i|j;i;f;|!;/:|:i:i;i;i|| .l:^'' ^ 4i ttki JlS$.A .i' |Y;;;;;;!!;:i;i;!'(:|;;;|;:;> ...„J^ ::!K;cl»ac;CK;c,\ k;: ;;.-:):;:.:;; !ft;:r;r;ftcir-n ■;*!'•? 'Pi* )l?p A GEHEEiOU: BIQlOCSy •.',';■';';'] r^ ilil h r:;-t-i :/'^ K#;1 s fn Marine Biological Laboratory Library ffl dl Woods Hole, Mass. *^ E ffl in Dl Ptesentei Ly jTj S Dr. Walter H. Wolff ffl ffi August, 1954 ffl IB I Adventures WITH ANIMALS AND PLANTS n K ^/ ANIMALS ■i*ii%. AND PLANTS BT ELSBETH KROEBER WALTER H. WOLFF 4*/*jfe ^ *^ -« - GENERAL BIOLOGY D. C. HEATH AND COMPANY BOSTON '^ The Authors ELSBETH KROEBER is First Assistant in Biological Science; Adminis- trative Assistant at the Midwood High School, Brooklyn, New York. She was formerly Chairman of the Department of Biology^ at James Madison High School, Brooklyn, New York. WALTER H. WOLFF is Principal of the William CuUen Bryant High School, Queens, New York. Among his former positions are the follow- ing: Instructor, School of Education, The City College, College of the City of New York, and Chairman of the Department of Biology and General Science, DeWitt Clinton High School, Bronx, New York. THE ILLUSTRATIONS The cover design for this book was executed by Richard Bartlett from a drawing by W. A. Dwiggins, the frontispiece and title page ^^'ere painted by Else Bostelmann, the text drawings were made by Paul Wenck and Joseph Lenhard, and the diagrams by iMagnuson and Vincent. The photo- graphs reproduced in the text are acknowledged where they occur. The montage on page z was assembled with the professional assistance of Marion Howe. Copyright, /(}-^S, Kjyo by D. C. Heath and Company No parr of the material covered by i.his copyright mav be rcpro- ducctl in an\- form without written permission of the jiubhslier. Offices: Boston New York Chicago Atlanta Sax Francisco Dallas LoNiX)N Printed in the United States of Avieridx (504) PREFACE As you begin the study of biology you begin a most exciting adventure, the study of animals and plants — the living things of the earth. You are one of these living things, so you will learn much about yourself. The study of living things is not only exciting; it is impor- tant to all mankind. Our knowledge of biology has made it possible for us to avoid many diseases, to provide more and better food, and to understand our- selves better. The study and teaching of biology is the lifework of many people. They are professional biologists. It is possible that you will make the study of biology your lifework. If so, you will find much in this book to help you toward that goal. In writing Adventures ivith Animals and FlajJts, however, the authors had in mind, principally, the much larger num- ber of people who will not become pro- fessional biologists. All of us need to know many of the facts and principles of biology in order to understand our- selves and make the best use of many of the things we see, hear about, and read about. Whether or not you make biology your lifework, you will want to know how a professional biologist works and thinks, how he discovers the facts and principles that are so useful to all of us. Biologists, and other scientists as well, use a special method of discovering and testing facts and principles. It is called the scientific method. As you study this book, the scientific method will be brought to your attention many times. Hygiene, which is the science of main- taining health and the prevention of dis- ease, is based upon a knowledge of many parts of biology. Throughout the book you will find information that will be useful to you in keeping healthy. We learn the facts and principles of biology by three methods. One is by ob- serving animals and plants, a\ riting down what we observe, and comparing what we see with what others have learned. By a second method we also use observa- tion, but we observe and interpret the results of an experiment which was set up to try to answer some question or problem. A third method is to read what others have learned bv the use of the first two methods. In using- this book you will make use of all three methods: you will read, you will observe, and you will experiment. Perhaps, if you are a keen observer, or become one, you will discover something no one else has ever learned. In this book you will read about many of the facts that biologists have learned by observations and experiments; and you will learn what conclusions or prin- ciples have been stated to summarize or explain the facts. You will frequently Vlll find suggestions for helpful class discus- sions and for experiments that will either add to the information contained in the text or make the text discussions more clear. These suggestions are grouped at the end of each Problem and are called Exercises. At the most appropriate places in each Problem these Exercises are re- ferred to. You cannot possibly do all of them; the authors hope you will find time to do many of them. Each of these Exercises has been chosen with great care to help you understand some part of bi- ology, to help you to learn how a biolo- gist works (the scientific method), or to help you to find out something new. The Questions at the ends of the Prob- lems are designed for your use in re- viewing what you learn in studying the Problem. If you can answer all the Ques- tions, you can feel pretty sure that you have done a good job on that section of the text. If you are one of those who like biol- ogy very much, you will want to try some of the Further Activities in Biology that are listed at the end of each Prob- lem. You may also wish to read some of the many books and articles that are listed at the end of the book, just before the Index. Since this book was designed to fit the courses of study in schools throughout Preface the United States, it may contain some topics that are not required in your school. Therefore your teacher may pre- fer not to assign certain sections of it. Some sections are marked "Optional." These may be omitted, if your teacher so desires, without interfering with your understanding of the parts that follow. All the authors' long experience in teaching, directing other teachers, and writing for students has been applied to the writing of this text, which is a suc- cessor to Adve?inires with Livmg Things. To insure accuracy, the authors have asked a number of people to read por- tions of this book. In addition to the large number of specialists who critically read many portions of the authors' earlier text, they wish now to thank: Mr. Aiaurice Bleifeld, Chairman, Department of Biology, Newtown High School, Queens, N. Y.; Professor A. L. Kroeber, Emeritus, University of California; Pro- fessor Laurence H. Snyder, Dean, The Graduate College, University of Okla- homa; and Dr. Charles Tanzer, DeWitt Clinton High School, New York Citv. The authors thank also Airs. Charlotte O. Wolff for assistance in preparing the Index. Elsbeth Kroeber Walter H. Wolff TABLE OF CONTENTS Introduction: Biologists Study Aiiiuials and Plants JJjiit I. THE LIVING THINGS OF THE EARTH ARE MANY AND VARIED 14 Problem i. What Kinds of AniTimls Inhabit the Earth? 15 The Vertebrates i6 The Invertebrates 39 Problem 2. What Ki?ids of Plants hi habit the Earth? 72 Flowerless Plants 73 Plants with Flowers and Seeds 80" Problem 3. Hoiv Are Livijig Things Named and Classified? 95 II. ALL LIVING THINGS ARE BASICALLY ALIKE 104 Problem i. Of What Are All Living Things Composed? 105 Problem 2. How Do Their Activities Keep Cells Alive? 118 Problem 3. How Are the Cells Arranged in Anijnals and Plants? 129 III. GREEN PLANTS MAKE THE FOOD USED BY ALL LIVING THINGS 136 Problem i. What Part Do Leaves Play i?i Making and Using Foods? 137 Problem 2. What Part Do Roots and Ste?ns Play i?i Maki?ig and Usi?ig Food? 148 IV. HOW A COMPLEX ANIMAL USES FOOD FOR ENERGY AND GROWTH 166 Problem i. How Can We Choose Foods Wisely? 167 Problem 2. How Does the Digestive System Make Foods Usable? 188 Problem 3. How Are Materials Moved to and from Our Body Cells? 206 Problem 4. How Are All Our Cells Provided with a Constant Supply of Oxygeji? 226 Problem 5. How Does the Body Get Rid of Wastes Formed by Cell Activity? 237 Problem 6. What Substances Help Regidate Cell Activities? 246 68951 X Tciblc of Contents Unit V. WHY Ll\ ING THINGS BEHAVE AS THEY DO 260 Problem 1. What Arc the Simplest Forms of Bcl^avior in Animals? 261 Problem 2. What Makes Coinplex Behavior Possible iji Many-celled Animals? 269 Problem ^. Hove Does the Behavior of Complex Ani/nals Differ from That of Simpler Forms? 286 Problem 4. Hov: Do Plants Respojid to Their Enviroiimoit? 301 VI. CONSTANT CARE IS NEEDED FOR MAINTAINING OUR HEALTH 310 Problem 1. Hove Are Our Bodies Protected against Microorga/nsi/is? qii Problem 2. ]]'hat Have Scientists Learned about Conqneriiiir Sovie Covnnon Diseases? 320 Problem 3. {Optional) How Have Recent Discoveries Changed Some of Our Ideas about Disease? 338 Problem 4. Hove Do We Attevipt to Stop the Spread of Disease? 343 Problem 5. Ho\e May We Achieve Better Health for All? 359 Ml. HOW IJ\ ING THINGS AFFECT ONE ANOTHER 372 Problem i. TF/m? Makes Possible the Continued Existence of Plants and Anntials? 373 Problem :. What Are Our Relationships to Other Organisms? 381 Problem ^ Hove Do We Try to Solve Our Insect Problevis? 389 P1UIBLEM 4. Why Must We Practice Conservation? 399 \ III. now ANIMALS AND PLANTS MAKE MORE OF THEIR OWN KIND 410 Problem 1. Hov: Do the Simple Anii/ials and Plants Reproduce? 411 Problem 2. How Do the More Complex Annuals Reproduce? 421 Problem ^ Hove Do the More Complex Plants Reproduce? 438 IX. THE ORGANISM IS THE PRODUCT OF ITS HEREDITY AND ITS EN \' I RON Ml- NT 454 Problem i. Why Do Off spring Resemble Their Parents? 455 Problem 2. Hov: Can Some of the Differences between Parents and Offspring Be Explained? 464 Problim 3. How Can New Hereditary Characters Appear? 479 Problem 4. How Does the Environment Affect the Characters of an Organism? 485 Table of Contejtts Unit Problem 5. What Have We Learned about Frodiicing Neiv Types of Animals and Plants? Problem 6. To What Exte?n Can Mankind Be biiproved? X. THE EARTH AND ITS INHABITANTS HAVE CHANGED THROUGH THE AGES Problem i. What Can We Learn from Rocks about the History of the Earth? Problem 2. What Can We Learn from Fossils about Prehistoric Living Things? Problem 3. What PiLZzUng Facts May Be Explained by Onr Theory of the Origin of Neiv Organisms? Problem 4. What Theories Have Been Offered to Explain the Origin of Different Kinds of Animals and Plants? Problem 5. What Were the Stages of Man's Development on the Earth? BIBLIOGRAPHY GLOSSARY INDEX XI 493 508 520 521 533 547 564 580 583 599 Hoxv To Use This Book 1. How this book is organized. Adven- tures ivith Aniinals and Plants is divided into Units, each of which presents a major topic in biology. When you have rinished studying a Unit you will have learned the most important facts pre- sented in that Unit, and should under- stand the important ideas gro^ving out of those facts. To aid you in reaching this understanding, each Unit is divided into two or more Problems. These Problems may be said to be the chapters of the book. Each Problem title poses a ques- tion, the answer to which is to be ob- tained by studying the text that follows. When the answers to all the Problem questions contained in a single Unit are understood, you will have all the infor- mation necessary to an understandincr of the statement at the head of that Unit. Each Problem is composed of "para- graphs" headed by a title in boldface type. Each of these paragraphs supplies some information necessary for arriving at the answer to the Problem question. A simple, step-by-step study of the para- graphs, as suggested in the following sec- tion, will help to put vou on the road to success in your biology course. 2, How to learn from this book. There Xll are many devices in this book designed to help you to learn biology readily. Of these, the Unit headings, Problem ques- tions, and paragraph titles are the most important, because they tell you what you are supposed to learn. From the very beginning of any study period you should know what you are trying to learn. After reading a paragraph title, think over the meaning of the title and ask yourself what, you already know about that subject. When vou have thought through and organized your previous knowledge, you will be better equipped to grasp the additional infor- mation that is supplied by the book. You will find it helpful to do the Exercises referred to throughout the text as vou are studying the section those Exercises are intended to supplement. Perhaps the class as a whole can plan with the teacher how to do some of the Exercises. This is more interesting than following direc- tions laid down by others. If, at first reading of the text, you do not understand a sentence, finish the par- agraph to find out if your questions are answered. Then go back and re-read the sentence as it stands in relation to the rest of the paragraph. If you still have questions, make a note of them and have them explained in class. If it is a word that vou do not understand, look it up. If that is not possible, make a note of the How to Use This Book word so that you can learn its meaning in class. The field of biology makes use of many special words that you will need to learn. These words are printed in italics and defined when they first ap- pear. If you do not recall the meaning of a word when it is used later in the book, look it up in the Index to find where it was used first. A good way to learn the special vocabulary of biology is to pre- pare a glossary for yourself in your note- book. A glossary is simply a special dic- tionary. You can list the new terms you learn and write their definitions in your own words. As a basis on which to build your o\\ n more complete list of words you will find a glossary prepared by the authors beginning on page 583. There are many illustrations in this book. Every one has been chosen to add to your understanding and information. It will be useful for you to look at them carefully and to study the legends. Both the printed text and the illustra- tions will undoubtedly raise questions in your mind. These are the most precious results of study because they lead to interesting class discussions and, later, to a more complete understanding of the subject. Such questions will also empha- size to you that in biology, as in other sciences, there is much that remains to be learned. Adventures WITH ANIMALS AND PLANTS Fk;. I All aviumls and plants are subjects for biologists to study. Students of biology learn what kinds of living things there are, how they are constructed, how they re- maiii alive, why they behave as they do, how they reproduce, why they reseynble their parents, why there are so many kinds, how they are dependent upon each other, how vtan ajjects them, and how they affect man. (photos by cruicksiiank-nationai, audu- BON society, national ZOOLOGICAL SOCIETY, TYRELL-NATIONAL AUDUBON SOCIETY, PHILIP GENDREAU, UAI.PII ANDERSON, AND MUSEUM OF NATURAL HISTORY) Biologists Study Animals and Plants What is biology? Biology is the study of Hving things. This means that biology is the study of all animals, including man, of all plants, and of those simple living things which we do not know whether to call animal or plant. Since biology is the study of all living things, all of us have been biologists (students of biology) in a small way all of our lives. When you learned the name of the robin you were, for the moment, a bi- ologist. To be more exact you were a zoologist (zoh-ol'-o-jist), a student of animals. Would it make it seem more important if you knew that this branch of zoology was called ornithology, the study of birds? You were learning biol- ogy w^hen you noticed that a dog would dash after a ball (the science of animal behavior) and when you noted green leaves come out in the spring (botany, the science of plants). You were an unwilling biologist, too, when you had measles or scarlet fever and discovered how other organisms can affect man. Evidently biology is the study of living things in any way in which a biologist wants to study them. You may think that this makes biology a large and varied science — and so it does. There are many sub-sciences that make up the larger science of biology. You have just read the names of a few of them; there are many others which you will read about in this book. What to study about living things. Most people will say that one of the first things to learn about a living thing is its name. This is true. Most of the living things you see frequently have common names and you will want to learn some of them. You can learn to know an oak tree from a maple tree and a woodchuck from a skunk. In some cities you will see maples, elms, and poplars along the streets; in others palms and pepper trees. You will enjoy knowing these names as well as the names of common breeds of dogs and cats and of many other animals and plants. But more important than the names of living things is a knowledge of their structure; that is, the parts of which a living thing is made and how these parts fit together to make a whole orgaiiism (or'gan-ism), a single living thing. Since you are more interested in your- selves than in any other organism, it is especially useful to you to know the structure of your body. When you have completed a year's work in biology, you will know something about how you and all other human beings are constructed: what your heart is like and your stomach and your brain and the other parts of your body. Of course in one year's time you will not be able to learn very much about living things. The men and women who spend their entire lives studying just one part of biology do not then feel that they have mastered it completely. The knowledge of how organisms are constructed becomes especially valuable when you go on to learn how organisms carry on life activities. If you know how vou digest and absorb food, how you breathe, how your blood circulates, how your actions are controlled, how it happens that human beings are like their parents, and how human beings have developed through the ages, you will have important information about yourself. To understand this w^ell you will need to learn something about the structures of other organisms, such as lower animals and even plants, and how they carry on their life activities. Man and other living things. There are even better reasons for learning how other organisms carry on their life ac- tivities. Consider plants; it is important to you and to me that plants be raised for our use. If the wheat crop is a great deal smaller than usual, we may have less bread; if the corn crop fails, cattle and hogs are scarcer and the price of meat goes up. In fact, if there were no plants on this earth we would not be here at all. Then consider the many animals such as rabbits, moles, and particularly in- sects, that injure crops and interfere with the production of food and mak- ing a living. There are also many organ- isms that attack man directly, causing disease. It is well to know something about all these organisms and to know how we can protect ourselves and our crops against them. Men are constantly affected by other living things. Biologists Study Anmials and Planus The work of biologists. Since the field of biology is so large, the work of bi- ologists is varied. Some biologists live out of doors, exploring and learning about plants and animals at first hand by observation and recording. Some biologists work in the laboratory, ex- perimenting with living things or with chemicals in test tubes; some study plants or animals at close range through the microscope to learn the secrets of living matter. Before you plunge into the study of living things let us see how some of these biologists do their w^ork. Biologists explore the world. Do vou know what kinds of plants and animals live on this earth? Do you know w^hat plants and animals live on the island of Borneo or along the Amazon River? Could you describe a scene in the Gobi Desert of Asia or picture to yovu'self the plants that make summer beautiful within the Arctic Circle? It seems that similar questions have always interested man. There have al- ways been men bold and adventurous enough to undertake long voyages to distant parts of the earth merely to see and collect the plants and animals liv- ing there. About two hundred years ago Carolus Linnaeus (lin-nee'us), a young student at a Swedish university, was sent by his country to Lapland to make collections of living things. He started alone, carry- ing in his leather bag a simple micro- scope, a telescope, paper for drying plants, and writing materials for taking notes. For many months he endured great hardships. During this time he reached the Arctic Ocean on foot. Then he returned to his university with a few Biologists Study Aimnals mid Plants specimens of rocks and animals and plants, and complete notes on every- thing he had seen. He had learned a great deal about the customs of the native Lapps, had become acquainted with the wild animals of the country, and had made a thorough study of the plants, for botany was the subject of greatest interest to him. It is said that he traveled more than four thousand miles. Linnaeus' accounts of his journey in- spired other biologists to explore foreign lands. Often these trips last for several years during which the biologist is far from any civilized country, completely dependent upon his ability to make friends with native tribes. He has to win their confidence slowly, learn their language, and persuade them to take long trips on foot, on horseback, or by boat through parts of the country the natives may fear. Here the explorer devotes himself to his search for new types of animals and plants. Many of these are collected and stored to be taken back to museums and universities. Complete notes are kept of all observations so that no mistake will be made when the scien- tific reports are later prepared. Some of these exploring scientists are also excel- lent artists and prepare their own sketches of the strange scenes they see. Exploring is not at an end. Exploring nowadays is frequently very complex. Large expeditions are organized. They include experts in many branches of science and are equipped with scientific instruments of many kinds. Photog- raphers and secretary-historians are among the specialists included. Despite their size, such expeditions still meet B"» ../ k.... ■-..:' --tf^'- i'>^ . .'t-'i'iT^^. Fig. 2 What water-living plants and ani?nals might this collector find? (ward's natural SCIENCE establishment) with exciting adventures. Even as you read this, investigators are at work in the field in many parts of the world, searching high in the mountains, and deep in the sea, , in the frozen wastes of the arctic and antarctic, and in the hot, wet jungles. Exploring the depths of the ocean. You may join exploring biologists in imagi- nation, if you wish. Would you care to stroll through a garden in the warm seas twenty feet below the surface? Get into your bathing suit, strap your div- ing helmet to your shoulders, and climb down the ladder that hangs over the side of the boat. When you reach the last rung, drop off. You will sink gently to the bottom. Take care not to scratch yourself on the corals that are part of the lovely undersea gardens. If you have remembered your zinc pad and lead Biologists Study Ani?nals and Plants Fig. 3 The Central Asiatic expedition of the American Museii/u of Natural History jueets with an accident in the Mongolian Desert. What abilities iiiiist the explorer have besides a knowledge of biology? (AMERICAN MU- SEUM OF NATURAL HISTORY) 'VM^*.*?V,**"^i« Fig. 4 Exploring in a jtmgle. Dr. Williaju Beebe and two fellow scientists take motion pictures of living things oji the floor of a jungle in Venezuela, (jocelyn crane —NEW YORK ZOOLOGICAL SO- CIETY) pencil, you will be able to take notes as soon as your eyes grow accustomed to the dim light. The sunlight filters through this clear tropical water and flashes from the bril- liant reds and yellows of the many kinds of fish. The beauty of the ocean floor with its brightly colored animals will delight yiake of its tail? (gehr) Fig. 19 This picture of a brown bat shows how the 7He?nbranes attached to body and legs are stretched out by the long finger bones. (AMERICAN MUSEUM OF NAT- URAL history) 20 The Living Things of the Earth unit i Fig. 20 The spiny anteater of Australia and a Fig. 21 The duckbill of Australia. This iinvnnial model of the egg it has laid. (American museum also lays eggs. (American museum of natural OF natural history) history) in a pouch for a long time after birth. See Figure 384, page 433. The kanga- roos of Australia and the opossums of our country belong to this group. In one common species, the Virginia opos- sum, the animal when discovered pre- tends it is dead; it "plays 'possum." There are several other kinds of mar- supials in Australia besides kangaroos. The simplest mammals lay eggs. Duck- bills lay eggs and have bills like a duck but since they have mammary glands and hair they are considered to be mam- mals. Spiny anteaters and armadillos are other simple mammals. Now do Exer- cises 2, 3, and 4. If you would like to continue your study of mammals, you will find it useful to refer to some of the interesting books on mammals listed in the bibliography at the end of the book. CLASS - BIRDS The characteristics of birds. Birds have feathers. There are no exceptions. That is the characteristic by which you recoij- nize them. The feathers are usually lacking on the legs, which are covered with scales. There are two other char- acteristics almost as striking as the first: birds have beaks or bills without teeth and the forelimbs have the structure of wings. Birds, like mammals, are \\arm- blooded; their temperature, in general, is higher than that of mammals. Some of them, indeed, have a temperature of 112°. Like mammals they have four- chambered hearts and they breathe by means of lungs. There is much that \()u can discover for yoursrlf if you will fol- low the directions ir Exercises 5 and 6 carefullv\ Subdivision of the class. This class is subdivided into many different orders but the differences between the orders are technical and difficult to learn. In this section, we shall use a simple group- ing based mostly on the kind of feet and bill: birds of prey, scratching birds, PROBLEM I . The Kinds of Anmmls birds that wade or swim, perching birds, and birds that cannot fly. Birds of prey. These are the eagles, hawks, vultures, and owls. Their wings spread wide and firm; their talons (claws) are cruel, curved daggers which can be driven deep into the body of a small mammal or other bird; their strong beaks used for tearing flesh are hooked and sharp. Some hawks, eagles, and vultures are easily recognized in flight because of their remarkable ability to soar, that is, to remain aloft with almost no movement of the wings. They do this by taking advantage of the air currents. In spite of common belief, birds of prey, with few exceptions, are useful to man. Their natural food is rabbits, field mice, other small mammals, and even certain species of insects which are destructive to crops. The vultures and some of their rela- tives are scavengers; they feed on the dead and decaying flesh of animals. of the Earth 21 Scratching birds. These live on the ground and scratch for seeds and small insects; such birds are the common fowl, the grouse or partridge, and the turkey. Some of these birds are strong and swift flyers, too, but for the most part they rely on their legs instead of their wings. Domestic fowl such as chickens, ducks, and turkeys have prac- tically lost the power of flight. Birds that wade or swim. These are, mostly, large birds. They squawk and call hoarsely but never sing. Their food comes from the water and they spend much of their time in the water or on it. The storks, the herons, the cranes, and the flamingos (fla-ming'gos) wade. Their tall legs keep their bodies well out of the water and their long pointed beaks and flexible necks make it pos- sible for them to snatch the frogs or fish that make up their diet. Among the swimming birds are the ducks, geese, and swans. Their legs are Forehead Upper mandible Lower mandible Throat Wing coverts Breast Crown Claw Abdomen Scales Back Scapulars Rump Upper tail coverts Lower tail coverts Heel-joint Tail feathers Fig. 22 This drawing of a mockingbird is labeled to show the nairres of the various parts. It is helpful to know these na?nes when you are learning to identify birds. Bird descriptiofis in books use these terms because all students of birds know thetn. Coidd you describe the colors of a robin or of a canary, using some of these words? 22 Fic;. 23 A young owl. The owl 1mm s at yilght. What do you notice about tl?e size of its pupils? How does this help the owl? (American mu- seum OF NATURAL HISTORY — OVERTON) Kic. 24 The American eagle. In which way is it fitted for obtaining food? (nature magazine — fisher) ll?c Living Things of the Earth unit i strong and attached far back enabling them to exert a powerful push against the water. The position of the legs makes it easy for them to tip their heads down for a dive. Their feet are large and webbed. Water birds all produce much oil which protects their feathers from get- ting wet. This fact has given rise to the common expression, "as water rolls off a duck's back." Birds which cannot fly. A few species live wholly on land and never fly. The ostrich, the largest living bird, and its less familiar relatives have ^\'ings which are too small to be of any use. But all are good runners, running as fast as sixty miles an hour. When attacked and cornered, an ostrich defends itself by means of a kick which is dangerous to man. Perching birds. These, for the most part, are the birds that sing. You may kno\\' best the house (English) sparrows and the starlings of our crowded cities; the robins and the bluebirds of our suburbs; or the swallows and the crows of the countryside. These, and about four hundred fift\- other species, are perching birds. They are the birds to which man omcs much thanks for keep- ini^- down insect pests and for eating the seeds of weeds that would spoil crops and gardens. The songbirds often steal our fruit, but their bill of fare consists largely of insects or seeds of weeds that are harmful to man. Migration of birds. Many birds and some other animals migrate. They move from one place to another and back airain in tlie course of a year. The migrating season is generally the spring PROBLEM I. The Kinds of Anhnals and the fall. Many of our songbirds spend the summer in the more northerh' states and the winter in the south. Some winter over in the northern states and fly to the arctic in the spring. iMigrat- ing birds may perform amazing feats of flying. The arctic tern, a water bird, builds its nest in the far north; several months later it flies to the antarctic. Although the route has not yet been completely traced, it is known that these birds fly about ii,ooo miles each way. The golden plovers travel a shorter dis- tance, from Canada to South America, 2000 miles or more, but they fly over the ocean in one stretch. They complete the journey in two days and nights without stopping to rest or feed. There are many interesting questions about migration still unsolved. "How can birds travel so far without food and rest?" "How can thev find their way?" "How can some return not only to the same state and town but to the very nest in which thev were reared?" And difficult as any: "Why do birds migrate, anyway?" Bird flight. Upward and forward mo- tion of birds is supplied by a powerful downward and backward beat of the wings against the air. The large wing feathers overlap while the wings beat backward, but the feathers separate as the wing comes forward and up. Because the feathers separate during the forward motion, little resistance is offered to the air and not much speed is lost. When birds soar, they move their wings very little; instead, they depend on air cur- rents, just as a glider does. What helps the bird in its flight? Its wings are enormously long as compared of the Earth 23 Fig. 25 Compare the position of the eyes of this sandhill crane with the positio?i of the o'wl''s eyes. Note also the legs and bill, (new york ZOOLOGICAL society) Flycatcher \' C^" Fig. 26 The bill often tells you something about the bird's food. For what kinds of food is each bill fitted? 24 The Livivg Things of the Earth unit i Fig. 27 Spriiii^ iiiigratioii routes of some comvion birds. Some of these birds follow:) the same routes south in the fall. Which of these birds travel the loiigest distance? Some of the 60 species which follow route 2 are the bobolink, chuck-wiW s-widow, the gray-cheeked thrush, the bank swallow, the black-poll warbler, and the night- hawk. The picture above the map is of Canada geese taken during migration. You will find it interesting to find out the migration routes of the Canada goose, (ewing galloway) PROBLEM 1. The Kinds of Anv/Jials of the Earth 25 Fig. 28 Carolina Wren Fig. 29 Sierra Jiinco The birds of Figures 28, 29, 30, and 32 are called perching birds. What do these birds eat? How are they helpful to man? What can we do to protect thefn? The birds that built the nests of Figure 5/ are also helpfid. Can you find out why? (Fig. 28, HUGH davis; Fig. 2p, nature mag- azine; Figs. 50, 5/, and 32, American museum OF natural history) J- Fig. 31 Nests of the cliff swallow Fig. 30 Chickadee Fig. 32 Hummingbird The Living Things of the Earth unit i Fig. 3:5 The garter snake. This snake is one of the conunoiicst found in the United States. It is frequently seen on farms, even near the bnildings, and frequently, also, in lawns and gardens of thickly settled connimnities. The garter snake may bite when it is handled rmighly, but its bite is harmless, except as a possible source of infection. It does not lay its eggs as many other snakes do. The eggs hatch within the mother s body and the young are born alive. All snakes move by wriggling and by many small inoveinents of their ribs which are attached to the sharp scales on their underside. (U. S. BUIUEAU OF BIOLOGICAL SURVEY) to the size of the body; there are very powerful breast muscles which move these win^s. The breast bone to w hich the muscles are attached and many other bones are hollow, making the body ex- ceptionally light in weight. In the bibliography at the end of the book there are listed several books about birds. Perhaps you will wish to read one of them and learn more about birds. CLASS - REPTILES What is a reptile? Like mammals and birds, reptiles have lungs. Some la\- eofrs as do the birds; some bring forth their young alive. But they differ from mam- mals and birds in that they are covered with scales. Scales, you remember, are characteristic of fish also. How, then, can one distinguish between reptiles and fish? This is easy, for fish in ocneral get air from the water by means of gills. and their scales arc slinn'. Reptiles have lungs and dv\ scaly skins. Reptiles are the first vertebrate ani- mals you have met in this book that are cold-blooded. The body of the cold- blooded animal is sometimes \\arni and sometimes cold, depending on the sur- roundings. Reptiles are most common in the tropics; as you go north\\'ard you may expect to find fewer and fewer rep- tiles. In a climate such as that of the northeastern states where A\inters are cold, reptiles are active and visible during only a short season. As fall comes on they become sluggish and soon go into a state of hibernation (winter sleep) un- derground. Some reptiles run on four legs, some on two, while some wriggle without an\' legs at all. Many live on land; others dwell in fresh water or in the salt\- ocean. Zoologists divide them into three main orders which \'ou can easil\ recognize: the snakes and lizards, PROBLEM I. The Kinds of Animals of the Earth 27 Fig. ^4 How Tiiciiiy ratllcs has this rattlesnake'!' It is not true that one can tell a rattle- snake's age by the inanber of rattles, (u. s. bureau of bio- logical survey) Fig. 35 The head of a rattle- snake ready to strike. Where is the poison gland located ■ivith relation to the fangs? Poison gland Poison duct Fang (foofhj alligators and crocodiles, and tuxtles. Our poisonous snakes. The feeling of horror that snakes arouse in some people is unreasonable. As a child you may have seen your elders shrink at the sight of a snake and you may have learned to imitate them. Children left to them- selves have no more fear of snakes than of any other animals that seem strange. Most snakes are harmless; poisonous snakes are the exception. In this country there are only four kinds of poisonous snakes: the rattlesnake, the copperhead, the water moccasin, and the coral snake. On our continent man is rarely bitten, even where poisonous snakes are nu- merous, for with the exception of the water moccasin our poisonous snakes are timid; they do not attack unless they are disturbed. Still more rarely does any one die of the bite. An understanding of the methods of treating a bite and the Gland-squeezing muscle 'y- Jaw-opening muscle courage to remain calm almost always prevent serious results from the poison. The poison is injected through a pair of large, hollow, very sharp fangs (teeth). These are in the upper jaw, folded back out of the way until the snake strikes. The swiftly-moving little tongue contains no poison; the snake uses it to learn of its surroundings. Rattlesnakes are widely scattered over the United States. When disturbed, they sound their rattles, which are located at the tip of the tail, so that it is easy to avoid them. It is only when they are taken by surprise that they strike with- out warning. The amount of poison in- jected depends on the size of the snake. Large rattlers are therefore more dan- gerous than small ones. The copperhead is found in various regions in the north- ern half of the country. The water moccasin and the coral snake are not 28 r The Living Things of the Earth unit i Fig. 36 (above) Aj7 adult copperhead may be two or two and one half feet long. As in rattlers and water vioc- casins, the head is triangiilar. (u. s. bu- reau OF BIOLOGICAL SURVEY) Fig. 37 (right) This x-ray photograph of a snake shows the long backbone and the 7?iany ribs which help in locomotion, (general electric x-ray CORP.) uncommon in the south. The water moc- casin, which lives in swamps, is some- times called "cottonmouth" because the inside of its mouth is white. The coral snake is smaller than the water moccasin and has short fangs but when it bites, it hangs on, and sometimes its bite is serious. It often burrows in damp ground. Do Exercises 7 and 8. Peculiarities of snakes. Snakes have an enormously long backbone, consist- ing of many vertebrae each of which, except at the tail end, has a pair of ribs. Muscles connect the ribs with the scales on the lower part of the snake. By mov- ing the ribs, the scales are hooked onto the uneven surface of the ground, one after the other. Thus the snake really wriggles on its scales, but this happens so fast and evenly that it looks like a smooth gliding motion. No snakes have legs, although the pythons (pie'thons) of Asia have tiny stumps of hind legs which are not used. Because of its peculiar formation, a snake's mouth can be opened so wide that it will admit an animal broader than the head of the snake. The animal must be swallowed whole since the teeth are not used for biting off or chew- ing food. At irregular intervals as snakes gro\\' they develop a nt\x skin under- neatii the old one. The old skin is then shed as in the photograph. Figure 39. Snakes of other countries. While snakes in our part of the world arc not a real danger, in India, Central and South America, and other tropical regions PRDKLEM I. The Kwds oj Annuals oj the Earth 29 snakes are a serious menace. It is esti- mated that in India alone they kill about 20,000 people ever^^ year. One of the most deadly snakes of India is the cobra. It- is vicious, and injects a particularly strong venom (poison). There are also huge pythons in India which reach a length of more than thirty feet. They coil themselves around their victims and crush them to death. Some of the boa (boh'a) constrictors and anacondas of the tropical Americas may also reach a large size. Many reptiles, unlike other animals, keep on growing throughout their lives and they live long. Lizards — the closest relatives of snakes. People often call the little four-legged, soft-bodied salamander, so common in the woods, a lizard; but since it lacks Fig. 39 (above) A hog-nosed snake losing its old skin. As a snake grows its skin becomes too small. A new skin jornis under the old one. (AMERICAN MUSEUM OF NATURAL HISTORY) Fig. 38 (left) This swift is a typical lizard. Notice the claws on its toes. What characteris- tics of a lizard does it have? Why is it classed as a reptile? (American m:useum of natural history) a scaly covering you know it cannot be a reptile, and must not be called a lizard. Lizards have, as a rule, slender bodies with long tails and four rather short legs which can move with great speed. Lizards live in warm climates. Lizards of the United States are, with one exception, harmless. The one lizard which bites and has poison fangs is the red and black striped Gila (hee'la) monster. It lives in the deserts of Ari- zona and New Mexico. Alligators and crocodiles. Alligators and crocodiles are large reptiles which inhabit only the warmer portion of the globe. Even there they are sluggish, resting motionless in shallow streams with their eyes and nostrils above the surface of the water. However, the sight !0 The Living Things of the Earth unit i \'\G. 40 (above) These tadpoles arc the yonn of the