the purpose of Plant Studies are entirely applicable to Ani- "The book is intended to serve as a supplement to “(1) The teacher, who must amplify and suggest ANIMAL STUDIES CHAPTER I CONDITIONS OF ANIMAL LIFE 1. Divisions of the subject.-Biology is the science which treats of living things in all their relations. It is subdivided into Zoology, the science which deals with animals, and Botany, which is concerned with plants. The field covered by each of these branches is very extensive. Within the scope of zoology are included all subjects bearing on the form and structure of animals, on their development, and on their activities, including the consideration of their habits and the wider problems of their distribution and their relations to one another. These various subjects are often conveniently grouped under three heads: Morphology, which treats of the form and structure or the anatomy of organisms; Physiology, which considers their activities; and Ecology, which includes their relations one to another and to their surroundings. All the phases of plant or animal existence may be considered under one or another of these three divisions. 2. Difference between animals and plants. It is easy to distinguish between the animal and plant when a butterfly is fluttering about a blossoming cherry tree or a cow feeding in a field of clover. It is not so easy, if it is, indeed, possible, to say which is plant and which is animal when the simplest plants are compared with the simplest animals. It is almost impossible to so define animals as to distinguish all of them from all plants, or so to define plants as to distinguish all of them from all animals. While most animals have the power of locomotion, some, like the sponges and polyps and barnacles and numerous parasites, are fixed. While most plants are fixed, some of the low aquatic forms have the power of spontaneous locomotion, and all plants have some power of motion, as especially exemplified in the revolution of the apex of the growing stem and root, and the spiral twisting of tendrils, and in the sudden closing of the leaves of the sensitive plant when touched. Among the green or chlorophyllbearing plants the food consists chiefly of inorganic substances, especially of carbon which is taken from the carbonic-acid gas in the atmosphere, and of water. But some green-leaved plants feed also in part on organic food. Such are the pitcher-plants and sun-dews, and Venus-flytraps, which catch insects and use them for food nutrition. But there are many plants, the fungi, which are not green —that is, which do not possess chlorophyll, the substance on which seems to depend the power to make organic matter out of inorganic substances. These plants feed on organic matter as animals do. The cells of plants (in their young stages, at least) have a wall composed of a peculiar carbohydrate substance called cellulose, and this cellulose was for a long time believed not to occur in the body of animals. But now it is known that certain sea-squirts (Tunicata) possess cellulose. It is impossible to find any set of characteristics, or even any one characteristic, which is possessed only by plants or only by animals. But nearly all of the many-celled plants and animals may be easily distinguished by their general characteristics. The power of breaking up carbonic-acid gas into carbon and oxygen and assimilating the carbon thus obtained, the presence of chlorophyll, and the cell walls formed of cellulose, are characteristics constant in all typical plants. In addition, the fixed life of plants, and their general use of inorganic sub |