In this volume, occupying the place in the series assigned to the subject "Zoölogy," the writer was called upon to survey the whole range of animal life on the globe, and to keep in view the fact that these books were to be a library of science. The casual reader, with no particular interest in natural history, seeks in such a book little more than stories of animal life thought of mainly as "big game," with an appetite for the adventurous and wonderful. But beasts and birds and snakes, although they number in the aggregate thousands of kinds, are but few compared with the almost innumerable hosts of the lower orders of animal life that dwell in the wildernesses of the world, or throng in the seas, or hover about us in the air; yet they are a part of the zoölogy of the globe, and a most important part. Although they may rarely have the picturesque interest that attaches to the vertebrate groups, they exhibit great beauty in many cases, and are the foundation on which the others rest, for they furnish the food on which the more highly organized creatures subsist. To the student this lower half is often more attractive than the upper half; and the history and philosophy of animal life could not be understood unless it was fully considered. The author has therefore devoted a proportionate space to the lower orders, at the expense of detailed descriptions of birds and beasts, knowing that these are easily accessible elsewhere. The arrangement of the matter in the volume is according to the latest results of critics of classification, and it illustrates, as well as any lineal arrangement can, the principle of the development of the higher classes from the inferior by a gradual evolution toward more and more complex forms. Space did not permit of much exposition of methods of development, as revealed by fossils; and the volume on Paleontology should be read in connection with this one. ERNEST INGERSOLL. CONTENTS CHAPTER PAGE I. HOW THE GLOBE WAS STOCKED WITH LIFE 9 II. THE SEA A VAST AQUARIUM 16 III. A CHAPTER OF FOUNDATIONS 25 IV. THE HUMBLEST OF ANIMALS--SPONGES 30 V. FLOWERS OF THE SEA 33 VI. UNINVITED GUESTS 44 VII. DWELLERS BETWEEN TIDE MARKS 46 VIII. BUILDERS OF THE PEARLY SHELLS 57 IX. BUILDERS OF THE PEARLY SHELLS--_Continued_ 64 X. ANIMALS WITH JOINTED FRAMES 81 XI. FROM BUTTERFLIES TO BEETLES AND BEES 99 XII. AT THE DOORWAY OF THE "UPPER CLASSES" 127 XIII. FISHES--THE ARISTOCRACY OF THE WATERS 132