474 



GENERAL BIOLOGY 



must have reached a proper stage of development, and the 



silk glands, now nearing the climax and the end of their use- 



fulness, must be charged with the secretion that is to form 



the cocoon, and a host of other physical (somatic) conditions 



must be fulfilled. When fulfilled, we may say, speaking in 



figures, the ship of instinct is laden and tugging at its cables ; 



its course is laid out from beginning to end, the points of 



call, the discharges of cargo, the 



bells that shall be rung and the 



whistles that shall blow are all 



pre-arranged, and only the 



signal to start is needed, to 



initiate all the events of the 



voyage. Nothing could more 



plainly show the essentially 



autogenetic nature of respon- 



ses. 



The bird builds her nest when 

 the condition of body and brain 

 impels to it. No stimulus has 

 any effect whatever until body 

 and brain are ready. Maturity 

 must be reached, and eggs must 

 grow, and mating must take 

 place; and when all is ready, 

 the simplest sprt of stimulus, 

 the sight of suitable materials 

 (straw or fiber or hair, not 

 conspicuously different from a 

 thousand other things the eye 

 might fall upon) , serves to set 

 the complex activities of nest 

 building going. The stimulus 

 is but the spark that sets off the 



ure pLto p by e 



