Nearctic, defined, 79
Nearctic, distinct from Palæarctic, 79
Nearctic, subdivisions of, 80
Regions, zoological, 50
zoological, how they should be formed, 53
zoological, may be defined by negative or positive characters, 54
zoological, by what class of animals best determined, 56
for each class of animals, not advisable, 58
zoological, proposed since 1857, 58
zoological, Mr. Sclater's, 59