of animals, [12] ff., [32], [51], [134], [219] f., [247], [267];

of plants, [13] f.,31 f., [230];

problem of human, [14] ff., [18], [113], [148], [231], [326] f.;

method of, [18] ff.;

has recently become experimental, [25] f., [34];

scope of, [30] ff., [329];

classification of, [31] ff.;

differential, [31] f., [309];

immaturity of, [25] f., [34];

difficulties of, to beginner, [34] ff., [90], [112] ff., [321] ff., [325] f.;