82 ICTERID.E. 



origin of the instinct in Molothrus, it will perhaps seem premature to 

 found speculations on the few facts here 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 affection in other species to propagate itself, 

 seems a great mystery. Nevertheless, I cannot refrain from all conjec- 

 ture 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 apparently transitional nesting-habits of 

 several species, and one remarkable habit of M. bonariensis, seem to me 

 to throw some light on a point bearing 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 

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

 themselves are not unchangeable. Thus it happens that, while a species 

 seems well adapted to its state in its habits, it frequently seems not so 

 well adapted in its relatively immutable structure. For example, with- 

 out going away from the pampas, we find a Tringa with the habits of 

 an upland Plover, a Tyrant-bird (Pitangus bellicosus) preying on mice 

 and snakes, another Tyrant-bird (Myiotheretes rufiventris) Plover-like in 

 its habits, and finally 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, 

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

 altered the habits of a species being widely different 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 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 

 recurrence 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 



