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 sort 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 



w5h 



