XXIV. STUDIES IN CRYPTOGAMS P 182 PART II. ANIMAL BIOLOGY I. INTRODUCTION A 1 II. PROTOZOANS A 10 III. SPONGES A 17 IV. POLYPS A 22 V. ECHINODERMS A 34 VI. WORMS A 42 VII. CRUSTACEANS A 51 VIII. INSECTS A 63 IX. MOLLUSKS A 97 X. FISHES A 109 XI. BATRACHIANS A 126 XII. REPTILES A 139 XIII. BIRDS A 150 XIV. MAMMALS A 184 PART III. HUMAN BIOLOGY I. INTRODUCTION H 1 II. THE SKIN AND KIDNEYS H 16 III. THE SKELETON H 28 IV. THE MUSCLES H 39 V. THE CIRCULATION H 51 VI. THE RESPIRATION H 70 VII. FOOD AND DIGESTION H 89 VIII. THE NERVOUS SYSTEM H 117 IX. THE SENSES H 142 X. BACTERIA AND SANITATION H 158 GENERAL INDEX i GENERAL INTRODUCTION =PRELIMINARY EXPERIMENTS= These experiments are inserted for those pupils who have not had instruction in chemistry and physics, to give them a point of view on the subjects that follow. At least a general understanding of some of these subjects is necessary to a satisfactory elementary study of biology. =Elements and Compounds.=--The material world is made up of elements and compounds. An _element_ is a substance that cannot be separated into two or more substances. A _compound_ is formed by the union of two or more elements. All the material or substance of which the earth and its inhabitants is composed is formed of the chemical elements; this substance taken all together is known as _matter_.