52 H. G. Kribs 



2 The "exploring" movements, which consist of Httle side 

 thrusts of the head in various directions associated with a pucker- 

 ing of the prostomium. 



3 The crawhng movement, in which progress is made only by 

 muscular contraction and extension. Progress may be assisted 

 by alternate holding to the substratum by means of the pharynx 

 and caudal papilhe. 



4 The feeding reaction, which consists of the extrusion of the 

 pharynx, and the swallowing of food particles. 



Other movements are protective. 



1 The avoiding movements, which consists of a backward 

 dart of the head and its projection in another direction. 



2 A vigorous contraction of the body segments which squeezes 

 out many gland cells, mucus and globules. 



3 Burrowing in the sediment. 



4 Holding to substratum by means of pharynx or caudal 

 papillae. 



More or less associated with all of the above movements are peri- 

 staltic waves and the constriction of zooids. 



The Physiological States 



The emphasis with which these movements may find expression 

 and their coordination in the animal economv varies widely under 

 changing conditions. These changing conditions in the ambient 

 medium have an immediate effect on the equilibrium of the inter-, 

 nal states of the animal. These physiological states, as associated 

 with changes in external conditions, for our present purpose, may 

 be grouped under the following categories: 



1 State of Relaxation. This state is peculiar to a cool environ- 

 ment when the light is subdued. 



2 State of Normal Activity. This embraces the phenomena of 

 the feeding and exploring reactions, the crawling and gliding move- 

 ments. It marks the time when the processes of metabolism and 

 anabolism are in balance. 



3 State of Tension. This marks the period when destructive 

 forces are in ascendency. The movements are energetic and 



