230 HELEN WOODBRIDGE. 



Sometimes this resulted in bringing the larva in contact with 

 the eel grass immediately, in which case it would follow up the 

 surface of the blade for a few centimenters before lapsing again 

 into inactivity. More often it failed to touch an eel grass blade, 

 and after swimming upward a centimeter or so, it would relapse 

 into inactivity, only to be stimulated again as it sank into the 

 shadow a second time. The value of these responses to the 

 larva when in its natural environment is strikingly evident. 



If, as it appears, these responses function in a way which tends 

 to lead the larva to a suitable place for metamorphosis, we have 

 a basis for the belief that they are of survival value to the 

 species, and that they have been in the past and perhaps are still 

 operative in its continued evolution. 



