ADAPTATION 213 



any missing part ; but at present we know absolutely 

 nothing about such conditions. 1 



But no amount of negative instances can disprove an 

 existing positive which is what we have been studying. 

 Our analysis based upon the existence of regulations is 

 as little disparaged by cases where no regulability exists 

 as optical studies are by the fact that they cannot be 

 undertaken in absolute darkness. 



1 Experiments carried out in the " Biologische Versuchsanstalt " at Vienna 

 indeed have shown that many animal types are capable of at least a certain 

 degree of restitution, although they had previously been denied this faculty 

 by zoologists. 



