Extensive correspondence exists between MÃ 1\/4 ller and Darwin , and MÃ 1\/4 ller also corresponded with Alexander Agassiz , Ernst Krause , and Ernst Haeckel . Extensive correspondence exists between MÃ 1\/4 ller and Darwin , and MÃ 1\/4 ller also corresponded with Hermann MÃ 1\/4 ller , Alexander Agassiz , Ernst Krause and Ernst Haeckel .