1^07] Jennings. — Bfliavior of the Starfish. 129 



variation, even when carried out in the purely typical way. But 

 to these must be added a very great proportion of irregular 

 reactions, which may be classified as follows : 



1. In methods 1, 2 and 3 the rays frequently become attached 

 at first in such a way as to oppose each other's action, — one or 

 more rays being twisted in the wrong direction for the way of 

 turning that finally prevails. Examples of this are seen in figs. 16, 

 18 and 19. This complicates the reaction greatly. These wrongly 

 attached rays either (1) release their hold entirely and are 

 swung passively over by the other rays; or (2) they release, un- 

 twist, and take hold properly anew, again aiding in the pulling 

 over; or (3) they untwist while still remaining attached, by a 

 process of rotation on the long axis, "walking" by means of their 

 tube feet; or (4) they remain attached until the righting is quite 

 accomplished, becoming twisted 360 degrees; then untwist after 

 the starfish as a whole has reached its normal position. Since 

 any one or more arms may go through any of these maneuvers, 

 the possibility of variation is extremely great. 



2. A righting reaction that is begun by one method may be, 

 and often is, finished by another. Four rays may work for a 

 time ; then one or two may release ; or after one or two arms 

 have initiated the turning, others may take hold and assist, or 

 may modify the method. The animal may begin to turn in one 

 direction ; then change and turn in another. All sorts of com- 

 binations of the various possible methods occur. 



Now, since it is clear that the phenomena we are studying are 

 extremely variable, the next step is to discover, as far as possi- 

 ble, the causes of the variations. For every variation there must 

 be some determining factor or factors ; these must be worked 

 out. Mere proof of the existence of variation and of its dis- 

 tribution does not, in any field, carry us far; it always constitutes 

 essentially a plan for further work. Where the descriptive study 

 of variation ends, physiological study of its causes begins. We 

 wish to analyze the reaction, bringing out so far as possible the 

 determining factors for eveiy thing that occurs, and for the 

 variations in different cases. 



Let us begin our analysis by observing the first reactions of 

 the starfish, — just what it does immediately after being turned 

 over. Again we find much vai-iation; we may classify as follows: 



