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 Columbide 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 
