ARGENTINE COW-BIRD 89 



traces of ancient and disused habits frequently 

 reappear. Seemingly capricious actions too numer- 

 ous, too vague, or too insignificant to be recorded, 

 improvised definite actions that are not habitual, 

 apparent imitations of the actions of other species, 

 a perpetual inclination to attempt something that is 

 never attempted, and attempts to do that which is 

 never done these and other like motions are, I 

 believe, in many cases to be attributed to the faint 

 promptings of obsolete instincts. To the same cause 

 many of the occasional aberrant habits of individuals 

 may possibly be due such as of a bird that builds 

 in trees occasionally laying on the ground. If recur- 

 rence to an ancestral type be traceable in structure, 

 coloration, language, it is reasonable to expect some- 

 thing analogous to occur in instincts. But even if 

 such casual and often aimless motions as I have 

 mentioned should guide us unerringly to the know- 

 ledge of the old and disused instincts of a species, 

 this knowledge of itself would not enable us to 

 discover the origin of present ones. But assuming 

 it as a fact that the conditions of existence, and the 

 changes going on in them, are in every case the 

 fundamental cause of alterations in habits, I believe 

 that in many cases a knowledge of the disused in- 

 stincts will assist us very materially in the enquiry. I 

 will illustrate my meaning with a supposititious case. 

 Should all or many species of Columbids manifest 

 an inclination for haunting rocks and banks, and for 

 entering or peering into holes in them, such vague 

 and purposeless actions, connected with the fact 



