First, then, let us examine the problem from the point of view of the food-supply. There are many species whose success in rearing offspring is largely dependent upon the rapidity with which they can obtain food; and it makes but little difference which species we choose out of many--Finch, Bunting, Warbler, or Chat. I shall choose the Buntings, as their life-history in broad outline conforms to the general type, and, moreover, their behaviour is fresh in my mind. The young are born in a very helpless state; they are without covering--fragile organisms, ill-fitted, one would think, to withstand extremes of temperature, and wholly incapable of protecting themselves from enemies of any description. For the first three days after they are hatched the female spends much of her time in brooding them, and, when she is thus occupied, the male sometimes brings food to her, which she proceeds to distribute or swallows. But all the young cannot be fed, neither are they ready to be fed, at the same moment; and the parents have besides to find food for themselves, and the nest has to be cleaned--all of which necessitates the young being exposed to the elements at frequent intervals. Now it is impossible to observe the instinctive routine of the parents, when the young need attention, without being impressed with the conative aspect of their behaviour. Why, we ask, are the movements of the female so brisk; why does she seek food and clean the nest so hurriedly; why, if her instinctive routine is interrupted, do her actions and her attitude betray such bewilderment? I take it that the only answer we can give to these questions is that the part of her inherited nature which predominates just at this particular time is to brood. But why is brooding of such importance? Partly to maintain the young at the proper temperature, and thereby to induce sleep--and sleep for offspring newly hatched is as important as food--and partly to protect them from the risk of exposure to extremes of temperature. This latter danger is no imaginary one. Examine a young bird that has recently left the egg; observe its nakedness; and consider what it has to withstand--a temperature that may rise to 70° F. or may fall to 40° F., the tropical rain of a thunderstorm or the persistent drizzle of many hours' duration, the scorching effect of a summer sun or the chilling effect of a cold north-easterly wind, and, constantly, the sudden change of temperature each time that the parent leaves the nest. One marvels that it ever does survive; one marvels at the evolution of a constitution sufficiently elastic to withstand such changes. But, however much the constitution may give us cause to wonder, it is clear that much depends upon the parents. A slight inefficiency of the instinctive response which the presence of the young evokes, a little slowness in searching for food or sluggishness in returning to the nest, might lead to exposure and prove fatal. And, however much is demanded of