Elementary biology : descriptive and experimental

Front matter

PRACTICAL ELEMENTARY SCIENCE SERIES

DESCRIPTIVE & EXPERIMENTAL

'CaV , $ ms mkm

Preface

This work on Elementary Biology has been prepared mainly for teachers who are preparing for the examinations of the Board of Education. The Board of Education has issued a syllabus under the title “ Elementary Biology,” which indicates that teachers seeking certificates are expected to obtain a general knowledge of the structure and physiology of higher plants and animals, and that this knowledge should be based in large part on practical acquaintance with a few leading types. I have endeavoured to meet these requirements, not only in the descriptions and expositions given, but also in the illustrations and practical directions. The descriptive text is intended to be clear and precise, but it has not been loaded with too many technical terms. Such as are used are explained as they occur. The illustrations are numerous, and intended to be a real help to the understanding of the text. Several of them have been specially drawn for the work, while others have been obtained by permission from the source acknowledged. I wish, however, especially to thank Professor Jayne, of the Wistar Institute, Philadelphia, as he was kind enough to supply me with the electro from which Fig. 148 is produced.

The practical directions for observation and experiment will be found partly in the course of the text and partly

VI

Preface.

under the .distinct head, “ Experiments.” Many of them are of such a nature that the student should have no difficulty in carrying them out at his own home.

It will be found that the requirements of the syllabus, “ Structure in relation to movement, as represented by some simple quadruped,” is met by selecting the cat as the type of animal, but I have considered it best to found this knowledge on an account of the general build of the human body, as I am convinced that this will be the most interesting and successful way.

Besides being serviceable to students preparing for the examinations mentioned, it is hoped that the book will prove useful to all teachers engaged in promoting Nature Study.

A set of carefully prepared Questions and Exercises, with occasional hints and explanations, will be found at the end of the book.

J. THORNTON.-

September io, 1902.

Preface To Revised Edition

In order to make the book more complete for the full Certificate Examination in Elementary Science, Part II., I have added a rather long Chapter on the Structure and Habits of Frogs and Birds. It is believed that the book now contains more than enough to enable the candidate to do well in this part of the examination.

January , 1907.

Contents

CHAPTER PAGE

I. The Living World i

II. The Biological Importance of Air, Water,

Chapter I. The Living World

1. The Three Kingdoms of Nature. — As the result of simple observation, the natural objects found on the earth are often divided into three great classes or kingdoms, termed the Animal Kingdom, the Vegetable Kingdom, and the Mineral Kingdom. The three members of these classes are then described somewhat as follows : —

(a) Animals are bodies which live, grow, move, and possess a certain sensibility.

A worm, a butterfly, a dog, and a man, for example, belong to the animal kingdom.

(b) Vegetables, or plants, are bodies which live and grow, but do not move from place to place, and have no sensibility.

Grass, a rose, and an oak, for example, belong to the vegetable kingdom. v

(c) Minerals are bodies which have not only no power of spontaneous movement and no sensibility, but no life.

A pebble, a quartz crystal, and a piece of clay, for example, form part of the mineral kingdom. Water and air also belong to the mineral kingdom, being neither animals nor vegetables. So also do all the various metallic compounds found in the earth’s crust.

Elementary Biology.

The above division of natural objects is often convenient to iefer to, but the definition and description of each kingdom can hardly be considered complete or scientifically accurate. Some animals, for example, are fixed to one spot, and show no more movement than is seen in the rising and falling of leaves and the opening and closing of flowers, while the leaves of the sensitive plant move and respond to a gentle touch. Again, while there is no difficulty in knowing that a cat is an animal and a hawthorn bush a vegetable, yet it is very difficult to say whether some of the simplest and smallest living objects are animals or plants. There are, however, besides the properties common to all matter, certain qualities or characters that belong to all living things, whether plants or animals, and that sharply and clearly divide them from non-living bodies. Our first clear classification, therefore, of natural bodies may be thus represented :

1. Living bodies

2. Non-living bodies

( Animals.

( Plants.

Minerals.

We will now state the characters common to all living things, and which distinguish them from mineral bodies. Some of these distinctive properties will be better understood after the reader has been once through the book.

2. Characters of Living Bodies. — Besides the general properties belonging to all matter, living things have certain additional and distinctive qualities or characters. These special marks are —

I. Power of Growth. — All living beings grow — that is, increase in size by taking within themselves matter different from themselves, called food, and by transforming this matter into their own substance. A plant, for example, absorbs from the soil by its roots water and certain mineral salts that are in solution, and this absorbed nutriment spreads through all parts,

The Living World.

and is to some extent changed and then assimilated — that is, made to enter into the substance of the plant itself. In animals, growth by nutrition is still more evident, so that the body of an animal, as well as that of a plant, consists of substances that are constantly being renewed from without.

Nothing resembling this growth by nutrition in living bodies takes place among minerals. It is true that a crystal of salt suspended in a saturated solution of salt exposed to the air will become larger, but this increase in the size of the crystal only takes place by the addition of similar matter to the external surface. This “growth” of a crystal by matter similar to itself added to the outside is essentially different from growth in a living being, which manufactures material like itself from materials quite different, and deposits this material in its own living substance in every part of its interior, making it, in fact, a part of itself.

II. Living Things respire. — All living matter is continually absorbing oxygen from the air, and this oxygen combines with some of the carbon in the living being, and is then given off as colourless carbon dioxide, C02. The absorption of oxygen in connection with the elimination or setting free of carbon dioxide is termed respiration, so that we may say that living things are respiratory.

As will be shown later, every plant, while alive, is taking in oxygen and giving out carbon dioxide (par. 57), though the process is not so active as in animals, and is hidden, to a large extent, by an opposite process carried on by the green parts of plants when in the light (par. 52).

Oxygen, indeed, may be regarded as a kind of food indispensable to the living matter of both plants and animals, while the carbon dioxide given off is a waste product. . Deprived of oxygen, either alone or as it exists in the air mixed with other gases, living matter dies.

Mineral bodies show no continuous absorption of oxygen and disengagement of carbon dioxide. They may exist apart from any supply of oxygen.

III. Living Beings consist essentially of Protoplasm containing Proteids. — The matter forming a living being contains, besides other substances, certain complex compounds

Elementary Biology .

of carbon, hydrogen, oxygen, nitrogen, and sulphur called proteids, and proteid substances are only found in nature in animals and plants. In other words, although the same chemical elements enter into the composition of mineral matter and living matter, yet these elements are united in living bodies to form compounds that do not exist in the mineral world.

Among the proteids found in living bodies are such substances as albumen, gluten, fibrin, and casein (see pars. 6 and 1 1 3). These proteid substances exist in living matter associated with water, fats, starchy and mineral matter, to form a highly complex, viscous, and granular substance termed protoplasm (Gk .protos, “ first ; ” plasma , “ mould or form ”). Protoplasm, therefore, may be called the substance that forms the essential constituent of living matter, while proteids are compounds forming the essential basis of protoplasm. “ It has been found that so long as any sign of life is visible, this protoplasm is in a continual state of slow combustion, absorbing oxygen from outside and decomposing with the liberation of energy ; and whilst some of the products of decomposition are cast off, others apparently reconstitute the original substance by combining with some of the materials of the food. The energy liberated is the cause of the movements which constitute the visible manifestation of life.” 1

While, therefore, mineral bodies consist of comparatively simple chemical compounds that often undergo no structural change for long periods, living bodies consist of highly complex protoplasm that is constantly taking in new material as it lives and grows, and as constantly giving off waste products and expending energy. Waste and repair go on continuously in every living organism. But sooner or later the process of restoration ceases, and the organism ceases to live. When life ceases, the body becomes subject to external agencies alone, both physical and chemical, and these at last reduce it to simple compounds that pass into the air and soil.

IV. Living Beings move spontaneously and react to Excitation (Stimulation). — In living bodies of all kinds, motion of a part or whole often occurs from some internal impulse or

1 “ Zoology,” by Shipley and Macbride.

condition without any traceable outside influence, but no such spontaneous motion occurs in stones or other mineral bodies.

Living organisms are also irritable — that is, possess a power of responding to mechanical, thermal, or other stimulation by action of some kind.

It is true that movement of one sort or other is more marked in animals than plants, but in every plant there is constant movement of matter in its interior. There is also the movement of young shoots, of twining stems and tendrils, as well as the rising and falling of leaves, and the opening and closing of flowers.

V. Living Bodies have a Power of Development and Reproduction. — If we take a pea or bean from a last year’s plant and sow the seed in ground where there is warmth and moisture, the grain will germinate and produce a plant which will bear flowers and seeds. At the end of the season the plant dies, having passed through a series of changes forming its life-history, but each detached part called a seed is able to germinate in its turn and produce a plant like its parent. A similar life-history, often of long duration, is found in. other plants, and all are able to reproduce their kind.

It is the same among the living beings known as animals. A bird produces an egg which contains the rudiment or embryo of a similar bird ; for, when the egg is kept at a suitable temperature for a certain time, the embryo grows and develops by making use of the food material in the white and yolk, and in due time a young bird breaks its way through the shell and grows up. When grown up, a male and female bird give rise to fertile eggs from which other birds arise, the parents at last growing feeble and dying.

As the student progresses in his studies, he will find that all other animals are produced and give origin to others in a similar or analogous way. We therefore see that living beings take their origin in a germ (a spore, a seed, or an egg) that was developed in a parent, and the matured offspring is like the parent. The non-living or mineral world has no such origin as living matter, nor any such power of reproduction.

We see from the above-numbered statements that there

Elementary Biology.

are at least five distinctive co-existing marks that distinguish the objects of the living world from the objects of the non-living or mineral world ; that living, in fact, consists of performing the processes called feeding, breathing, feeling, and multiplying ; and that living matter is a highly complex, assimilating, respiring, moving, sensitive, and reproducing substance.

A body showing the phenomena of life and attended by structural changes as a result of its living processes is often spoken of as an organism and as consisting of organized matter. Organism as thus used is equal to living being.

The science that treats of organized or living things is called Biology (Gk. bios , “ life,” and logos, a “ discourse ”). The branch of Biology that treats of plants is called Botany (Gk. botane, “ a plant ”), and the branch that treats of animals Zoology (Gk. zooti , “an animal”).

3. A Simple Living Creature. — If we examine under the microscope a drop of water taken from the surface of the mud at the bottom of a stagnant pool, we may often notice one or more specks of a jelly-like substance. These specks are slowly but frequently changing their shape. Each speck, in fact, is of irregular shape, and moves with a kind of flowing motion ; the locomotion being caused by the streaming forward of the substance into projections or processes at some points, and the withdrawal of processes at other points. The tiny object we see is a living creature called an amoeba. Careful scrutiny under a high power of the microscope will show that the jelly-like mass forming the amoeba shows a clear outside and a rather granular interior. There is also seen with a high power a denser central body called the nucleus, and usually a clear space called from its action the pulsatory vacuole.

The jelly-like mass of which the amoeba consists is present in all living matter, and is called protoplasm. Such a minute mass of nucleated protoplasm is the unit mass of living matter, and is known as a cell. An amoeba is therefore a living creature consisting of a single cell. Chemically considered, protoplasm

The Living World.

is a mixture of water and various solids, the chief of which are chemical compounds called proteids and carbohydrates. The amoeba manifests life not only by its motion, but in several other ways. It undergoes waste, giving off carbon dioxide and other waste products, and to repair this waste it takes in food. It feeds by putting forth a process round a particle of food and gradually engulfing it, the food-particle undergoing digestion in the interior, and being changed into the ingredients of protoplasm by assimilation. Any particle that is indigestible is excreted. The taking in and digestion of food not only repair waste, but lead to an increase of the quantity of protoplasm, so that an amoeba grows. An amoeba responds to certain excitations or stimuli , such as warmth and shock. Gentle warmth increases its movement, a sharp shock checks its movement. An amoeba is, therefore, said to be irritable. It can be shown that an amoeba breathes by taking in at every part of its surface

F IG • An amoeba, showing granular protoplasm, nucleus, and small vacuole. At

2 ^ throwing out a process to take in a particle of food ; at 4 it is in process

of dividing into two, the nucleus having undergone division ; at 5 the division into two is complete, each part containing its own nucleus.

oxygen dissolved in the water, and giving out carbon dioxide at any part. In pure distilled water that contains no dissolved oxygen the amoeba cannot live. It also possesses the power of reproducing itself, for on careful watching an amoeba for some time we may often notice that the creature becomes constricted and divides into two, the detached portion performing all the actions just described (Fig. i). The amoeba, therefore, although possessing no separate parts or organs, such as mouth, stomach, heart, and lungs, to perform its separate vital functions, is yet a distinct living creature as much as a bean or a man, and is quite different from a particle of clay or a grain of sand. The amoeba is, in fact, one of the simplest of living creatures.

4. Organs and Tissues. — The simplest plants and animals are those whose bodies are simplest in structure and which perform the living processes, such as feeding, breathing, moving, and reproducing in the most simple way. As we have just seen, an amreba consists of a single mass of nucleated protoplasm called a cell and this organism performs all the various life-processes without having any portions set apart for these processes. Any part seems capable of taking in food, responding to a stimulus, or putting out a process. For reasons which will shortly be understood, the amoeba is regarded as an animal. There are, also, plants that have the same simple structure and that consist of a single cell.

In the higher plants and animals, however, the bodies are composed of separate distinct parts doing different functions or kinds of work. Such a distinct part is called an “ organ.” An organ, then, is “ a part of the body of a living being definitely fitted to perform some special function for the general benefit of the whole.” Thus in an ordinary flowering plant, like the wallflower, we find such special parts or organs as the root, the stem, the leaves, and the flowers. The root serves to fix the plant to the soil and to absorb the liquid nutriment from the soil, while each of the other organs, as we shall see later, is adapted for certain special functions. In the higher animals, the separation of the body into organs is still more marked. As examples of such organs, we need only name the heart as the organ for the propulsion of blood, the eye as the organ of sight, and the muscles as the organs of motion and locomotion.

An examination of the organs of any living body will soon reveal that each organ is made of different kinds of materials called textures or tissues. A leaf of a plant, for example, on being pulled to pieces, may be easily seen to contain a soft tissue that forms a great part of the blade, and a tough fibrous tissue forming the stalk and the leaf-veins. With the aid of a microscope the materials of the leaf may be further distinguished.

The Living World.

In our own bodies, or in those of any of the higher animals, we can readily distinguish different kinds of substance, i.e. different tissues. There is, for example, the red flesh or muscular tissue ; the soft greyish-white matter forming the brain and nerves, which is called nervous tissue ; the hard compact substance forming bone or osseous tissue, and others. The various tissues are, as it were, the different kinds of building materials that enter into the structure of a living body, and it is by a combination of tissues that an organ is formed, each organ answering to a particular part of a complex machine, but all associated and so co-ordinated as to work together for the general advantage.

We have thus separated a living body into organs, or parts with a special function to discharge, and we have then seen that an organ is made up of one or more tissues. But with the aid of the microscope the division can be carried further, for each tissue consists of a number of minute units called cells, or else of units formed from cells. A cell is a minute mass of protoplasm with a nucleus, and it usually possesses a wall or limiting membrane. All plants and animals have a cellular structure, the cells being either simple spherical or polygonal sacs, or forms derived from these. There thus arise different kinds of cells and of cell products.

The cells of each tissue are like one another and do the same kind of work, but they differ somewhat from the cells of another tissue which do another kind of work. As just stated, tissues are arranged and bound together into instruments or organs, each organ of a plant or animal usually having one of the tissues composing it as the important one in relation to its special work.

We may classify tissues and organs according to the most distinctive character and function in each case. We have ( a ) supporting tissues and organs, whose work is mainly mechanical ; (/;) nutritive tissues and organs, whose

IO

Elementary Biology.

function is connected with the reception and use of food-materials; ( c ) motor tissues, connected with the movement of parts of the body and of the body as a whole ; (. d) sensitive or irritable tissue, whose business it is to respond to external excitations called stimuli; (e) protective tissues, that cover free surfaces ; (/) reproductive

Fig. 2. — Different kinds of cells, much magnified. A, young plant cells ; B, wood cells ; C, ciliated animal cells ; D, flattened cells ; E, nerve cells.

tissues, that are concerned in the production of offspring ; and in higher animals most manifestly (g) co-ordinating tissues, as observed in the action of the nerve tissue of the brain and its connections.

The classification of organs according to function can be made more easily in the case of animals than in the case

The Living World. u

of plants ; for a plant organ, as a leaf, serves several purposes at the same time, more so than in the case of animals, as we shall learn later. Accordingly, we have in the higher animals not only organs connected with the great life-processes of respiration, digestion, excretion, etc., but a system or set of organs connected with each of these processes. The digestive organs, for example, include parts of the mouth, the stomach, the liver, the pancreas, and the intestines. In a later chapter we shall describe the organs of respiration, circulation, and digestion in some detail.

5. Biological Division of Labour. — In early ages, and under primitive conditions of society, every man used to make the things he required from the materials he himself obtained from nature. Every man of an uncivilized tribe was his own hunter, toolmaker, tailor, shoemaker, etc. As a consequence every process was but slow and laborious, and the result but poor. Gradually, however, men found that greater and better results could be acquired by confining the efforts of each to one kind of work, and obtaining from other special workers, by exchange, the other things that they needed. The various kinds of work belonging to daily life were thus distributed or divided among the workers, and there arose distinct occupations. Some became farmers and raised grain, and when they wanted protection for their feet, they gave some of their grain in return for the shoes made by those who confined their work to shoemaking. From this division of labour quicker and better results were obtained. By confining attention to one kind of work the worker becomes more expert and skilful, and does the work with the least expenditure of energy and material. The farmer, shoemaker, tailor, etc., however, only illustrate a moderate division of labour, for the principle can be extended until there is a vast number of distinct kinds of work — until one man no longer makes shoes, but only shapes toe-caps or puts on the heel. In a modern shoe factory at

Elementary Biology .

least fifty different workers take part in making a single shoe. It may also be noticed that besides the increase in the efficiency of the work, owing to the increase in the division of labour, there arises in the community, and in each factory even, the need for a mechanism to distribute the various products to the parts where they are needed, and also the need of a regulative mechanism to arrange and co-ordinate the various activities for the general benefit of the whole. Modern society thus becomes, as regards its industries, a very complex structure of mutually dependent parts.

Much in the same way as different occupations arise owing to division of labour in a civilized state, so the various functions of a living being become attached to special parts of the body in all higher plants and animals. There is thus a biological division of labour, or a “ division of physiological labour.” 1 Each of the different organs has its own function, and all are so connected that they work together for the welfare of the whole body. To one organ or system of organs is assigned the work of nutrition, to another the work of respiration, to another the duty of responding to stimuli, and so on. The higher we go in the plant or animal world, the more complex does the body become in proportion to the degree in which the different functions of life are assigned to different parts, and this complexity of the body is due to a specialization or differentiation of parts for special work. We speak of a plant or animal as being high or low in organization according to the degree of differentiation that it exhibits — that is, according to the extent of the setting apart of special organs for special portions of its life-work.

1 “ The expression ‘ division of physiological labour ’ was invented by the great French physiologist, Henri Milne-Edwards, to express the fact that a sort of rough correspondence exists between lowly and highly organized animals and plants on the one hand, and lowly and highly organized human societies on the other ” (Prof. T. J. Parker, “ Elementary Biology ”).

The Living World.

The biological “ division of labour ” can be recognized and studied in both divisions of the living world. In the plant world the simplest plants are either single cells or collections of similar cells, each one of which is able to carry on all the various life processes — feeding, respiring, multiplying, etc. The algae, lichens, and fungi are cellular plants without true root, stem, or leaves. In mosses we may distinguish a kind of stem and leaves, but there are no true roots, the root-like rhizoids serving only for attachment. But in the ferns these various parts are all present, as the life-work of these plants requires that special portions should be set apart for certain definite duties.

The division of labour is found not only in the external parts, but in the minute internal structure of the plants. The plants below ferns are termed cellular plants, as they are made up of nothing but typical cells, but in ferns and flowering plants the microscope shows besides cells what is termed “ vascular tissue ”

(Lat. vas, “ a vessel that is, a tissue which consists mainly of minute tubes that serve as conducting vessels, and hence both these great plant groups — ferns and flowering plants — are termed vascular plants. Flowering plants are, however, of a higher order than ferns, as the organs and tissues are more highly specialized for the work of nutrition, support, and especially for reproduction.

In the case of the animal world, progress from the simple to the complex, from the lowly organized to those of the highest grade, is clearly evident. From an animal like the amoeba, which eats, and breathes, and feels, and moves with any part of its body, and which has neither tissues nor organs, we find a progressive change from the general to the special. We may, for example, next pass to an animal like the sea-anemone . This is a brightly coloured animal found in the sea near the shore,

Fig. 3. — Vertical section of a sea-anemone, showing m, the mouth, leading into a stomach, which leads into the body cavity s ; in' and m" , partitions in the body cavity ; e, ectoderm or outer coat ; e\ endoderm or inner coat ; t, tentacle ; t', ovaries ; d, disc of attachment. (Prom Macalister’s “Morphology.”)

Elementary Biology.

where it may often be seen with its tentacles expanded and looking like a flower. It may also be found with its tentacles withdrawn as a mere rounded gelatinous mass clinging to a rock from which the tide has receded. Now, this animal is of a higher type than the amoeba, for there is in the cells composing it some difference in function, that is, some small division of labour ; for some cells are modified so as to devote themselves to food-taking and digestion, some are specially sensitive, and some specially contractile. There is an approach to tissues and organs, but although there is a kind of mouth between the tentacles leading into a stomach, there is no heart, no blood, no special breathing organs, no eyes nor limbs. The animal usually multiplies by small eggs developed in ovaries in the body cavity and emitted at the mouth.

A higher type of animal than the sea-anemone is represented by one of the Mollusca, a division which includes oysters,

Fig. 4. — Diagram of the anatomy of a Lamellibranch, or bivalve mollusc, g, stomach, i, intestine surrounded by the liver. The two tubes on the left marked by arrows are the canals of the siphon. The current of water enters by the lower and gets out by the upper tube, a, the anus ; b, hinder abductor muscle, under which is the parieto-splanchnic nerve ganglion ; c, heart ; d, nerve ganglia ; e , fore abductor muscle ; f mouth with labial tentacles, usually only two in number ; the dotted line from g passes between the pedal ganglion which lies in front of it and the ear-vesicle ; h , gills. The right valve of the shell has been removed, and the right side of the mantle, to show the internal structure. (From Macalister’s “ Zoology of the Invertebrate Animals.”)