1907] Jennings. — Behavior of the Starfish. 149 



forms habits, and that these set tendencies are due to habits pre- 

 viously formed. To investigate whether this is true is the pur- 

 pose of the present section. 



The formation of lasting habits has been demonstrated 

 among lower animals in the Crustacea (Yerkes, Spaulding), in 

 annelids (Mrs. Yerkes, 1907), and in flatworms (Bohn)^ All 

 these animals have the nervous system so centralized that one 

 or more important ganglia can be distinguished, the largest of 

 which is commonly called a "brain." In the starfish there is 

 no such centralization of the nervous system. There is a nerve 

 cord which forms a ring about the mouth, and from the five 

 angles of this ring nerve cords run outward in each ray. Be- 

 sides these parts there are fine networks of nerve fibers over the 

 surface and among the tissues. The ganglion cells are scattered 

 in the cords and nets, along with the fibers; there is no concen- 

 tration anywhere into ganglia. 



It has never been shown that animals with so simple a type 

 of nervous system can form habits^". "Whether the possibility 

 of habit-formation depends on a certain complexity of the nerv- 

 ous system is a matter of much interest. Furthermore the gen- 

 eral question of the distribution of the power of habit-formation 

 is one of great importance. I have, therefore, attempted to test 

 this matter in the starfish with great care. 



By the word habit there is commonly understood a lasting 

 modification of behavior due to experience. In taking up the 

 question of habit formation, one is compelled to deal at the same 

 time with modifications of behavior that may show themselves 

 only for a short period. There appears to be no precise term 

 for designating these, though their acquirement is often spoken 

 of as learning by experie^ice, or as a manifestation of intelli- 

 gence, — both expressions having a somewhat subjective tinge that 

 it is desirable to avoid in an objective investigation. It will, 

 perhaps, be impossible to avoid them completely, but the word 

 Jiabit may be stretched a little, so that we may designate these 

 non-permanent modifications as temporary habits. If after be- 

 ing trained to right itself in a certain way, the starfish should 



" See the review of this matter in my book on the Behavior of the Lower 

 Organisms, pp. 254-259 (1906). 



" Certain statements of Prej^er on this matter will be taken up later. 



