Beetles, why have they hard horny wing-cases, 1320 Beetles, why have many of them hard horns, 1321 Bile, why does it separate nutritious from innutritious matter, 884 Birds, why have water-fowls feathers of a close and smooth texture, 1033 Birds, why are they covered with feathers, 1030 Birds, why does black down grow under their feathers on the approach of winter, 1036 Birds, why have they hard beaks, 1040 Birds, why are their beaks generally long and sharp, 1041 Birds, why are their bones hollow, 1050 Birds, why do they lay eggs, 1051 LESSON IX. Birds, why have those with long legs short tails, 1052 Birds, why have aquatic web-feet, 1059 Birds, why have those that swim and dive short legs, 1060 Birds, why have some deep rough notches on the under surfaces of their feet, 1061 Birds, why have they gizzards, 1072 Birds of prey, why have they no gizzards, 1084 Birds, why may wet and thunder be expected when they cease to sing, 1121 Birds of passage, why, if they arrive early, may severe weather be expected, 1121 Birds, geological distribution of, 1326 Birds, tameness of in unfrequented countries, 1327 Birds, why are birds of song not also remarkable as birds of plumage, 1328 Birds, what are the velocities of their flights, 1329 Birds, what is the cause of their migrations, 1330 Black, why should parts of kettles and saucepans be allowed to remain, 204 Blood, in what proportions are the gases found in it, 39 LESSON X. Blood, what is venous, 41 Blood, what is arterial, 42 Blood, what is the constitution of the, 899 Blood, what quantity does the human body contain, 920 Blood, how frequently does the whole quantity pass through the system, 922 Blowing upon tea, why does it cool it, 174 Bow, why does it propel the arrow, 847 Bow and arrow, what line does the arrow describe, 848 Bow and arrow, what forces tend to arrest the arrow, 849 Bow and arrow, why are there feathers at the ends of arrows, 850 Bones, how many are there in the human body, 923 Bones, of what substances are they composed, 924 Bones, what are the uses of the, 925 Bones, why are those of the back hollowed out, 927 Bones, why are those of the skull arched, 930 Bones, why are those of the skull divided by small sutures, 931 Bones, why are they hollow, 934 LESSON XII. Bones, why are those of the arms and legs formed into long shafts, 935 Bones, why are those of the feet and hands numerous and small, 936 Botanical geography, 1208 Brain, why is it placed within the skull, 926 Bread-fruit trees, where are they natives of, 1223 Breathing, is it a kind of combustion, 17 Breaths, have people ever been poisoned by their own, 24 Breezes, why are summer said to be cool, 170 Breezes, what is the cause of sea and land, 235 Bubbles, why do they ascend in the air, 236