And now you say the cuckoos leave before the end of July. I think you must have made a mistake somehow." I am glad that you have found out the error, if it is one. Old rhymes are not always to be trusted; but I suspect that the couplet "Come August, go he must," means to imply that the cuckoo does never really stay so late with us. I must not, however, forget to tell you that it is the old parent birds that leave us early; young birds remain till September, and even October, but they have not by that time acquired the cuckoo note. If you ask why cannot the old cuckoos stay with us a little longer, and then all go away together as a family party, young and old, in September, instead of being in such a hurry, I have only to say that it is the fashion amongst cuckoos, and of course cuckoos, like certain other animals, must be in the fashion. This is Dr. Jenner's explanation of the peculiar habits of the cuckoo in respect of its eggs. I am not prepared to say whether or not it is sufficient to explain them. The cuckoo's egg is very small when compared with the size of the bird; it is of a pale grey tinged with red. "But how does the cuckoo's egg get into some of the nests?" asked Willy; "for some of the nests in which the cuckoo's egg is found are too small to allow the cuckoo herself to enter to lay her egg." You are quite right; I believe it has been proved that the cuckoo lays her egg on the ground, and carries it in her bill into other birds' nests. [Illustration: HORSE-TAIL.]