142 Trans. Acad. Sci. of St. Louis 
they are placed; prior to this time, they wriggle about when 
taken from the nest. They leave the nest on the tenth day 
and now they express fear by hopping and calling wildly 
when disturbed. An expression of this type of fear, prior to 
the tenth day, would take them from the nest prematurely. 
7. Growth of the young. Tables 18, 19, 20 and 21, together 
with Figures 12, 13, 14, 15, 16 and 17, give extensive statistics 
of growth of weight, length, length of tail and length of flight 
feathers. A lessening in weight growth occurs, normally, 
between the seventh and eighth days. This is brought about 
by the simultaneous unsheathing and drying of most of the 
feathers. On the other hand growth in length shows, if any- 
thing, an acceleration at this period due to the extension of 
the tail. Marked variations in growth occurred in the various 
broods measured and in the different young of the same brood. 
This was brought about by two things: the fact that a slight 
difference in age gave the older Larks a great advantage in 
securing food from the parents; and the fact that food was 
more plentiful later in the season than at the beginning. 
Weight growth curves show a gradual increase over the first 
three days, a very precipitate rise (except for April nestlings), 
for the next three or four days, a marked levelling during 
seventh and eighth (in one case the sixth), and a gradual rise 
during the ninth and tenth. Nestlings in May grew slightly 
more in the same period than a nestling in June and much 
more than a nestling in April. This decrepancy of growth 
seems closely (though perhaps indirectly) correlated with the 
temperatures of these seasons. 
Length growth curves show a precipitate rise during the 
first three days, a slight levelling during the next three days, 
and a precipitate rise during the sixth, seventh, eighth, ninth, 
and tenth days. The cause for the intermediate levelling is 
not understood, but the rise toward the end of the nesting 
period is brought about by the growth of the tail. 
8. Descriptions of the young at various ages. The recently 
hatched nestlings are rather heavily covered with down (a 
hecessary protection against sun and cold in their exposed 
location). The down is cream-buff in color. At nest-leaving 
age the young Lark is completely feathered, but presents an 
appearance quite unlike that of the adults; each feather of 
