINODERMS 71 



crawl upward, it is difficult to see why they should 

 not drive the animals down from the vertical side. 

 As a fact, however, Asterina gibbosa, as well as Cucu- 

 maria cucumis, remains on the highest point of the 

 vertical side. I believe it is much nearer the truth to 

 ascribe the vertical upward movements of certain 

 starfish to an action of the force of gravity. 



BIBLIOGRAPHY. 



1. ROMANES, G. J. Jelly-fish, Starfish and Sea Urchins. New 

 York, 1893. 



2. PREYER, W. Ueber die Bewegung der Seesterne. Mit- 

 theilungen aus der zoologischen Station zu Neapel, Bd. vii, S. 96. 



3. LOEB, J. Ueber Geotropismus bei Thieren. Pfluger's Ar- 

 chiv, Bd. xlix, 1891. 



