192 
FRANCIS H. HERRICK 
the bird passes from center of influence 1 to center 2, 3, and so on, 
to the end of the cycle. It remains under the influence of a given 
instinct or series of instincts, such as nest-building, incubation, 
or care of young, until its impulses in each direction have been 
satisfied, before entering a new sphere, or being swayed by new in- 
stincts. ^^Tien the correlation or attunement is relatively perfect 
the instincts of parent and child fit like lock and key. To change 
the figure, like clocks beating synchronously the instincts of parent 
and child are generally in harmony, but one of the clocks occa- 
sionally gains or loses, stops or runs down ; one term is liable to 
be weak or to drop out altogether, so that there is a gap in the 
series, w^hich leads to eccentric behavior and often proves serious 
to eggs and young. On the other hand, one term may be unduly 
strengthened, like nest-building or incubation, and a preceding or 
following term correspondingly weakened. Such disturbances 
which are more common than is generally known in all birds, 
vary with the individual, but are more prevalent in certain fami- 
lies and species than in others. They have been described in a 
former paper under the head of the '^blending" and overlap" 
of instincts, 22 wherein it was shown that they account for many 
puzzling and hitherto unexplained eccentricities of conduct 
such as repairing the old nest or building a new one at the close 
of the breeding season (in eagles, fish hawks and gulls) , temporary 
suspension of nest-building and dropping the eggs on the ground 
(in ostriches, cowbirds, and many other species) leaving the young 
to perish in the nest and starting on migration (most frequently 
noted in swallows), building supernumerary (in robins, wrens and 
other species) and superimposed nests (in warblers with cowbirds' 
eggs), and other anomalous actions, which have been subject to 
general and varied misinterpretation. 
In many species, the cycle is normally repeated one • or more 
times within the season, and in most cases when the series is 
broken at 3, or at 4, by fear, or by loss of the eggs, the cycle is 
begun anew at 3. In the most aberrant cases of behavior as 
in some of the Megapodes of Austraha and the East Indies, 
« Op. af., p. 781. 
