the parents, it is clear that much also depends upon the relationships in the external environment; for no matter how sensitive or how well attuned the instinctive response of the parent may be, it will avail but little in the presence of unfavourable conditions in the environment. Everything turns upon the question of the effect of exposure. And in order to ascertain how far extremes of temperature are injurious, I removed the nests of various species containing newly hatched young, and, placing them in surroundings that afforded the customary amount of protection from the elements, I made a note of the temperature and the atmospheric conditions and then observed the condition of the young at frequent intervals. Details of these experiments will be found at the end of the chapter. The experiments with the Blackbirds and the Whitethroats gave the most interesting results. Both broods of each species were respectively of much the same age, yet one brood of Blackbirds survived for five, and the other only for two and a half hours, and one brood of Whitethroats lived for twelve hours whilst the other succumbed in a little over an hour. This difference is rather remarkable; and it seems clear that the power of resistance of the young diminishes rapidly when the temperature falls below 52° F. It must be borne in mind, however, that the conditions under which the experiments were made were, on the whole, favourable--the weather was dry, the temperature was not unusually low, nor was the wind exceptionally strong or cold; and even in those cases in which the young succumbed so rapidly, the atmospheric conditions could by no means be regarded as abnormal.