198 GENERAL ZOOLOGY 



bearing five equally important sets of sense organs (eyes, 

 tactile tentacles, etc.) and what little power of attention 

 it has must vacillate between these or be continually divided. 

 This is important because the development of higher 

 psychical processes (memory, power of attention, reason, 

 etc., as they appear in animals with well-centralized nervous 

 systems) depends upon seriously attending to one thing 

 at a time. 



The behavior of a starfish is largely made up of more 

 or less automatic " reflexes." If an individual is turned 

 with its mouth uppermost, it slowly pulls itself over again, 

 by using the tube-feet. Observers have noticed that 

 various individuals may have different methods of righting 

 themselves that is, they have different " habits" of doing 

 the same sort of work, and, therefore, show some individ- 

 uality. Professor Jennings induced starfishes to forsake 

 their usual methods of turning over, and taught them new 

 ways. For example, a certain individual always began to 

 turn with a particular arm, and when prevented from using 

 that, learned to begin with another. Such lessons are very 

 simple, but they show the limits of the starfish's "mind." 



A starfish has its nervous system separated into three 

 divisions; all essentially alike in structure. There are 

 five nerves running longitudinally in each of the arms, and 

 these are connected in the disc. Two divisions are near 

 the oral surface, and the third lies in the aboral body wall. 

 If the central connections are cut, the arms no longer 

 work together, but e.ach can still carry on its own activities. 

 If an individual in which the connecting nerves have been 

 severed is turned over, each of its arms tries to get back by 

 itself. So far as its psychology is concerned, a starfish 

 consists of five centers, or individuals, which usually work 

 in harmony through the influence of the central connections. 



The behavior made necessary by radial symmetry has, 

 then, made the starfish unprogressive, and generally diffuse 

 psychologically. And, if we look at the starfishes' ances- 

 tral tree, there is evidence that there has been retro- 



