Traces of the egg-tooth were retained until the ninth day in two owls and until the 11th day in another. In owl IV, the egg-tooth was lost sometime between the 9th and 14th day. Changes in the length of the culmen are indicated in Table 1. The length of total culmen of owl IV when 47 days old is slightly greater than the average for three adult male owls from Lawrence, Kansas (40.0 mm. as contrasted with 39.2 mm. in the adults). The length of exposed culmen, without cere, in the same bird when 47 days old is less than the average of this measurement in the three adults from Lawrence (23.7 mm. as contrasted with 26.5 mm. in the adults). The femur was measured on three occasions as accurately as possible through the skin and flesh. The precise boundaries of the femur could not be determined and the thickness of the skin and certain muscle is included. These measurements are not given to indicate actual length of the femur, but to indicate the relative changes in length of this bone. Remnants of the yolk stalk were clearly evident at seven days of age (see fig. 5) in the owl hatched in 1946 and were still present when the owl was last examined (49 days of age) just before the young left the nest. The scablike remnant was not noted in the three young hatched in 1945, but close inspection was not made to see if it was present. The instinctive reactions of young horned owls shortly after hatching have been fully described by Sumner (1934). By the third day our owls could raise their heads, but when a bird was undisturbed its head lay on the nest floor and the wings were slightly spread. The eyes of owls I and II opened at about 7-1/2 days, those of owl III on the 6th day, and those of owl IV sometime between the 7th and 9th days. After the eyes opened, the head was held erect more of the time. The young responded with "cries" when disturbed by handling, when stimulated by certain movements of the parent, or by movements of our hands near their heads, which suggested to them the possibility of being fed. Cries were evident but weak in the unhatched, pipped, egg, but soon after hatching increased in intensity, and beginning at six days of age were replaced, in part, by the characteristic "bill-snapping" of more mature birds. These cries of the young may serve, among other things, for recognition, inasmuch as they were given when the parent was inspecting the young. When the parent returned to the nest and covered the young, after having been flushed, it sometimes uttered a special note, "hut, hut, hut," much like the "cluck" note of the hen of the domestic chicken. The young responded to these notes with faint cries, in contrast to the loud cries signifying alarm and possibly hunger, which they gave when the parents were absent from the nest.