Even the crawfish's legs and the spider's legs have seven joints. In those members of the crawfish and lobster family where there are fewer than seven joints, either some of these joints have grown together, or they have shrunk up, from not being used, until they don't look or act like joints at all. Sometimes we find them turned into little thread-like legs or feelers. You can see these feelers fringing the crawfish's jaw-feet, and the end of his flipper tail.
Why and how did Nature get into this way of counting by the odd numbers, I, 3, 5, 7? There is a reason given for this which you could not understand now. But you can easily understand it when you are older, if you keep on studying this wonderful Nature book which you see open all around you—in the woods, the water, the fields and the air.
This you can easily understand now: That, having begun with one part, then having added two to this one, as you see in the growing plant to keep it balanced, things must go on by adding twos if they are to grow sym-met'ri-cal-ly. That is a long word, but you should learn to use it. Look it up in a dictionary and see how much it means. In plants and animals Mother Nature, whatever else she does, always builds sym-met'ri-cal-ly.
