An introduction to zoology, with directions for practical work (invertebrates)

Front matter

ot lies ate is x i ce, ror ree wr ter

Cornell Aniversity Library

BOUGHT WITH THE INCOME FROM THE

Preface

Ir is desirable, perhaps, to give some reason for adding another book on Natural History to the many that already exist, and to indicate in what way the book is intended to be used.

The danger of the multiplication of small text-books is that they may conceivably be used in place of that first-hand investigation which must form the basis of all scientific work ; nevertheless, so long as the time allotted to Natural History is as limited as it is in the ordinary curriculum of school and college in this country, it is necessary to use to the best advantage the hours which teacher and pupils spend together, and I suggest that this time can at first be most profitably spent in practical work, during which the teacher directs and supplements the observations of the class, leading his pupils to reason about the facts they observe, and to record them by means of clear accurate drawings with brief explanatory notes.

This method, however, leaves little time for ordinary notemaking in which the facts are woven into a coherent whole that may be used for future reference and revision ; and it is partly for this reason that I venture to think there is room for such a book as this, which, as well as giving directions for the practical study of a number of different types of living animals, gives also a general account of their structure and life-history, and indicates their relationship to other creatures so that they do not remain as isolated types in the

v vi INTRODUCTION TO ZOOLOGY student’s mind, but fall into place as representatives of the varied branches of the animal kingdom. It is, however, strongly recommended that the practical study should always precede the reading of the chapter dealing with the type under inwestigation.

It is hoped that this book may be of use to pupils in the top classes of secondary schools; to the students of “ Nature Study” in Training Colleges ; perhaps also to those entering upon a systematic course of Zoology such as that in preparation for University examinations, who may feel the need of some first-hand knowledge of the living creatures which, in their academic course, they usually meet only as dead laboratory specimens ; and finally to those students, working alone, who may desire some guide as to what path to follow in the wide field of Natural History, and for whose sake numerous references are given to books where fuller information may be obtained.

The book deals almost entirely with the habits and external structure of common British Invertebrate animals; occasionally a few points of -internal structure have been touched upon, either because a knowledge of them was necessary for the explanation of the external phenomena, or because they must be known before the relationships of the various types of animals described could be appreciated. Microscopic structure is only given in a few of the first types, where it seemed to be desirable in order to illustrate some of the stages in the evolution of a more complex form of body from the simple unicellular form.

The types described in this book include those Invertebrates which occur in the syllabuses for the National Froebel Union, the Cambridge (junior and senior) Local examinations, and also, with one or two exceptions, those of the Board of Education (South Kensington) (Stages 1, 2, and 3) and of the Central Welsh Board.

The statement given above explains to some extent why this book has been published: why it has been written is

PREFACE vil another matter—connected not so much with such things as examinations and the needs of classes of students, as with the delight of merely watching living things, of trying to trace out their strange life-histories, and then of comparing notes with what other investigators have recorded. The author is, however, very conscious that in a book of this kind, which skims over such a wide field, there will be many omissions, and also observations may be recorded in it which ought first to have been further verified ; notification of errata or of facts elucidating doubtful points will therefore be most gratefully received by her.

In conclusion, I wish to express my thanks to Miss Violet Sheffield for the skill and care with which she has carried out my directions in the preparation of the illustrations, an exceptionally difficult task, as a very large number have been drawn from the living creatures in order to reproduce as far as possible their characteristic appearance in life.

I am indebted to Messrs. Macmillan and Co. for permission to reproduce Figs. 32, 40, 49, 50, 51, 53, 56, 57, and 303 from the Cambridge Natural History; Figs. 6, 7, 18, 24, 28, 29, 52, 55, 58, 59, 94, and 112 from A Teat Book of Zoology by T. J. Parker and W. A. Haswell ; and Figs. 172 and 186 from Aquatic Insects by Professor Miall ; also to Messrs. Cassell and Co. for Fig. 82 from The Outdoor World by W. Furneaux, and Fig. 298 from Eyes and No Eyes by Mrs. Fisher ; to the Trustees of the British Museum for Figs. 36, 102, and 117, taken from the Guides to the Museum ; to Messrs. A. and C. Black for Fig. 137 from 4 Teat Book of Zoology by O. Schmeil; to Messrs. Newnes for Figs. 118 and 120 from Flashlights on Nature by Grant Allen; to Messrs. Methuen for Figs. 294 and 295 from The Bee People; and to the Columbia University Press for Figs. 315- 319 from Ants by W. M. Wheeler.

Finally, my heartiest thanks are due to Miss Collins, the Principal of the School of Nature Study and Gardening, Clapham near Worthing, for the many beautiful specimens vili INTRODUCTION TO ZOOLOGY with which she has provided me; to Miss M. E. Everett and Miss G. Rowland for their very valuable assistance in the criticism and correction of the proof-sheets; and to Miss Bulkley for the careful Index which she has made.

Contents

PAGE INTRODUCTION . : 3 2 , ' ; 1

CHAPTER I Paytum I.: Protozoa . : ‘ : F 3 5

Introductory ; general classification and nomenclature ; the Amoeba ; the formation of chalk rock ; the Springing Monad ; the Slipper Animalcule ; the Bell Animalcule ; classification of Protozoa ; the differences between unicellular animals and plants; directions for practical work.

CHAPTER II Puytum II.: CokLENTERATA . ; ? r . : 23

Cuass 1. Hydrozoa,—The Hydra ; Colonial Hydra-like forms, Sertularia, Bougainvillea ; the formation of Medusae ; directions for practical work.

Chapter III

Puytum II: CosLenrErata’ (continued) . F : . 37

Chass 2. Scyphozoa.—The Common J elly-fish. Crass 3.

Anthozoa.—Sea-anemones and Corals. Classification of Coe-

lenterata ; practica] notes, how to start a sea-water tank, etc. < ix x INTRODUCTION TO ZOOLOGY

CHAPTER VII Puytum V.: ANNELIDA (continued)

Cass 1. Chaetopoda, Sus-ctass Polychaeta (the Bristle-worms of the sea).—The Paddle-worm, Sea-mouse, Lugworm, Sand Mason, Comb-worm, Sabella, Serpula, Pomatoceros, Spirorbis. Cuass 2. Hirudinea.—The Horse Leech, the Medicinal Leech. Affinities of worms, Classification of Annelida ; directions for practical work.

Chapter VIII

Porta VI, VII, VIII, anp IX.: PLatyHeLMInruss, Nematopa, Potyzoa, AND RoTiFERA

Platyhelminthes.—Whirl- worms, Liver- flukes, and Tapeworms. Nematoda.—Thread-worms. Polyzoa.—Sea-mats and Corallines. Rotifera.—Wheel Animalcules. Classification ; directions for practical work.

PAGE

CONTENTS xi

CHAPTER Ix PAGE Puytoum X.: Monnusca 105 Univalve Molluscs (Aquatic Snails).—Common Pond Snails, Trumpet Snails, Bladder Snails, Hooked Snails, Fresh-water Winkles, Periwinkles, Whelks, Cowries, Limpets ; directions for practical work ; how to start a fresh-water tank. CHAPTER X Puytum X.: Mowzusca (continued) . 126 Univalve Molluscs (Land Snails and Slugs).—The Garden Snail, White-lipped Snail, Grove Snail, Apple Snail, Greedy Snail, Chrysalis Snail, Vertigo, Door-shell Snail; Black Slug, Tree Slug, Cellar Slug, Field Slug, Snail Slug. Classification of Univalve Molluscs ; directions for practical work. CHAPTER XI Pxrytum X.: Moniusca (continued) . 139 Bivalve Molluscs.—The Swan: Mussel, Orb-shell Cockle, Pea-shell Cockle, Oyster, Sea-mussel, Zebra Mussel, Common Cockle, Scallop. Classification ; directions for practical work. CHAPTER XII Puytom XI.: ArrtHRopops. Class I. Crustacea . . 153

Sus-ciass 1. Malacostraca.—The Common Prawn, Lobster, Crab, Hermit Crab, Fresh-water Shrimp, Sand-hopper, Water Slater, Wood-louse. Sus-ciass 2. Entomostraca.—The Water Flea, Cyclops, Cypris, Barnacles. Classification of Crustacea ;

directions for practical work.

xil INTRODUCTION TO ZOOLOGY

CHAPTER XIil

ARTHROPODA (continued): Class II. ARacHNrIDA; Class ITI. Myrtapopa ,

Arachnida: ORDER 1. Araneae.—The Common Cross Spider, Orb-weavers, Line- weavers, Cobweb-weavers, the Water Spider, Wolf Spiders, Jumping Spiders, Trap-door Spiders, the Drassids, Crab Spiders. OrnpEr 2. Phalangidea.—The Harvesters. ORDER 8. Acarina.—Mites. Myriapoda.

CHAPTER XIV

ARTHROPODA (continued): Class IV. Insecta

Introductory ; General Structure; Metamorphosis; Subdivision of the Class into Orders.

CHAPTER XV

Cuass Insecta: Order I. Lerrpoprera

SuB-oRDER 1. Rhopalocera (Butterflies),—The Cabbage White Butterfly and other Pieridae, Nymphalidae, Lycaenidae.

CHAPTER XVI

Crass Insecta: Order I. Leprpoprera (continued)

Sus-orpER 2. Heterocera (Moths).—The Silkworm Moth, Buff Tip Moth, Hawk Moths, Burnet Moths, Tiger and Ermine Moths, Goat Moths, Looper Moths, China Mark Moths, Tussock Moths, Leaf-rolling Moths, Clothes Moth, Leaf-miners. Classification of Lepidoptera; directions for practical work.

PAGE

CONTENTS

CHAPTER XVII

Crass Insecta: Order II. CoLEoprera

Sup-orpER 1. Adephaga.—The Carnivorous Water Beetle and allied genera, Screech Beetles, Tiger Beetles, Ground Beetles. Sus-orpER 2. Clavicornia.—Ladybirds, Cock-tail Beetles, Silver Water Beetles, Whirligig Beetles. Sus- ORDER 3. Serricornia.—Click Beetles, Glow-worm Beetles, Furniture Beetles. Sup-orpER 4. Lamellicornia.—Cockchafers, Stag Beetles. SuB-oRDER 5. Rhyncophora.—Weevils, Bark Beetles. Classification of Coleoptera; directions for practical work.

CHAPTER XVIII

Crass Insecta: Order II]. OrtHorTEra .

Sus-oRDER 1. Cursoria.—The Cockroach, Earwigs. Sus- ORDER 2. Saltatoria.—Grasshoppers, Crickets. Classification of Orthoptera ; directions for practical work.

CHAPTER XIx

Crass Insecta: Order IV. Rayncota

SuB-orDER 1. Heteroptera.—The Water Scorpion, Water Stick Insect, Water Boatman, Corixa, Pond-skater, Water Cricket, Water Gnat. Sus-orpER 2. Homoptera.—Green-fly or Blight, Chermes or Bark-lice, Frog-hoppers, Scale Insects. Classification of Rhyncota ; directions for practical work.

CHAPTER XxX

Crass Insecta: Order V. NrEvRopreRa

FAMILY 1. Odontata (Dragon-flies).—The Blue Dragon-fly, the chief genera of the sub-families Libellulidae, Aeschnidae, Agrionidae, and Calopteryginae ; directions for practical work.

xlil

“PAGE xiv

CHAPTER XXI

Crass Insecta: Order V. NEvRoprERa (continued)

FamiLy 2, Ephemeridae.—May-flies. Faminy 3. Perlidae.— Stone-flies. Famiry 4. Stalidae.—Alder-flies. Faminy 5. Chrysopides. —Lacewing-flies. Faminy 6. Phryganeidae (= Trichoptera).—Caddis-flies. Classification of Neuroptera ; directions for practical work.

CHAPTER XXII

Crass Insecta: Order VI. Drprera

Sus-orDER 1. Brachycera (Short-horned fiies)—The House-fly, Blow-fly, Tsetse-fly, Hover-fly, Volucella, Drone-fly, Chameleon-fly ; directions for practical work.

CHAPTER XXIII

Cuass Insecta: Order VI. DirrEra (continued)

SuB-oRDER 2. Nemocera (Thread-horned flies).—Gnat, Mosquito, Phantom-fly, Harlequin-fly, Splay-footed Fly, Horn-bearing Fly, Sand-fiy, Daddy-long-legs or Crane-fly, Gall-midges. SuB-oRDER 3. Aphaniptera.—Fleas. Classification of Diptera ; directions for practical work.

CHAPTER XXIV

Cuiass Insecta: Order VII. Hymenoprera

SUB-ORDER Hymenoptera Aculeata: Famity 1. Apidae.— The Honey. Bee, Earth Humble Bee, Stone Humble Bee, Moss-carding Bee, Burrowing Bee, Leaf-cutting Bee, Mason Bee ; classification of Bees ; directions for practical work.

CHAPTER XXV

Cuass Insecta: Order VII. Hymenoptera (continued)

Famity 2. Vespidae.—The Common Wasp, the Hornet. Famity 3. Zumenidae.—Solitary Wasps. Famity 4. Pompilidae.—Running Wasps. FAmMILy 5. Sphegidae.—The Sand Wasps. Classification of Bees and Wasps; directions for practical work.

PAGE

CONTENTS xv

CHAPTER XXVI

PAGE Crass Insecta: Order VII. Hymenoptera (continued) . 401

FamiLy 6. Formicidae (Ants).—The Yellow Meadow Ant, Slave-making Ants, Harvesting Ants, Honey-storing Ants, Driver Ants, Leaf-cutting Ants; classification of Ants; directions for practical work.

CHAPTER XXVII

Cuass Insecta: Order VII. Hymunoprera (continued) . 430

SUB-ORDER Hymenoptera parasitica: Famtty 1. Tenthredtnidae (Saw-flies).—-The Pine Saw-flies, Rose Saw-flies, Currant Saw-flies, Bean Gall Saw-flies, Turnip Saw-flies. Faminy 2. Siricidac.—The Wood Wasps. Famity 8. Cynipidaec.—The Gall Wasps and Inquilines. Fami.y 4. Ichnewmonidae.—The true Ichneumon Wasps. Faminy 5. Braconidae.—The false Ichneumon Wasps. Classification of Hymenoptera parasitica ; directions for practical work.

INTRODUCTION AND GENERAL CLASSIFICATION

ZooLocy (Gr. zoon, animal ; /ogos, discourse) is the study of animal life, as distinguished from Botany (Gr. botane, a herb), the study of plant life, the two together forming the science of living organisms known as Biology.

It is well to bear in mind from the first that these two branches of the tree of life, though bearing such markedly different forms at their apices, unite at their base ; the animal and plant characteristics become merged together, so that in the simplest forms it is often difficult, if not impossible, to distinguish with certainty as plant or animal, the little speck of living matter which constitutes the whole organism.

General If we consider all the members of the animal Classification. kingdom known to us, the great variety of them Nomenclature.i, remarkable, and, at the same time, no less remarkable is the fact, that when we come to examine their structure closely we find they can be grouped in quite a small number of primary groups, with a peculiar type of structure characteristic of each; these primary groups of animals are known as Phyla or sub-kingdoms. Most of these phyla contain an enormous_number of forms, which, though having certain underlying characters in common, in many ways display great variety, and so we subdivide each phylum into Classes, the members of each class being alike in certain secondary characteristics. which distinguish them from the other classes of the same phylum.

Similarly we divide each class into Orders, each order into Families, each family into Genera, and finally each genus into Species. The individuals included in one species will display only those slight variations which we are accustomed to

1 B

2 INTRODUCTION TO ZOOLOGY note amongst individuals of the same kind, variations which are not constant from generation to generation.

Sometimes, however, these groups may still contain forms with so much constant variation of structure that further subdivision may be desirable, eg. an order is very often divided into sub-orders or tribes, and then these into families; sometimes it is even necessary to distinguish separate varieties of one species.

This system may be more clearly understood if we take a special example and attempt to classify it. Let us take, ¢.9., the common, well-known Large Cabbage White Butterfly. We know this butterfly by its size and colouring, the white wings being marked in a special way with dark-brown pigment (Fig. 149), and also we know its caterpillar by its special form and colouring (Fig. 145). There are other very similar white butterflies, 29. the “Small White” and the “ Black-veined White,” but these two are obviously different “kinds” of butterfly, as we say, for they differ slightly, but constantly, in size and in details of marking from the “ Large White,” also the habits and external appearance of their caterpillars are different ; hence, whilst popularly we call them all ‘“ White Butterflies,” we distinguish them as Large White, Small White, and Black-veined White. Such popular names, however, vary in different countries, and so it is convenient to have Latin or Greek equivalents which are used by all observers, irrespective of locality. Scientifically, therefore, we include all these three forms in one genus, the genus Pieris, and we express our sense of the differences between them by giving each, a specific name in addition. The Large White we call Pieris brassicae, the Small White, Pieris rapae, and the Black-veined White, Pieris cratoegi. This method of calling each kind or species of creature by a double name, was introduced by Linneus, and it has proved a most convenient one.

Now there are several other genera of butterflies that resemble Pieris in general form of wing, and in the general habits and form of caterpillar and chrysalis, eg. the Orange Tip Butterfly (Huchloé cardamines, Fig. 153), and the Brimstone (Gonepteryx rhamni) ; these, therefore, although too dissimilar to be included in the same genus, are all grouped together in one family, the Pieridae. Then again there are many different

INTRODUCTION 3 families of butterflies which differ in minor points, but which are all alike in having club-shaped antennae, in holding their wings vertically when at rest, and in the general form of the pupa—characters in which they differ from those forms we call Moths, which have typically feathery antennae pointed at the tip, fold their wings horizontally over their backs when at rest, and have dark, oval-shaped pupae. On the other hand, Butterflies and Moths are alike in such important points as the structure of their mouth-parts, the presence of minute scales over the wing-surfaces, and in the complete metamorphosis characteristic of their development; they are therefore grouped together in the order Lepidoptera (Gr. lepis, scale ; pleron, wing), though butterflies are separated in the special sub-order Rhopalocera.

Then again, in the general structure of the body, in the number of legs present, in the possession of wings, and in their method of breathing, Butterflies and Moths (Lepidoptera) resemble Beetles, Dragonflies, Bees, Flies, and Cockroaches ; all these forms, therefore, are grouped together in the class Insecta.

Finally, Insecta resemble Spiders and Crustaceans (Lobsters, Crabs, etc.) in having a hard shelly covering to the otherwise soft body, and in having jointed limbs ; hence all these forms are included in the phylum Arthropoda, one of the primary divisions of the animal kingdom.

The position amongst animals which we assign to the Large White Butterfly may therefore be summarised thus :—

Kingdom—Animalia.

Phylum—Arthropoda.

Class—Insecta.

Order—Lepidoptera.

Sub-order —Rhopalocera.

Family— Pieridae.

Genus—Prerrs.

Species—brassicae.

This scheme of classification is of course dependent on our present knowledge, and is provisional only. The aim of zoologists in making such a scheme has been to try and

1 Only certain of the obvious external characteristics have been cousidered in this classification, but it should be noted that it is based also on similarity of internal structure.

4 INTRODUCTION TO ZOOLOGY express what seem to be the natural relationships of the animals classified, so far as we can at present determine them with our still imperfect knowledge of the course of evolution, which has resulted in all the manifold forms of life on the earth.

The twelve primary divisions, or phyla, of the animal kingdom at present recognised are :—

‘T. Protozoa (unicellular microscopic forms). II. Coelenterata (Hydra, Jelly-fish, Sea-anemones, etc.). IIT. Porifera (Sponges).

IV. Echinodermata (Starfish, Sea-urchin, etc.). V. Annelida (Ringed Worms, e.g. Earthworm). VI. Platyhelminthes (Flat-worms, Liver-fluke, etc.). VII. Nematoda (round unsegmented Worms). VILL. Polyzoa+ (Sea-mats, ¢.g. Flustra, Bugula, etz.). IX. Rotifera (Wheel Animalcules).

X. Mollusca (Snails, Mussels, etce.).

XI. Arthropoda (Crustaceans, Insects, and Spiders). XII. Chordata (all vertebrate animals).

In the following pages, types of all these phyla will be described, with the exception of the last, the Chordata, the phylum which includes all Fishes, Amphibia, Reptiles, Birds, and Mammals, such a vast and important assemblage of forms that they are left for fuller treatment than is possible in this volume.

1 The Polyzoa should perhaps be united with the Brachiopods, the Lampshells, in « phylum Molluscoidea, but in this book only the Polyzoa are described.

Chapter I Phylum I.: The Protozoa

Tue Protozoa are the simplest animal forms known ; in them the whole living body consists of a single speck of the jelly-like living substance, Protoplasm, the body being so minute as to be in nearly all cases invisible to the naked eye. Because of their simple delicate structure, and their lack of special organs for carrying on the different vital functions of the body, these Protozoan organisms are able to exist only under special limited conditions, and are nearly all to be found living in water, fresh or salt, though some are parasitic in the tissues of other animals.

In this group are included all the naked unicellular forms such as the fresh-water Amoeba and Vorticella, and also those marine forms such as Globigerina, which secrete round their bodies calcareous shells.

Type: The Amoeba, or Proteus Animalcule.

This simplest of animals is unfortunately so small, that a microscope is necessary for its examination. However, an understanding of certain points in its structure, and of its vital processes, is so helpful as a basis for the study of more complex forms, that it is well, if possible, to acquire some practical knowledge of it, when commencing the study of different types of animal life.

Amoebae are to be found very abundantly in the mud at the bottom of most ponds, but as each individual is only about z$oth of an inch in diameter, a microscope with a high magnifying power is needed to render its structure visible.

When so magnified, it is seen as a round, or more or less irregular, body, of a semi-fluid consistency, the greater part of it being finely granular, whilst round the margin is a clear non-granular border. It is colourless or slightly greyish in tinge, but within the transparent body can be seen various opaque food particles which have been absorbed. The body is continually changing _ its shape, sending out a process now in one direction, now in another, or, if touched, withdrawing all its processes, and becoming round in outline.

Structure.

Pia, 1.—.lmoeba proteus. x 300. The substance of which uu, Nucleus; ps, pseudopodium; en. this body is formed is that vac, contractile vacuole; f. vac, ‘ J i ood. vACAGIES: Protoplasm, of which Professor

cal Basis of Life” ;! for it is the substance which is present

in all living things, be they plant or animal, and which, so

far as we know, alone renders possible the phenomenon which we call physical life.

On carefully examining this protoplasmic body, two structures can usually be readily detected, embedded within it. There is a small, oval or round, darker mass known as the nuweleus of the protoplasm. In chemical composition, this is very similar to the rest of the living protoplasm, but it is denser, and it performs special important functions within the cell, controlling apparently the nutritive and reproductive processes.

Then, after a little search, a clear round space can also be seen, which will disappear suddenly, and then slowly form again, thus gaining the name of the contractile vacuole. When visible, the space is filled with a watery fluid; when the vacuole contracts, this Huid is driven in radiating streams out of the protoplasmic body.

Such a mass of living protoplasm with its nucleus is known as a cell, and Amoeba is therefore said to consist of one cell, or to be unicellular.

1 Lay Sermon in Collected Essuys, vol. i.

The Nature By chemical analysis, the constituent elements of Proto- of which this protoplasm is formed can be plasm. determined. It consists of carbon, hydrogen,

oxygen, nitrogen, and sulphur, with minute traces of phosphorus and other elements, but by no method of chemical synthesis, yet known to us, can we cause these elements to reunite to form living protoplasm once more. The secret of life is hidden from us.

Such living protoplasm, however, exhibits certain definite phenomena, which, though we know not their ultimate origin, we learn to recognise as characteristic of life—tne phenomena, namely, of irritability, or power to respond to stimuli, of movement, of absorption and digestion of food, of respiration and excretion of waste matter, and, finally, of growth and reproduction. Even such a simple organism as Amoeba exhibits these vital phenomena, though in their simplest forms.

In Amoeba, movement consists merely of the streaming of the protoplasm towards one point, so forming a long process, the rest of the protoplasm gradually flowing after it in the same direction; each such process is known as a “ pseudopodium,” or “false-foot” ; in this manner the Amoeba can make its way over the mud and debris amongst which it lives.

The absorption of food takes place by a modification of the process of motion. Two pseudopodia are formed by the streaming outwards of the protoplasm, and these gradually surround the object desired, which consists usually of some very minute animal or vegetable organism. The processes fuse round the food particle, so that it is actually engulfed in the protoplasm, together with a little drop of water forming a “food vacuole.” The soft, soluble parts of the food are then dissolved, probably by some digestive juice secreted by the protoplasm, and so the food is rendered capable of absorption and assimilation, new protoplasm being built up from it. Undigested solid portions of food are got rid of by the simple flowing of the protoplasm away from the matter to be rejected, just the reverse process from that by which it was at first engulfed.

Locomotion.

Nutrition,

1 For account of experiments to illustrate the nature of protoplasm, refer to Investigations on Microscopic Forms and on Protoplasm, by O. Biitschli, English translation by E. A. Minchin (A. and C. Black, London, 1894),

The protoplasm in a living body is in a constant state of change, new protoplasm is continually being built up by the assimilation of food, and then this very complex compound breaks down again into simpler compounds, which are finally excreted from the body in gaseous or liquid form. One of the chief gaseous excreta is carbon dioxide. This is formed by the union of the carbon of the disintegrating protoplasm with the free oxygen which has been dissolved by the surrounding water from the air above, and has passed from the water into the protoplasm of the body. The carbon and oxygen combine in the proportion of one part of carbon to two of oxygen to form carbon dioxide, the chemical composition of which is expressed by the formula CO,. This gas is given off from the surface of the protoplasm and disperses, dissolving in the surrounding water. A change is therefore continually taking place in the gaseous contents of the water in which the Amoeba lives, the amount of dissolved oxygen lessening and being replaced by carbon dioxide. This oxidation of the carbon of the disintegrating protoplasm by the oxygen from the surrounding medium (be it air or water), and the resultant excretion of carbon dioxide, is the process known as Respiration: the essential nature of the process is the same in all animals and plants, though— owing to the complexity of the bodies of the higher animals —special organs have been evolved in them for facilitating the interchange of gases.

The simpler nitrogenous substances, which are also formed when protoplasm disintegrates, probably accumulate in liquid form in the contractile vacuole, and are expelled from the body when this suddenly contracts.

Growth Tf the assimilation of food is more rapid than

and Repro- the disintegration of the protoplasm and the exduction. cretion of waste matter, then Growth results, but this is always limited in extent, the limit being probably reached when the bulk of the body is so great, compared with its surface, that any further enlargement of it would demand a greater increase in the absorption of oxygen and of food than is possible to the absorbent superficial layer. Having reached its full limit of size, the Amoeba proceeds to divide into two ; the nucleus first divides, and then the whole body lengthens out, the two daughter nuclei moving apart ; finally a constric-

Excretion.

tion appears in the protoplasm, which gradually deepens and separates it into two halves, each of which contains half of the original nucleus. In this way, by “simple fission” of the parent organism, reproduction has taken place.

Each daughter Amoeba lives exactly as did the parent cell, finally dividing to form two new Amoebae, and so the life of the first individual never ceases, but becomes extended in the separate lives of its descendants. There seems no necessary natural end to the life of such a simple form, though death must frequently occur through an accident, such as the drying up of the necessary water environment, or the digestion of the Amoeba by another higher form.

An Amoeba can only live under certain conditions of life as to temperature, moisture, and air supply. If external conditions become unfavourable to its active life, it can protect itself for a time by secreting from the superficial layer of its protoplasm a horny or chitinous substance, which hardens and forms a thin shell or “cyst” over it; within this it can remain passive for a time, until conditions are favourable again and it can once more resume its normal activity; it then ruptures the cyst and escapes from it.

Two Amoebae, on meeting, have been observed to fuse together for a time and then to separate, and it is thought that as a result of the stimulus given by such fusion, they may afterwards carry on their separate lives more vigorously, for this is known to be the case in some other forms.

From the above observations we see that this very simple unicellular form, which has no definite sense perceptions and no organs of any kind, though to a certain degree sensitive to external: stimuli, yet exhibits all the main phenomena of life, and the very simplicity of its structure and meagreness of its requirements seem to further its success in the struggle for existence.

There are several species of Amoebae differing in size and in the character of the nucleus and in other small points, but all so similar in their main characters that they are called by the same generic name, Amoeba.

The species of Amoeba described above is Amoeba proteus,

Resting Stage.

Temporary Fusion.

Genus and Species.

whilst another form, with shorter pseudopodia and several nuclei, is distinguished as Amoeba quarta.

Unicellular Forms which seerete a Shell.

Many forms closely allied to Amoeba have taken one step upward on the ladder of life, by acquiring the habit of secreting round — their bodies a covering, which is not temporary as in the case of the Amoeba’s “cyst,” but is permanent,

| Gilobigerina and is of sucha form, that Galea whilst allowing all vital | Pulvinulina Teetulans processes to continue unchecked, it serves as some slight protection to the soft protoplasmic body.

These protective “shells” are usually of calcium carbonate (chalk), or of silica, and they are perforated by one or more pores through which the protoplasm can freely project; incidentally thev exhibit a wonderful variety and beauty of form.

Pocuation A few of these are shown in Fig. 2. The of Chalk special forms illustrated are all taken from sea- Rock. water forms, which, when alive, float freely in the