Early in the summer months, the frog orchestra seems well tuned, but as the cold days come on the toads crawl into a hole, making it as they go, while the frogs go into the mud to sleep through the winter, out of reach of frost and snow, where they lie dormant until the spring air shall again inspire them with the joy of living. CHAPTER IV. _The Birds and Their Families._ The next step to be taken was the study of the birds. Everywhere could be seen father and mother birds busy making their house for the babes, which were soon to come to live with them. Great fun it was to hunt for nests and count the number each one discovered. First, right in Bobby’s yard was a young horse chestnut tree, and here in this tree Mr. and Mrs. Thrush had already built their nest, or house, and were even now waiting for the first egg to come. Again the children were told that Mrs. Bird was more active and more intelligent than Mrs. Frog or Toad; that altogether she was a _higher_ creature than either the flower, the fish or the frog; that all father birds and all father creatures on up the scale of development use greater care to fertilize the egg than either Mr. Buttercup, Mr. Fish, Mr. Toad or Mr. Frog. For, instead of fertilizing it in the water, or with the help of the insects or wind, the egg of the higher creatures is fertilized while still in the mother’s body. Just like the flowers, Mrs. Bird has an ovary, where the little seeds or eggs are kept. This ovary is attached to a tiny tube, and this tube has no separate opening directly out of the body, but runs into the intestine very close to the outer opening of the body, where the intestines throw off the waste food. Now, these little eggs have been within the Mother Bird’s body _always_, ever since she herself came out of the egg, and they have been growing slowly all the time until a time comes when, like the stigma of the pistil (which at a certain time is ripe for fertilization and becomes moist and sticky), they, too, are ripe for fertilization. That this time has arrived is shown by many outward signs—such as beautiful plumage and charming songs. Especially in the male bird does this show itself. His whole nature seems bubbling over with the desire to mate and the knowledge that at last he, too, has developed. For though there are no eggs within his body, there is something else there just as important to the creating of new little birds, and he feels the time has come when this fertilizing substance is ready to do its work. His color becomes bright, even brilliant, and his voice becomes enchanting. Thus he tells the world of this glorious happiness. This period is called the mating season—the time when both father and mother birds awaken to the desire of building their nest and creating offspring.