OF THE .UNIVERSITY 9F GASSELL'S NATURAL HISTORY LION CASSELL/S NATURAL HISTORY • By F. Martin Duncan, F.R.P.S., F.R.M.S., Member of the Marine Biological Association of the United Kingdom, Author of " Denizens of the Deep," etc. WITH 16 COLOUR PLATES AND MORE THAN 200 ILLUSTRATIONS FROM PHOTOGRAPHS BY THE AUTHOR GASSELL AND COMPANY, LIMITED LONDON, NEW YORK, TORONTO AND MELBOURNE 1913 BIOLOGV LIBRARY INTRODUCTION IN the pages of this volume I have endeavoured to place before my readers in as simple and non-technical language as the theme permits (though the entire avoidance of technical terms has been neither possible nor desirable), the wonderful story of the gradual evolution of animal life, from the simplest unicellular organism to the most complex type. I have aimed to give a broad survey of the animal kingdom, describing only those creatures most typical or possessing some characteristic trait, from each divi- sion, rather than giving what in the space at my command would be the briefest possible description of a large number of animals. In this way each great division of the animal kingdom is placed, as it were, in a series of tableaux before the reader, the whole forming a pageant of animal life. The study of animal life is full of interest and fascination, opening up new fields for investigation the farther one advances, always becoming more and more deeply absorbing as one's know- ledge and experience increase. There is so much one would desire to know, and so short a time in which to accomplish it. And to-day, how infinitely wider and more interesting is our outlook upon the study of animal life ! A hundred years ago, he who could correctly name and classify the largest number of speci- mens under their respective divisions was considered the greatest authority, though probably he had never seen any of them alive in their natural habitat. Classification — specie-mongering one might almost call it, with a total disregard for the importance of study- ing the living animal and its environment — was the almost uni- versal order of the day. Indeed, the few men who had heard vi INTRODUCTION the voice of Nature, and had gone forth into the fields and lanes, and along the seashore to pursue their studies, were laughed to scorn, or looked upon as revolutionary, if not dangerous heretics. But these early pioneers laboured not in vain ; interest was aroused, and gradually the old pedantic, narrow outlook widened, until the publication of Darwin's " Origin of Species " established and vindicated for all time the importance of biology, the study of the organism in relation to environment. Since that time the history of the study of animal life has been one of rapid and steady progress, fraught with far-reaching and important results. Take, for example, the rapid progress within the last fifteen or twenty years of our knowledge of the protozoa, and of the important part which we now know many of these unicellular organisms to play as the primary cause of many deadly tropical diseases, such as malaria, yellow fever, and sleep- ing sickness. Biological investigation has revealed not only the organisms that produce the malignant diseases, but the transmitting agents that carry them from man to man — discoveries of far- reaching economic importance, making for the commercial advance and prosperity of tropical lands, where formerly fevers rendered life almost insupportable. The engineer will proudly acclaim the completion of the Panama Canal as one of the wonders of mecha- nical science, but its successful accomplishment has only been rendered possible by biological research, through which the know- ledge of how to combat the ravages of malaria and yellow fever among the vast army of workers employed upon the undertaking has been acquired. v The study of life in the sea — marine biology — has made con- siderable progress of late years, and is becoming of ever greater importance, not only from the purely scientific point of view, but in connection with fishery questions and the " harvest of the sea." Thanks to the energy of Sir E. Ray Lankester, the Marine Biological Association of the United Kingdom was founded in 1884, and since its inception has carried out investigations of far-reaching scientific and economic importance, adding to our INTRODUCTION vii knowledge of the life, habits, and migrations of various market- able marine fishes, their rate of growth, and the organisms upon which they feed : subjects to which I shall have occasion to refer in the chapter on marine fishes. The occupation of wide areas of hitherto virgin country by civilised man is producing the most profound changes in the dis- tribution of animal life, owing to the incessant and often sense- less war of extermination which he wages upon the so-called " lower animals " in his conquest of the wild. Of the vast herds of bison which roamed the prairies of North America seventy years ago, but a few hundred head, if so many, survive to-day, carefully sheltered in reservations and zoological gardens. The fur seal has also been nearly exterminated, and the whales are doomed. Unless active steps are taken to protect them, the same fate awaits the whole of the large and many of the small quad- rupeds, with the exception of those already under or amenable to domestication, and another hundred years will probably see their total extinction. So, too, with many of the birds ; every year sees the disappearance of some gaily coloured species that helped alive to make the face of the earth more beautiful, slaugh- tered as an offering to woman's vanity, to satiate the barbaric lust of Fashion ; while the so-called " sportsman " who shoots every rare bird at sight and the misguided agriculturist who can- not distinguish between those birds which, as insect eaters, are his best friends, and those which take serious toll of his seed, help on the work of destruction. That man will have to pay bitterly in the future for this ruthless destruction there can be no doubt, for the balance of Nature cannot be upset with im- punity. The destruction of carnivorous animals automatically removes the natural check on the increase of those plant-devour- ing animals which formed their prey ; while the disappearance of many species of birds can only foster the steady increase of crop- devouring hordes of insects. It is impossible nowadays for one man to write or speak authoritatively out of his own personal knowledge upon the whole viii INTRODUCTION of the animal kingdom, and therefore in writing the present book I have consulted the latest published works of the leading authori- ties on each division, so that I might have the benefit of their knowledge upon those divisions with which I am less familiar, as well as their confirmation upon those to which I have devoted many years of original research. I believe that in every case where extracts from other works have been included they have been placed between quotation marks and their authorship acknow- ledged either in the text or in a footnote. Whenever it has seemed desirable, the origin and full meaning of less familiar technical words have been given. The whole of the illustrations, both in colour and half-tone, have been prepared from my own original photographs. I would express my thanks to Mr. H. E. Garraway, of the Queensland Government Office, London, for enabling me to photograph a specimen of that deeply interesting animal the Ornithorhynchus, and also to my dear Wife for much valuable assistance. If the book and its illustrations should help to awaken and stimulate an interest in the wonders and beauties of animal life, then my labours have not been in vain. F. MARTIN DUNCAN. 1 CONTENTS CHAPTER PAGE 1. THE PROTOZOA— THE DAWN OF LIFE . . /. . i 2. THE SPONGES . V ' . V V • • V 30 3. THE CCELENTERATES OR HYDROIDS : jELLY-FlSH, ANEMONES AND CORALS .-i -v . *^ . ^ 39 4. THE ECHINODERMA : STARFISHES, SEA URCHINS, AND HOLOTHURIANS ,r 59 5. WORMS, ROTIFERS, LEECHES, POLYZOA 73 6. THE MOLLUSCA 92 7. THE CRUSTACEA ... . . . . . 116 8. SCORPIONS, SPIDERS, CENTIPEDES, AND MILLIPEDES . 126 9. BUTTERFLIES AND MOTHS 140 10. THE COLEOPTERA : BEETLES 153 n. HYMENOPTERA : ANTS, BEES, AND WASPS . . . 163 12. DIPTERA, ORTHOPTERA, HEMIPTERA, AND NEUROPTERA . 184 13. ASCIDIANS AND LANCELETS ...... 198 14. INTRODUCTION TO THE FISHES ..... 202 15. THE ROUND-MOUTHED AND CARTILAGINOUS FISHES . 211 16. THE TELEOSTOMI, OR " PERFECT-MOUTHED " FISHES . 223 17. THE AMPHIBIA ........ 241 18. THE REPTILES . . . . . . 248 19. AVES : THE BIRDS . . . . . . 261 20. THE BIRDS (continued) . . . . . 277 21. THE BIRDS (continued) , . * . . 296 * x CONTENTS CHAPTER PAGE 22. THE ECHIDNA AND DUCK-BILLED PLATYPUS . ^ ( . 318 23. THE MARSUPIALS, OR POUCHED ANIMALS ",. . . 321 24. THE SLOTHS, ANT-EATERS, AND ARMADILLOS . ; 327 25. THE WHALES, DOLPHINS, AND MANATEES i . . 336 26. THE UNGULATES, OR HOOFED QUADRUPEDS . . . 346 27. THE EVEN -TOED UNGULATES . . . . 354 28. THE CARNIVORA . . . , . ,s . . . 369 29. THE RODENTIA, OR GNAWING ANIMALS . . . 384 30. SHREWS, MOLES, AND BATS ., -^ .;1^ . .. 390 31. PRIMATES: APES AND LEMURS . . . * . 399 INDEX ->-^' ' ;i ... ..+•-•••:,».. ... , ,,.>; -^ . 411 LIST OF COLOURED PLATES Lion ......... Frontispiece FACING PAGE Portuguese Man-of-War (Physalia) ...... 46 Corals and Sea Fans 50 Sea Mice (Aphrodite Aculeata) 84 Bivalve and Univalve Shells . . . . . . 101 Indian Leaf Butterfly . . . . . . . .144 Group of Tropical Butterflies . . . . . . .146 Butterflies showing warning colours . . . . .148 Group of British Moths ....... 152 Group of Longicorn, Scarab, and Carib Beetles . . .158 Locusts, Cicadas, and Leaf Insect . . . . . .192 Kingfisher . . . . . . . . . 272 Macaw .......... 302 Bullfinch .......... 314 Jay ._. . . 316 Tiger . . . •-.-- 382 LIST OF ILLUSTRATIONS FACING PAGE Amoeba with ingested diatoms 4 Globigerina Ooze ......... 4 Foraminifera (N. depressula) . 5 Radiolaria . • .. \ * . ... . . . . . . 5 Noctiluca miliaris . • • - . . . '• .'*;' . . . 16 SpJiavozoum punctatum, SL Colonial Radiolarian . . . 16 Ceratium . » . . . . . . . .16 Trypanosoma gambiense. Cause of sleeping sickness . . 17 Trypanosoma bvuccii. Cause of nagana in cattle and horses 17 Leucosalinia blanca . . . . . . . .32 A branching sponge . . . . . - .';v • - 32 Venus's flower-basket sponge . . '.""; ... 33 Glass-rope sponge . - . ' * • . • * . - . . . . 33 Fresh-water hydra with tentacles partially contracted . . 40 Polyparies of hydrozoa "'• .' . . . . . .40 Portion of living hydroid colony • - - . . 41 Portion of living hydroid colony, showing the vase-like gonotheca 41 Hydra Fusca, with young bud ...... 48 A hydroid medusa . . •. . * . •'" ... 48 Beroe ovatus . . - \, ' .:. . • . .... 48 Sea anemones . . . * . , •• ^ • . . . • 49 Polyps of Pennatula phosphoria, the sea-pen .... 52 Polyps of Corallium rubrum, the red coral . ... 52 A mushroom coral . . . . . -53 Caryophyllia smithii, the so-called " Devonshire " coral ; dead and expanded specimens 53 A branching coral ........ 58 A massive stony coral . . . . . • » • 58 xiv LIST OF ILLUSTRATIONS FACING PAGE Upper surface of Common Starfish 59 Starfishes climbing side of tank and turning over ... 59 Astropecten irregularis . . . . . . . . 62 A " Sun " Starfish 62 Palmipes membranaceus, the so-called " Bird's Foot " Starfish . 63 Ophiothrix fragilis, the Common Brittle Star ... 63 Ophiopluteus larva of O. fragilis 63 Egg and larva of Asterina gibbosa ...... 64 Advanced larva of Asterina gibbosa . . . • .64 Adults of Asterina gibbosa . «. . . . . * 64 The Rosy Feather Star : Antedon rosacea . * * $ • 65 Rosy Feather Star . . \ .• . . ^ . . 65 Pentacrinoid larva of Antedon . . ft .v,,. 68 Pentacrinoid larva of Antedon: later stage . . , . 68 Upper and under surface of Sea Urchin (Echinus esculentus) . 69 Sea Urchin with extended tube feet . ... . . . 70 Test and jaws of Echinus (Echinus miliaris) . . • 7° Heart Urchin (Echinocardium cor datum) . '[ . . ^ *, , • 71 Tests of Heart Urchin: upper and under surface . ^ . 71 Holothuria nigra . . , •. * • ^. .. . . 72 Cucumaria normani . . . . . ,^; ... .^.^ • 72 Synapta, a worm-like Holothurian i *, . ^. . 72 Auricula larva of Synapta . . . . .,,*». 72 Leptoplana tremellaris . . . . . . • ? 73 Trichina spiralis encysted in muscle . . ?f ^ ;,»:;; . 73 Tomopteris scolopendra . . .- > . ^v w.^ ~ . 74 Amphiglina mediterranea . • . • . *. . 74 Phyllodoce laminosa . . - . . > . j^^ . 75 Nephthys Hombugi. . •:^., ..;>:jfi. /,,.#>:. • 75 Nereis cultrifera . . . . • ^ ». > • • • 7^ Arenicola marina . . . ... >..,» . . 76 Two free swimming Rotifers ....... 77 Melicerta, the so-called " Brick-maker " Rotifer ... 77 Part of a colony of Flustra foliacea „>•;, .... 88 Part of a colony of Bugula avicularia . . . - . .88 LIST OF ILLUSTRATIONS xv FACING PAGES Chaloptevus varipedatus . 89 Sabella Pavonia ......... 89 Lanice conchelegia 89 Lophopus : a fresh-water Polysoa . ... . .92 Plumatella repens ......... 92 Argonaut or Paper Nautilus (Argonauta ay go) 93 Nautilus pompilius, the Pearly Nautilus 93 Octopus Vulgaris ......... .96 Octopus (Eledon) attacking a Crab 96 Sepia elegans stranded ........ 97 Sepiola atlantica . . .. . . . . 97 Cuttlefish swimming 98 Cuttlefish resting ......... 98 LimncB Stagnalis and two shells of Planorbis .... 99 Univalves, showing right- and left-handed spirals . . . 99 Studies of the Whelk expanding its foot . . . .102 The Ormer (inner surface of shell) . . . . .103 A chain of Slipper Limpets 103 Razor-shell or Solen with foot extended . . . . 106 Aplysia, the " Sea-Hare " 106 Queen Scallops with Serpula tubes upon their shells . . 107 Scallops opening their shells, and showing the fringe of the mantle 107 A Starfish forcing open an Oyster 112 A Whelk boring through the shell of an Oyster . . .112 The Great Swan Mussel . . . . . . .113 The Prickly Cockle . , . . . . . .113 Zoaea stage of Porcellana sp . .116 Megalopa stage of Carcinus sp. . . . . . .116 The Great or Edible Crab . . . . . . .117 Male and female Masked Crabs . . . . . .117 MacYopodia rostratus . . . . . . . .118 Inachus dorsettensis . . . . . . ..118 "Dressed" Spider Crabs 119 The Spiny Spider Crab 119 Female Velvet Fiddler Crab, with eggs 120 xvi LIST OF ILLUSTRATIONS FACING PAGE Female Velvet Fiddler Crab, with tail drawn down to show processes to which the eggs are attached . • .120 Hermit Crab .121 Hermit Crab removed from Whelk-shell to show soft body . 121 The Stone Crab, Lithoides maia . . . . . .122 Galathea squamifera, the so-called " Squat Lobster " . . 122 A Palanurus, or Crawfish, from Indian waters . . ^ .123 A Baby Spiny Lobster (Palanurus) 123 Lobster : Carapace, Cervical Groove, Cephalothorax . .124 The Common Lobster 125 Lobsters^under hypnotic condition standing on their heads . 125 Argulus foliaceous, a parasitic crustacean . . . .124 Pycnogons . . . . . » * • . . .124 Acorn Barnacles ......... 124 Stalked or Ship Barnacle .125 Cypris stage of Barnacle . . . . . . .125 Ship Barnacle cut open to show animal in shell . . , 125 The Water Flea (Daphnia) .... :r . ^ 126 A Copepod (Gegenbauri) , » jj . 126 A Giant Centipede . . . . . f *v , k* $,f j . 127 Scorpion 127 Tarantula and Mygale Spiders . . •»& : . . > 138 Two female Garden Spiders and a male Spider . . .138 Wing of Butterfly, showing tile-like arrangement of scales . 139 Trachea! tubes of Caterpillar . . . . . , 139 A spiracle or "breathing pore" of Caterpillar . / ./' . 139 Larva of Privet Hawk Moth .... *».:,< . 142 American Silk Moth, and cocoons . . . ';&>•:•. . 142 Life-history of the Swallow-tail Butterfly . . . .143 European Emperor Moth . . . . . . .150 "Old Lady" Moth at rest on tree- trunk • . . . .150 Male Stag Beetle . . . . . <• * . . .151 Male, larva, and female Water Beetles (Dytiscus) . . .156 The second leg (middle pair) of Dytiscus . . . .156 Front leg of male Dytiscus Beetle . . . . .156 LIST OF ILLUSTRATIONS xvii FACING PAGE Comb-like antenna of Cockchafer, showing the delicate hairs and pits . 157 The Palm Weevil 157 Great Hydrophilus Beetle 157 Goliath Beetle .160 Sacred Scarab Beetles . . . . . . . .160 Rhinoceros Beetle 161 Hercules Beetle . . . . . . . . .161 Elephant Beetle 161 Solitary Wasps 176 Ection and Wood Ants . . . . . . .176 Ichneumon Flies 176 Queen, Worker, and Drone Hive Bees . . . . .177 Humble Bees and Purple-winged Carpenter Bee . . . 177 Group of Diptera ......... 186 Shield Bugs 186 Stick Insects .187 European Mantis 187 The English Cicada; a very rare British insect . . .190 Ranatra . . . . . . . . . . 190 Chinese and Brazilian " Lantern Flies " . . . .191 Adult and young Cockroaches 191 Leaf -like Locusts 194 Leaf Insects . . . . . . . . . 194 Mole Cricket 194 Great Green Grasshopper 194 Ant-lion and Ascalaphus . . . . . . .195 May-fly ........ . . . 195 Larva of Frageria elegans . . . . . . .198 Clavellina lepadiforme . . . . . . . .198 Salpa mucronata . . . . . . . . .199 Tonaria larva of Balanoglossus 199 Lancelots (amphioxus) resting on the sand under water . .199 Embryos of Goby ........ 208 Ear-stones or otoliths of the Plaice . . • 208 ' xviii LIST OF ILLUSTRATIONS FACING PAGE Scale of Sole . . . 208 Scale of Haddock . . 208 Embryos of Dog-fish 209 Dog-fish and Rays . . . -. . . . . 209 Angel or Monk-fish . 218 Butterfly Gurnard . .218 Ray swimming . . . ...... 219 Under surface of Ray < 219 Sticklebacks . . . . ' .• . * V*'' . . 226 Blenny • > ' * r »••;' . . 226 Gurnard . . . . 226 A school of PoUack . . . •..'..'• .•.'** . . 227 Pipe-fish 227 Embryo of Flounder • . . 234 Migration of eye in head of Flounder . - > • - -« '"•'' . . 234 Marked transplanted Plaice . . . . • . - i> . 235 Turbot - . -.••••• •••-•V* • 235 Young Hippocampus . • . '..•*• ;. . * » * * • ¥ ••* • • 238 Ribbon-fish . . . . , . >' * ; -J.?*. I > **ti . 238 Boar-fish with mouth contracted . /./..* . . . 239 Boar-fish with mouth expanded . . 'Y;^ . 1 i>*+ . 239 Newts 244 Common Toad * . . . 245 Edible Frog , . ( • , . , ^v_ . 245 Common Tortoise . . . | ... . » j*Z- . 250 Giant Galapagos Tortoises ...... * $& . 250 A young Crocodile . . . ^ . . --^^ f^ . 251 The Alligator's Smile . . . , , r . , • . • , .251 Lizard «v ..,%^ . #-,-& • • 254 Lizard capturing prey . . ..... . . 254 Chameleon on the watch . . . .^- . . 255 Bearded Chameleon, showing change of colour markings . .255 1. Chameleon capturing insect . . . . • .256 2. M with tongue fully extended » 256 3* „ swallowing insect . . . . . 256 LIST OF ILLUSTRATIONS xix FACING PAGE Boa Constrictor 257 Boa Constrictor resting on branch . . . . . . 257 Head of Boa Constrictor . . . . . .258 Adder about to strike 259 Adder pursuing prey 259 Great Bustard ......... 276 Ruff challenging in mating season . • . . .276 Head of Cassowary . . . . . . . .277 Cassowary * 277 Great Auk .......... 284 Cape Penguin . . . . . . . . 284 Pelican 285 Dark-bodied Pelican 285 Cormorant nesting . . 285 Young Lapwing or Peewit 292 Avocets .......... 292 Night Heron 293 Golden-crested Crane . . . . . . . 293 Spoonbill 298 Black-necked Swan 298 King Vulture • . . 299 Griffon Vulture . . . ^ r . . . . 299 Golden Eagle . . . . . . . . 304 Harpy Eagle 304 Australian Fawn-breasted Kingfisher ..... 305 The Great Hornbill 305 Barn Owl 320 Little Owl 320 Duck-billed Platypus .321 Kangaroo 321 African Elephant . . . . . . . . 348 Zebra 348 Rhinoceros 349 Tapir 349 Hippopotamus . 356 xx LIST OF ILLUSTRATIONS FACING PAGE Wild Boar . ... • 35$ Head of Llama . -357 Llamas 357 Young Bactrian Camel 3°2 Dromedary - * ' • ' • ' * 3 Head of Giraffe, showing long tongue ..«,. . .... . . 3^3 Studies to show positions of Giraffe when picking an object off the ground . • • • • . • • • 363 Eland . .... ; * Wapiti Deer . - - •„.;•• . « . ' .'i ' 366 Old EngUsh Wild White Bull ; . . . . . :&$ • 3^7 Markhoor . • • , • , • ' , * * *.* • 3 7 Zebu . . . • - • * .' ' 368 Head of Bison . . • • ', • T r &+'< **» * - 368 Sea Lion . • • • • • I • * <•; Polar Bear standing erect . | * , *. . . ? • . • • 369 Young S5rrian Bear . • , * • . • . •• • ^r1 • 376 Brown Bear .... v * , • • • •' ••'->-* "-' • • 37 Young Somali Hyenas . • • , » . •- ,- • - ..•., • 377 Grey-maned Hyena . • • , • / v >*! • • 377 Fox •'• •.*• African Black-legged Jackals . . . . . , * ? . .380 Leopard * Jaguar Grey Squirrel Sleeping Dormice t .*. • • • 3 080 Porcupines . Coypu Rat :»^» rt, • Chackma Baboon . . • • .,,• . , • ". f • • '40° Sacred Baboon . -.- '*•-.. Japanese Ape • Young male and female Chimpanzees 4°i Adult male Chimpanzee 4° Young female Orang-Utan 4°9 CASSELL'S NATURAL HISTORY CHAPTER I THE PROTOZOA— THE DAWN OF LIFE THE simplest members of the animal kingdom are called the Protozoa,1 and, with few exceptions, are too minute to be clearly visible without the aid of a microscope, those which may be detected by the unaided eye appearing as tiny, inert specks or moving particles. They are universal in their geographical dis- tribution, from the Equator to the Arctic and Antarctic, and are to be found living under the most varied conditions, in the soil, in stagnant pools, in rivers and lakes, and in the sea ; while many live in the bodies of the higher animals and are responsible for some of the most serious and fatal diseases from which man and beast can suffer. Malaria, sleeping sickness and blackwater fever are inflicted by them on mankind, and rinderpest, nagana and surra on cattle and horses, the organisms being conveyed from one host to another through the agency of various biting insects. Primitive as these organisms are, they are not sufficiently so to be considered as primordial in the sense of being the first created animals ; they must have been preceded by a still simpler organism, of which we have no definite knowledge, but to which the Amoeba, and some of the Mycetozoa,2 at certain stages, probably most nearly approach. The riddle of the origin of life still remains unsolved, though its ultimate solution is within the bounds of possibility. If it is ever accomplished, there is little doubt that the key will be dredged up from out the sea. In the light of the most recent scientific investigation, it is 1 Greek, prttos, first i zoa, animal. • Greek, myees, a fungus ; xoa, animal. B 2 THE PROTOZOA-THE DAWN OF LIFE now very generally considered that the dawn of life took place upon the wet sands, or in the quiet waters of some shallow sea of the primeval world ; for the warm water-logged mud of the seashore would have been a specially suitable medium, owing to its constant temperature, its moisture, and soft surface, for the development and support of the first forms of animal life, and for the accumulation of the first formed organic matter from which these primordial organisms probably sprang ; for the essential chemical constituents of living matter are all soluble in, and con- stituents of, sea-water. The Protozoa are all organisms characterised by the compara- tive simplicity of their structure, and by existing either as single cells or colonies of similar cells, mere repetitions of each other, each capable of maintaining an independent existence. It is to these primitive organisms that we must first turn our attention if we are fully to realise the significance of all the beautiful and wonderful creatures, with their varied shapes and habits, to be met with in the animal kingdom, and how, step by step, the higher forms of animal life have been gradually evolved from simple forms. Of the great antiquity of the Protozoa we have a graphic record in the rocks of the earth, for their fossil remains have been found in the oldest known rocks that have retained any indication of the existence of life on the earth. The limestones and sand- stones of many mountain ranges are largely composed of the fossil remains of Protozoa ; the wonderful pyramids of Egypt are really vast piles of an extinct Protozoon whose skeleton was about the size of a large pea ; while the white chalk cliffs of old England are largely composed of the skeletons of these organisms ; for while some Protozoa remain soft, jelly-like specks of changing form, leaving no record of their existence, others evolve the most exquisite skeletons of lime and silica, imperishable, outlasting the mountains they served to form. We will begin our study of these primitive forms of animal life by examining a tiny microscopic creature to be found in the mud at the bottom of ponds and streams, and in the shallow pools on the seashore. It is called the Amoeba, from an old Greek word which means changeful, and when first discovered was called the " Proteus Animalcule," after the changeable sea god of the ancient THE PROTOZOA— THE DAWN OF LIFE 3 Greeks. Under the microscope the Amoeba looks like a tiny, semi- transparent jelly-speck, about ^ inch in diameter, composed of a soft, slimy, semi-fluid substance in which can be seen a slightly denser globular body called the nucleus, the whole organism being very irregular and varying in shape, changing ever as we watch it, becoming round, oval, oblong, or lobed like a distorted hand — changes effected by the streaming of its proto- plasm and the pushing out and withdrawal of blunt finger-like processes. As we watch the expansion and contraction of these finger-like processes, we shall see that as a result of their move- ments the whole mass of the Amoeba is slowly drawn along, with a curious streaming sort of motion. The Amoeba may contract its finger-like expansions and come to a pause in its progress, and assuming a globular shape, secrete a thick, almost shell-like coat, probably composed of some nitro- genous substance, which completely envelops it, forming a cyst or cell-wall. The formation of this enveloping cyst is of very great importance to the Amoeba. Protected by its horny case, it is enabled to survive periods of drought should the pond dry up during the summer months. When the rains of autumn replenish the pond, and conditions suitable for its active life are once more restored, the Amoeba ruptures the cell-wall and makes its escape. The Amoeba moves continually in all directions, its constantly changing finger-like processes being merely temporary projections of its semi-fluid body, and not special organs in the anatomical sense for producing movements ; hence the reason for their being called " pseudopodia," or " false-feet." The jelly-like, somewhat granular substance called proto- plasm,1 of which the Amoeba is composed, appears surrounded by an outer glassy-looking and extremely thin pellicle or layer.2 In the interior mass of protoplasm may be made out the denser and small rounded body of the nucleus, which does not alter in form during the changes of shape which the Amoeba undergoes as a whole. This nucleus consists of material closely resembling the 1 From the Greek, protos, first ; plasma, a formation, from plasso, I shape or moxild. The simplest life-matter known, and present in the tissues of both plants and animate. 2 The glassy outer portion is called by some observers the ectoplasm ; the denser mass being called, in contradistinction, the tndoplasnt. 4 THE PROTOZOA— THE DAWN OF LIFE protoplasmic body mass, but is of a slightly higher refractivity, which renders it conspicuous ; it contains granules of a substance called chromatin, because of the readiness with which it absorbs certain dyes. Another minute feature which we shall see in the interior of the Amoeba is a clear, rounded space in the protoplasm, which, as we watch it, will be seen gradually to increase in size up to a certain point when, by a sudden contraction of its walls, it will disappear from view, only to reappear in a short time and again expand. This transparent, pulsating space is called the contractile vacuole, and probably secures to some degree the aeration and purification of the mass of protoplasm. If an Amoeba be kept under observation for a little while, the streaming movements of the protoplasm will be seen not only to effect locomotion, but also to bring about the successful cap- ture of food. The drop of water in which the Amoeba is moving contains minute particles of mud, and also probably several of those unicellular plants called " Diatoms," which swarm in both fresh and sea water. Should one of these microscopic plants lie in the path of the Amoeba, the latter will press one of its pseudopodia, or one side of its body, against the Diatom, which will be seen gra- dually to sink into the soft protoplasm and pass into the interior of the Amoeba. The engulfed Diatom becomes surrounded by a little globule of watery fluid, and by degrees the whole of its soluble parts disappear, only the siliceous frustule or skeleton remain- ing. This insoluble skeleton is soon passed outwards from the protoplasm into the surrounding water; and the Amoeba fre- quently appears to get rid of the frustule of the Diatom by the simple process of streaming away from it. If food is abundant the Amoeba increases in size, and it is not long before a very remarkable change takes place. The pseudo- podia are withdrawn, partially if not entirely ; the body mass begins to elongate ; and a fissure appears, dividing the Amoeba into two parts. As the waist-like constriction forms, the nucleus may be seen to divide into two, each half moving off into the two lobes of the dividing Amoeba, so that when separation is com- pleted, and we have two distinct Amoeba resulting from the divi- sion of the one, each possesses a nucleus developed from the original nucleus. It is by this simple process of division into Amoeba with ingested diatoms Globigerina Ooze Foraminifera (A7, depressula) Radiolaria THE PROTOZOA— THE DAWN OF LIFE 5 two, binary fission as it is called, that reproduction or multiplica- tion chiefly takes place in the Amoeba and many of the Protozoa. It is hardly exact to call the two resulting Amoebae the children of the original, for they are simply the original Amoeba cut in halves ; it is convenient, however, to speak of these products of binary fission as " daughter-cells." The new Amoebae absorb and assimilate food, thus adding new material to the original matter of the parent body, and then each of them again divides into two. So the process of food assimila- tion, growth, and subsequent division is repeated again and again, an ever lessening part of the actual body substance of the original ancestor being passed on to each succeeding generation. It is obvious, therefore, that an Amoeba never dies a natural death, or, to put it another way, " no Amoeba ever lost an ancestor by death." An Amceba may be killed outright, but in that case it leaves no descendants ; but if it once produces new Amcebae, it never dies, although it ceases to exist as a single individual. Occasionally, two Amcebae may be seen to flow towards each other, and fuse in a way which may be considered as an incipient form of sexual union, and this fusion acts undoubtedly as a re- vivifying process or " rejuvenescence," arresting that constitu- tional weakening which seems to be set up by, and the inevitable result of repeated fission. As Professor F. W. Gamble states, (t simple division carried beyond a certain number of cleavages appears to be ineffective. The process, though long, is not endless, and after a time it slows down and ceases. Exactly why it should do this is not very clear, but it would seem that the slackening is not due to deterioration of the environment so much as to some constitutional weakening. Any weakness is, owing to the simple cleavage of one into many, conveyed to the descendants, and there seems to be no rectifying property. It has been found that if such a strain or culture, the members of which are derived from a single Protozoon by re- peated fission, is isolated, it gradually dwindles and dies. If, however, it is allowed access to another culture of exactly similar appearance, it undergoes renewal of this dividing property, and after an interval once more populates the water." From the above brief description of the Amceba, it will be seen that although this interesting and remarkable organism is 6 THE PROTOZOA— THE DAWN OF LIFE but a single protoplasmic cell, yet it is capable of all the functions of a multicellular animal — movement, feeding, growth, reproduc- tion— and that in it we have, to quote Professor Haeckel, " an approximate illustration of the ancient common unicellular an- cestor of all the Metazoa, or multicellular animals." Further, a simple Amoeba has a striking resemblance to the " primary cell " or " ovum " of all animals, whether vertebrate or invertebrate. It may be regarded as equivalent to this uni- cellular stage which is the beginning of all the higher organisms. The so-called "white corpuscles" or leucocytes of our blood are amoeboid. As they circulate along the blood-vessels, they execute movements like those of Amoebae, constantly modifying their shape, and engulfing foreign substances, or organisms such as bacteria, which have entered the system, just in the same manner as the Amoeba takes in its food. While the distinction between the higher plants and animals is perfectly sharp and obvious, it becomes increasingly difficult to maintain such a distinction as the two groups are traced down- wards to ever simpler forms, until they merge in an assemblage of organisms which partake of the characteristics of both king- doms. Of the Protozoa certain groups are distinctly animal in their chemical activities or metabolism, in their mode of nutri- tion, and their locomotive powers ; while in others it is very difficult to draw a distinction between them and the lower fungi, making it extremely difficult to separate sharply the Protozoa from the Protophyta, the lowest animals from the lowest plants, and therefore the term Protista, first introduced by Professor Haeckel, is now generally applied to designate these lowly forms of life, organisms which do not consist of an aggregation of differentiated cells. A large number of the Protozoa resemble Amoeba in the pos- session of pseudopodia, or false-feet, and these pseudopodia-bearing organisms constitute one of the great divisions or classes into which the Protozoa are divided — the class Rhizopoda.1 But it is only a comparatively small proportion of these Rhizopods which, like Amoeba, possess comparatively short, blunt pseudo- podia, and they are consequently grouped together by this natural distinguishing feature to form one of the leading divisions 1 Greek, rhixa, a root ; pous, a foot. THE PROTOZOA— THE DAWN OF LIFE 7 or orders of the Rhizopoda — the order Lobosa, of which Amoeba is one of the simplest.1 Some of the Lobosa differ from Amoeba in the possession of a comparatively dense outer coat, forming a shell or test enclosing the protoplasm. One of these, called Difflugia, is fairly common in fresh water, and collects minute sand grains to form its flask- shaped test, the particles being agglutinated together. While the bulk of the protoplasm of Difflugia is contained within the interior of this curious test, the organism pushes out comparatively long pseudopodia. Equally interesting, and also a commoner member of this group, is Arcella, an organism which has a convex, transparent shell of a tough material, said to be chitinoid from its resemblance to chitin, a horny substance such as we find the integument or outer skin of insects composed of. This transparent shell of Arcella is convex on one side, flat on the other, and in the middle of the flat surface there is a rounded opening through which the pseudopodia are protruded. All the other Rhizopods differ from the Lobosa in having their pseudopodia in the shape of long, slender threads. The Foraminifera have these thread-like pseudopodia, and form a most interesting order, the members of which chiefly inhabit the sea, and, with a few exceptions, are provided with tests of the most varied and exquisite shapes, composed of carbonate of lime, or of cemented particles of sand. D'Orbigny first described the Foraminifera as minute cephalopods or cuttlefish, from the re- semblance of the shells of some species to the Pearly Nautilus, and used the name Foraminifera to express the fact that the chambers of their shells communicated by pores, and not by a tubular siphon as in the nautilus. Their true nature as Pro- tozoa was elucidated later, thanks to the careful and laborious investigations of Williamson, Carpenter, Dujardin, and Max Schultze. That the Foraminifera are of very ancient origin we realise 1 The Animal Kingdom is divided into phyla (sub-kingdoms), the phyla into classes, the classes into orders, the orders into families, the families into genera, the genera into species, while the species themselves are assemblages of individual animals agreeing with one another in certain constant characters. Thus, in terms of classification, we should describe the Amoeba as follows : — Kingdom — animalia. Phylum (sub-kingdom) — protozoa. Class — rhizopoda. Order — lobosa. Family — amoebae. Genus — amoeba. Species — amoeba proteus. 8 THE PROTOZOA— THE DAWN OF LIFE when we come to seek for their fossil remains in the rocks, for then we find that they range in geological time from the Lower Cambrian strata to the present day. The beautiful chalk cliffs that form a natural bulwark along many miles of the English coast, and the noble North and South Downs, consist almost wholly of the fossil remains of Globigerinids, while another species of Foraminifera, the Nummulites, have contributed largely to the composition of the great Eocene limestones, and are the chief constituents of the stone that was used in the building of the great Egyptian pyramids. The species of Foraminifera to be found between tide marks on the seashore, and extending to the deep water beyond, are very numerous, and may be collected from the surface of the sand and mud left exposed by the receding tide, and upon the fronds of the seaweeds in the pools. Some may be met with in the brackish waters of estuaries ; some are only to be found at various depths of the sea, or living among the bottom ooze ; while others again float freely at or near the surface of the sea, and form at times a considerable proportion of the surface Plankton.1 Such pelagic 3 forms as Globigerina, and its allies, have the surface of their shells extended by extraordinarily delicate spines, which not only help to prevent the organisms from sinking, but also permit the protoplasm protruding from the mouth and fine holes in the shell to form a curious bubbly film between them, and to stretch out long, fine threads for the capture of food. On the death and decay of the protoplasm of these buoyant Fora- minifera, their shells gradually sink to the bottom, losing in their passage downwards their more readily soluble delicate spines, and at last accumulating at depths where their more solid cal- careous parts form a light oozy mud termed " Globigerina-ooze." At depths between 1,000 and 2,000 fathoms, on the floor of the Atlantic, great beds of this Globigerina-ooze, or modern chalk, are forming to-day in just the same way as the chalk cliffs of England were formed on the floor of a sea during a past geological age. The shells of the Foraminifera are in many species composed of carbonate of lime ; in one group, called the Arenaceous Fora- minifera, the shells are composed of foreign particles, such as sand 1 From a Greek word with the meaning " that which is drifted." * Pelagic— buoyant, floating at whatever depth found. THE PROTOZOA— THE DAWN OF LIFE 9 grains, cemented together, while in certain fresh-water forms the shell is chitinoid. In all cases the shell at first has but a single chamber, and in some species persists as such throughout the life of the organism ; but the general tendency is for the number of chambers to increase, with the result that they assume the most varied forms. Indeed, as Dr. Carpenter wrote in reference to the Arenaceous Forams, " There is nothing more wonderful in Nature than the building up of these elaborate and symmetrical structures by mere jelly-specks, presenting no traces whatever of that definite organisation which we are accustomed to regard as necessary to the manifestations of conscious life. The tests (shells) they con- struct when highly magnified bear comparison with the most skilful masonry of man. From the same sandy bottom one species picks up the coarsest quartz grains, unites them together with a ferruginous cement, and thus constructs a flask-shaped test, hav- ing a short neck and a single large orifice ; another picks up the finer grains, and puts them together with the same cement into perfectly spherical tests of the most extraordinary finish, per- forated with numerous small pores disposed at pretty regular intervals. Another species selects the minutest sand grains and the terminal portions of sponge spicules, and works them up to- gether— apparently with no cement at all, but by the mere laying of the spicules — into perfect white spheres like homoeopathic globules, each showing a single-fissured orifice. And another, which makes a straight, many-chambered test, the conical mouth of each chamber projecting into the cavity of the next, while forming the walls of its chambers of ordinary sand grains rather loosely held together, shapes the conical mouths of the chambers by firmly cementing together the quartz grains which border it." An examination of a number of the shells or tests of different species of Foraminifera will show that while in some the shell has a wide opening on the exterior, in others this large opening is not present, its place being taken by numerous minute pores scat- tered over the surface of the shell : distinctions at one time used for the purpose of classification. Thus the Foraminifera were formerly classified, according to the structure of the shell, into Vitreous or Perforate, Porcellanous or Imperforate, and Arena- ceous ; but this classification is now considered too artificial, as it separates apparently adjacent forms. Brady, who described io THE PROTOZOA-THE DAWN OF LIFE the Foraminifera of the Challenger Expedition, has classified them in ten families.1 In the living Foram the bulk of the protoplasm is enclosed within the shell, though part of it streams out from either the large opening or from the numerous minute pores, in slender, radiating, thread-like pseudopodia, which sometimes join and form a living network. Diatoms, particles of animal or vegetable matter, organisms even more minute than the Foram itself, may become captured in the net and engulfed in the protruded proto- plasm, and the soluble parts dissolved and assimilated, after the manner already described in connection with the Amoeba. Soon after the first simple shell has been formed a little mass of pro- toplasm begins to project through the single large opening, or through the scattered pores, as the case may be, and, increasing in size, becomes enclosed in a shell like the original one, but generally a size larger, and firmly connected with it, the cavities of the two communicating with each other through the original opening or pores. This process may be repeated again and again, until, in place of a single speck of protoplasm enclosed in a single shell, a composite structure has been built up, composed of many particles of protoplasm, each having its own nucleus, each enclosed in a shell, and all the shells firmly united together ; while the whole of the particles of protoplasm are in continuity through the apertures of communication. Although the shells of a large number of different species have been most carefully described, there is need for further investiga- tion into the processes of reproduction of the Foraminifera, but multiplication by fission appears to be most typical. A method of reproduction has been observed, in which the protoplasm inside the shell divides up into a number of particles, and each of the minute bodies so formed, instead of possessing pseudopodia, has a single delicate flagellum or lasher, by means of which it moves about. In the more typical fission process the nucleus may divide into several parts, and round each of these products of nuclear division a little mass of protoplasm gathers, and in this way young individuals are formed, which in due course become enclosed in shells and liberated from the parent. 1 The name-giving types are Gromia, Miliolina, Astrorhiza, Lituolina, Textularia, Chilostomella, Lagena, Globigerina, Rotalia, and Nummulites. THE PROTOZOA—THE DAWN OF LIFE n The Radiolaria are marine Protozoa, well known to most amateur microscopists on account of their extremely beautiful skeletons, formed of silica, which are very favourite objects for exhibition under the microscope. While present in all seas, and in every latitude, living at the surface, at varying depths, and near the bottom, the Radiolaria are most numerous in tropical seas, and their siliceous1 skeletons form a deposit or Radiolarian ooze at depths of 2,000 to 3,000 fathoms. Like the foraminifera, their history can be traced far back in the records of the rocks, their fossil skeletons occurring so remotely as the Cambrian strata, and in each succeeding geological epoch. The living Radiolarian has the protoplasm divided by a per- forated membranous sac (called the central capsule), into a central mass surrounding the nucleus, and an outer layer from which the slender thread-like pseudopodia are protruded. The nucleus contained in the enclosed or intra-capsular protoplasm, as it is termed, is always at first single, but later may divide again and again. The skeleton, usually composed of silica, may be a globu- lar, conical, star-shaped, or disk-shaped perforated shell, frequently supported by spines radiating out from the centre, or may con- sist of loosely woven needle-like spicules; while some Radiolaria have the skeleton composed of a chitinoid substance called acan- thin. Reproduction takes place by simple binary fission, and in some species by spore formation, in which the protoplasm con- tained in the central capsule breaks up into small masses which become flagellate spores or flagellula. When we examine a living Radiolarian under the microscope, we shall see some minute yellow cells embedded in the proto- plasm, which are living unicellular plants. These minute, simple plants are microscopic algae, called Zooxanthella, and multiply by binary fission in the protoplasm of the Radiolarian, to whom they are of considerable benefit. In fact, we have here an example of that intimate association between two living organisms, to which the scientific term symbiosis 2 is applied. Now, during the process of respiration the Radiolarian is continu- ally taking up oxygen from the surrounding water and giving off 1 Latin, silex, quartz or flint ; used for the kind of mineral forming the siliceous spicules of sponges, of Radiolarians, and the frustules of diatoms. 8 Symbiosis, from the Greek, meaning " living together." 12 THE PROTOZOA— THE DAWN OF LIFE carbon dioxide, which it cannot work up into food products, as it is destitute of chlorophyll, the green colouring matter present in all green plants. The minute plant, on the other hand, under the action of light and by the presence in its tissue of chlorophyll bodies (Chloroplastids) can utilise the carbon dioxide for nutri- tion, the carbon being used for the building up of such compounds as starch and sugar, while the oxygen is liberated. Here, then, is an association beneficial to both organisms, and in this sym- biosis existing between the Radiolarian and the alga Zooxanthella the latter benefits the former, contributing to its respiration by the oxygen which it gives off, and to its nutrition by the sugar and starches which it forms, while the Radiolarian supplies the carbonic acid and other substances necessary to the alga. Diatoms are also found sometimes living symbiotically in the protoplasm of certain species ; while an amphipod crustacean (Hyperia) has been observed as parasitic on colonial forms. Such colonial forms, which may attain considerable size, and float freely in the sea, are produced by the original central capsule dividing again and again, thus giving rise to a number of central capsules which remain embedded in a firm, gelatinous substance. Mention must be made of the Proteomyxa,1 a division of the Protozoa chiefly of interest to the specialist, and containing a number of somewhat obscure forms which cannot well be placed under the Rhizopoda. Very little is known about the life-history of these organisms. In many instances only one stage has as yet been observed, but it seems probable, according to our pre- sent knowledge, that most, if not all, at some stage, form cysts or spores. The spores escaping from such cysts may have pseudo- podia like Amoeba, when they are called Amcebulce, and they may be furnished with one or two flagella. To this group belongs the Protamceba of Professor Haeckel, an organism more primitive than Amoeba, for it is without any definite nucleus or contracting vacuole, and is found, like Amoeba, living in both fresh and sea water. A number of the Proteomyxa are parasitic upon fresh-water algae, at least at one stage of their life-history, and one species is known to occur in the muscles of the domestic pig, but apparently without causing any harm to its host. The only species that is at present recognised as of any economic importance, and in some 1 Greek, protos, first ; myxa, mucus. THE PROTOZOA— THE DAWN OF LIFE 13 years causes very serious loss to the agriculturist, is Plasmodio- phora brassica, which attacks the turnip and cabbage crops, pro- ducing the disease popularly known as " Fingers and Toes," " Anbury," or " Club-root." The name Plasmodiophora has reference to the slime-like character of the organism, and its re- semblance to the so-called " Slime-fungi," or Myxomycetes, which are now generally included as Protista. The roots of cabbages, turnips, cauliflowers, and other allied plants are frequently to be seen greatly distorted and deformed by swellings of varying size and shape, the result of the presence of Plasmodiophora in the root-tissues, while the plants present a miserable, stunted, starved appearance. If a carefully cut sec- tion from one of these diseased root-swellings be examined under the microscope, it will be seen that not only are the vascular bundles or strands of woody tissue displaced and altered, but that many of the cells of the tissues are enormously overgrown, and their contents quite different from those of normal, healthy cells. Some of these giant cells will be seen to be filled with a semi- translucent, granular, foamy mass of protoplasm, which undergoes slow movements, while the embedded granules are constantly changing their position. The cell is, in fact, tenanted by a plas- modium 1 consisting of a translucent mass of protoplasm con- taining water- vacuoles, oily drops, granules, etc. Other giant cells will be seen to be packed with minute, sphere- shaped spores. These spores become scattered in the soil as the diseased roots of the host-plant rot. Under suitable conditions of temperature and moisture the spores swell, rupture, and tiny protoplasmic organisms possessing a nucleus and a single flagellum make their escape into the surrounding soil. These penetrate into the roots of the seedling cabbages or turnips, probably gain- ing entry by the root-hairs, in much the same way as the proto- plasmic zoospores of Pythium, the fungus which causes " damp- ing-off " of seedlings. Having obtained entry into the cells of the root, the Amcebulae lose their flagella, soon increase in size, and their nuclei divide. The tissues of their host once entered, the Amoebulae commence a battle with the living protoplasm of the cells for possession, 1 Plasmodium, Plasmodia — derived from the same root as protoplasm, and referring to the protoplasmic nature of the organism. 14 THE PROTOZOA— THE DAWN OF LIFE The result of this irritant activity of warring life within the cells is to attract greater supplies of available food materials, so that the growth of the cells becomes abnormally accelerated, producing a monstrous growth. The increased supplies of food material benefit the Amcebulae at the expense of the cell-contents of the host -plant, and after a time neighbouring Amcebulae fuse together and plasmodium-formation begins. The plasmodia so formed are capable of passing slowly from one cell to another, devouring their contents and increasing in size, while the ravaged tissues of the host-plant begin to disintegrate. Finally the plasmodia break up into extremely minute particles of protoplasm, which form into spherical spores. The Mycetozoa l comprise a group of simple organisms now generally looked upon as primitive Protozoa, though at one time claimed by botanists as fungi, and chiefly of interest to the bio- logist. They are to be found living as composite, multinucleate 2 plasmodia upon the damp, mouldering walls of ancient cellars, upon rotting timber, the decaying haulms of beans, and similar vege- table matter, feeding upon the organic debris ; while one, called Fuligo varians, or " Flowers of tan," is a large and conspicuous species inhabiting tan-pits, where it is sometimes a great pest. The composite plasmodia are formed by the complete fusion of numerous units, or, in a few rare cases, by their close contact with each other. The margins of these plasmodia masses exhibit amoeboid movements, slowly streaming out towards food particles and engulfing them, spreading out towards moisture and warmth, but withdrawing from concentrated light. A dor- mant encysted stage sets in as a result of scarcity of food, lack of moisture, or cold, enabling the organism as a resting spore pro- tected by a surrounding cyst-wall to await the return of favour- able conditions for renewed growth and activity. On the rup- ture of the cyst-wall, a swarm spore, which generally possesses a whip-like flagellum, makes its escape, and always eventually loses the flagellum, becoming like a little Amoeba in appearance and habit ; and in the uniting of these minute Amoebae we have the formation of the composite plasmodia. The Sporozoa are a class of the Protozoa to which in only 1 Greek, myces, a fungus ; zoon, an animal. * Multinucleate, having many nuclei. THE PROTOZOA— THE DAWN OF LIFE 15 quite recent years scientific investigation has been closely applied ; but since this class has been recognised to contain organisms which induce malarial fever in man, and various other diseases in man and animals, there has been no lack of workers, and much success- ful investigation has been carried out. To the researches of von Siebold, Kolliker, and van Beneden we owe our earliest accurate, though partial, knowledge of the class ; while some thirty years ago Sir E. Ray Lankester began the study of those species which live in the blood, an epoch-making piece of biological investigation of unique and immense importance to mankind. The work be- gun by these pioneers has been carried on by Manson, Ross, Minchin, Grassi, Laveran, Blanchard, Leger, Cuenot, Schaudinn, and many other distinguished English and Continental workers. The result of the work of these numerous investigators has shown the Sporozoa to be of very widespread occurrence, exclusively parasitic in habit, and infesting the internal organs or tissues of animals belonging to nearly every class and order of the Metazoa.1 The greatest diversity of structural and developmental char- acters are exhibited by the Sporozoa, and there is a general, though not universal tendency for each species to be parasitic on a particular species of host, and to be confined to certain organs or tissues of that host. The effects produced by the Sporozoa upon the animals they infest vary greatly, in many cases, possibly in most, causing no apparent discomfort or injury to the health or vitality of their host, but in others producing most dangerous, not infrequently fatal diseases, and ravaging epidemics. Wide limits as regards size are reached by the different species, some being so minute that several can be contained in a single blood- corpuscle, while others, like the Gregarine Sporozoon (Porospora gigantea), parasitic in the lobster, are clearly visible to the naked eye. Considered as a group, the Sporozoa will be found to possess in common certain very characteristic features. Thus food- vacuoles or contracting vacuoles are never present, the nutri- ment consisting of the juices of the host, and therefore always of a fluid nature, being absorbed by diffusion through the cuticle of the parasite's body ; while, where flagella or pseudopodia are present they exist essentially as organs of locomotion and not of nutrition. 1 From the Greek — many-celled or multicellular animals, as distinct from the Protozoa or unicellular animals. 16 THE PROTOZOA-THE DAWN OF LIFE The life-cycle typical of a Sporozoon may be divided into three main periods : the first chiefly the period of growth, during which the minute sporozoite, by the absorption of food from the host, is growing into what is termed the sporont ; the second is the period of reproduction or multiplication, which is accom- panied by conjugation, and the resulting formation of a large number of minute, often sickle-shaped germs, destined ultimately to spread the species ; while the third is the period of rest, dur- ing which the parasitic germs pass out from the old host to effect, if circumstances are favourable, the infection of a new host. Up to the present three modes of infection have been observed. The commonest, which may be called casual infection, takes place by the host accidentally swallowing the spores along with its food. The second, or inoculative, method is typical of the malarial parasites, and is effected through the agency of an inter- mediate host, such, for example, as the spot-winged anopheline mosquito. The third is a very rare type, that of hereditary infection, in which, as has been demonstrated in the silk-worm disease, caused by a sporozoon parasite called Glugea bombycis, the parasites penetrate the ovum of the host and produce spores there, which germinate and infect the new generation of the host. It would be impossible here to describe all the numerous species of Sporozoa, their appearance, habits, and life-history ; but on account of the far- reaching economic importance of their discovery, special mention must be made of those Sporozoa which are the cause of malarial fevers in man. To Laveran, a French medical man, we owe the discovery of the minute parasite in the red blood-corpuscles of man which is the cause of malaria, while Golgi demonstrated the coincidence of the stages of the inter- mittent fever with those of the life-cycle of the parasite in the human host which is the febrile cycle producing auto-infection (regularly recurring attacks of fever every one, two, of three days)1 of the patient. In the blood of the affected person the parasite passes through an asexual cycle, entering the red blood-corpuscle as an amoeboid organism, and therein attaining its full size and becoming filled with granules of black pigment, which are probably a decomposi- tion product of the red colouring matter (haemoglobin) of the 1 Termed, according to their periods, quotidian, tertian, and quartan fevers. if* J~ IBgjiftL THE PROTOZOA— THE DAWN OF LIFE 17 corpuscle. The nucleus of the parasite now divides repeatedly, after which the parasite divides into a number of spores and bursts the corpuscle, thus liberating the newly-formed spores and the black refuse-matter, which acts as a poison, producing chill, nausea, shivering, and fever in the patient. The liberated spores at once attach themselves, each to a fresh red corpuscle, and a repetition of the life-cycle ensues. After the disease has persisted for some time, certain of the full- grown parasites, instead of dividing up, pass, as it were, to a period of rest as either round or blunt crescent-shaped cells (termed " half-moons "). These are sexual cells, which only develop further when the blood containing them is withdrawn from the human host. This sexual cycle of the parasite was discovered by Major Ronald Ross to take place in the gut of the spot-winged mosquito (Anopheles), which he has also proved to be the trans- mitting agent of the parasite of malaria from man to man. When the Anopheline mosquito pierces the skin and sucks up the blood of a person suffering from malaria, it also sucks up a number of the resting sexual cells of the parasite, which at once begin to undergo a series of changes ; they become spherical, and the males produce flagella-like sperms, which break away and fuse with and fertilise the female spheres or egg-cells. The fertilised cell takes on an active worm-like form, and partially pushing itself through the wall of the mosquito's gut, feeds on the insect's blood. It soon swells up, divides internally again and again, and becomes enclosed in a firm, transparent cell or cyst. Finally, the cyst-wall is ruptured, and the needle-shaped spores escape and accumulate in the salivary glands of the mosquito, passing out of the mouth of the insect when it stabs a fresh human victim, who thus becomes infected. It is only in species of Anopheles that the parasite can undergo its sexual development and the process of the production of needle-shaped spores, for if the sexual cells are swallowed by an ordinary gnat or mosquito of the genus Culex they are digested by the insect and destroyed. These joint discoveries of the malaria parasite by Laveran, and of its sexual cycle in the gut of the transmitting agent, the spot-winged mosquito, by Major Ronald Ross, are of the greatest economic importance and far-reaching in effect. They rendered the cutting of the Panama Canal possible, and have c i8 THE PROTOZOA-THE DAWN OF LIFE converted many a fever-haunted district into a healthy, prosper- ous neighbourhood. Wherever the Anopheline mosquito has been stamped out, malaria has disappeared, and the health, vigour, and prosperity of the people increased. The life-history of the Anopheline mosquito, and the methods employed for its exter- mination, will be dealt with in a later chapter. The first Sporozoa to be closely observed and studied were the Gregarines, on account of their comparatively large size. They are to be found living in the internal organs of various insects, crustaceans, echinoderms, and worms, and the majority appear to exert no ill-effects upon their host, feeding upon the liquid food of the host as it exists in the intestine. In most species the body is rather elongated and flattened, in the species which infests the intestine of the so-called " meal-worm " l some- what resembling an Indian club in shape. When about to mul- tiply, the Gregarine contracts its body into a ball-shaped mass and becomes encysted. The nucleus and protoplasm within the cyst divide into numerous minute spores, which ultimately make their escape and grow into new Gregarines. We have seen that in the course of their life-history some of the Protozoa we have had under consideration pass in the process of multiplication through a spore stage characterised by the presence of a slender lasher or flagella. In a great number of Protozoa, however, we shall find that this flagellate condition of the cell is not a transitory one, but is the permanent condition of the adult organism. These forms are included in the class Flagellata 2 of the Protozoa, and comprise a very heterogeneous assemblage of organisms, very interesting and very puzzling to the student, for in this, more than in any other class, those formal distinctions which are commonly drawn between the animal and vegetable kingdoms disappear. Nevertheless the organisms com- prising this class possess in common certain characteristic traits of organisation, such as a single nucleus, one or more contractile vacuoles, and one or more flagella, which link them together. The vast amount of biological investigation which has been accom- plished has greatly widened the field of knowledge concerning 1 " Meal-worms " are the larvae of Tenebrio molitor, a small beetle all too common in granaries and flour mills. * The Flagellata as here described correspond to Butschli's group of the Masti- gophora. THE PROTOZOA-THE DAWN OF LIFE 19 these organisms, so that the old, and at times bitter, controversy as to whether such and such an order of the Flagellata should be placed among the unicellular plants, or among the Protozoa, is practically ended, Professor Haeckel's term Protista sufficiently describing their somewhat elusive character. Living urder varying conditions, the Flagellata exhibit vari- ous methods of nutrition. Some of the simplest forms live in liquids containing decaying organic matter, which they absorb through their surface ; 1 some engulf their food either amoeba- fashion, or into a food-vacuole, or by a definite mouth ; 2 while others, owing to the possession of coloured plastids or chromato- phores, which may be green, brown, or yellow, are able to manu- facture their own food-supply, after the manner of plants.3 Again, there are some species which, while possessing these chromato- phores at one stage of their life, lack them at another ; or, as in the case of Euglena, an organism common in fresh-water pools, to which, owing to its presence in vast numbers, it often imparts a greenish hue, the same individual may combine the characteristic- ally animal (holozoic) with the typically vegetable (holophytic) mode of nutrition, during the course of its life. The Euglena has a spindle-shaped body, with, at the blunt end, a depression or gullet, from the inner surface of which arises a long flagellum used for locomotion. The greater part of this microscopic organism is green in colour, due to the presence of the characteristic vegetable pigment, chlorophyll, and contains grains of a carbohydrate allied to starch, called paramylum. A bright red speck of pigment is also noticeable, which is thought probably to function as a light-perceiving organ, a sort of very rudimentary eye. The whole body is invested by a very thin skin, or cuticle, so that, though the Euglena does go through cer- tain worm-like movements of expansion and contraction, it is incapable of the free and ever-changing pseudopodial movements of amoeba. By means of its chlorophyll the Euglena is able to decompose the carbon dioxide of the air dissolved in the water of the pool in which it is living, and, by assimilating the carbon, 1 The Saprophytic method of feeding, which is also characteristic of certain fungi. 8 Holozoic. 8 Holophytic. It is by means of the microscopic green chlorophyll-bodies or plastids that the higher plants, under the influence of sunlight, manufacture their food-supply, drawing the carbon dioxide from the air. 20 THE PROTOZOA— THE DAWN OF LIFE set free the oxygen; while by absorbing the nitrogen and other elements in the form of mineral salts in solution in the water, it is thus nourished like a typical plant. At the same time the move- ments of the flagellum have been seen to create a current by which minute fragments of organic matter are propelled down the gullet into the soft internal protoplasm, where they are digested, so that a characteristically animal mode of nutrition also takes place. Among the Flagellata are to be found the bulk of those marine organisms which form a very large proportion of what is called the micro-plankton of the sea, and which may be said to consti- tute the primary food-supply of the higher forms of marine life. Therefore, investigations which will help to throw light upon their life-histories, and the conditions which are most favourable to their development and multiplication, will be of the greatest value in the consideration of many problems connected with fishery questions, and the successful rearing of marketable marine fishes in the early stages of their lives. The marine Dinoflagellata, which chiefly compose this floating plankton, are in many instances phosphorescent, lighting up the sea on a dark night with their wonderful glow so that every wave seems to break in a cascade of silvery light. They are char- acterised by the presence of two flagella : one is conspicuous and filiform, arising in a longitudinal groove extending its whole length and projecting beyond the animal ; the other also arises in the longitudinal groove, but is band-like in appearance and extends along a somewhat spiral transverse groove from which it never protrudes during life, but in its movements resembles a girdle of cilia — a deceptive appearance which led to these organisms formerly being called Cilioftagellata. The true character of this second flagellum was discovered by Klebs. Multiplication usually takes place by oblique division of the body into two dissimilar halves, each half undergoing a peculiar growth to reconstruct the missing portion. Most of the Dinoflagellata possess a complete membrane or cuirass of cellulose, the typical material of the cell-walls of plants, usually hard, with distinctive form and markings, and divided into plates. Cemtium, which is remarkable for the horn-like backward prolongations of its lower end, is an interesting and abundant genus in the sea. THE PROTOZOA-THE DAWN OF LIFE 21 Extremely abundant round our English coasts, and one of the chief causes of the phosphorescence of the sea on summer nights, Noctiluca miliaris is a familiar object to most students of the microscope. It belongs to the sub-class Cystoflagellata, and has a very wide geographical distribution. Noctiluca is quite a giant Flagellata, measuring about I mm. or more in diameter. In shape it is something like a peach, having a similar indentation or cleft on one side, from which arises the large, stout, striated flagellum. Two lip-like prominences may be seen in front of the base of this large flagellum ; one, transversely ridged, and slightly firmer than the other, is called the " tooth." At the junction of these two prominences is a second and minute flagellum, the cilium, and behind these is the oval mouth, through which food is absorbed. The phosphorescence glows with a bluish or greenish light when the little Noctiluca is disturbed, disappearing when the cause of irritation ceases. One large group of Flagellates inhabiting both fresh and salt waters, and called Collared Monads (Choanoflagellata) are of particular interest as probably representing a link or transition towards the sponges. The members of this group are charac- terised by a remarkable outgrowth of the protoplasm around the base of the single flagellum, giving to that organ the appear- ance of being surrounded by a transparent collar. This collar is contractile, and its movements appear to produce currents in the water which carry the organic particles of matter upon which the monad feeds down to the soft protoplasm between the base of the flagellum and that of the collar, when a food-vacuole is formed for their ingestion. The ordinary mode of multiplication among these Collared Monads is by longitudinal fission extending up through the funnel or collar. Belonging to this group is a colonial form called Protero- spongia, which secretes a gelatinous investment by which it be- comes attached to solid bodies. According to the observations of the late Mr. Saville Kent, the central members of the colony retract their collar, lose their flagellum, become amoeboid, finally undergoing brood-formation to produce minute zoospores, com- parable to the spermatozoa of a sponge. A colony of Proterospongia strongly recalls many of the characteristics of the true sponges, and indeed has been regarded as a transition towards them, for 22 THE PROTOZOA— THE DAWN OF LIFE the flagellate, nutritive cells of the sponges are provided with a collar similar to that of the Proterospongia and its allies, a form of cell which does not exist in any other group of the Metazoa. If we dip a collecting bottle into a pond or clear pool during the summer months, we may sometimes see, on holding the bottle up to the light, that its fluid contents is peopled by a number of very small, brightish green spheres, which roll about through the water in all directions, and which are specimens of the inter- esting Volvox globator. Each hollow sphere represents a colony composed of a single layer of individual cells, each contained in its own cell-wall or capsule, united together by protoplasmic bridges, the entire colony numbering from 1,500 to 22,000 cells. Botanists and zoologists in the past fought long for the sole pos- session of the Volvox, the former claiming it as belonging to the algae, the latter equally firmly claiming it as a flagellate colonial Infusorian ; for the Volvox has characteristics both vegetable and animal. Its possession of flagella, contractile vacuoles, and eye- spots attest to its animal properties, while the presence of chroma- tophores, starch granules, and proteid granules (pyrenoids) demon- strate its vegetable affinities. The life-history of this remarkable Protista has many inter- esting points, which seem to foreshadow the more complex life of the Metazoa or multicellular animals. In that half of the Volvox hemisphere which is posterior in swimming, some five to eight larger cells can be seen, which, as they grow, segment to form new colonies. At first each young colony is a plate, but as its cells multiply the plate bends up and finally forms a hollow sphere. When at last the parent sphere ruptures for the liberation of the young colonies, it sinks to the bottom of the pond and dies. This is the first example of a progressive change leading to the intro- duction of death as a constant phenomenon, as it occurs in the higher animals. The ordinary Protozoon, as we have seen, is a single cell, and forms no body. It divides, and in this way multiplies, but the products of division go asunder. In most Protozoa division takes place without any loss, there is no distinction between parent and offspring, there is continual self-recuperation, and as there is no body formed there is no death. Now in Volvox, the cell which THE PROTOZOA-THE DAWN OF LIFE 23 starts one of these colonies divides, and the products of division do not separate, but remain connected as a loose body of numer- ous cells. In this hollow spherical cluster of cells, some are set apart and eventually liberated as reproductive cells which will start new colonies ; while other cells surrender their power of fission so inherent in the Protist cell, becoming vegetative cells, the supply of food material due to their living activities going to the nourishment of the reproductive cells. It is these vegetative cells which perish when the ruptured sphere sinks down into the mud on the floor of the pond. Under certain conditions the reproductive cells may give rise to two distinct types of cell ; one small, yellow in colour, rod-like, and with two flagella ; the other an enlargement of the original cell, which has become enriched at the expense of neighbouring vegetative cells. Conjugation takes place between these dis- tinctive cells ; the flagellate forms escaping, swim about freely, and conjugate with the large motionless cells to form a zygote, which, after a period of rest, divides and gives rise to a new colony.1 Here, then, we find a differentiation of reproductive cells in an active flagellate male cell, a passive richly stored female cell, each functioning in the same manner as the active and passive male and female reproductive cells of the higher animals, and by their union or conjugation producing a similar result. Of recent years the Haemoflagellata or Trypanosomes have attracted a great deal of attention, on account of the appal- ling destruction of human life from diseases set up by the pre- sence of these organisms in the blood system. Like the malarial parasite already described, these Haemoflagellates are transmitted to man through the agency of certain blood-sucking insects, but the disease set up, on account of its peculiarly fatal character, is far more appalling than malaria. Sleeping sickness, or human trypanosomiasis, as this terrible disease is called, appears to have existed among the natives of the West African coast from the remote past, and to occur, though rarely as a very serious scourge, throughout tropical West Africa. But from there it has crept 1 When two individual cells come together and become completely fused, the process is known as Conjugation, the body formed by the union of the cells being known as a Zygote. 24 THE PROTOZOA— THE DAWN OF LIFE up the newly opened trade-roads of the Congo basin and spread through Uganda into British East Africa. " In the west of Uganda, since the disease was first noticed, in 1901, more than 200,000 people have died of it. Out of 300,000 living on the shores and islands of the great Lake Victoria Nyanza less than 100,000 remain, the rest having perished from sleeping sickness or human trypanosomiasis. In every case the disease has been transmitted from one victim to another by certain species of true flies." l The organism which by its presence and multiplication in the blood is the cause of this terrible disease is the Trypanosoma gam- biense. Other Trypanosomes are the cause of various more or less fatal diseases in domestic animals, such as surra, a disease which affects horses in India; nagana or tsetse-fly disease among cattle and horses in South Africa; dourine, which attacks horses and mules in Northern Africa; and the mat de caderas of horses in South America. Members of all the chief classes of vertebrates, with the excep- tion of the Cyclostomes 2 (which may prove on further investiga- tion not to be immune), harbour these parasites, mammals, birds, and fishes furnishing the greater number of hosts, though neither amphibians nor reptiles are exempt. In the consideration of the occurrence of these Trypanosomes, it is necessary to draw a careful distinction between true or natural hosts and strange or casual hosts, for in the case of the natural host a condition of mutual toleration has been reached, owing to the long-existing association between parasite and host. The entry of a Trypanosome into a host which has never been previously liable to its invasion, however, usually produces serious, if not fatal, results, owing to the casual host being unaccustomed and unadapted to its presence. Recent research all points to the probability that every patho- genic or lethal Trypanosome has some tolerant indigenous wild animal host which serves as a latent source of supply from which strange animals entering the district may become affected ; the c* ?ron} rmy lecTture on " Industrial Entomology : The Economic Importance of a Study of Insect Life," delivered before the Royal Society of Arts, May aoth, 1908, and published in the Society's Journal, Vol. Ivi., p. 688. « The Cyclostomata (literally " round mouths ") are a class of vertebrates separ- ated from the true fishes by certain fundamental divergences. The hag-fish and lamprey are types of the two orders into which the Cyclostomes are divided THE PROTOZOA-THE DAWN OF LIFE 25 parasite is almost invariably transmitted from the natural passive hosts to the newly introduced animal by certain species of blood-sucking invertebrates (insects and leeches). It was in this way that the recently introduced cattle and horses of the settlers in South Africa were attacked by nagana or tsetse-fly disease, as they passed through belts of country inhabited by herds of big game and the blood-sucking insects which prey upon them ; for it has been shown that the nagana parasite (Trypanosoma brucii] is almost certainly to be found in the blood of the native buffalo, the gnu, and the koodoo. Nagana is transmitted from one animal to another in South-east Africa by the blood-sucking tsetse-fly, Glossina morsitans ; while Trypanosoma gambiense, the cause of sleeping sickness, is conveyed from man to man by another tsetse-fly, the Glossina palpates. Trypanosomes possess one or two flagella, both originating close together at or near the anterior end of the body, one being free and directed forwards, while the other turns back and is attached by means of an undulating membrane to the side of the body for the greater part of its length, its free end being directed posteriorly. Should only one flagellum be present, it appears to be invariably attached in this manner. Reproduction appears most frequently to take place by binary longitudinal fission, though multiple division or segmentation also occurs. There is need for much further investigation of the life-cycle of these para- sites, as comparatively little is known in most cases about the true alternate host (transmitting agent), in which/ definite phases of the life-cycle, including probably sexual conjugation, take place. Thanks, however, to the researches of Minchin, Schaudinn, Laveran, Bruce, Plimmer, Woodcock, and other well-known protozoologists, great additions have been made to our knowledge of the Haemoflagellates and of the hosts, passive and casual, which they inhabit. The Infusoria form a complex group of the Protozoa, and were originally grouped under this title from their frequently inhabiting fluids containing an infusion of organic matter. Their food consists chiefly of microscopic forms of animal and vegetable life even more minute than themselves, and of particles of organic matter that may be floating in the water they inhabit; many thrive in water which contains putrefying matter, feasting upon 26 THE PROTOZOA— THE DAWN OF LIFE the swarming bacteria present in such media. While the majority are inhabitants of fresh water, a considerable number are marine ; others are entozoic in their habits, living in the intestines, blad- der, and blood of higher animals. Although these are sometimes spoken of as ''Parasitic Infusoria," it is doubtful if the term is accurately applied, for, so far from gaining their living at the expense of their host, they do not appear to feed upon anything except such substances as would otherwise be ejected from the body ; therefore it would seem highly probable that their presence is really beneficial to their host. They are grouped into two sub-classes : (i) the Ciliata, the members of which are either free or fixed forms, with cilia disposed in tracts or bands upon the body for purposes of locomotion and the capture of food; and (2) the Acinetaria, which are fixed sedentary forms possessing suckers or tentacles, and bearing cilia only during their active youth. Reproduction in the simplest forms takes place by transverse fission, while in the higher forms it is accomplished by longitudinal fission and by encystment and spore-formation. Encystment may also be purely a resting stage, from which only one individual escapes. Such resting cysts are capable of resisting the effects of dry air for a consider- able time, and in this way periods of long drought are tided over, the cyst remaining dormant in the dried mud at the bottom of the pond or pool, until the rains once more restore the supply of water. In the same way such resting cysts may be carried away by the wind from their dried-up homes and transported for considerable distances, always with the possibility of falling into other waters. We can very readily become familiar with the appearance of some of the Ciliata, by examining under the microscope a drop of water taken from any stagnant pool. This will be almost cer- tain to contain a number of the so-called " Slipper-animalcules" (Paramcecium) , moving about in the most active manner. Their bodies are long, narrowish, bluntly-pointed at one end, and more sharply at the other, so that the general outline of the body some- what resembles the sole of a slipper. They are flat, and with a little attention we shall be able to make out on the ventral side of the body a large oblique depression, the buccal groove, lead- ing into a short gullet which in turn ends in the soft internal protoplasm. The body is covered by small, delicate lashers, or THE PROTOZOA— THE DAWN OF LIFE 27 cilia, arranged in longitudinal rows, and these cilia are kept in an incessant to-and-fro vibration by means of which the Infusorians move about and obtain their food. The cilia in the neighbourhood of the buccal groove produce currents in the water, in which minute particles of organic matter are caught and carried down the gullet into the soft protoplasm, where they become surrounded by a globule of water or " f ood-vacuole " ; they circulate through the protoplasm, and the soluble parts become gradually digested and assimilated ; the insoluble and effete matters are ejected at a definite anal spot. Several of these " food-vacuoles " may be seen in the body of the Slipper-animalcule, and also two large contractile vacuoles, one at each end of the body, which keep up a regular pulsation of expansion and contraction. There are two nuclei, one a com- paratively large ovoid body, called the meganucleus ; the other, closely applied to the meganucleus, is a small rounded body, and is called the micronucleus. Multiplication in the Slipper-animalcule takes place by trans- verse fission, the nuclei dividing prior to the division of the body. This process of multiplication, however, cannot be continued in- definitely, and there comes a time when the Paramcecium must conjugate with another of its species or perish. In this process, two Paramcecia become applied by their ventral surfaces, but do not actually fuse together ; then their meganuclei break up and disappear, while an interchange of the micronuclei of the con- jugating individuals takes place, with the result that each develops a new mega- and micro-nucleus, partly from the substance of its own micronucleus, partly from that of its partner. It will be observed that in Paramcecium we have something more complex than a mere sexual cell, for of its whole body it is only a very small part, the micronucleus, which functionally conjugates; we therefore find an advance in the complexity of the individual and towards the differentiation of sex, for the micronucleus is only to be compared with the nucleus of the sexual cells of the, Metazoa. Gradually, step by step, we may trace the evolution of the sexes. In the free-swimming Ciliata, such as the Paramcecium we have just been examining, there appears to be no distinction of sex into definite male and female form, all the individuals in which conjugation is taking place being of exactly 28 THE PROTOZOA— THE DAWN OF LIFE the same size and structure ; here the outstanding feature is the interchange of the micronuclei, which exerts a revivifying or fecun- dating effect upon the conjugating individuals. In the case of a sedentary 'Infusorian called Spirochona, which is to be found attached to the gills of Gammarus (one of the Amphipod crus- tacea), no external features of differentiation have been observed, and possibly do not exist between individuals capable of con- jugating with each other. Two apparently identical individuals will bend towards each other and join by their oral surfaces, one of the individuals ultimately separating from its basal support and becoming partially or wholly absorbed by the other one, thus ceasing to exist as an individual. In the graceful Vorticella or Bell-animalcule and some of its allies, the difference between individuals that can conjugate is well marked prior to the process taking place. The Bell-animal- cule is a very common inhabitant of ponds, attaching itself to the leaves and stems of the submerged vegetation by a slender spirally contractile stem. Its body is slightly oblong, shaped like a bell or wine-glass, the slender stem of which forms the con- tractile stalk. The rim of the bell encloses an elevated disc of protoplasm, between which and the rim on one side is the open- ing of the mouth leading to the gullet. Cilia run in a spiral band round the rim of the bell, round the edge of the disc, and down into the gullet, producing active currents in the water by their motion, and so capturing and carrying down into the gullet par- ticles of organic matter upon which the Infusorian feeds. Mul- tiplication often takes place by division of the bell-body longi- tudinally, one of the halves being set free furnished with an addi- tional posterior circlet of cilia by means of which it swims actively about for a time, eventually becoming attached to some base by a spirally contracting stalk. After division, the remaining un- detached individual may rapidly divide into eight small units — male cells — which, becoming detached, swim away by means of their cilia, but do not ultimately settle down as the normal seden- tary stalked form. The sedentary stalked form, which may be called the female, is not capable of conjugating with another individual of the same kind, but only with one of the small free- swimming forms (males) that are periodically produced. Nor can these free-swimming forms conjugate with each other, but THE PROTOZOA-THE DAWN OF LIFE 29 only with the sedentary stalked form ; so that in Vorticella we have the sexes distinctly differentiated in form and habit prior to conjugation. In the foregoing outline sketch of the Protozoa, attention has been drawn, so far as space and the avoidance of very technical questions would permit, to the most interesting points concern- ing these remarkable organisms. In the Amoeba we have had an example of a very primitive form of life, of an organism complete in itself, though of comparatively simple structure, capable of carrying on all the processes of life — the capture and assimilation of food, movement, growth, multiplication — without the develop- ment of any special organs for carrying out these vital functions, excepting, of course, the part which the nucleus plays in its mul- tiplication by binary fission. And we have seen the comparative immortality of these organisms. In the fusing or conjugation of similar cells, identical in appearance, we may trace the dawn of sex and the gradual differentiation into the typical active male and sedentary female cells (sperm and ovum) ; while in the colonial form of Volvox we caught a glimpse of the introduction of death as a constant phenomenon, through the modification to special ends of certain cells. Of the economic importance of the study of certain groups of the Protozoa, the malarial parasite and the Trypanosome of sleeping sickness are sufficiently impressive examples. Indeed, the story of the discovery of the malarial parasite, of its sexual cycle within the gut of the spot-winged mos- quito, and the means that discovery has placed in our hands of successfully combating one of the most dreaded tropical diseases, and of thereby bringing health and prosperity to wide regions of country, should eloquently convince even the most hardened sceptic of the inestimable value of biological research. CHAPTER II THE SPONGES FOR a long time the Sponges, or Porifera, were a great puzzle to naturalists, and were bandied about from the animal to the vegetable kingdom and back again. Thus we find Aristotle con- cluding that they were lowly forms of animal life bearing a certain resemblance to plants ; while old Gerard, writing in the sixteenth century in his famous " Herbal," would have us believe them formed of " a certain matter wrought together of the foame or froth of the sea." So late as the middle of the eighteenth century it was suggested that Sponges were really formed by certain marine worms as shelters from their foes, the spongy mass being " merely a nidus or secretion." This was contradicted by Ellis (1765), who, in the course of his examination of a living Sponge, " plainly perceived the small tubes inspire and expire," and concluded that the " openings of the branched tubes are the mouths by which it receives its nourishment and discharges its excrements." It was not until after the fundamental discoveries of Robert Grant, in 1825, that the right of the Sponges to a place in the animal kingdom was universally admitted. Even then they were at first relegated to the Protozoa, and from the discovery of the resemblance of their collared-cells to the flagellate Infusoria, were for some time regarded as mere aggregates of those Pro- tozoa. Since then, however, the very precise and thorough in- vestigations which have been carried out concerning the structure and embryology of the Sponges has left little doubt as to their real character as primitive Metazoa or multicellular animals. Marking, as it does, an epoch in the scientific investigation of the Sponges, Grant's own account of his earliest observations is of the greatest interest : — " In the month of November last," he writes, " I therefore put a small branch of the Spongia coalita, with some sea-water, into a watch-glass, under the microscope 3 THE SPONGES 31 and, on reflecting the light of a candle up through the fluid, I soon perceived that there was some intestine motion in the opaque particles floating through the water. On moving the watch- glass, so as to bring one of the apertures on the side of the Sponge fully into view, I beheld, for the first time, the splendid spec- tacle of this living fountain vomiting forth from a circular cavity an impetuous torrent of liquid matter, and hurling along, in rapid succession, opaque masses which it strewed everywhere around. The beauty and novelty of such a scene in the animal kingdom long arrested my attention ; but, after twenty-five minutes of constant observation, I was obliged to withdraw my eye from fatigue, without having seen the torrent for one instant change its direction, or diminish in the slightest degree the rapidity of its course. I continued to watch the same orifice, at short intervals, for five hours, sometimes observing it for a quarter of an hour at a time, but still the stream rolled on with a con- stant and equal velocity. About the end of this time, however, I observed the current become perceptibly languid ; the opaque flocculi of faeculent matter, which were thrown out with so much impetuosity at the beginning, were now propelled to a shorter distance from the orifice, and fell to the bottom of the fluid within the sphere of vision, and in one hour more the current had entirely ceased." Although Grant suspected that these currents were due to the movement of cilia, he failed to detect them, and they were subsequently observed by other workers. That we may gain some idea of the main characteristics of the Sponges, we will first examine a small, simple Sponge which is to be found attached to the rocks in deep pools on the shore at low-tide mark. This is the little Sycon Sponge (Sycon gelatinosum), which grows as a tuft of short, branching cylinders, about 2 or 3 inches long, all connected together at the base where the Sponge is attached to the rock. In its simplest form the body of a Sponge is shaped like a cylinder or vase, attached to a base at its closed end, and with the upper, free end open ; so that Sycon may be likened to several of these single cylinders joined together at their base. If a portion of the Sycon Sponge be examined under the microscope, it will be seen that there are groups of minute open- ings— the inhalent pores — pretty evenly distributed over the outer surface, and that the free end of each branch or cylinder has a 32 THE SPONGES slightly larger terminal opening — called the osculum — sur- rounded by what looks like a delicate fringe. If our specimen has been recently collected, and is therefore still in a vigorous con- dition, we shall be able to witness the same interesting sight as described by Professor Grant, particularly if we add a very small pinch of carmine powder to the sea-water in the vessel contain- ing the Sponge. We shall then see how the very fine particles of the carmine powder appear to be drawn towards the sides of the branches, and to pass into the interior of the Sponge through the minute inhalent pores, only to be ejected by an outward current issuing from each large terminal opening, demonstrating that there is some motive power within the Sponge that produces an indraw- ing current of water through the minute inhalent pores (ostia) and an exhalent expelling current from the terminal openings (oscula). How these incoming and outgoing currents are produced we can only discover by the aid of the dissecting knife and micro- scope. If, therefore, we cut longitudinally through one of the branches of the Sycon Sponge, using a sharp dissecting knife so as to cleave it cleanly from top to base, we shall see that the terminal opening (osculum) leads into a central passage called " the exhalent canal," which runs the entire length of the cylinder or branch, and joins the passages belonging to the other branches, where they unite at the base, so that there is a regular system of communication throughout the Sponge. Under the microscope we shall be able to see that the walls of these cavities are per- forated by numerous fine apertures, called " the radial" or " fla- gellate canals." We shall also be able to make out that these flagellate canals run side by side with the incurrent canals, and actually communicate with them at certain points by small openings. We shall now see that the incurrent canals end blindly at their inner extremities, and do not, as we might have supposed, com- municate directly with the large exhalent canal ; on the other hand, the flagellate or radial canals, while communicating with this central cavity, have no opening at the exterior, their outer ends terminating a little below the outer surface of the branch. There- fore the inflowing current of water, carrying with it particles of organic matter and small living organisms, enters through tl THE SPONGES 33 incurrent canal, passes through the openings in the walls com- municating with the flagellate canal, along which it travels to be expelled into, and finally discharged from, the large exhalent canal ; and in this way a constant circulation of water is main- tained throughout the Sponge. The body of the Sponge is composed of three layers of cells, of which the outer layer is called the ectoderm, the inner layer the endoderm, and the middle layer the mesoderm. The outer surface of the Sponge and the walls of the incurrent canals are covered by a single layer of flattened, scale-like cells composing the ecto- derm layer, while the endoderm lining the exhalent or para- gastric cavity is composed of cells very similar in shape. Not so, however, the cells lining the radial or flagellate canals ; their structure is quite different, and will require a higher magnification to be clearly seen. They consist of a close continuous layer of column-shaped cells, each terminating in a single long, slender lasher (flagellum), surrounded at its base by a delicate, collar-like, transparent upgrowth. These specialised cells, with which the radial canals are lined, are of very great interest, because they are only to be found in the Sponges, and not in the tissues of any other animal belonging to the Metazoa. Each of these specialised cells, in addition to the collar-like upward expansion and terminal flagellum, has a nucleus and one or more vacuoles, so that it really very closely resembles a miniature collared-monad (Choano flagellate) of the Infusoria. It is by the constant movement of the flagella of these cells that the water is drawn in from the incurrent canals, and apparently so similar are the movements of the collar and lashers to those of the collared-monads that particles of food are captured by those cells in just the same way ; while the effete and insoluble matters are swept onwards by the lashers and discharged through the exhalent canal. In the light of recent research, the evidence seems to point to the Sponges having developed from a collared-monad pro- genitor, through some such ancestral type as the colonial In- fusorian Proterospongia, described by the late Mr. Saville Kent. The middle layer, or mesoderm, consists chiefly of a clear, jelly- like, greyish mass in which lie the skeleton or spicule and spongin- forming cells, and also certain curious cells called, from their D 34 THE SPONGES amoeba-like movements, ''wandering cells" (Archcvocytes), and " capable of first performing elementary functions of digestion, dis- tribution, and probably excretion, and later of becoming germ cells." * The reproductive cells, the ova and spermatozoa, are also found in the mesoderm, the ova commencing their existence as cells closely resembling the amoeboid ones, and chiefly distinguished by their large bladder-like nucleus and its large round nucleolus ; while the oval-headed slender-tailed spermatozoa occur in globu- lar clusters or sperm-balls, each the product of a single cell. Both ova and spermatozoa may be developed in the same Sponge, though rarely at the same time, so that probably in most cases the ova are fertilised by spermatozoa from another Sponge. Reproduction in the Sponges is effected by sexual or asexual methods. In the latter, multiplication takes place by the pro- duction of internal buds in the shape of groups of cells called gemmules, which eventually become detached from the parent Sponge and develop into new individuals. In the sexual process the ovum, after impregnation, usually becomes enclosed by certain neighbouring cells, which form a brood-capsule around it, and in this enclosure, and still within the parent Sponge, passes through the earlier stages of its development. Finally it escapes as a ciliated, somewhat oval-shaped larva, and by means of its cilia swims about and for a short time leads an active existence, but eventually becomes fixed to a base and develops into the sedentary adult stage. The majority of the Sponges possess a skeleton or supporting framework, composed of material secreted by the Sponge itself, and in some instances supplemented by an admixture of sand, the tests or shells of foraminifera and radiolaria, or the spicules of other Sponges. The skeleton may be composed of calcareous 2 or siliceous 8 spicules, or of an organic substance called spongin* which occurs either as a cementing mass which glues the spicules together into a more or less definite system of skeletal fibres, or as an elastic felt-like tissue destitute of spicules, as, for example, in the common Bath Sponge, the skeleton of which is composed entirely of a soft, perforated mass of spongin. 1 Professor Minchin in Lankester's "Treatise on Zoology." 2 Calcium carbonate, lime. • Silica, silex, flint. * Spongin, a substance allied to silk in its chemical composition. THE SPONGES 35 The beautiful Venus' s Flower Basket (Euplectella) and the strange-looking Glass Rope (Hyalonema) Sponges offer a contrast in structure to the Bath Sponge, their skeletons consisting throughout of siliceous spicules bound together by a siliceous cement. In the Slime Sponges (Myxospongida) l no skeleton is formed. The minute spicules of lime or silica vary greatly in shape in different species, forming most beautiful objects for the micro- scope, and as they are of very great importance in the study and classification of the Sponges, a systematic and highly technical nomenclature of the principal types of form has been established.2 The Sponges are grouped under three divisions, each founded on the character and composition of the skeleton. The three classes are : (i) the Calcarea, all of which are characterised by a skeleton in which the material is calcareous ; (2) the Hex- actinellida,3 characterised by the possession of six-rayed or hexactinal spicules ; 4 and (3) the Demospongiae,5 in which the skeleton may be composed of siliceous spicules of various types (never triaxon), or of spongin occurring either alone or in com- bination with siliceous spicules or foreign bodies, or the skeleton may be altogether absent, as in the Slime Sponges. Although this third division comprises such a vast assemblage of different forms, yet the most divergent are linked together by a complete and gradual series of intermediate forms. The Sponges included in the class Calcarea mostly frequent shallow water, and grow most luxuriantly in shady, sheltered alities. They form a comparatively small group (some 200 recent species), all characterised by a skeleton composed of spicules of carbonate of lime, the spicules being three-rayed, four-rayed, and needle-shaped. Examples of Sponges belonging to this class are the simple vase-shaped Ascon, Leucosolenia, and the Sycon already described. The Hexactinellida include many very beautiful and inter- esting Sponges, nearly all inhabiting great ocean depths, ranging 1 Muxa, slime. 8 For a systematic description of the Spicules, see Vol. I. Cambridge Nat. Hist. ; and Part II. of Lankester's " Treatise on Zoology." * Hex, six; aktis, ray. * Known as a triaxon type of spicule : tri, three ; axon, axis. * Demes, multitude. 36 THE SPONGES from 90 to 3,000 fathoms, and characterised by having the skele- ton built up of siliceous spicules, each typically possessing three axes and six rays, or of spicules derived from such a type. To this class belongs the beautiful Venus' s Flower Basket (Euplectella aspergillum), which forms a most wonderful lattice-like skeleton, shaped like a graceful cornucopia. It is obtained from a depth of some 90 fathoms off Cebu in the Philippine Islands, while another and much larger form (Euplectella imperialis) comes from Japan. Another interesting example, the Glass Rope Sponge (Hyalonema sieboldii), is obtained by the Japanese deep-sea shark-fishers, by means of hooks attached to their deep-sea lines. The " glass rope," or twisted strand, which is such a striking feature of this Sponge, is really a root-tuft composed of immensely long spicules, which terminate in toothed grapple-like discs, and securely anchor the Sponge in the mud. When these root-strands were first brought to Europe, without the body of the Sponge attached, they were thought to be artificial productions. The body of the Glass Rope Sponge is somewhat like a closed cup in shape, the walls of loose texture and comparatively soft to the touch, and with large and small circular openings, which connect with the interior. The beautiful Lace Sponge (Semperella schultzii) also belongs to this class, and has a straight or curved cylindrical and somewhat conical body, the upper surface of which shows a delicate, fine lace-like network, with bands and patches of a coarser pattern. The class Demospongise includes all sponges other than the Calcareous and Hexactinellida. Familiar examples are the huge Neptune's Cup Sponge (Poterion patera), which comes from the East Indies and is one of the largest of the Sponges ; the Sea- Kidney Sponge (Chondrosia reniformis) ; the curious Boring Sponge (Cliona), which excavates extensive galleries in oyster shells, so that a shell may often appear to be covered with small round holes ; the Horny or Bath Sponges ; the Slime Sponges ; and the Freshwater Sponges. The Encrusting Sponges are some- times a great pest on the oyster grounds, as they grow over the shells of the oysters and starve the inhabitants by capturing the food particles floating in the water, which would otherwise reach the unfortunate molluscs. To get over this trouble, in some places the oysters are grown on frames, which from time to time are drawn above the surface of the sea and left exposed during a THE SPONGES 37 downpour of rain. The fresh rain-water kills the Sponges, but the oysters close their shells and so escape injury. Many of the Encrusting Sponges cover the rocks in deep tidal pools and are very beautiful in their rich colouring of red, yellow , orange, etc. The cup-shaped fine Turkey Sponge (Spongia offi- cinalis), the cake-shaped Common Horse or Bath Sponge (Hippo- spongia equina), and the flat, disc-shaped Hard Sponge (Spongia zimoced) are the three typical commercial species ; the Levant Lappet, which forms great thin flaps like an elephant's ear, is a variety of the Turkey Sponge. All the commercial Sponges live in sub-tropical and tropical seas, at depths of 2 to 100 fathoms, the world's supply being drawn almost entirely from the eastern half of the Mediterranean, and from the West Indies. They are collected by divers, who descend to the floor of the sea and detach them from the rocks ; or are hooked up by means of a kind of long harpoon, or by dredges in the deeper waters. These commercial Sponges are also cultivated from cuttings, the time taken by a small cutting about a cubic inch in size to grow into a marketable Sponge being about seven years. Sponges appear to be very distasteful to other animals, and to be eaten by very few. Consequently it is not altogether sur- prising to find an intimate association or symbiosis existing between them and other animals, more particularly crabs. Many of the spider crabs cover themselves with pieces of Sponge, which they attach to their body and legs, where the Sponge grows quite healthily. Dromia, the sleeping crab, invariably holds a living Sponge upon its back, certain of its legs having become modified and adapted for the purpose, the Sponge growing and moulding itself to the shape of the body, so that the crab, when at rest, is completely concealed. Another Sponge (Sttberites) very commonly grows upon the whelk-shell inhabited by a hermit crab, and soon absorbs the shell, so that the hermit crab inhabits a cavity in the Sponge ; while within many Sponges minute algae live in constant partnership. The Sponges seem to have made their appearance very early in the history of animal life, as one would expect from their com- paratively lowly organisation ; their fossil remains have been found in the Cambrian strata and in the strata of each succeeding 38 THE SPONGES geological epoch, down to the present day. Chiefly marine and all aquatic in habit, they have a world- wide distribution, the marine forms inhabiting the seas at all depths, from between tide marks to abysmal depths. Sponges are among the lowest of the multicellular forms of life, occupying a more isolated position than any other group of animals, for they are destitute of multi- cellular relations, though linked by their collared-cells to the colonial Infusorian Protozoa, from which their past history and gradual evolution seem likely to be eventually completely estab- lished. But, to quote such a high authority upon the subject as Professor Minchin, " The most conflicting opinions have been, and still are, held upon this point." On account of their isolated posi- tion, the Sponges or Porifera are placed in, and are the sole repre- sentatives of the Phylum or Sub-Kingdom Parazoa. CHAPTER III THE CCELENTERATES OR HYDROIDS: JELLY-FISH. ANEMONES AND CORALS WE have seen that the sponge in its simplest form is a cylinder, closed at one end where it is attached to a base, open at its free end, with its walls perforated by minute openings or pores, and composed of three layers of cell-structure — ectoderm, mesoderm, and endoderm — this last layer consisting of collared flagellate cells. Imagine a transformation to take place in which the minute open- ings in the wall of the cylinder have disappeared, so that the internal cavity now only communicates with the exterior by a single terminal opening ; that the inner layer of tissue or meso- derm has become converted into a very thin structureless layer containing no cells, while the endoderm has lost its collared cells ; and that a circle of waving arms or tentacles, formed of the same layers as the body-wall, have grown out round the terminal open- ing which now serves as the sole aperture for the reception of food as well as for the discharge of effete matters. Such a trans- formation completed, the resulting organism would serve as an example of the general structure of the group of animals we are now going to consider, while the organism itself would be a typical Polyp or Hydroid. The animals grouped together and forming this great division of the animal kingdom are characterised by the possession of a single internal cavity (or ccelom), this body-cavity, which is the primitive gut or intestine (enter on), only opening to the exterior by a single aperture. It is to signify the possession of this im- portant anatomical feature, absent in all the organisms we have so far examined, that the name Coelenterata 1 was given to this division in which are to be found the Hydra of our ponds, the Sertularian Polyps of the sea, the large Jelly-fish, the graceful 1 Greek — koilost a hollow ; enteron, bowel. 39 40 HYDROIDS AND JELLY-FISH Comb-bearing Jellies, the lovely Sea Anemones, Alcyonarians, and wonderful stony Corals. The Coelenterata are divided into four classes : (i) the Hydrozoa (the Sertularians or Sea-firs and the Pond Hydra) ; (2) the Scyphozoa (Jelly-fish) ; (3) the Ctenophora (Comb-bearing Jellies) ; and (4) the Anthoza (Sea Anemones and Corals). If on a fine summer afternoon we should visit a pond, the surface of which is partly covered by a green mantle of duck- weed, we should probably have little difficulty in obtaining several specimens of the interesting little Hydra or Fresh-water Polyp. A glass jar should be partly filled with clear pond- water, and some of the duck-weed carefully transferred to it. Then if we closely examine the slender stems of the weed as they hang down in the water, we shall see that attached to some of them are minute green objects about J inch in length — specimens of the common Green Hydra (Hydra viridis). If now we examine one of these little objects through a pocket magnifying glass, we shall see that it has a very slender cylindrical body, and that the free end is crowned by a circlet of waving feelers or tentacles, from six to ten in number ; while the base of the body is slightly expanded, disk- shaped, and acts as a sucker, grasping the stem of the duck-weed for support. On continuing to watch the little Hydra, we shall see that the body slowly elongates and sways from side to side, while the tentacles expand and contract and wave about in all directions. Along with the Hydra, we have probably captured a number of very minute crustaceans, the so-called "water-fleas," which are now swimming about with their peculiar jerky motion. One of these, in its progress through the water, touches against a waving tentacle of the Hydra and is held fast. The other tentacles bend towards it, and the little creature soon disappears down the mouth of the Hydra. Now, each tentacle of the Hydra is provided with most remarkable stinging cells, called " thread- cells," or nematocysts, for the capture of prey. Each of these peculiar cells, which are embedded in the outer skin, or ectoderm, contains a cyst with a very fine hollow thread coiled up inside ; while a pointed process projecting from the outer surface of the cell acts as a trigger, so sensitive that at the least touch it causes the coiled stinging thread to be discharged and to sting and Fresh-water Hydra with tentacles partially contracted Polyparies of Hydrozoa HYDROIDS AND JELLY-FISH 41 paralyse the microscopic creature that has brushed against the tentacle. These remarkable thread-cells, or nematocysts, are very characteristic organs of the Ccelenterates. It is quite possible by keeping the jar of water in a cool place near a window to watch the habits of the Hydra at leisure, for the little creature is very hardy, and so long as the weed flourishes, oxygenating the water and keeping it pure, all will be well. It will then be seen that the Hydra does not remain permanently attached to one spot, but that it sometimes goes for a walk, its mode of progress being a series of slow and cautious somersaults. When about to change its quarters the Hydra elongates its body, and, bending over, brings its crown of tentacles into contact with the base to which it is attached. Having fixed itself by its ten- tacles, the Hydra then detaches the sucker end of its body, and literally, for a second or two, stands upon its head. Then the body is slowly moved over until the sucker is brought into contact with the base, and the whole process is again repeated. Some- times, however, the Hydra will get as close to the surface of the water as it possibly can, and then, releasing its hold, turn the base of its body upwards and swim along just beneath the surface, head downwards, and by waving movements of its tentacles. During the summer the Hydra multiplies by a curious budding process. A little roundish swelling makes its appearance on the side of the slender body of the Hydra, and soon becomes furnished at its free end with a crown of tentacles, so that it closely resembles its parent in appearance. A second may form, and the parent stem and buds thus constitute a miniature colony. But the buds do not remain permanently attached ; after a little while they drop off, and, developing a detachable base, become free individuals cap- able of capturing food and fending for themselves. In the autumn ova and sperms are developed by the Hydra, and after fertilisation the eggs, which form little wart-like swellings on the surface of the body, escape into the surrounding water ; from them, in due course, another generation develops. The Hydra has a most remarkable power of reparation of injuries, and the reproduction of individuals out of portions of itself. Thus, if a Hydra should lose two or three tentacles, new ones are quickly grown to replace them ; while should the animal itself be cut into several pieces, provided each contains a portion 42 HYDROIDS AND JELLY-FISH of the two cell layers, each fragment is capable of developing into a complete animal ; so that really the little creature is very appro- priately named Hydra, after the monster of the old Greek fable. In general structure the Hydra is a simple sac, the walls of which are composed of an outer or ectoderm layer one or more cells deep, and an inner or endoderm layer one cell deep, the two layers being separated by a thin, structureless middle lamella or mesoderm. The inner layer or endoderm lines the whole inner cavity of the sac-like body and the interior of the tentacles, and is concerned in the digestion of food, which is taken in at the single opening or mouth in the centre of the circle of tentacles, the insoluble portions being ejected later through the same aperture. Such is fundamentally the structure of all the Hydroida. We have seen that the Hydra forms buds upon its sides, and that these ultimately drop off. Now, supposing that the Hydra were to grow much larger, form a horny protective cover- ing to its outer surface, produce numerous buds which, instead of separating, elongated and in turn gave rise to other buds, all remaining connected together, each bud crowned with its waving circle of tentacles — a plant -like colony would result. In fact, we should have a typical Hydroid colony, such as may be seen grow- ing in the deep rock-pools, and whose graceful, feathery, horny textured branches are familiar treasures of the seashore, under the name of Zoophytes l or Sea-firs. Such a typical Hydroid colony is formed by the pretty little Obelia, to be found growing in branching filaments upon the submerged wooden piles of piers and breakwaters, and also upon the fronds of the wrack seaweeds. Under the microscope part of a living colony presents a very striking and beautiful appearance, every branch bearing numerous tentacle-crowned polyps, all vitally connected with each other by the common living tissue, which looks like a central pith inside the stem. Both stem and branches are encased by a horny outer cover, and each little polyp is enclosed in a glassy cup-like receptacle or hydrotheca. When the polyps are fully expanded, they give to the colony the appearance of some exquisite miniature tree that is covered with tinted, slender- petalled, ray-like flowers. 1 Greek, zoon, animal ; phyton, plant : the name originally given to these com- pound Hydrozoa on account of their plant -like habit and appearance. HYDROIDS AND JELLY-FISH 43 Less numerous than the flower-like polyps, but dotted here and there about the colony, are long cylindrical bodies (blastostyles),1 each enclosed in a transparent urn or vase-shaped case (gonotheca),2 and bearing numerous roundish upshoots, which vary considerably in shape according to their stage of development, and called " medusa buds." Now, the tentacle-crowned polyps are the feeding or nutri- tive polyps (nutritive zooids), whose duty it is to obtain and digest food for the general growth and upkeep of the colony ; while the less numerous generative polyps (blastostyles) form and carry the medusa buds (generative zooids). These buds, at first, are mere hollow offshoots of the generative polyp (blasto- style), but as they develop they assume the appearance of tiny saucers attached by the middle of their convex surface, the edge of each saucer bearing a fringe of some sixteen short tentacles ; while a curious blunt process, like a sort of bell-clapper (called the manubrium), and terminating in an opening, or mouth, projects from the centre of the concave surface of each saucer. Ultimately the little saucers become detached from the generative polyp or blastostyle, and, making their escape through an aperture at the top of the transparent gonophore which has served them as a kind of nursery, they swim away as tiny medusas or jelly-fish. These tiny medusae or jelly-fish of Obelia are very beautiful and interesting little creatures. They swim about by rhythmic movements of their saucer or umbrella-shaped bodies, and in their progress through the water the little umbrella may become turned inside out, exposing the manubrium and the four-sided mouth to view. However, this is not a serious accident, and the little jelly- fish soon rights itself, for it has no brittle ribs to crack like those of a real umbrella. Although such a small, transparent, gelatin- ous creature, the little* medusa is quite a complex animal. The margin of the umbrella is furnished with a varying number of tentacles, and in many cases with a series of small sacs enclosing one or more refractive spherules, probably rudimentary sense organs ; while at the base of the tentacles there is often a collec- tion of pigment cells in which a crystalline body is embedded, the whole forming a coloured spot or ocellus, which may function as 1 Greek — blastos, a bud ; stylos, a column : columniform zooids destined to give origin to generative buds. » Greek — gonos, offspring : a receptacle for the generative buds. 44 HYDROIDS AND JELLY-FISH a primitive eye. The mouth leads into a digestive cavity (enteron) which occupies the whole of the interior of the manubrium, and from its base sends off four very fine tubes (radial canals), which, passing at equal distances from each other through the mass of the umbrella to its margin, open into a circular tube or canal which runs parallel with and close to the edge of the umbrella. By means of its fringe of tentacles, which are well armed with thread or stinging cells, the medusa captures its microscopic prey, and the food, swallowed by the mouth, is digested in the manubrium and distributed throughout the entire medusa by the system of canals. Placed at equal distances on the under surface of the umbrella, and in immediate relation with the radial canals, are four oval bodies, each containing a mass of cells which will develop into ova or sperms, for each medusa bears organs of one sex only, and therefore, according to whether it is a female or a male medusa, will produce only ova or sperms. When these sexual cells are ripe the sperms of the male medusa are shed into the water and carried by the currents to the females, where they fuse with the ova. The fertilised egg develops into a little oval creature called a planula, covered with cilia, by means of which it swims about in the sea. After a little time the tiny planula gives up its active, free-swimming life, and, settling down on a piece of submerged timber, rock, or seaweed, fixes itself by one end and becomes con- verted into a little polyp with a waving circle of tentacles. It captures food, grows, sends out lateral buds, and soon be- comes converted into a complex, branching Obelia colony, the polyp members of which are destitute of fully developed sex cells. In Obelia we have an instance of what is termed an alternation of generations — a branching colony of polyps, certain of which produce asexually formed medusae, which in turn become detached, develop male and female organs, and produce sexually a ciliated offspring, which becomes the founder of a colony of sexless polyps multiplying by a process of budding. This interesting pheno- menon is very common among the Hydrozoa, being particularly marked in cases like Obelia and allied species, where the asexually formed generative polyp or medusa becomes detached and swims away. But these free-swimming generative medusae do not occur HYDROIDS AND JELLY-FISH 45 in all the Hydroids ; in many species they remain attached to the colony, looking like little umbrellas fastened by their ferrules to the colony, and produce their eggs and ciliated planulas in that situation. These permanently attached generative buds gener- ally lose to a greater or less extent the umbrella-like form char- acteristic of the free-swimming medusas. On almost any shore, specimens of the dead and dried polyparies of various Hydroids, such as the " Squirrel's-tail," the " Sea-cypress," the " Bottle- brush," the " Sea-fir," and the " Sea-beard " or " Lobster's-horn," to quote the popular names expressive of their general appear- ance, are to be found. The graceful, branching forms of the colonies, varying in the most wonderful degree in different species, the delicate, varied tints of the tentacle-crowned polyps, and their extraordinary life- history, make the Hydroida most deeply interesting forms of life. To quote Professor Hincks, who devoted many years of his life to the closest study of these remarkable organisms, " there must always be a certain fascination in a history which tells us of animals composed of multitudes of individuals living an associated life, and so combining as to produce the most graceful plant- like structures — vegetating like a tree — putting forth thousands of polyps, like leaves, each a provider for the commonwealth — putting forth also a company of buds, charged with the perpetua- tion of the species, ripening in transparent urns and scattering their winged seeds broadcast, or sent forth, moulded and painted by the highest art, like fairy emigrant ships freighted with young life, to colonise distant seas. And these are the simple facts of Nature." 1 The Hydrocorallina resemble the Reef Corals in forming a calcareous skeleton, and indeed were at one time supposed to belong to the same class. Thanks, however, to the researches of Professor L. Agassiz, Professor H. N. Moseley, and Professor Hickson, their true character and life-history has been worked out and proves them to belong to the Hydroids. The Hydro- corallines are divided into two families, called respectively Milli- pores and Stylasters. The Millipores form massive laminate or branched growths of a strong coral-like character, dotted over with minute pores, and having within a tubular structure crossed 1 "Quarterly Journal of Science," Vol. II., No. 7, P- 46 HYDROIDS AND JELLY-FISH by platforms or tabulae. They are reef-builders, and contribute to the solidity of the coral reef structure. Free-swimming minute sexual medusae are produced, which swim away from the parent colony, and having deposited their eggs, shrivel up and die. The second family, the Stylasters, are remarkable for the elegance and beauty of their branching fan-shaped forms, and exquisite colour- ing. Their branches are covered with numerous groups of pores, each pore having a calcareous spiny projection or style. Numer- ous blister-like swellings or ampullae on the surface of the colony contain the generative buds, which, however, never become free medusae. The Siphonophora l are free-swimming Hydrozoa, each con- sisting of a colony or assemblage of individuals united in a com- mon stock (called a hydrosoma), and placed under a more or less tough, bladder-like bag, which acts as a float. To this order belongs the well-known " Portuguese Man-of-war " (Physalia), whose air-sac is in the form of a somewhat pear-shaped bladder, pointed at one end and rounded at the other, crowned by a long, low crest which acts as a sail. Very often in the tropics a regular fleet of these Portuguese Men-of-war are to be seen sailing along upon the surface of the sea, their coloured floats all well above the water, so that the crest acts as a miniature sail ; while from beneath the float hang an assemblage of polyps, medusa-buds, and long trailing tentacles, sometimes many feet in length, and armed with batteries of stinging cells sufficiently powerful to produce very painful results ; indeed, the natives inhabiting the island of Funafuti are said to have a very great fear of being stung by them. Drifting along on the surface of the sea, these Physalia present a very pretty appearance, and always excite admiration and interest. Sometimes during the summer months they are to be seen off the south-west and west coasts of England. Another very beautiful form is called the " By-the-wind Sailor " (Velella), which looks like a dainty circular raft, with an obliquely placed semicircular-shaped sail ; and is just the graceful little craft one might imagine the sea-fairies of old voyaged in. All round the edge of the dainty disk-shaped raft depend a fringe of gaily coloured tentacles, which may be purple, bright blue, or brown in colour. .» Tube, or siphon-bearers. PORTUGUESE MAN-OF-WAR PHYSALIA) HYDROIDS AND JELLY-FISH 47 The Scyphozoa include the larger and commoner kinds of Jelly-fish, hundreds of which may be seen during the summer months swimming along by gracefully expanding and contracting their umbrella-shaped disks, or drifting quietly along the tidal currents. At night many of them present a very beautiful appear- ance, becoming lit up by a soft yet brilliant phosphorescence, veritable living lamps, glowing with many-coloured lights as they rise from out the dark, mysterious depths. One of the commonest of these large Jelly-fish, often cast up in large numbers on the shore, is the Aurelia,1 easily recognised by its saucer-shaped umbrella measuring 3 or 4 inches in diameter with four red or purple horseshoe-shaped bodies (the reproductive masses) embedded in the jelly near the centre of the body. The margin of the umbrella is fringed by very short, fine tentacles, and indented at regular intervals by a series of eight notches, each containing a little cyst, which is regarded as a pri- mitive eye-spot and is covered by a pair of minute flaps. Hence these larger Jelly-fish have been called " Covered-eyed Medusae," to distinguish them from the Hydroid type, which are without these flaps, and were called " Naked-eyed Medusae." The mouth is in the centre of the under surface of the body, and from it project four groups of gastral filaments well armed with thread or stinging cells. The fertilised egg of Aurelia develops into a hollow oval embryo, covered with cilia by means of which it moves through the water. It soon settles down, however, and becomes attached at one end to some base on the floor of the sea, where it changes into a small polyp with a mouth, stomach, and sixteen tentacles ; it was formerly thought at this stage to be a distinct individual, and received as such the name of Hydra tuba, or the " Trumpet Polyp." After feeding for a while, the little polyp begins to show a series of transverse constrictions or waists, which become smaller and smaller until the little creature looks like a pile of saucers with deeply indented edges. In due course the little saucers detach themselves and swim away, their transformation being completed by the filling in of the spaces between the eight deep indentations of the margin of the saucer, and the development of the fringe of fine tentacles, when the little creatures are recognised as small Aurelias. 1 Aurelia aurita* 48 HYDROIDS AND JELLY-FISH Most of the Scyphozoa resemble Aurelia in the general features of their structure, but vary considerably in certain points. Thus the umbrella, instead of being saucer-shaped, may be cup-shaped, or conical ; though many pass through an alternation of genera- tions such as I have briefly described in Aurelia, others do not, the ciliated larvae developing directly into Jelly-fishes like the parents without passing through a fixed polyp stage. Lucernaria (Halidys- tus octoradiatus), a small and interesting form, differs widely from the rest in attaching itself by a short stalk developed from the centre of the outside of the umbrella to seaweeds and rocks, and can creep about or swim at pleasure. The Comb-bearing Jellies (Ctenophora) have no disk or um- brella, and do not resemble the true Jelly-fish or medusae, either in shape or movement. Generally globular or cylindrical, rarely ribbon-shaped, they form a group of active, free-swimming, gela- tinous, transparent animals, at times appearing in vast numbers in the surface waters of the sea. The beautiful, crystal-bright, so-called "Sea-gooseberry" (Hormiphora plumosa) is a familiar Comb- bearer, frequently to be seen in large numbers during the late spring and early summer months, swimming close in to shore, hundreds often being left stranded by the receding tide. It has a wonderfully bright, transparent, globular body, provided with eight rows of swimming-plates or combs ; each plate consisting of a comb-like band of quite large cilia, the rapid movements of which present a most interesting sight. As the Hormiphora swims about in the collecting-jar, we shall see that two long, feathery tentacles are protruded from each side of the body, and wave about in the water, only to be as suddenly retracted within their sheaths. They are destitute of thread-cells or nematocysts, which are replaced by a number of adhesive cells, carrying out the same function as organs for the capture of prey. At one end of the body is a single opening, the mouth, which communicates with a gullet and stomach ; from the latter canals pass beneath the swimming-plates or combs, and two canals pass from the base of the stomach to the opposite end of the body, where they open as two minute excretory-pores. Centrally placed between these pores is a remarkable structure which functions as the nerve centre as well as an " audatory " or balancing sense organ. There is no budding, colony formation, or alternation of generations among Hydra Fvsca, with young bud A hydroid medusa Beroe o