vide for themselves; this would bring
the date to about the 25th of July, when there is hardly a parent bird
in the country; they have left for other parts of the world. "Oh! but,
papa," said Willy, "you said in the lines you told us to remember--

In July,
He prepares to fly.
Come August,
Go he must.

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.]

"Oh! papa," said Jack, "what is this curious plant that grows so
abundantly on the grass here? I know it well by sight, but do not know
its name." It is a spike of horse-tail; see how the stem is marked
with lines, and how curiously jointed it is, and quite hollow except
where the joints occur. The fruit is borne at the top of the plant
(_a_); see, as I shake it, what a quantity of dust comes from it; this
dust is the fruit, or spores as they are called; each spore is of an
oval form, with four elastic threads. If I were to put some of this
dust on a glass slide, and look at it under the microscope, I should
see a curious