In an old pear-tree with dense foliage, at the foot of the garden, a black-headed warbler had built its nest. Day by day Jules had watched the bird as it brought blades of dry grass, one by one, and wove them into the shape of a cup, after which it furnished the interior with a hair mattress. Then came the eggs, to the number of five, light chestnut in color, marbled with darker streaks. Parting the branches very gently in the mother’s absence, and standing on tiptoe, Jules had peeped into the nest, but of course without touching anything; he had merely cast a rapid glance at the pretty cluster of five eggs lying together at the bottom. The laying was over, his uncle told him; now would begin the incubation, and in a few days five little creatures, blind and featherless, would at the slightest rustling of the foliage stretch their yellow beaks wide open in mute appeal for food. Already Jules was looking forward to the good time he would have in watching, from a distance, the bringing up of the brood, and was planning how, when the little birds should have grown a trifle larger, he would put some small caterpillars and worms on the end of a stick and drop them into the nest for the young ones to eat. Then before long the new-fledged warblers would leave the nest and the garden would have five more caterpillar-destroyers repaying with their services and joyful songs the kind-hearted attentions of their boy friend. That was what Jules was eagerly looking forward to yesterday, but to-day he returns from his visit to the nest with a troubled look on his face. A strange thing has happened: with the warbler’s five eggs there is a sixth one, a little larger and of a different color. Whence comes this strange egg? Who put it in the nest, and why? Uncle Paul, on being consulted, went to the nest and came back with the egg. “Your warbler’s nest, my dear child,” he said, “has had a fortunate escape; but for your visit this morning the young birds would have been lost almost as soon as they were hatched. This egg that I have brought back is a cuckoo’s egg.” “But I don’t see how it came to be in the warbler’s nest or what danger it threatened to the young birds that are coming.” “You will see when I tell you the cuckoo’s habits. It is a curious story. The cuckoo is the bird that in early spring, when the meadows are sprinkled with violets and the trees are just putting forth their leaves, keeps repeating its cry of cuckoo, cuckoo, in a clear and plaintive tone.” “I have often heard it,” said Jules, “singing on the edges of woods, but have never been able to get a good look at it.” “I have seen it flying away,” Emile put in, “and it seemed to me pretty large.”