98 Trans. Acad. Sci. of St. Louis 
Nest cleaning —One of the most peculiar and at the same 
time most highly developed of instincts is that of nest sanitation. 
So highly developed it is that frequently it inhibits instincts of 
protection solicitude. Thus at one time a female was coaxing 
the last of her young from the nest, away from my presence, 
when she spied excreta in the empty nest. She promptly 
deserted her nestling, leaving it there near me, the offending 
enemy, picked up that dropping and flew away with it. Drop- 
pings carried away were usually removed fifty to one hundred 
feet, deposited, and the bill whetted thoroughly afterward. They 
could not be left near the nest. On one occasion the male flew 
up to an old cabbage stump near the nest with a bolus of 
excreta (Plate XXIX, Fig. 1). My camera shutter, trained on 
the stump, surprised him into dropping his burden. That acci- 
dent inhibited his alarm, however, for he hopped down among 
the weeds at the base of the cabbage stump, hunted for a 
moment, found his dropping, then flew off with it. In March 
and April nearly all excreta was eaten by the adults; in June 
and July nearly all was carried away and dropped. There is 
here, very probably, a close connection between the variation in 
this habit in the various seasons, and the available food supply. 
Developmental reactions of the young.—Why young birds 
have no fear at hatching and why this instinct and others should 
suddenly appear in them at a surprisingly definite period, can- 
not be fully explained. It is instinctive certainly, lying dormant 
however until the physical state of the nestling can carry out, 
logically, its promptings. The Larks reach the age of discrim- 
ination about twenty-four hours after their eyes are open, that 
is, on the fifth or sixth day. Prior to that time they will respond, 
i. @., Open their mouths, at any sound, especially a whistle. 
Failure to respond, or discrimination, is not an instantaneous 
acquisition but becomes noticeable over a period of one or two 
days, at times three or four. Shortly after discrimination be- 
comes apparent in the young they learn to withdraw at the touch 
of a hand and also there is the first evidence of an instinet for 
concealment, for then they remain wonderfully quiet in the nest. 
Also at this time, the seventh to ninth day, they learn the 
crouch-concealment for, upon being removed from the nest, they 
sit quietly upon any object upon which they may be placed 
though at any younger age they will struggle and wriggle 
