250 ORIGIN AND NATURE OF LIFE 



secreting glands, where the precursors of the 

 secretion accumulate during rest, and are 

 discharged on activity, leading to exhaustion 

 which ushers in a new period of rest. Some 

 external stimulus forming an act in a greater 

 cycle in the body usually wakes the gland 

 into activity, but, failing this, if the time- 

 interval becomes too long, it automatically 

 passes into activity and discharges itself. 



A most interesting and beautiful example 

 of such a rhythm dependent upon external 

 stimulation under normal conditions, but 

 capable of becoming automatic in absence 

 of the wonted stimulus, or its delayed arrival 

 beyond the accustomed time, is found in the 

 case of the phosphorescent organisms so 

 abundant in our seas especially in the autumn 

 months. 



It might be supposed at first thought that 

 these phosphorescent organisms are not ob- 

 served to emit light during the day because of 

 the presence of sunlight, and that if taken into 

 a dark room, such as is used foi photographic 

 purposes, they would be found to phos- 

 phoresce just as brilliantly as at night. 

 Such is, however, not the case, not a spark 

 can be elicited from them even by vigorous 

 shaking, so long as there is daylight in the 

 outer world. But if one stands by and 



