[6] See Lloyd Morgan, ’20; Washburn, ’13; Köhler, ’21.
[7] Huxley, ’12.
[8] See Babcock and Clausen, ’19.
[9] See Conklin, ’22.
[10] See Carr-Saunders, ’22.
[11] See Huxley, ’12.
[12] See Woodward, ’98; Osborn, ’10.
[13] See Carr-Saunders, ’22.
[14] See Köhler, ’21.
[15] See Whetham, ’21; Castle, ’12.