THE HOUSE FLY

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way without turning. There is one thing I cannot do, and that is look straight forward.

"I will not take time to tell you what you can so easily see yourselves by looking at the underside of my body, but every one thinks it curious that the saliva to moisten my food is in two little sacs which the proboscis can reach and draw from as I need.

"The mosquito and I, having but one pair of wings, which are kept open, value very highly our poisers, pairs of winglets which help to balance us as we fly.

Any one can tell you what fine contrivances we have in our feet to hold us fast as we light or crawl on walls or ceiling. The secret of it is a fluid that oozes out against the wall or windowpane. It does not fasten us so as to make it hard to get away, but it holds while we press. How the fluid gets to the feet is still a mystery.

"There are other things about the great family of flies, with its thousands of country cousins, but this is enough to tell at once."

XXXIII. THREE LIFETIMES

IN telling its story the fly omitted to say that it belongs to the great and wonderful race of insects. It would take a whole book to tell but a little about each of the insect tribes. We can think only of the

Some of the insects have wonderful powers and organs. We saw that the roughskin babies were the first in the upward scale to change their forms. The insect children are born from eggs, and they do not bear the least resemblance to their parents. The fly had probably never been told that in its early life it was only a wriggling maggot, for in its middle or pupa state it lost nearly every trace of being alive.

THREE LIFETIMES

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If the insect we are considering is a gorgeous butterfly, its first or larval state was that of a caterpillar; if it is a beetle, it was a grub.

That first life, which might have been a few hours long, but was probably months, seems quite distinct and separate. We wonder if the little creeping or crawling or swimming thing knew what it was going to become. Before it came to its perfect state, which is called imago, because it is then the image of its mother, it had a middle life, called pupa.

This was longer or shorter, according to its kind, but whatever went on in it was covered or masked, as if it were not to be observed. It was a sort of sleep out of which it would wake by and by. Something like a cocoon of its own making wrapped it around.

In the perfect state length of life does not seem to count for anything. The insect may live but a few hours or days. There will be time for it to lay eggs in the right sort of place to have the grub or maggot or caterpillar find the food it wants.

Just below the insects in the scale of life come spiders, crabs, and lobsters; and above them, though you might not think it, are the shell or armor bearers, as you shall learn in the next lesson.

XXXIV. MANTLES AND SHELLS

THE most of us are acquainted with some of the animals this lesson tells about. Children have a rhyme: Open your mouth and shut your eyes,

I'll give you something to make you wise.

Perhaps we know the clam and oyster better by taste than by their organs to work with.

If you have ever seen a common slug you have had a good specimen of the use of a mantle. Slugs are not pleasant to look upon, but it is worth while to see the thick, elastic skin which covers the soft flesh. By means of this the slug can make itself long or short, round or flattened. It moves chiefly by stretching

forward.

Creatures like the clam and oyster had the mantle, but being good to eat they needed a better protection. Let us see along what line it came to them.

The good fairy that watched over their growth was not pleased to have them so exposed to enemies as the jellyfish kind are.

The water all about them was full of lime, but since it was not food few of the creatures had seemed to find