Morgan, Lloyd, 148.
Morphology, 32.
Moths, 67.
Müller, 293.
Mutation theory, 146.
Naegeli, 143, 148.
Natural Selection, doctrine of, 116, 117, 118; the struggle for existence, 124, 125; simply trial and error, 131; Darwin recognized it as incomplete, 142; germ-plasm theory supplements, 145.
Nebula, gaseous, 84.
Nervous systems, 201, 202, 205, 206, 211; of worker-bee, 232.
Niagara, 85, 86, 89.