[ Pollen Grains much enlarged. ]

The water plants manage in much the same way. They, for the most part, turn loose in the water what in them corresponds to the pollen, and waves and currents carry it to the young seeds. The simpler water animals, sponges and sea-anemones and shell-fish do much the same. While the female sea-urchin or star-fish produces eggs as small as dust, the male produces a still finer pollen-dust, which we call milt or sperm. If one grain of this happens to float against an egg, the egg at once begins to change to a young animal. Otherwise after a week or so the egg dies and that is the end of it. Of course, under these conditions, the chance of egg and milt getting together is pretty slim, and the waste of eggs is enormous. So the fishes, which can move about, have a much better plan. When the female salmon, for example, swims up the rivers to leave her eggs among the gravels in the swift water, the male goes along with her. After she has laid her eggs and gone away, along comes her mate and scatters milt over them. So the salmon egg is pretty sure to grow; and the salmon can afford to have few eggs and larger, and so give her little ones more yolk to live on and a better start in the world.

The bees have a still better device. The single queen bee, as everybody is supposed to know, lays all the eggs of the hive. When the queen is young and the new swarm is just starting, she annexes enough of this pollen-milt-sperm to last her the rest of her life, and stores it up in a little sack. Then whenever she lays an egg, all she has to do is to give this sack a squeeze, press out a little of the contents, and start the egg growing into a new bee.

Strangely enough, however, altho this practice of having two parents is so very common among both animals and plants, and so universal among human beings, it is not, so far as we can see, at all necessary. Potatoes are thick underground branches, and not seeds at all. Yet we plant them and they answer exactly as well. Many lowly creatures, like the yeasts, the bacteria, the infusorians of stagnant water, and the like, never have anything resembling seeds or eggs. There is a parent. The parent splits in halves. There are two children. And where is the parent?

Among the common green plant-lice which swarm on the leaves in the summer, the males all die early in the season. After that the females go on laying eggs, and these hatch more females which lay more eggs, for ten and twelve generations, before the cold weather comes on and some of the eggs begin to hatch out males once more. They get along exactly as well when each insect has only one parent, as when it has two.

In the case of the queen bee, if while the egg is being laid she squeezes the sack, then the egg hatches out a worker, which has therefore, two parents. But if she does not, then the egg hatches out a drone, which has only one. There are many other strange facts of this sort, which have been known for a long time, but which nobody has yet been able quite to understand.

Some facts still stranger have recently come to light. It has found that in the case of many sea creatures, star-fish, sea-urchins, shell-fish and others, that if the eggs are kept in common sea water, but kept carefully away from any milt, they soon die, and never grow up at all. But if any one of a considerable number of substances is added to the water, sugar, salt, acids, and other things, then the eggs, tho they still have only one parent, proceed to grow into the proper sort of little sea creatures, just as if they had two.

It is really a great mystery; the most that any one can say is that the eggs are there, but something in the water, or the absence of something, stops their growing. Add sugar, salt, acid, or milt and they grow. In the case of the land animals, this something is probably in the blood—for as you know, the blood is salt like the sea, and in many other ways much like it.

At any rate, this is practically a most convenient arrangement. A mother bird, for example, is herself born with all the eggs she is ever going to lay already formed inside her. But something in her blood keeps those eggs from growing bigger than pin heads. They don’t grow into proper eggs, that can hatch into little birds, until the mother bird gets a mate to help her build the nest, and to feed the little birds when they come, and sometimes to feed her too. Then some of them do grow up and hatch; and the two old birds take care of them.