As June went on and polliwogs turned to frogs, the leaves came fully out, clover and buttercups were blooming, and the pond algae had increased at a fast rate so that a thick green scum gathered behind the dam, and the pond waters were yellow-green. Still you could see the fish gathering at intervals massed sometimes fifty feet or more behind the two outlets. There is a small wooden footbridge over the board dam at the head of the pool. When I lay down on the bridge and looked under at the curved lip of the water I could see the fish gathering behind. Against the steady rush and whine I could hear a dull, deep change in sound as the fish suddenly turned and plummeted over. Their bodies, enlarged behind a green curve of water, had a metallic sheen, a dull silver, as they would wheel in, loom up, and drop away. I came back at night, and could still hear that heavy sound in this lens, or gong, of water. In each new phase of migrant action there is an old ceremony. The alewives approach the dam, in groups of varying sizes. They circle, withdraw, and swim back again. Some of them swim between the two outlets as if to decide which one to take. Coming closer, they show an increasing animation, a quicker circling and flipping, as if the outward pull of the water resulted in a more vital excitement between them. After many more starts and withdrawals, lasting anywhere from fifteen minutes to an hour or more from the approach of a given group, or school--using that term in the sense of larger numbers--one or more fish will drop over, and then the rest will follow. I watched one school making these ceremonious retreats and approaches for two hours. When they finally started dropping over I counted some fifty fish a minute for about fifty-five minutes, until there were only three left. This remaining three must have lacked the common stimulus to go, the rhythm of sufficient numbers, and they stayed behind, as more fish began to draw in closer from the pond. I have seen this often. Sometimes seven, nine, and up makes enough of a group to start over on its own; very occasionally one alewife will go it alone; but it does seem as if a certain variable minimum will not take the move upon itself. Though a single fish may be the first to go over, or to advance upstream, it is hard, from my observation, to attribute any leadership to individuals, male or female. The crowd provides its own pressure and momentum. Perhaps the circling of these groups and schools, and their dropping over, might be analogous, though it is a looser motion, to a flock of sandpipers flying off simultaneously as if they were cast out by a lithe, invisible wire, and then turning on an instant, glinting in the sun. The impulse is in the rhythmic unity of the group, even though in the case of the fish some may be left off or behind until they are rejoined in it.