world even earlier, the mother shad leaves the ocean where she lives and swims up one of the rivers that empties into it. She swims sometimes for more than one hundred miles until she has left the salt water behind her and has
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Courtesy of the United States Bureau of Fisheries.
reached the fresh water as it flows toward the sea. There she finds a place where the stream is shallow and quiet and where the sun takes the chill from the water. Here she lays her eggs. They have been staying in her ovaries—she has two ovaries—just as the eggs of the plants stay in the ovaries of the flowers. But,
