THE COWBIRDS. 611 



instinct in Molothrns, it will perhaps seem premature to found specula- 

 tions on the few facts Lere recorded and before we are acquainted with 

 the habits of other members of the genus. That a species should totally 

 lose so universal an instinct as the maternal one, and yet avail itself of 

 that afteetion in other species to i)ropagate itself, seems a great mystery. 

 Nevertheless, I can not refrain from all conjecture on the subject, and 

 will go so far as to suggest what may have been at least one of the many 

 concurrent causes that have produced the parasitic instinct. The a])iKir- 

 ently transitional nesting habits of several species, and one remarkrable 

 habit of .1/. hotutriemis, seem to me to throw some light on ai)oint bear- 

 ing intimately on the subject, viz, the loss of the nest-making instinct 

 in this species. 



Habits vary greatly; were it not so, they would never seem so well 

 adajtted to the conditions of life as we find them, since the conditions 

 themselves are not unchangeable. Thus it happens that while a spe- 

 cies seems well adapted to its state in its habits, it frequently seems 

 not so well adapted in its relatively immutable structure. For exam])le, 

 without going away from the pampas, we find a Tringa with the habits 

 of an upland Plover, a Tyrant Bird, ntangiis helUcosus, preying on 

 mice and snakes, another Tyrant Bird, Myiotheretes rujiventris, Plover- 

 like in its habits, and linally a Woodpecker, Colaptes campestris, that seeks 

 its food on the ground like a Starling; yet in none of these — and the list 

 might be greatly lengthened — has there been anything like a modifica- 

 tion of structure to keep pace with the altered manner of life. But, how- 

 ever much the original or generic habits of a species may have become 

 altered — the habits of a species being widely difterent from those of its 

 congeners, also a want of correspondence between structure and habits 

 (the last being always more suited to conditions than the first) being- 

 taken as evidence of such alteration — traces of ancient and disused 

 habits frequently reappear. Seemingly capricious actions, too numerous, 

 too vague, or too insignificant to be i ecorded, improvised definite actions 

 that are not habitual, apparent imitations of the actions of other species, 

 a peri^etual 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 occa- 

 sional aberrant habits of individuals may possibly be due — such as of 

 a bird that builds in trees occasionally laying ou the ground. If recur- 

 rence to an ancestral type be traceable in structure, coloration, language, 

 it is reasonable to expect something analogous to occur in instincts. 

 But even if such casual and often aimless motions as I have mentioned 

 should guide us unerringly to the knowledge 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 



