FLIGHT-FUNCTION IN THE SILKWORM. 12$ 



this function is a part of the sum total of inheritance, the over- 

 whelming development of the one instinct, that of mating, serves 

 habitually to inhibit its activity. On the other hand, something 

 has preserved both the wing structure and the flight function in 

 spite of persistent non-use and natural selection, and although 

 these have no relation to the preservation of the race in its present- 

 day activities. 



In the general conception of " instinct," its failure means 

 extinction of the species.^ In the case at hand, on the contrary 

 its manifestation would mean extinction of the species. Its 

 failure of manifestation is associated with the present-day life of 

 the insect. Its manifestation under conditions herein observed 

 attests the persistence in heredity of an ancestral function long 

 after it has lost everything of a purposeful nature. 



Laboratory of Entomology and Bionomics, 

 Stanford University, California. 



1 Jordan and Kellogg, "Evolution and Animal Life," p. 430. 



