DIRECTION OF LOCOMOTION OF THE STARFISH 31 



VII. SUMMARY 



The principal points brought out in this paper maj^ be sum- 

 marized as follows: 



1. Experiments indicate that the starfish (Asterias forbesi, 

 and probably other species), in the absence of directive stimuli, 

 does crawl more frequently with a particular part of the body 

 in advance, namely the part in proximity to the madreporite. 

 This demonstrates a 'physiological anterior,' and a plane passed 

 through the madreporite or one of the adjacent rays divides 

 the animal into symmetrical physiological halves. 



2. The correlation between direction of locomotion and mean 

 arm length is doubtful and the results obtained are probably 

 not significant. 



3. A definite 'impulse' is established on account of which the 

 starfish tends to crawl in the same general direction in succes- 

 sive trials. 



4. There is a tendency for this impulse to shift or 'rotate' 

 gradually around the body in one direction or the other. 



5. After righting itself, the starfish more often crawls in the 

 general direction of the rays opposite to those which it has used 

 primarily in righting. 



6. Preyer's results from his experiments fall substantially in 

 line with those on Asterias forbesi. 



7. The 'physiological anterior' of the starfish corresponds to 

 anterior in the spatangoids, with respect to the position of the 

 madreporite. 



8. The position of the madreporite may perhaps be what 

 determines 'anterior,' and it is possible that this may be from 

 purely mechanical causes. 



LITERATURE CITED 



Aqassiz, Elizabeth C, and Alexander 1865 Seaside studies in natural his- 

 tory. 157 pp. 



BoHN, G. 1908 Introduction a la psychologie des animaux a sjTii^trie rayonnee. 

 Deuxieme Md'inoire. Les essais et erreurs chex les Etoiles de mer et 

 les Ophiures. Bui. Inst, gener. psychol., 8e annec, pp. 21-102. 



Cole, L. J. 1901 Notes on the habits of pycnogonids. Biol. Bull., vol. 2, 

 no. 5, pp. 195-207. 



