| lal «| ‘ Riu MI a i} }* é ; : fA @ patra) fe a : ’ Cee ae ‘hs THE CAMBRIDGE NATURAL HISTORY aoe EDITED BY S. F. HARMER, Sc.D., F.R.S., Fellow of King’s College, Cambridge ; Superintendent of ‘tie University Museum of Zoology AND A. E. SHIPLEY, M.A., F.R.S., Fellow of Christ’s College, Cambridge ; U niversity Lecturer on ete Morphology of Invertebrates VOLUME I i qtnsonian Inetitutjs. OCT 25 | 1G 5bo0 Metional Wyse: +32 aob “PROTOZOA, ph By MARCUS (artos, Meas; *.Crinity College - (D.Sc. Lond.), Professor of Natural History in the Queen’s College, Cork Pe mWiEERA (SPONGES) By IceRNA 5. J. SOLAS; B.Sc. (Lond.), Lecturer on Zoology at Newnham College, Cambridge SOPRMENTERATA & CIENOPHORA By 2.J. HICKSON, M.A.,-F.RiS., formerly Fellow and now Honorary Fellow of Downing College, Cambridge ; Beyer Professor of Zoology in the Victoria University of Manchester ECHINODERMATA By E. W. MacBribe, M.A., F.R.S., formerly Fellow of St. John’s College, Cambridge ; Professor of Zoology in McGilf University, Montreal AHSONIAN JUN 9 1989 LIBRARIES London MACMILLAN AND ‘CO,, LIMITED NEW YORK: THE MACMILLAN COMPANY 1906 1g) ee nye 2 © Pome s) Ao Pr ele 7 And pitch down his basket before us, All trembling alive ' . Li With pink and grey jellies, your sea-fruit; You touch the strange lumps, ¥ he pe And mouths gape there, eyes open, all ‘manner ; Of horns and of humps, oY ea Brownie, The } sal " te ] oo Yh ‘ | . | i@ : Sere 7" ue y ca s 4 ted oo? — CONTENTS PAGE SCHEME OF THE CLASSIFICATION ADOPTED IN THIS Book ‘ : , : 1x PROTOZOA CHAPTER 1 Protozoa — INTRODUCTION — FUNCTIONS OF PROTOPLASM— CELL-DIVISION— ANIMALS AND PLANTS . : . ! : : : s : é 3 (CHELAN MM IB AR, JUL PROTOZOA (CONTINUED); SPONTANEOUS GENERATION—CHARACTERS OF Pro- TOZOA—CLASSIFICATION . : z : ; : , ‘ ; 42 (CHELAAIE IDM Ry JUUL PROTOZOA (CONTINUED): SARCODINA 51 CHEAPAMENRy Vi PROTOZOA (CONTINUED) : SPOROZOA 3 P : ; : ; : . 94 CHAPTER V PROTOZOA (CONTINUED): FLAGELLATA . : : : ‘ ‘ : o) LU9 CHAPTER VI Prorozoa (coNTINUED): INFUSORIA (CILIATA AND SUCTORIA) = ‘ 36 Vv vl CONTENTS PORIFERA (SPONGES) CHAPTER Vil PAGE PoRIFERA (SPONGES) — INTRODUCTION — History—DeEscrieTION OF HALI- CHONDRIA PANICEA AS AN EXAMPLE OF BRITISH MARINE SPONGES AND oF EPHYDATIA FLUVIATILIS FROM FrresH WaAtTER—DEFINITION—PostI- TION IN THE ANIMAL KINGDOM ‘ : : i P : ; Ge CHAPTER VIII PoRIFERA (CONTINUED): Forms OF SpicuULES —CALCAREA — HoMOCcOELA— HETEROCOELA — HEXACTINELLIDA — DEMOSPONGIAE — TETRACTINELLIDA —MonaXONIDA—CERATOSA—KEY TO BRITISH GENERA OF SPONGES , 183 CHAPTER IX PoRIFERA (CONTINUED): REPRODUCTION, SEXUAL AND ASEXUAL — PuHysiIo- LOGY—DISTRIBUTION—FLINTS é : E : : P : eee PAG COELENTERATA CHAPTER X CoELENTERATA—INTRODUCTION—CLASSIFICATION— HyDROZOA— ELEUTHERO- BLASTEA — MILLEPORINA — GYMNOBLASTEA—CALYPTOBLASTEA—GRAPTO- LITOIDEA—STYLASTERINA : : : ; ; : é ; . 245 CHAPTER XI Hyprozoa (CONTINUED): TRACHOMEDUSAE—N ARCOMEDUSAE—SIPHONOPHORA 288 CHAPTER XII CoELENTERATA (CONTINUED) : SCYPHOZOA =SCYPHOMEDUSAE < ‘ 2 310 CHAPTER XIII COELENTERATA (CONTINUED) : ANTHOZOA=ACTINOZOA—GENERAL CHARAC- TERS—ALCYONARIA : : ; : : , j ; : - 82 for) CHAPTER XIV ANTHOZOA (CONTINUED): ZOANTHARIA . ; eed: : : : . 365 CONTENTS Vil ——— —_—— _ = CTENOPHORA CHAPTER XV PAGE CTENOPHORA . : , : ; : : . : : : . 412 ECHINODERMATA CHAPTER XVI ECHINODERMATA — INTRODUCTION —CLASSIFICATION—ANATOMY OF A STAR- FISH—SYSTEMATIC ACCOUNT OF ASTEROIDEA . ; : ; : ~ 42g CHAPTER XVII ECHINODERMATA (CONTINUED): OPHIUROIDEA=BRITTLE STARS. , a) ATE COMBE NTE MIDE SWINE EcHINODERMATA (CONTINUED): ECHINOIDEA=SEA-URCHINS . : : DOS CHAPTER XIX EcHINODERMATA (CONTINUED) : HOLOTHUROIDEA = SEA-CUCUMBERS : Doo CHAPTER XxX ECHINODERMATA (CONTINUED): PELMATOZOA — CRINOIDEA = SEA - LILIES — THECOIDEA—CARPOIDEA—CYSTOIDEA—BLASTOIDEA : : : 5 Deo CHAPTER XXI ECHINODERMATA (CONTINUED): DEVELOPMENT AND PHYLOGENY . : . 601 INDEX : - : : ; : < : : : WE te wa J, be nel Ses , = ar. | SCHEME OF THE CLASSIFICATION ADOPTED IN THIS BOOK The names of extinct groups are printed in italics. PROTOZOA (pp. 1, 48). ( Rhizopoda f Lobosa (p. 51). | {Goetgly, \ Filosa (p. 52). Allogromidiaceae (p. 58). Astrorhizidaceae (p. 59). Lituolidaceae (p. 59). Miliolidaceae (p. 59). Foraminifera } Textulariaceae (p. 59). (p. 58) Cheilostomellaceae (p. 59). Lagenaceae (p. 59). Globigerinidae (p. 59). Rotaliaceae (p. 59). Nummulitaceae (p. 59). | Aphrothoraca (p. 70). Heliozoa Chlainydophora (p. 71). (p. 70) Chalarothoraca (p. 71). | Desmothoraca (p. 71). ( Collodaria SARCO- (eff) DINA 4 (p. 51) Spumellaria == Peripylaea< rail) i) Sphaerellaria Porulosa Gee 7/70) =Holo- ) trypasta | Radiolaria ; (p. 76) (p. 75) Acantharia = Actipylaea pp. 76, 78) . Osculosa (~~ i ee Nassellaria ei = = Monopylaea { Le 6) | (pp. 76, 78) Continued on the next page. pag 1X | $a, Colloidea (p. 77 ce as (p. 'Sptiameiies (p. V7 Te Prunoidea (uaa): Discoidea (p. i i fis Larcoide a (p. i 7 ). Actinelida (p. 78). Acanthonida (p. 78). Sphaerophracta (p. 78). Prunophracta (p. 78). Nassoidea (p. 78). Plectoidea (p- 78). x SCHEME OF CLASSIFICATION | ( Stephoidea (p. 78). Nassellaria ee ren bas Botryoidea (contd. ) (p: 79). | Osculosa Cyrtoidea Radiolaria ; =Mono- | (p. 79). (contd.) \ trypasta } Phaeocystina (contd. ) (pe, 7S)e SARCO- Phaeodaria Phaeosphaeria DINA | = Cannopylaea (569): (contd. ) =Tripylaea | Phaeogromia (pp. 76, 79) (p. 79). Phaeoconchia \ ( (p. 79). [eee { Zoosporeae (p. 89). Proteomyxa ps8) \ Azoosporeae (p. 89). (p. 88) las: (p. 89). Acrasieae (p. 90). Pe ae { Bicpissnoties (p. 90). ge Myxomycetes (pp. 90, 91). Gregarini- (Renicon tee amar (p. 97). daceae + Acephalinidae (p. 97). Telosporidia (pp. 97, 98) | Dicystidae (p. 97). SPORO- (p. 97) Prat Coccidiidae (pp. 97, 99). ZOA - Cec eon | Hacmosporidue (pp. 97, 102). (p. 94) (Ppa Gna) | Acystosporidae (pp. 97, 102). ase Myxosporidiaceae (pp. 98, 106). ee noes { Actinoraysidiaceas NG 98). ae) Sarcosporidiaceae (pp. 98, 108). ¢ Pantostomata (p. 109). Distomatidae (p. 110). Oikomonadidae (p. 111). Bicoecidae (p. 111). Craspedomonadidae (pp. 111, 121). Protomasti- | Phalansteridae (p. 111). gaceae < Monadidae (p. 111). (p. 110) Bodonidae (p. 111). Amphimonadidae (p. 111). Trimastigidae (p. 111). 5 Polymastigidae (p. 111). cogs J | Trichonymphidae (pp. 111, 123). (p. 109) l Opalinidae (pp. 111, 123). oN Chryso- ( monadaceae- (pp- 110, 125) (@ ryptomonadaceae (p. 110) Volvocaceae (a (pp. 111, (pp. 110, 125). 111) | Volvocidae (pp. 111, 126). Chloromonadaceae (p. 110). Euglenaceae (pp. 110, 124). Silicoflagellata (pp. 110, 114). * Cystoflagellata (pp. 110, ne _Dinoflagellata (pp. 110, 130), Coccolithophoridae (p. 114). SCHEME OF CLASSIFICATION Gymnostomaceae (pp. 137, 152). | Aspitotrichacae (pp. 137, 153). INFUS- ae Heterotrichaceae (pp. 137, 153). ORIA (p. 136) | PORIFERA (p. Hypotrichaceae (pp. 137, 138). Peritrichaceae (pp. 138, 155). Suctoria=Tentaculifera (p. 158). (p. 137) | Hypotriha eae (pp. 137, 155). 63). Sub-Family. ( Dialytinae Class. Sub-Class. Order. Family. ( ear en ; Homocoela ay 185). (p. 185) Clana ee 185). ee (:. a ) MEGA. Sar am ae, Calcarea (p. 192). é . 184) } Am phoriscidae (pp. 183 (p I ) Heterocoela (p. 192). (p. 187) Pharetronidae (p. 192) L Astroscleridae L ( (p. 194). ( Myxospongiae (p. 196). Hexactin- ee Taare (p ane Hexasterophora C (p. 203). Receptaculi- tidae (p, 207). OCTACTINELLIDA (p. 208). ITETERACTINELLIDA MICRO- (p. 208). MASTIC- | Tetractin- [ Choristida TORA ellida (p: 212). (pp. 183, (pp. 211, | Lithistida 195) 212) \ (pp. 212, 215): Monaxon- ( Halichondrina maniO- ide | (p. 217). 2 : (pp. 211, | Spintharophora jpongiae : O17 (p. 209) 216)‘ (p. 217). Foe c “ Spongidae DO a (p. 220). Ceratosa | ( 330) | Spongelidae I (p. 220). 220) (pp. 211, Dendroceratina (p p- 220, PANY (p. 192). | Lithoninae (p. 193). SCHEME OF CLASSIFICATION xil COELENTERATA (p. 243). Class. Order. Sub-Order. Family. Sub-Family. ; Eleutheroblastea (p. 253). Milleporina (p. 257). Bougainyilliidae (p. 269). Podocorynidae (p. 970). Clavatellidae (p. 270). Cladonemidae (p. 270). Tubulariidae (p. 271). Ceratellidae (p. 271). sa card peeane ; Pennariidae oO 272). ( 262) usae) 1 Corynidae (p. 272). epee Clavidae (p. 272). Tiaridae (p. 273). Corymorphidae (p. 273). Hydrolaridae (p. 273). Monobrachiidae (p. 274). Myriothelidae (p. 274). ( Pelagohydridae (p. 274). ( Aequoreidae (p. 278). Thaumantiidae (p. 278). Cannotidae (p. 278). Sertulariidae (p. 278). ta per sce as f Eleutheroplea (p. 279). HYDRO- Cotten ste Plumulariidae (p. 279) \ Statoplen (ts 249), ZOA + ( aes usae) ; Hydroceratinidae (p. 249) spat} (p. 279). C: ee a aacete 280). Eucopidae (p. 280). weet ograptidae (p. 281). ’ t Monoprionidae (p. 282). oi a es eae Diprionigne’| (p. *B0) (ae 2) Retiolitidae (p. 282). Stromatoporidae (p. 283). Oe aan { Stylasteridae (p. 285). Olindiidae (p. 291). [Petite p. 294). Trachomedusae Sena” (p. 294). (p. 288) | Asti p. 294). z Aglauridae (p. 294). Geryoniidae (p. 295). [Poca (p. 296). Narcomedusae Peganthidae (p. 296). (p. 295) ee p- 296). Solmaridae (p. 296). Siphono- ( Calyco- ( | Bre bor) | phoraes Monophyidae (p. 306) C ee eee (Gob 274) (p. 305) | | ie 306). (Continued on the next a SCHEME OF CLASSIFICATION xii Class. Order. Sub-Order. Family. Sub-Family. Aimphicaryoninae = (p. 306) 39 Prayinae (p. 306) | = Desmophyinae yo (p. 307) = Stephanophyinae | ¢ Calyco- a : E Deny = fete Diphyidae (p. 306) (p. 307) & (contd. ) Galeolarinae \ 2 (p. 307) | eee HYDRO- Siphono- Diphyopsinae aS ZOA | phora eo) ane (contd. ) (contd. ) Abylinae ne : (p. 307) ID Polyphyidae (p. 307). reas (p. 307). Apoleminae (p. 307). ee sonectidae (p. 307) | Physophorinae > (p. 308). hae Auronectidae (p. 308). ! ai eee uiidae (p. 307) _ 308). Chondeptorida (p. 308). ( Charybdeidae (p. 318). a Chirodropidae (p. 319). We Tripedaliidae (p. 319). Lucernariidae (p. 320). oe pao a 1 Depastridae (p. 321). MEreee | Stenoseyphidae (p. 321). Perip] Mid ( 22) eriphyllidae (p. 322). SCYPHO- Weer ; Ephyropsidae (p. 322) ZOA = \ ems | Atollidae (p. 322). SCYPHO- | Semaeo- Pelagiidae (p. 323). MEDUSAE } stomata ) Cyanaeidac SS. 324), (pp. 249, (p. 323) | Ulmaridae (p. 324). ey Cassiopeidae (p. 324) \ * eae Discophora | : \= ae rect aria (p. 323) Rhizo- Cepheidae (p. 324) ac stomata- JEG (p. B24) Rhizostomatidae (p. aa Poe Lychnorhizidae (p. 325) | =Cyclomyaria yi I Ly, Leptobrachiidae (p. al (p. 325). Catostylidae (p. 325) Class. Sub-Class. Grade. Order. Family. ( f Pe { Haimeidae (p. 342). i eae (p. 344). Stolonifera J) Clavulariidae (p. 344). ANTHOZOA (p. 342) | Tubiporidae (p. 344). =ACTINO-- Alcyonaria ~- Synal- _Favositidae (p. 344). ZOA (p. 329) cyonacea. + Heliolitidae (p. 346). (pp. 249, $26) (p-ge 42) | Coenothecalia ae A ee ‘ 344) Coccoseru ae(p 9: 6). | Be Thecidae (p. 346). l Chaetetidae (p. 346). (Continued on the next page.) XIV SCHEME OF CLASSIFICATION Class. ANTHO- ZOA ¢ (contd. ) Sub-Class. Alcyonaria (contd. ) Rac pee Grade. Synal- cyonacea - (contd. ) Continued on the next page. ) Pade. | ) ) Order. Sub-Order, Family. ( Xeniidae (p. 348). Telestidae (p. 348). Coelogorgiidae (p. 349). 4 Alcyoniidae (p. 349). Nephthyidae (p. 349). Siphonogorgiidae L (p. 349). » (ee (p. 350). Aleyonacea (p. 346) Pecudaxone Sclerogorgiidae (p. 350) poy wsitedidae (p. 351). Coralliidae (p. 382). Isidae (p. 353). Gorgonacea_ Primnoidae (p. 354). (p. 350) Chrysogorgiidae (p. 355). 4 Muriceidae (p. 355). Plexauridae (p. 356). Gorgoniidae (p. 356). Gorgonellidae OC Gch sai) Pteroeididae (p. 361). Pennatuleae | Pennatulidae (p. 361) | (p. 361). Axifera (p. 353) ( Virgulariidae (p. 362). Funiculinidae (p. 362). Anthoptilidac Penna- Spicatae (p. 362). tulacea} (p. 362) Kophobelemmnonidae (p. 358) (p. 362). Umbellulidae (p. 362). Verticilladeae (p. 363) Renille: oe ae ee 363) { Renillidae (p. 363). Veretilleae (p. 364) L Edwardsiidae Edwardsiidea (p. 377). (p. 375) Protantheidae (p. 377). Haleampidae (p. 380). Actiniidae (p. 381). Sagartiidae SS yeas anbiidae (p. 882). (Daan) Gre au) Phyllactidae (p. 382). Bunodidae (p. 382). Minyadidae (p. 383). SCHEME OF CLASSIFICATION XV Class. Sub-Class. Order. Sub-Order. Family. ( Corallimorphidae ee (p. 383). Actiniaria | a cia | Discosomatidae (p. 383). (contd. ) a aaa) Rhodactidae (p. 383). | Ee eae) Thalassianthidae L (p. 383). Cyathophy tlidae (p. 394). Cyathaxoniidae (p. 394). Cystiphyllidae (p. 394). Entocnemaria f Madreporidae (p. 395). (p. 394) \ Poritidae (p. 396). ( Turbinoliidae(p.398) | Oculinidae (p. 399) Astraeidae (p. 399) A. Gemmantes (p. 400) A. ee atiees Madreporama:) te aaa ANTHOZOA | Zoantharia |, (p. 384) | [Sub-Fam.] (p. (contd.) 1 (contd.) : ! Cyclocnemaria | 401) (p. 397) ; Pocilloporidae (p. 401) Plesiofungiidae (p. 403) ieee . 403) eueeine (p. 404) Plesiopor Vidas (p. 404) Eupsammiidae | L lL (p. 404) Zoanthidea f Zoanthidae (p. 404). (p. 404) \ Zaphrentidae (p. 406). Antipathidea Reale eres (p. 408). = Anti- Leiopathidae (p. 409). patharia Dendrobrachiidae (p. 407) (p. 409). | Cerianthidea L ( (p. 409). Aporosa (p. 397). ~-————__-— Fungacea (p. 402). — CTENOPHORA (p. 412). Class. ‘ Order. Family. f Mertensiidae (p. 417). Cydippidea (p. 417) ~ Callianiridae (p. 417). Pleurobrachiidae (p. 418). Lesueuriidae (p. 419). Bolinidae (p. 419). Deiopeidae (p. 419). 4 : Eurhamphaeidae (p. 419 TENTACULATA (p. 417) 4 Lobata (p. 418) meena see cach ) Mnemiidae (p. 420). Calymmidae (p. 420). \ Ocyroidae (p. 420). Cestoidea (p. 420) ay (P. 420). Ctenoplanidae (. 421). | Platyctenea (p. 421) \ Core aianiane i 422), NUDA (p. 423) Beroidae (p. 423). XVI SCHEME OF CLASSIFICATION ECHINODERMATA (p. 425). Sub-Phylum. — Class. Order. Sub-Order. Family. Echinasteridae (p. 462). : Solasteridae (p. 462). Baris Asterinidae (p. 463). PI 462 Poraniidae (p. 464). ) Ganeriidae (p. 464). Mithrodidae (p. 464). Velata [ees (p. 464). (pp. 461, Myxasteridae (p. 464). 464) Pterasteridae (p. 466). = Archasteridae (p. 466). ene een (p. 467). Aster- (PP. 466) megeea asteridae oidea | (p. 470 (pp. 430, | Linckiidae (p. 471). 27% Pentagonasterid: 431) | valvata meer aa ve (PP. cas Gymnasteridae (p. 471). ! Antheneidae (p. 471). Pentacerotidae (p. 471). Asteriidae (p. 473). Heliasteridae (p. 474). : Zoroasteridae (p. 474). Bares Stichasteridae (p. 474). EDs Pedicellasteridae (p. 474). ELEU- L Brisingidae (p. 474). THERO g : © ZOA ‘ oo ae 2 p. de Ose, Gulia (cet (p. 495) P id Zygophiurae Amphiuridae (p. 497). ie Sak (pp. 494, 495) ‘) Ophiocomidae (p. 499). Ex 477) | Obhiothricidae (p. 499). A Astroschemidae (p. 501). ac ugan eo, Trichasteridae (p. 501). ale a as Euryalidae (p. 501). Cidaridae (p. 533). Echinothuriidae (p. 535). Saleniidae (p. pei): Arbaciidae (p. 538). Endocyclica } Diadematidae (p. 538). (pp. 529, 5380) Echin- Echinidae (p. 539) oidea } (pp. 431, 1 503) Protocly peastroidea (p. 548 ; Clype- Fibularidae (p. 549). astroidea! ya lye Echinanthidae (pp. 529, saree | =Clypeastridae 542) astroidea (p. 849). (Pp. O%¢ I \ (Continued on the next page. ) Laganidae (p. 549). Scutellidae (p. 549). | Sub-Family. Temno- pleurinae (p. 539). Echininae (p. 589). SCHEME OF CLASSIFICATION XVil Sub-Phylum. Class. Order. Family. Echinonidae (p. 553) Nucleolidae (p. 554) Cassidulidae (). wets Spatangoidea | Ananchytidae (p. 554 (pp.529, 549) | Palaeostomatidae (p. 554) . Spatangidae (p. 554) agentes Taeeidne (p. 556) me Archaeocidaridae (ms 55%))s Melonitidae ()p. 557). TViarechinidae (p. 557). ELEU- Holectypoidea (p. 558). THEROZOA , Echinoconidae (p. 558). (contd. ) Collyritidae (p. 559). Aspidochirota (p. 570). Elasipoda (p. 571). Pelagothuriida Holothuroidea _ (p. 572). (pp. 431, 560) | Dendrochirota (p. 572). Molpadiida (peso): Synaptida \ (p. 575). ( Hyocrinidae (p. 590). Rhizocrinidae (p. 590). Pentacrinidae (p. 591). Holopodidae (p. 592). Comatulidae (p. 594). INADUNATA Bo ak (p. 595). (p. 580) Articulata (Qe1ooe): PELMATO- | CAMERATA ZOA 4 (p. 595). (pp. 430, 579) | 7’HECOIDEA = EDRIOASTER- OIDEA (pp. 580, 596). CARPOIDEA (pp. 580, 596). CYSTOIDEA (pp. 580, 597). BLASTOIDEA s L (pp. 580, 599). | Asternata | (p. 554). | Sternata (p. 554). PROTOZOA BY MARCUS HARTOG, M.A., Trintry CoLLEGE (D.Sc. Lonp.) Professor of Natural History in the Queen’s College, Cork. 7 CHAPTER I PROTOZOA—INTRODUCTION——_FUNCTIONS OF PROTOPLASM— CELL-DIVISION——ANIMALS AND PLANTS The Free Amoeboid Cell.—I{ we examine under the microscope a fragment of one of the higher animals or plants, we find in it a very complex structure. A careful study shows that it always consists of certain minute elements of fundamentally the same nature, which are combined or fused into “ tissues.” In plants, where these units of structure were first studied, and where they are easier to recognise, each tiny unit is usually enclosed in an envelope or wall of woody or papery material, so that the whole plant is honeycombed. Each separate cavity was at first called a “cell”; and this term was then applied to the bounding wall, and finally to the unit of lving matter within, the envelope receiving the name of “cell-wall.” In this modern sense the “cell” consists of a viscid substance, called first in animals “sarcode ” by Dujardin (1835), and later in plants “ protoplasm ” * by Von Mohl (1846). On the recognition of its common nature in both kingdoms, largely due to Max Schultze, the latter term prevailed ; and it has passed from the vocabulary of biology into the domain of everyday life. We shall now examine the struc- ture and behaviour of protoplasm and of the cell as an introduc- tion to the detailed study of the Protozoa, or better still Protista,” the lowest types of living beings, and of Animals at large. ' For detailed studies of protoplasm see Delage, Hérédité, 2nd ed. 1903 ; Henneguy, Lecons sur la Cellule, 1896; Verworn, General Physiology, English ed. 1899; Wilson, The Cell in Development and Inheritance, 2nd ed. 1900. All these books contain full bibliographies. ? As we shall see later, it is by no means easy to separate sharply Protozoa and Protophyta, the lowest animals and the lowest plants ; and therefore in our pre- a ~) 4 PROTOZOA CHAP. It is not in detached fragments of the tissues of the higher animals that we can best carry on this study: for here the cells are in singularly close connexion with their neighbours during life; the proper appointed work of each is intimately related to that of the others; and this co-operation has so trained and specially modified each cell that the artificial severance and isolation is detrimental to its well-being, if not necessarily fatal to its very life. Again, in plants the presence of a cell-wall interferes in many ways with the free behaviour of the cell. But in the blood and lymph of higher animals there float isolated cells, the white corpuscles or “leucocytes” of human histology, which, despite their minuteness (1/3000 in. in diameter), are in many respects suitable objects. Further, im our waters, fresh or salt, we may find similar free-living individual cells, in many respects resembling the leucocytes, but even better suited for our study. For, in the first place, we can far more readily reproduce under the microscope the normal conditions of their life; and, moreover, these free organisms are often many times larger than . the leucocyte. Such free organisms are individual Protozoa, and are called by the general term “ Amoebae.” A large Amoéba may measure in its most contracted state 1/100 in. or 250 w in diameter,’ and some closely allied species (Pelomyxa, see p. 52) even twelve times this amount. If we place an Amoeba or a leucocyte under the microscope (Fig. 1), we shall find that its form, at first spherical, soon begins to alter. To confine our attention to the external changes, we note that the outline, from circular, soon becomes “ island-shaped” by the outgrowth of a promontory here, the indenting of a bay there. The promontory may enlarge into a peninsula, and thus grow until it becomes a new mainland, while the old mainland dwindles into a mere pro- montory, and is finally lost. In this way a crawling motion is effected.” The promontories are called “ pseudopodia ” ( = “ false- liminary survey to designate lowly forms of life, not formed of the aggregation of differentiated cells, we shall employ the useful term ‘‘Protista,” introduced by Haeckel to designate such beings at large, without reference to this difficult problem of separation into animals and plants (see also p. 365 f.). ' The ‘‘ micron,” represented by the Greek letter u, is 1/1000 mm., very nearly 1/25,000 of an inch, and is the unit of length commonly adopted for microscopic measurements. ~ A solid substratum is required, to which the lower surface adheres slightly : that movement is complicated by a sort of rolling over of the upper surface. constantly I PROTOPLASM 5 feet”), and the general chararacter of such motion is called “ amoeboid.” The living substance, protoplasm,? has been termed a “ jelly,” a word, however, that is quite inapplicable to it in its living state. It is viscid, almost semi-fluid, and may well be compared to very soft dough which has already begun to rise. It resembles Fig. 1.—A moeba, showing clear ectoplasm, granular endoplasm, dark nucleus, and lighter contractile vacuole. The changes of form, a-f, are of the A. limaz type; g, h, of the A. proteus type. (From Verworn.) it in often having a number of spaces, small or large, filled with liquid (not gas). These are termed “vacuoles” or “ alveoles,” according to their greater or their lesser dimensions. In some cases a vacuole is traversed by strands of plasmic substance, just as we may find such strands stretching across the larger spaces of a very light loaf; but of course in the living cell these are constantly undergoing changes. If we “fix” a cell (7c. kill it by prolonging the front of the pseudopodium, while the material of the lower surface is brought up behind. H.S. Jennings, Contr. to the Study and Behaviour of the Lower Organisms, 1904, pt. vi. p. 129 f., ‘‘The Movements and Reactions of Amoeba.” ' If the protoplasm contains visible granules, as it usually does, within a clear external layer, we see that these stream constantly forwards along the central axis of each process as it forms, and backwards just within the clear layer all round, like a fountain playing in a bell-jar. This motion is most marked when a new pseudopodium is put forth, and ceases when it has attained full dimensions. * We use as a corresponding adjective the term “ plasmic.” 6 PROTOZOA CHAP. sudden heat or certain chemical coagulants),' and examine it under the microscope, the intermediate substance between the vacuoles that we have already seen in life is again found either to be finely honeycombed or else resolved into a network like that of a sponge. The former structure is called a “foam” or “alveolar” structure, the latter a “reticulate” structure. The alveoles are about 1 » in diameter, and spheroidal or polygonal by mutual contact, elongated, however, radially to any free surface, whether it be that of the cell itself or that of a larger alveole or vacuole. The inner layer of protoplasm (“ endo- plasm,” “endosare”) contains also granules of various nature, reserve matters of various kinds, oil-globules, and particles of mineral matter® which are waste products, and are called “excretory.” In fixed specimens these granules are seen to occupy the nodes of the network or of the alveoh, that is, the points where two or three boundaries meet.2 The outermost layer (“ ectoplasm ” or “ectosarc”) appears in the live Amoeba struc- tureless and hyaline, even under conditions the most favourable for observation. The refractive index of protoplasm, when living, is always well under 1°4, that of the fixed and dehydrated substance is slightly over 1°6. Again, within the outer protoplasm is found a body of slightly higher refractivity and of definite outline, termed the “nucleus ” (Figs. 1,2). This has a definite “ wall” of plasmic nature, and a substance so closely resembling the outer protoplasm in character, that we call it the “nucleoplasm” (also “linin”), distinguishing the outer plasm as “cytoplasm”; the term “protoplasm” including both. Within the nucleoplasm are granules of a substance that stains well with the commoner dyes, especially the “basic” ones, and which has hence been called “chromatin.” The linin is 1 For the study of the structure of protoplasm under the microscope it is necessary to examine it in very thin layers, such as can for the most part be obtained only by mechanical methods (section-cutting, etc.). These methods, again, can only be applied to fixed specimens, for natural death is followed by rapid changes, and notably by softening, which makes the tissue less suitable for our methods. We further bring out and make obvious pre-existing differentiations of our specimens by various methods of staining with such dyes as logwood and cochineal and their derivatives, and coal-tar pigments (see also p. 11 n.). * In many Protista these granules have been shown by Schewiakoff, in Z. wiss. Zool. lyii. 1893, p. 32, to consist of a calcium phosphate, probably Ca,P,0x. * It is not always possible to tell how much of these structures represents what existed in life (see p. 11). I RESPONSE TO STIMULI ai usually arranged in a distinct network, confluent into a “ parietal layer” within the nuclear wall; the meshes traversing a cavity full of liquid, the nuclear sap, and containing in their course the granules; while in the cavity are usually found one or two droplets of a denser substance termed “nucleoles.” These differ slightly in composition from the chromatin granules * (see p. 24 f.). The movements of the leucocyte or Amoeba are usually most active at a temperature of about 40° C. or 100° F., the “optimum.” They cease when the temperature falls to a point, the “minimum,” varying with the organism, but never below freezing- point; they recommence when the temperature rises again to the same point at which they stopped. If now the temperature be raised to a certain amount above 40° they stop, but may recommence if the temperature has not exceeded a certain point, the “maximum” (45° C. is a common maximum). If it has been raised to . . : : : Fic. 2.—Ovum of a Sea-Urchin, a still higher point they will not ~~ snowing the radially striated cell- recommence under any circumstances membrane, the cytoplasm con- 7 taining yolk-granules, the large whatever. nucleus (germinal vesicle), with (A@ain, a slight electric shock will = network: eb Tui) containing = z chromatin granules, and a large determine the retraction of all pro- — nucleole (germinal spot). (From ‘cesses, and a period of rest in a pee Embryology, — after spherical condition. A milder shock my will only arrest the movements. But a stronger shock may arrest them permanently. We may often note a relation of the movements towards a surface, tending to keep the Amoeba in contact with it, whether it be the surface of a solid or that of an air-bubble in the liquid (see also p. 20). If a gentle current be set up in the water, we find that the movements of the Amoeba are so co-ordinated that it moves up- stream; this must of course be of advantage in nature, as keeping the being in its place, against the streams set up by larger creatures, etc. (see also p. 21). If substances soluble in water be introduced the Amoeba will, 1 The chromatin and nucleoles are especially rich in phosphorus, probably in the combination nucleinie acid. 8 PROTOZOA CHAP. as a rule, move away from the region of greater concentration for some substances, but towards it (provided it be not excessive) for others. (See also pp. 22,23.) We find, indeed, that there is for substances of the latter category a minimum of concentration, below which no effect is seen, and a maximum beyond which further concentration repels. The easiest way to make such observations is to take up a little strong solution in a capillary tube sealed at the far end, and to introduce its open end into the water, and let the solution diffuse out, so that this end may be regarded as surrounded by zones of continuously decreasing strength. In the process of inflammation (of a Higher Animal) it has been found that the white corpuscles are so attracted by the source of irritation that they creep out of the capillaries, and crowd towards it. We cannot imagine a piece of dough exhibiting any of these reactions, or the like of them; it can only move passively under the action of some one or other of the recognised physical forces, and that only in direct quantitative relation to the work that such forces can effect; in other words, the dough can have work done on it, but it cannot do work. The Amoeba or leu- cocyte on the contrary does work. It moves under the various circumstances by the transformation of some of its internal energy from the “ potential ” into the “ kinetic” state, the condi- tion corresponding with this being essentially a liberation of heat or work, either by the breaking down of its internal substances, or by the combination of some of them with oxygen.’ Such of these changes as involve the excretion of carbonic acid are termed “ respiratory.” This hberation of energy is the “response” to an action of itself inadequate to produce it; and has been compared not inaptly to the discharge of a cannon, where foot-tons of energy are liberated in consequence of the pull of a few inch-grains on the trigger, or to an indefinitely small push which makes electric contact: the energy set free is that which was stored up in the charge. This capacity for liberating energy stored up within, in response to a relatively small impulse from without, is termed “irritability”; the external impulse is termed the “ stimulus.” The responsive act has been termed “contractility,” because it so often means an obvious contraction, but is better termed ' In chemical phrase the process is ‘‘ exothermic.” I ASSIMILATION 9 “motility ”; and irritability evinced by motility is characteristic of all living beings save when in the temporary condition of “rest.” Again, in the case of the cannon, the gunner after its dis- charge has to replenish it for future action with a fresh cartridge ; the Amoeba or leucocyte can replenish itself—it “feeds.” When it comes in contact with a fragment of suitable material, it enwraps it by its pseudopodia (Fig. 5), and its edges coalesce where they touch on the far side as completely as we can join up the edges of dough round the apple in a dumpling. It dissolves all that can be dissolved—‘.e. it “digests” it, and then absorbs the dissolved material into its substance, both to replace what it has lost by its previous activity and to supply fuel for future Fig. 3.—Aimoeba devouring a plant cell ; four successive stages of ingestion. (From Verworn.) liberation of energy; this process is termed “nutrition,” and is another characteristic of living beings. Again, as a second result of the nutrition, part of the food taken in goes to effect an increase of the living protoplasm, and that of every part, not merely of the surface—it is “ assimilated ” : while the rest of the food is transformed into reserves, or con- sumed and directly applied to the liberation of energy. The increase in bulk due to nutrition is thus twofold: part is the increase of the protoplasm itself—*assimilative growth,” part is the storage of reserves—“ accumulative growth”: these reserves being available in turn by digestion, whether for future true growth or for consumption to liberate energy for the work of the cell. We can conceive that our cannon might have an automatic feed for the supply of fresh cartridges after each shot; but not that it could make provision for an increase of its own bulk, so as to gain in calibre and strength, nor even for the restoration 10 PROTOZOA CHAP. of its inner surface constantly worn away by the erosion of its discharges. Growth—and that growth “interstitial,” operating at every point of the protoplasm, not merely at its surface—is a character of all living beings at some stage, though they may ultimately lose the capacity to grow. Nothing at all comparable to interstitial growth has been recognised in not-living matter.! Again, when an Amoeba has grown to a certain size, its nucleus divides into two nuclei, and its cytoplasmic body, as we Fic. 4.—Amoeba polypodia in successive stages of equal fission; nucleus dark, con- tractile vacuole clear. (From Verworn, after F. E. Schulze.) may term it, elongates, narrows in the middle so as to assume the shape of a dumb-bell or finger-biscuit, and the two halves, crawling in opposite directions, separate by the giving way of the connecting waist, forming two new Amoebas, each with its nucleus (Fig. 4). This is a process of “reproduction”; the special case is one of “equal fission” or “binary division.” The original cell is termed the “ mother,” with respect to the two new ones, and these are of course with respect to it the “daughters,” and ' The growth of crystals is a mere superficial deposit, and cannot at all be identified with protoplasmic growth. I VITAL PROCESSES lida “sisters” to one another. We must bear in mind that in this self-sacrificing maternity the mother is resolved into her children, and her very existence is lost in their production. The above phenomena, IRRITABILITY, MOTILITY, DIGESTION, NUTRITION, GROWTH, REPRODUCTION, are all characteristic of living beings at some stage or other, though one or more may often be temporarily or permanently absent; they are therefore called “ vital processes.” If, on the other hand, we viclently compress the cell, if we pass a very strong electric shock through it, or a strong con- tinuous current, or expose it to a temperature much above 45 C., or to the action of certain chemical substances, such as strong acids or alkalies, or aleohol or corrosive sublimate, we find that all these vital processes are arrested once and for all; hence- forward the cell is on a par with any not-living substance. Such a change is called “ DEATH,” and the “capacity for death” is one of the most marked characters of living beings. This change is associated with changes in the mechanical and optical properties of the protoplasm, which loses its viscidity and becomes opaque, having undergone a process of de-solution ; for the water it contained is now held only mechanically in the interstices of a network, or in cavities of a honeycomb (as we have noted above, p. 5), while the sold forming the residuum has a refractive index of a little over 1:6. Therefore, it only regains its full transparency when the water is replaced by a liquid of high refractive index, such as an essential oil or phenol. A similar change may be effected by pouring white of egg into boiling water or absolute alcohol, and is attended with the same optical results. The study of the behaviour of coagulable colloids has been recently studied by Fischer and by Hardy, and has been of the utmost service in our interpretation of the microscopical appearances shown in biological specimens under the microscope.! 1 A. Bolles Lee, in his Microtoimist’s Vade Mecum, 1st ed. (1885), pointed out that ‘‘ Clearing reagents are liquids whose primary fanction is to make microscopic preparations transparent by penetrating amongst the highly refractive elements of which the tissues are composed, having an index of refraction not greatly inferior to that of the tissues to be cleared” (p. 213). We showed later (‘‘The State in which Water exists in Live Protoplasm,” in Rep. Brit. Ass. 1889, p. 645, and Journ. Roy. Mier. Soc. 1890, p. 441) that since the refractivity of living proto- plasm is only 1°363-1°368, it follows that the water in the living protoplasm is in a state of perfect physical combination, like the water of a solution of gum [read a IEA PROTOZOA CHAP. The death of the living being finds a certain analogy in the breaking up or the wearing out of a piece of machinery; but in no piece of machinery do we find the varied irritabilities, all conducive to the well-being of the organism (under ordinary conditions), or the so-called “automatic processes” + that enable the living being to go through its characteristic functions, to grow, and as we shall see, even to turn conditions unfavourable for active life and growth to the ultimate weal of the species (see p. 32). At the same time, we fully recognise that for supplies of matter and energy the organism, hke the machine, depends absolutely on sources from without. The debtor and creditor sheet, in respect of matter and energy, can be proved to balance between the outside world and Higher Organisms with the utmost accuracy that our instruments can attain; and we infer that this holds for the Lower Organisms also. Many of the changes within the organism can be expressed in terms of chemistry and physics; but it is far more impossible to state them ad in such terms than it would be to describe a polyphase electrical installation in terms of dynamics and hydraulics. And so far at least we are justified in speaking of “vital forces.” The living substance of protoplasm contains a large quantity of water, at least two-thirds its mass, as we have seen, in a state of physical or loose chemical combination with solids: these on death yield proteids and nucleo-proteids.? The living protoplasm ““mucilage ”] or of a jelly. Now the phenomena of protoplasmic motions as studied in the Rhizopoda and in the vegetable cell, seem absolutely to preclude the jelly supposition, and for these cases we must admit that living protoplasm is a viscid liquid whose refractivity is probably the mean of the two constituents separated by death, the one solid, the other a watery solution: and death is for us essentially a process of precipation (or better, ‘‘desolution”’’). For further work on these lines see Hardy in Journ. Physiol. vol. xxiv. 1899, p- 158, and Fischer, Pixirung wu. Fdrbung, 1900. ' In its original use ‘‘ automatism” designates the continuous sequence and combination of actions, without external interference, performed by complex machines designed and made for specific ends by intelligent beings: thus we speak correctly of “automatic ball bearings ” that tighten of themselves when they become loose ; but even these cannot take up fresh steel and redeposit it, either to replace the worn parts or to strengthen a tube that is bending under a stress. * Proteids are organic compounds containing carbon, hydrogen, nitrogen, and oxygen, of which white of egg (albumen) is a familiar type. Nucleo-proteids are compounds of proteids with nucleinic acid, which in addition to the above elements contain phosphorus. ; METABOLISM I WwW has an alkaline reaction, while the liquid in the larger vacuoles, at least, is acid, especially in Plant-cells.' Metabolism.—The chemical processes that go on in the organism are termed metabolic changes, and were roughly divided by Gaskell into (1) “anabolic,” in which more complex and less stable substances are built up from less complex and more stable ones with the absorption of energy; and (2) “ cata- bolic” changes in which the reverse takes place. Anabolic processes, in all but the cells containing plastids or chromato- phores (see p. 36) under the influence of light, necessarily imply the furnishing of energy by concurrent catabolic changes in the food or reserves, or in the protoplasm itself. Again, we have divided anabolic processes into “ accumulative,” where the substances formed are merely reserves for the future use of the cell, and “assimilative,’ where the substances go to the building of the protoplasm itself, whether for the purpose of growth or for that of repair. Catabolic processes may involve (i) the mere breaking of complex substances into simpler ones, or (2) their combination with oxygen; in either case waste products are formed, which may either be of service to the organism as “ secretions” (like the bile in Higher Animals), or of no further use (like the urine). When nitrogenous substances break down in this way they give rise to “ excretions,” containing urea, urates, and allied substances ; other products of catabolism are carbon dioxide, water, and mineral salts, such as sulphates, phosphates, carbonates, oxalates, etc., which if not insoluble must needs be removed promptly from the organism, many of them being injurious or even poisonous. The energy liberated by the protoplasm being derived through the breakdown of another part of the same or of the food- 1 The specific gravity of living protoplasm has been estimated by determining the density of a solution of gum in which certain Infusoria float freely at any depth. It was found by the concurrent results of Julia B. Platt and Stephen R. Williams (see Amer. Natural. xxxiii. 1899, p. 31, xxxiv. 1900, p. 95) to be from 1:014 to 1019, while the Metazoon Hydra was found to give a density of only 1:0095 to1°0115. The difference of about 0°006, it is easy to show, is of the correct ‘‘ order of magnitude,” if we admit that the actual substance of the Hydra has about the same specific gravity as the Infusorian, while the density of the whole is lightened by the watery contents of the internal cavity, ete. Jensen obtained a much higher result for Paramecium, using a solution of the crystalloid substance, potassium carbonate; but it is almost certain that this would be readily absorbed by the organism, and so raise its density in the course of the experiment. 14 PROTOZOA CHAP. materials or stored reserves, must give rise to waste products. The exchange of oxygen from without for carbonic acid formed within is termed “respiration,” and is distinguished from the mere removal of all other waste products called “ excretion.” In the fresh-water Amoeba both these processes can be studied. Respiration,’ or the interchange of gases, must, of course, take place all over the general surface, but in addition it is combined in most fresh-water Protista with excretion in an organ termed the “contractile ” or “ pulsatile vacuole” (Figs. 1, 4, ete.). This particular vacuole is exceptional in its size and its constancy of position. At intervals, more or less regular, it is seen to con- tract, and to expel its contents through a pore; at each contrac- tion it completely disappears, and reforms slowly, sometimes directly, sometimes by the appearance of a variable number of small “formative” vacuoles that run together, or as in Ciliata, by the discharge into it of so-called “ feeding canals.” As this vacuole is filled by the water that diffuses through the substance, and when distended may reach one-third the diameter of the being, in the interval between two contractions an amount of water mnust have soaked in equal to one-twenty-seventh the bulk of the animal, to be excreted with whatever substances it has taken up in solution, including, not only carbon dioxide, but also, it has been shown, nitrogenised waste matters allied to uric acid.” That the due interchanges may take place between the cell and the surrounding medium, it is obvious that certain limits to the ratio between bulk and surface must exist, which are dis- turbed by growth, and which we shall study hereafter (p. 25 f.). The Protista that live in water undergo a death by “ difflu- ence ” or “ granular disintegration ” on being wounded, crushed, or sometimes after an excessive electric stimulation, or contact with alkalies or with acids too weak to coagulate them. In this process the protoplasm breaks up from the surface inwards into a mass of granules, the majority of which themselves finally dis- solve. If the injury be a local rupture of the external pellicle or ' Energy may be derived from the mere splitting up of complex substances within the cell: when such a splitting involves the liberation of CO, the process is (mis-)ealled ‘‘ intramolecular respiration.” : 2 A similar organ, but with ce//ulav walls, is the bladder of the Rotifers and certain Platyhelminthes, in connexion with their renal system (vol. ii. pp. 53, 199, and especially pp. 213-5). I RESPIRATION—DIGESTION 15 cuticle, a vacuole forms at the point, grows and distends the over- lying cytoplasm, which finally ruptures: the walls of the vacuole disintegrate ; and this goes on as above described. Ciliate Infusoria are especially hable to this disintegration process, often termed “ diftluence,” which, repeatedly described by early observers, has recently been studied in detail by Verworn. Here we have death by “solution,” while in the “ fixing” of protoplasm for microscopic processes we strive to ensure death by “ desolution,” so as to retain as much of the late living matter as possible. It would seem not improbable that the unusual contact with water determines the formation of a zymase that acts on the living substance itself. We have suggested’ that one function of the contractile vacuole, in naked fresh-water Protists, is to afford a regular means of discharge of the water constantly taken up by the crystalloids in the protoplasm, and so to check the tendency to form irregular disruptive vacuoles and death by diffluence. This is supported by the fact that in the holophytic fresh-water Protista, as well as the Algae and Fungi, a contractile vacuole is present in the young naked stage (zoospore), but disappears as soon as an elastic cell-wall is formed to counterbalance by its tension the internal osmotic pressure. Digestion is always essentially a catabolic process, both as regards the substance digested and the formation of the digesting substance by the protoplasm, The digesting substance is termed a “ zymase ” or “ chemical ferment,’ and is conjectured to be pro- _ duced by the partial breakdown of the protoplasm. In presence of suitable zymases, many substances are resolved into two or more new substances, often taking up the elements of water at the same time, and are said to be “ dissociated ” or “ hydrolysed ” as the case may be. Thus proteid substances are converted into the very soluble substances, “ proteoses” and “ peptones,” often with the concurrent or ultimate formation of such relatively sunple bodies as leucin, tyrosin, and other amines, etc. Starch and glycogen are converted into dextrins and sugars; fats are converted into fatty acids and glycerin. It is these products of digestion, and not the actual food-materials (save certain very sunple sugars), that are really taken up by the protoplasm, 1 Jn Rep. Brit. Ass. 1888, p. 714; Ann. Mag. Nat. Hist. (6), iti. 1889, p. 64. This view has been fully worked out, mainly on Ciliates, by Degen in Bot. Zeit. lxiii. Abt. 1, 1905. 16 PROTOZOA CHAP. whether for assimilation, for accumulation, or for the direct liberation of energy for the vital processes of the organism. Not only food from without, but also reserves formed and stored by the protoplasm itself, must be digested by some zymase before they can be utilised by the cell. In all cases of the utilisation of reserve matter that have been investigated, it has been found that a zymase is formed by the cell itself (or some- times, in complex organisms, by its neighbours) ; for, after killing the cell in which the process is going on by mechanical means or by alcohol, the process of digestion can be carried on in the laboratory.’ The chief digestion of all the animal-feeding Protista is of the same type as in our own stomachs, known as “ peptic” digestion: this involves the concurrent presence of an acid, and Le Dantec and Miss Greenwood have found the contents of food-vacuoles, in which digestion is going on, to contain acid liquid. The ferment-pepsin itself has been extracted by Krukenberg from the Myxomycete, “Flowers of tan” (Fuligo varians, p. 92), and by Professor Augustus Dixon and the author from the gigantic multinucleate Amoeba, Pelomyxa palustris (p. 52). The details of the prehension of food will be treated of under the several groups. The two modes of Anabolism—true “ assimilation” in the strictest sense and “ accumulation ”—may sometimes go on con- currently, a certain proportion of the food material going to the protoplasm, and the rest, after allowing for waste, being converted into reserves. Movements all demand catabolic changes, and we now pro- ceed to consider these in more detail. The movements of an Amoeboid® cell are of two kinds: “expansion,” leading to the formation and enlargement of out- ' See Hartog, ‘‘On Multiple Cell-division, as compared with Bi-partition as Herbert Spencer’s limit of growth,” in Rep. Brit. Ass. 1896, p. 833; ‘*On a Peptic Zymase in Young Embryos,” ibid. 1900, p. 786; ‘‘Some Problems of Reproduction,” ii. Quart. Journ, Micr. Sci. xlvii. 1904, p. 583. 2 «On the Digestive Ferment of a large Protozoon,”’ Rep. Brit. Ass. 1893, p. 801. * See for studies of the movements of Protoplasm, Berthold, Protoplasma- mechanik (1886); Biitschli, Investigations on Microscopic Foams and on Proto- plasm, English ed. 1894; Verworn, General Physiology, 1899; Le Dantec, La Matiere Vivante, 18932; and Jensen, ‘“ Unters. ueb. Protoplasmamechanik,” in Arch. Ges. Phys. \xxxvii. 1901, p. 361; Davenport, Experimental Morphology, i. 1897 ; H.S. Jennings, Contr. etc. 1904. I MOVEMENTS iy growths, and “ contraction,” leading to their diminution and dis- appearance within the general surface. Expansion is probably due to the lessening of the surface-tension at the point of out- growth, contraction to the increase of surface-tension. Verworn regards these as due respectively to the combination of the oxygen in the medium with the protoplasm in diminishing sur- face-tension, and the effect of combination with substances from within, especially from the nucleus in increasing it. Besides these external movements, there are internal movements revealed by the contained granules, which stream freely in the more fluid interior. Those Protista that, while exhibiting amoeboid move- ments, have no clear external layer, such as the Radiolaria, Fora- minifera, Heliozoa, etc., present this streaming even at the surface, the granules travelling up and down the pseudopodia at a rate much greater than the movements of these organs them- selves. In this case the protoplasm is wetted by the medium, which it is not where there is a clear outer layer: for that behaves like a greasy film. Motile organs.—Protoplasm often exhibits movements much more highly specialised than the simple expansion or retraction of processes, or the general change of form seen in Amoeba. If we imagine the activities of a cell concentrated on particular parts, we may well suppose that they would be at once more precise and more energetic than we see them in Amoeba or the leucocyte. In some free-swimming cells, such as the individual cells known as “ Flagellata,” the reproductive cells of the lower Plants, or the male cells (“spermatozoa”) of Plants as high as Ferns, and even of the Highest Animals, there is an extension of the cell into one or more elongated lash-like processes, termed “flagella,” which, by beating the water in a reciprocating or a spiral rhythm, cause the cell to travel through it ; or, if the cell be attached, they produce currents in the water that bring food particles to the surface of the cell for ingestion. Such flagella may, indeed, be seen in some cases to be modified pseudopodia. In other cases part, or the whole, of the surface of the cell may be covered with regularly arranged short filaments of similar activity (termed “cilia,” from their resemblance to a diminutive eyelash), which, however, instead of whirling round, bend sharply 1 The terms ‘‘ expansion” and “contraction ” refer only to the superficial area : it is very doubtful whether the volume alters during these changes. VOL. I C 18 PROTOZOA CHAP. down to the surface and slowly recover; the movement affects the cilia successively in a definite direction in waves, and pro- duces, like that of flagella, either locomotion of the cell or currents in the medium. We can best realise their action by recalling the waves of bending and recovery of the cernstalks in a wind-swept field; if now the haulms of the corn executed these movements of themselves, they would determine in the air above a breeze-like motion in the direction of the waves (Fig. 5). Such cilia are not infrequent on those cells of even the Highest Animals that, like a mosaic, cover free surfaces (“epithelium cells ”). In ourselves such cells line, for instance, the windpipe. One group of the Protozoa, the “ Ciliata,” are, as their name implies, ciliated cells pure and simple. The motions of cilia and of fiagella are probably also due to changes of surface tension—alternately on one side and the other Jf If i| {Pep | WH 4 Z = LE ie ne £ J = a Af ' Al ZL, KctFLl LZZL A Fic. 5. Motion of a row of cilia, in profile. (From Verworn.) in the cilium, but passing round in circular succession in the flagellum,” giving rise to a conical rotation lke that of a weighted string that is whirled round the head. This motion is, however, strongest at the thicker basal part, which assumes a spiral form like a corkscrew of few turns, while the thin lash at the tip may seem even to be quietly extended like the point of the corkscrew. If the tip of the flagellum adhere, as it sometimes does, to any object, the motions induce a jerking motion, which in this case is reciprocating, not rotatory. When the organism is free, the flagellum is usually in advance, and the cell follows, rotating at the same time round its longitudinal axis; such an anterior flagellum, called a “ tractellum,” is the common form in Protista that possess a single one (Figs. 29,7,8; 30,C). In the sperma- tozoa of Higher Animals (and some Sporozoa) the flagellum is posterior, and is called a “ pulsellum.” The cilium or flagellum may often be traced a certain distance into the substance of the cytoplasm to end in a dot of denser, 1 For discussions on the mechanism of ciliary action, see Schifer, Anat. Anz. Xxiv. 1904, p. 497, xxvi. 1905, p. 517; Schuberg, Arch. Protist. vi. 1905, p. 85. 5) = ° Like the line of most rapid growth in a circumnutating plant-stem. I MOTILE REACTIONS 19 . readily-staining plasm, which corresponds to a “centrosome ” or centre of plasmic forces (see below, pp. 115, 121, 141); it has been termed a “ blepharoplast.” Again, the cytoplasm may have differentiated in it definite streaks of specially contractile character ; such streaks within its substance are called “myonemes”; they are, in fact, muscular fibrils. A “muscle-cell,” in the Higher Animals, is one whose protoplasm is almost entirely so modified, with the exception of a small portion of granular cytoplasm investing the nucleus, and having mainly a nutritive function. ’ Definite muscular fibrils in action shorten, and at the same time become thicker. It seems probable that they contain elon- gated vacuoles, and that the contents of these vary, so that when they have an increased osmotic equivalent, the vacuoles absorb water, enlarge, and tend to become more spherical, 7.e. shorter and thicker, and so the fibril shortens as a whole. The relaxation would be due to the diffusion outwards of the solution of the osmotically active substances which induced expansion.” The Motile Reactions of the Protozoa’ require study from another point of view: they are either (1) “spontaneous” or “arbitrary,” as we may say, or (2) responsive to some stimulus. The latter kind we will take first, as they are characteristic of all free cells. The stimuli that induce movements of a responsive character are as follows :—(i.) MECHANICAL: such as agitation and contact ; (ii.) force of GRAVITY, or CENTRIFUGAL FORCE; (iiL) CURRENTS in the water; (iv.) RADIANT ENERGY (LIGHT); (v.) changes in the TEMPERATURE of the medium; (vi.) ELECTRIC CURRENTS through the medium; (vil.) the presence of CHEMICAL SUBSTANCES in the medium. These, or some of them, may induce one of three different results, or a combination thereof: (1) a single movement or an arrest of motion; (2) the assumption of a definite position ; (3) movement of a definite character or direction. 1 A similar body lies at the centre to which the axial filaments of the radiating pseudopodia of the Heliozoa converge, and might be termed by parity a ** nodoplast”’ ; but ‘‘ centrosome” is a convenient general term to include all such bodies. It is clearly of nuclear origin in Trypanosoma (Fig. 39, p. 120). 2 See for development of this view W. M‘Dougall in Journ. Anat. Physiol. xxxi. 1897, pp. 410, 539. I put it forward in the first draft of this essay in 1894. ’-The best general account is to be found in Davenport, Experimental Morphology, 1897. 26) PROTOZOA CHAP. (i.) MECHANICAL STIMULIL—Any sudden touch with another body tends to arrest all motion; and if the shock be protracted or severe, the retraction of the pseudopodia follows. It is to this reaction that we must ascribe the retracted condition of the pseudopodia of most Rhizopods when first placed on the slide and covered for microscopic examination. Free-swimming Protista may, after hitting any body, either remain in contact with it, or else, after a pause, reverse their movement, turn over and swim directly away. This combination of movements is characteristic as a reaction of what we may term “repellent” stimuli in general.’ Another mechanical reaction is that to continuous contact with a solid; and the surface film of water, either at the free surface or round an air-bubble, may play the part of a solid in exciting it; we term it “thigmotaxy ” or “stereotaxy.” When positive it determines a movement on to the surface, or a gliding movement along it, or merely the arrest of motion and prolongation of contact ; when negative, a contact is followed by the retreat of the being. Thus Paramecium (Fig. 55, p. 151) and many other Ciliates are led to aggregate about solid particles or masses of organic débris in the water, which indeed serve to supply their food. On contact, the cell ceases to move its cilia except those of the oral groove; as these lash backwards, they hold the front end in close contact with the solid, at the same time provoking a backward stream down the groove, which may bring in minute particles from the mass. Gi.) Most hving beings are able to maintain their level in water by floating or crawling against Gravity, and they react in virtue of the same power against centrifugal force. This mode of irritability is termed (negative) “ geotaxy ” or “ barotaxy.” We can estimate the power of resisting such force by means of a whirling machine, since when the acceleration is greater than the resistance stimulated thereby in the beings, they are passively sent to the sides of the vessel. The Flagellates, Buglena and Chlamydomonas, begin to migrate towards the centre when exposed to a centrifugal force about equal to } G (G = 32°2 feet or 982 cm. per second); they remain at the centre until the centrifugal force is increased to 8 G; above that they yield to the force, and are driven passively to the sides. The reaction ceases or is reversed at high temperatures. 1 See Jennings in Woods Holl. Biol. Lect. 1899, p. 93. I REACTIONS TO STIMULI 21 (iii.) RHEOTAXY.—This is the tendency to move against the stream in flowing water. It is shown by most Protists, and can be conveniently studied in the large amoeboid plasmodia of the Myxomycetes, which crawl against the stream along wet strips of filter paper, down which water is caused to flow. Most animals, even of the highest groups, tend to react in the same way ; the energetic swimming of Fishes up-stream being in marked contrast with their sluggishness the other way; and every student of pond-life knows how small Crustacea and Rotifers, no less than Ciliates, swim away from the inrush of liquid into the dipping-tube, and so evade capture. (See Vol. II. p. 216.) (iv.) The movements of many Protozoa are affected greatly by Licut. These movements have been distinguished into “ photo- pathic,” ze. to or from the position of greatest luminosity; and “ phototactic,” along the direct path of the rays.| Those Protozoa that contain a portion of their cytoplasm, known as a “ plastid” or “chromatophore ” (see pp. 36, 39), coloured by a green or yellow pigment are usually “phototactic.” They mostly have at the anterior end a red pigment spot, which serves as an organ of sight, and is known as an “ eye-spot.” In diffused light of low intensity they do not exhibit this reaction, but in bright sunlight they rise to the surface and form there a green or yellow scum, Most of the colourless Protista are negatively phototactic or photopathic ; but those which are parasitic on the coloured ones are positively phototactic, like their hosts. Here, as in the case of other stimuli,? the absolute intensity of the light is of importance; for as it increases from a low degree, different organisms in turn cease to be stimulated, and ' It is not always easy to distinguish these two classes of phenomena. * Jennings, in his studies on Reactions to Stimuli in Unicellular Organisms (1899-1900), has shown that whatever be the nature of the repellent stimulus, chemical or mechanical or thermal, the reaction of Parameciwm and many other Protista is always the same. It swims backward a short distance, turns towards the aboral surface, and then having thus reversed swims on again in the new direction, front foremost as before. Apparent “ positive taxies’’ are often really negative ones ; for if the Paramecium be placed in water containing CO, it shows the reaction not on entering the part charged with this acid, but on passing away from it into purer water, so that it continually tends to turn back into the acid part, while within it or in the water at a distance not yet charged it swims about irregularly. It appears due to this that the individuals become aggregated together, as they excrete this gas into the water. If a repellent substance diffuse towards the hinder end of a Parameciwm, the response, instead of carrying it away, brings it into the region of greater concentration, and may thus kill it. PROTOZOA CHAP. i) WN then are repelled instead of being attracted. The most active part of the spectrum in determining reactions of movement are the violet and blue rays of wave-length between 40 4/10 and 49 ~/10, while the warmer and less refractive half of the spectrum is inert save in so far as it determines changes in the tempera- ture of the medium. (v.) The movements of many Protozoa are rendered sluggish by cold, and active by a rise of TEMPERATURE up to what we may term the “optimum”; the species becomes sluggish again as the temperature continues to rise to a certain point when the movements are arrested, and the being is said to be in a state of “heat-rigor.” Most Protozoa, again, tend to move in an unequally heated medium to the position nearest to their respective optimum temperature. This is called “ thermotaxy.” The temperature to which Amoeba is thermotactic is recorded as 35° C. (95° F.); that of Paramecium is 28° C. (82° F.). (vi.) Most active Protozoa tend to take up a definite position in respect to a current of ELECTRICITY passing through the medium, and in the majority of cases, including most Ciliates, Amoeba, and Trachelomonas, they orient their long diameters in the direction of the lines of force and swim along these to assemble behind the cathode. The phenomenon is called “ valvanotaxy,” and this particular form is “negative.” Opalina (Fig. 41, p. 123), however, and most Flagellates are “positively galvanotactic,” aud move towards the anode. H. H. Dale’ has shown that the phenomenon may be possibly in reality a case of chemiotaxy, for the direction of motion varies with the nature and concentration of the medium. It would thus be a reaction to the “ion” liberated in contact with the one or other extremity of the being. Induction shocks, as we have seen, if slight, arrest the movements of Protozoa, or if a little stronger determine movements of contraction; if of sufficient intensity they kill them. No observation seems to have been made on the behaviour of Protista in an electric field) A magnetic field of the highest intensity appears to be indifferent to all Protista. (vii.) We have already referred to the effect of dissolved CHEMICAL SUBSTANCES present in the water. If the substance is in itself not harmful, and the effect varies with the concentra- tion, we term the reaction one of “tonotaxy,” which combines 1 “ Galvanotaxis and Chemotaxis,” Journ. of Physiol. vol. xxvi. 1900-1901, p. 291. I REPRODUCTION 23 with that of “chemiotaxy ” for substances that in weak solution are attractive or repellent to the being. Paramecium, which feeds on bacteria, organisms of putrefaction, is positively chemiotactic to solutions of carbon dioxide, and as it gives this off in its own respiration, it is attracted to its fellows. The special case of reaction to gases in solution is termed “ aerotaxy,” or “ pneumo- taxy,” according as the gas is oxygen or carbon dioxide. We find that in this respect there are degrees, so that a mixed culture of Flagellates in an organic infusion sorts itself out, under the cover of a microscopic preparation, into zones of distinct species, at different distances from the freely aerated edge, according to the demands of each species for oxygen and CO, respectively. Finally, we must note that the apparently “spontaneous movements ” of Protists can hardly be explained as other than due either to external stimul, such as we have just studied, or to internal stimuli, the outcome of internal changes, such as fatigue, hunger, and the like. Of the latter kind are the movements that result in REPRODUCTION. Reproduction.— We have noted above that the growth of an organism which retains its shape alters the ratio of the surface area to the whole volume, so necessary for the changes involved in life. For the volume of an organism varies as the cube of any given diameter, whereas the surface varies with the square only. Without going into the arithmetical details, we may say ‘that the ratio of surface to volume is lessened to roughly four-fifths of the original ratio when the cell doubles its bulk. As Herbert Spencer and others have pointed out, this must reduce the activities of the cell, and the due ratio is restored by the division of the cell into two.’ This accounts for what we must look on as the most primitive mode of reproduction, as it is the simplest, and which we term “fission” at Spencer’s “limit of 1 Let us take the case of a 1-centimetre cube, growing to the size of a 2-centimetre cube. The superficial area of the 1 em. cube measures 6 square centimetres, and its bulk is 1 cubic centimetre. The superficial area of the 2-centimetre cube measures 24 square centimetres, while its volume measures 8 cubic centimetres. Thus the larger cube has only 3 em. sq. of surface to every cubic em. of volume, instead of 6; in other words, the ratio of surface to volume has been halved by growth. Three successive bipartitions of the larger cube will divide it into eight separate 1-centimetre cubes, each now possessing the original ratio of surface to volume. 24 PROTOZOA CHAP. growth.” Other modes of reproduction will be studied later (p. 30), after a more detailed inquiry into the structure of the nucleus and of its behaviour in cell-division. All cell- division is accompanied by increased waste, and is consequently catabolic in character, though the anabolic growth of living protoplasm, at the expense of the internal reserves, may be concurrent therewith. CELL-DIVISION In ordinary cases of fission of an isolated cell the cell elongates, and as it does so, like other viscid bodies, contracts in the middle, which becomes drawn out into a thread, and finally gives way. In some cases (e.g. that of the Amoeba, Fig. 4) the nucleus previously undergoes a similar division by simple constriction, which is called direct or “amitotic” division. But usually the division of the nucleus prior to cell-division is a more complex process, and involves the co-operation of the cytoplasm ; and we inust now study in detail the nucleus and its structure in “rest” and in fission.’ We have noted above (p. 6, Fig. 2) the structure of the so-called “resting nucleus,’” when the cell is discharging the ordinary functions of its own life, with its wall, network of linin, chromatin-granules, and nucleole or nucleoles. The chromatin- granules are most abundant at two periods in the hfe of the cell, (1) when it is young and fresh from division, and (2) at the term of its life, when it is itself preparing for division. In the interim they are fewer, smaller, and stain less intensely. In many Protista the whole or greater part of the chromatin is densely aggregated into a central “nuclein-mass” or karyosome 1 The nucleus is regarded by some as equivalent to a central nervous organ for the cell; by others, such as G. Mann and Verworn, as the chief chemical centre of the cell, and notably the seat of the secretion of the zymases or ferments that play so important a part in its life-work ; for it is found that a Protist deprived of its nucleus can execute its wonted movements, but can neither digest nor grow. This conclusion may appear to be rather sweeping and premature, but we have seen that the changes of surface tension are the direct antecedents of the motions of the cytoplasm, we know that such changes are induced by chemical changes ; and thus the nucleus—if it be the central laboratory to which such changes are ultimately due—would really in a certain sense be a directive centre. ° The term ‘‘resting” is very ill-chosen, for even superficial observation shows that the relative position and characters of the internal structures of such a nucleus are constantly changing with the vital activities and functions of the cell. I CELL-DIVISION ra suspended in the linin network (long regarded as a mere Fic. 6.—Changes in nucleus and cell in indirect (mitotic) nuclear division. A, resting nucleus with two centrioles! in single centrosphere (c); B, centrosphere divided, spindle and two asters (#) forming; C, centrospheres separated, nuclear wall disappearing ; D, resolution of nucleus into chromosomes; E, mature plasmic spindle, with longitudinal fission of chromosomes; F, chromosomes forming equatorial plate (ey) of spindle. (From Wilson.) nucleole). Such a nucleus is often termed a “vesicular nucleus.” 1 The “‘ centriole” is a minute granule sometimes recognisable in the centre of the centrosphere, and undergoing fission in advance. But centrosomes are often found without a distinction into centrosphere and centriole, and there is muci confusion in the use of the terms. * For a detailed study of the nucleus in Protista, see Calkins in Arch. Protistenk. yol. ii. 1903. 20 PROTOZOA CHAP. When cell-division is about to take place the linin, or at least the greater part of it, assumes the character of a number of distinct threads, and the whole of the chromatin granules are distributed at even distances along these (Fig. 6, A, B, ©), so as to appear like so many strings of beads. | Each such thread is called a “chromosome.” Then each bead divides longitudinally into two. The thread flattens into a ribbon, edged by the two lines of chromatin beads. Finally, the ribbon splits longitudinally into two single threads of beads (Fig. 6, EK). During these changes the nucleole or nucleoles diminish, or even disappear, as if they had contributed their matter to the growth of the chromatin proper. In Higher Animals and Plants the nuclear wall next disappears, and certain structures become obvious, especially in the cytoplasm of Metazoa. Two minute spheres of plasm (themselves often showing a concentric structure), the “centrosomes,” ' which hitherto lay close together at the side of the nuclear wall, now separate; but they remain connected by a spindle of clear plasmic threads (Fig. 6, B-E) which, as the centres diverge, comes to he across the spot the nucleus occupied, and now the chromosomes lie about the equator of this spindle (Fig. 6, F). Moreover, the surrounding cytoplasm shows a radiat- ing structure, diverging from the centrosome, so that spindle and external radiations together make up a “ strain-figure,” like that of the “ lines of force” in relation to the poles of a magnet. Such we can demonstrate in a plane by spreading or shaking iron filings on a piece of paper above the poles of a magnet, or in space by suspending finely divided iron in a thick liquid, such as mucilage or glycerin, and bringing the vessel with the mixture into a strong magnetic field ;* the latter mode has the advantage 1 The origin of the centrosomes is a problem not yet certainly solved, if indeed it be susceptible of any universal solution. They are certainly absent in many plants ; and, on the other hand, structures which correspond to them often appear in mitotic divisions of Protista. In some cases the centrosomes are undoubtedly of nuclear origin, and pass out through the nuclear wall into the cytoplasm. 2 Though the forces at work in the dividing cell are similar in their effects to such physical forces as magnetism, static electricity, and even capillarity, and models utilising such physical forces have been devised to represent the strain- figures of the cell, the cell forces are distinct from any known physical force. For discussions of the nature of the forces at work, with bibliographies, see Augel Gallardo, Interpretacién Dindmica de la Division Celular, 1902; Rhumbler, in Arch. Entw. xvi. 1903, p. 476 ; Hartog, O.R. exxxviii. 1904, p. 1525, and ‘‘On the Dual Force of the Dividing-cell,” pt. i. Proc. Roy. Soc. 1905 B, Ixxvi. p. 548. I NUCLEAR DIVISION OY, of enabling us to watch the changes in the distribution of the lines under changing conditions or continued strain. The chromosomes are now completely spht, each into its two daughter-segments, which glide apart (Fig. 7, G, ep), and pass each to its own pole of the spindle, stopping just short of the § Fic. 7.—Completion of mitotic cell-division. G, splitting of equatorial plate (ey); H, recession of daughter chromosomes ; I, J, reconstitution of these into new nuclei, fission of the centrioles and of the cytoplasm. 77, Central fibres of spindle ; 1, remains of old nucleole. (From Wilson.) centrosome (I). Thus, on the inner side of either centrosome is found an aggregation of daughter-segments, each of which is sister to one at the opposite pole, while the number at either pole is identical with that of the segments into which the old nucleus had resolved itself at the outset. The daughter-segments shorten and thicken greatly as they diverge to the poles, and on their arrival crowd close together. A distinct wall now forms around the aggregated daughter- 28 PROTOZOA CHAP. chromosomes (J), so as to combine them into a nucleus for the daughter-cell. The reorganisation of the young nucleus certainly varies in different cases, and has been ill-studied, probably because of the rapidity of the changes that take place. The cytoplasm now divides, either tapering into a “ waist” which finally ruptures, or constricting by the deepening of a narrow annular groove so as to complete the formation and isolation of the daughter-cells. We might well compare the cell-division to the halving of a pumpkin or melon, of which the flesh as a whole is simply divided into two by a transverse cut, while the seeds and the cords that suspend them are each singly split to be divided evenly between the two halves of the fruit; the flesh would represent the cytoplasm, the cords the linin threads of the nucleus, and the seeds the chromatin granules. In this way the halving of the nucleus is much more complete and intimate than that of the cytoplasm; and this is the reason why many biologists have been led to regard the nuclear seg- ments, and especially their chromatic granules, as the seat of the hereditary properties of the cell, properties which have to be equally transmitted on its fission to each daughter-cell. But we must remember that the linin is also in great part used up in the formation of these segments, like the cords of our supposed melon; and it is open to us to regard the halving in this intimate way of the “linin” as the essence of the process, and that of the chromatin as accessory, or even as only part of the necessary machinery of the process. The halving or direct splitting lengthwise of a viscid thread is a most difficult problem from a physical point of view; and it may well be that the chromatin granules have at least for a part of their function the facilitation of this process. If such be the case, we can easily understand the increase in number, and size and staining power of these granules as cell-division approaches, and their atrophy or partial disappearance during their long intervening periods of active cell life. Hence we hesitate to accept the views so commonly maintained that the chromatin represents a “ germ- 1 See Th. Boveri, Ergebnisse web. d. Konstitution d. chromatischen Substanz des Zelikerns (1903), for the most recent defence of this view. He lays, however (p. 2), far more stress on the individuality of the segments themselves than on the actual chromatin material they contain, I MITOSIS OR KARYOKINESIS 29 plasm” or “idioplasm” of relatively great persistence, which gives the cell its own racial qualities. The process we have just examined is called “ mitosis,” ‘karyomitosis,” or “karyokinesis”; and the nucleus is said to undergo “indirect” division, as compared to “direct” division by mere constriction. In an intermediate mode, common to many Protista, the nuclear wall persists throughout the whole Fic. 8.—Fission with modified karyokinesis in the Filose Rhizopod ELuglypha. A, out- growth of half of the cytoplasm, passage of siliceous plates for young shell outwards ; B, completion of shell of second cell, formation of izéra-nuclear spindle ; C, D, further stages. (From Wilson, after Schewiakoff.) process, though a spindle is constituted within, and chromosomes are formed and split: the division of the nucleus takes place, however, by simple constriction, as seen in the Filose Rhizopod Huglypha (Fig. 8). In many Sarcodina and some Sporozoa the nucleus gives off small fragments into the cytoplasm, or is resolved into them ; 1 The fact that it is by mitotic division that the undifferentiated germ-cells produce the ‘‘differentiated” tissue-cells of the body of the highest animals, is again irreconcilable with such theories, whose chief advocates have been A. Weis- mann and his disciples. 30 : PROTOZOA CHAP. they have been termed “chromidia” by Rk. Hertwig. New nuclei may be formed by their growth and coalescence, the original nucleus sometimes disappearing more or less completely. In certain eases the division of the nucleus is not followed by that of the cytoplasm, so that a plurinucleate mass of protoplasm results: this is called an “apocyte”; and we find transitional forms between this and the uninucleate or true cell. Thus in one species of Amoeba (A. binucleata) there are always two nuclei, which divide simultaneously to provide for the outfit of the daughter-cells on fission. Again, we find in some cases that similar multinucleate masses may be formed by the union of two or more cells by their cytoplasm only: such a union is termed “permanent plastogamy,’ and the plurinucleate mass a “ plas- modium.”! Here again we find intermediate forms between plas- modium and apocyte, for the nuclei of the former may divide and so increase in number, without division of the still growing mass. Both kinds of plurinucleate organisms are termed “coenocytes ” without reference to their mode of origin. The rhythm of cell-life that we have just studied is called the “Spencerian” rhythm. Each cell in turn grows from half the bulk of its parent at the time it was formed to the full size of that parent, when it divides in its own turn. Lest is rare, and assumed only when the cell is exposed to such unfavourable external conditions as starvation, drought, etc.; 1t has no necessary relation to fission. Multiple fission or brood-formation.— We may now turn to a new rhythm, in strong contrast to the former: a cell after having attained a size, often notably greater than its parents, divides: without any interval for growth, the daughter-cells again divide, and this may be repeated as many as ten times, or even more, so as to give rise to a number of small cells—4, 8, 16—1024> etc., respectively. Such an assemblage of small cells so formed is called a brood, and well deserves this name, for they never separate until the whole series of divisions is completed. By this process the number of individuals is rapidly ' Temporary plastogamy is a process found in some Foraminifera, where two organisms unite by their cytoplasms so that there can be complete blending of these, while the nuclei remain distinct: they ultimately separate again. In the conjugation of the Infusoria, the union of the ecytoplasms is a temporary plastogamy (see p. 148 f.). “ See Figs. 9, 29; 31, 34, etc., pp. 54, 89, 95, 101. I BROOD-FORMATION—COLONIES oie! increased, hence it has received the name of “sporulation.” The term spores is especially applhed to the reproductive bodies of Cryptogams, such as Mosses, Fungi, etc.: the resulting cells are called “ spores,” “zoospores” if active (“amoebulae” if provided with pseudopodia, “ flagellulae” if flagellate), “ aplanospores,” if motionless. We prefer to call them by the general term “ brood- cells,” the original cell the “ brood-mother-cell,” and the process, “multiple fission” or “ brood-formation.” As noted, the brood- mother-cell usually attains an exceptionally large size, and it in most cases passes Into a state of rest before entering on division : thus brood-formation is frequently the ultimate term of a long series of Spencerian divisions. Two contrasting periods of brood-formation may occur in the life cycle of some beings, notably the Sporozoa.' Colonial union.— In certain cases, the brood-cells instead of separating remain together to form a “colony”; and this may enlarge itself again by binary division of its individual cells at their limit of growth. Here, certain or all of the cells may (either after separation, or in their places) undergo brood- formation: such cells are often termed “reproductive cells” in contrast with the “colonial cells.” Some such colonial Protista must have been the starting- points for the Higher Animals and Plants; probably apocytial Protista were the starting-points of the Fungi. In the Higher Animals and Plants, the spermatozoa and the oospheres (the male and female pairing-cells) are alike the offspring of brood-formation: and the coupled-cell (fertilised egg) starts its new life by segmentation, which is a brood-formation in which the cells do not separate, but remain in colonial union, to differentiate in due course into the tissue-cells of the organism. Retarded brood-formation.—The nuclear divisions may alternate with cell-divisions, as above stated, or the former may be 1 One obvious effect of brood-formation is to augment rapidly the ratio of superficial area to bulk: after only three divisions (p. 23, note) the ratio is doubled ; if the divisions be nine in succession so as to produce a brood of 512, the ratio is increased eightfold, on the supposition that the figure is preserved. How- ever, the brood-mother-cell is usually spherical, while zoospores are mostly elongated, thus giving an additional increase to the surface, which we may correlate with that increased activity; so that they disseminate the species, spreading far and wide, and justifying the name of ‘‘spore” in its primitive sense (from the Greek oreipw—I scatter [seed]). 32 PROTOZOA CHAP. completed before the cytoplasm divides; thus the brood-mother- cell becomes temporarily an apocyte,’ which is then resolved simultaneously into the 1-nucleate brood-cells. A temporary apocytial condition is often passed through in the formation of the brood of cells by repeated divisions without any interval for enlargement ; for the nuclear divisions may go on more rapidly than those of the cytoplasm, or be completed before any cell-division takes place (Figs. 31, 34, 35, pp. 95; 101, 104), the nuclear process being “accelerated” or the cytoplastic being “retarded,” whichever we prefer. to say and to hold. Thus as many as thirty-two nuclei may have been formed by repeated binary subdivisions before any division of the cytoplasm takes place to resolve the apocyte into true 1-nucleate cells. In many cases of brood-formation the greater part of the food-supply of the brood-mother-cell has been stored as reserve-products, which accumulate in quantity in the cell; this is notably seen in the ovum or egg of the Higher Animals. How great such an accumulation may be is indeed well seen in the enormous yolk of a bird’s egg, gorged as it were to repletion. When a cell has entered on such course of “miserly” conduct, it may lose all power of drawing on its own supplies, and finally that of accumulating more, and passes into the state of “rest.” To resume activity there is needed either a change in the internal conditions—demanding the lapse of time— or in the external conditions, or in both.2 We may call this resumption “ germination.” Very often in the study of a large and complex organism we are able to find processes in action on a large scale which, depending as they must do on the protoplasmic activities of its individual cells, reveal the nature of similar processes in simple unicellular beings: such a clue to the utilisation of reserves by a cell which has gorged itself with them so as to pass into a state of rest is to be found in that common multicellular organism, the Potato. This stores up reserves in its underground stems (tubers); if we plant these immediately on the completion of their growth, they will not start at once, even under what would outwardly seem to be most appropriate conditions. A certain lapse of time is an essential factor for sprouting. It would appear that in the Potato the starch can only be digested by a definite ferment, which does not exist when it is dug, but which is only formed very slowly, and not at all until a certain time has supervened ; and that sprouting can only 1 This condition may be protracted in the segmentation of the egg of certain Higher Animals, such as Peripatus (Vol. V. p. 20). It is clearly only a secondary and derived condition. ° The usual antecedent of change in the condition of the egg is ‘‘ fertilisation ’— its conjugation with the sperm ; but this is not invariable ; and a transitory sojourn of certain marine eggs in a liquid containing other substances than sea-water may induce the egg on its return to its native habitat to segment and develop. This has been mistermed ‘‘ Chemical fertilisation,” discovered within the last six years by Jacques Loeb, and already the subject of an enormous literature. I SYNGAMY—GAMETES——ZYGOTE 33 take place when soluble material has been provided in this way for the growth of the young shoots. We have also reason to believe that these ferments are only formed by the degradation of the protoplasm itself. Now obviously this degradation must be very slow in a resting organism; and any external stimulus that will tend to protoplasmic activity will thereby tend to form at the same time the digestive ferments and dissolve the stored supplies, to render them available for the life-growth and reproduction of the being. We now see why inactive “miserly” cells so often pass into a resting state before dividing, and why they go on dividing again and again when once they re-enter upon an active life, the living protoplasm growing at the expense of the reserves! Resting cells of this type occur of course only at relatively rare intervals in the animal-feeding Protozoa, that have to take into their substance the food they require for their growth and life- work, and cannot therefore store up much reserves. For they are constantly producing in the narrow compass of their body those very ferments that would dissolve the reserves when formed. Internal parasites and “sapro- phytes,” that is, beings which live on dead and decayed organic matter, on the other hand, live surrounded by a supply of dissolved food ; and rarely do we find larger cells, richer in reserves, than in the parasitic Sporozoa, which owe their name to the importance of brood-formation in their life-history. In Radiolaria (p. 75 f.) a central capsule separates off an inner layer of protoplasm ; the outer layer is the one in which digestion is performed, while the inner layer stores up reserves; and here brood-formation appears to be the rule. But the largest cells of all are the eggs of the Metazoa, which in reality lead a parasitic life, being nurtured by the animal as a whole, and contributing nothing to the welfare of it as an individual. Their activity is reduced to a minimum, and the consequent need for a high ratio of surface to volume is also reduced, which accounts for their inordinate size. But directly the reserve materials are rendered available by the formation of a digestive ferment, then protoplasmic growth takes place, and the need for an extended surface is felt ; cell-division follows cell-division with scarcely an interval in _the process of segmentation. Syngamy.’—The essence of typical syngamy is, that two cells (“ pairing-cells,” “ gametes”) of the same species approach one another, and fuse, cytoplasm with cytoplasm, and nucleus with nucleus, to form a new cell (“coupled-cell,” “zygote”). This process is called also “conjugation” or “cytogamy.” In the simplest cases the two cells are equal and attract one another equally (“isogamy”), and have frequently the character of zoospores. In an intermediate type, the one cell is larger and more sluggish (female), “ megagamete,” “ oogamete,” “ oosphere,” “egg” ; the other smaller, more active (male), “ microgamete,” “ spermo- gamete,” “spermatozoon,” “sperm”; and in the most specialised 2 1 See Hartog in Rep. Brit. Ass. 1896, p. 933, 1900, p. 786. 2 Commonly called “ fertilisation,” or ‘‘sexual union,” inadequate and mis- leading terms. VOL. T D 34 PROTOZOA CHAP. cases which prevail among the Higher Animals and Plants, the larger cell is motionless, and the smaller is active, ciliate, flagellate, or amoeboid: the coupled-cell or zygote is here termed the “oosperm.”* It encysts immediately in most Protista except Infusoria, Acystosporidae, Haemosporidae, and Trypanosomatidae. As the size of the two gametes is so disproportionate in most cases that the oosphere may be millions of times bigger than the sperm, and the latter at its entrance into the oosphere entirely escape unaided vision, the term “egg” is applied in lax speech, both (1) to the female cell, and (2) to the oosperm, the latter being distinguished as the “ fertilised egg,” a survival from the time when the union of fwo cells, as the essence of the process, was not understood. We know that in many cases, and have a right to infer that in all, chemiotaxy plays an important part in attracting the pairing-cells to one another. In Mammals and Sauropsida there seems also to he a rheotactic action of the cilia lining the oviducts, which work downwards, and so induce the sperms to swim upwards to meet the ovum, a condition of things that was most puzzling until the nature of rheotaxy was understood. A remark- able fact is that equal gametes rarely appear to be attracted by members ot the same brood, though they are attracted by those of any other brood of the same species.2 It may well be that each brood has its own characteristic secretion, or “smell,” as it were, slightly different from that of other broods, just as every dog has his, so easily recognisable by other dogs ; and that the cells only react to different “smells” to their own. Such a secretion from the surface of the female cell would lessen its surface tension, and thereby render easier the penetration of the sperm into its substance. Asarule, one at least of the pair-cells is fresh from division, and it would thus appear that the union of the nuclei is facilitated when one at least of them is a “ young” one. Of the final mechanism of the union of the nuclei, we know nothing: they may unite in any of the earlier phases of mitosis, or even in the “resting state” A fibrillation of the cytoplasm during the process, radiating around a centrosome or two centrosomes indicates a strained condition.® 1 For details see Hartog, ‘‘Some Problems of Reproduction,” Quart. Journ. Mier. Sci. Xxxlii. p. 1, xlvii. p. 583; and Ann. Biol. vol. iv. (1895) 1897 ; E. B. Wilson, Yves Delage, and Henneguy (references on p. 3, note) ; and for a singularly clear and full treatment of the processes in Protozoa, Arnold Lang, Lehrb. d. Vergl. Anat. 2nd ed. Lief. 2, ‘‘ Protozoa,” 1900. ° This phenomenon, which we have termed ‘‘exogamy,” is common in Proto- phyta ; it has been clearly demonstrated by Schaudinn in Foraminifera and the Lobose Rhizopod Trichosphaerium (p. 53 f. Fig. 9), and by Pringsheim in the Volvocine Pandorina (p. 128 f. Fig. 45). It is quite independent of the differentia- tion of binary sex. * Other modes of syngamy, such as karyogamy and plastogamy, we shall discuss below, pp. 69, 148 ; sce also p. 30. I REGENERATION—ANIMALS AND PLANTS 35 Regeneration.—Finally, experiments have been made by several observers as to the effects of removing parts of Protozoa, to see how far regeneration can take place. The chief results are as follows :— 1. A nucleated portion may regenerate completely, if of sufficient size. Consequently, multinucleate forms, such as Actinosphaerivum (Heliozoa, Fig. 19, p. 72), may be cut into a number of fragments, and regenerate completely. In Ciliata, such as Stentor (Fig. 59, p. 156), each fragment must possess a portion of the meganucleus, and at least one micronucleus (p. 145), and, moreover, must possess a certain minimum size. A Radiolarian ~“central-capsule” (p. 75) with its endoplasm and nucleus may regenerate its ectoplasm, but the isolated ectoplasm being non- nucleate is doomed. A “ central capsule ” of one species introduced into the ectoplasm of another, closely allied, did well. All non- nucleate pieces may exhibit characteristic movements, but appear unable to digest; and they survive only a short time." «“ ANIMALS” AND “ PLANTS ” Hitherto we have discussed the cell as if it were everywhere an organism that takes in food into its substance, the food being invariably “organic” material, formed by or for other cells; such nutrition is termed “ holozoic.” There are, however, limits to the possibilities in this direction, as there are to the fabled capacities of the Scillonians of gaining their precarious liveli- hood by taking in one another’s washing. For part of the food material taken in in this way is apphed to the supply of the energies of the cell, and is consequently split up or oxidised into simpler, more stable bodies, no longer fitted for food; and of the matter remaining to be utilised for building up the organism, a certain proportion is always wasted in by-products. Clearly, then, the supply of food under such conditions is continually lessening in the universe, and we have to seek for a manufactory of food-material from inorganic materials: this is to be found in those cells that are known as “ vegetal,’ in the widest sense of 1 See Gruber in Biol. Centralb. iv. p. 710, v. p. 137 (1884-6), in Ber. Ges. Freiburg, i. ii. 1886-7 ; Verworn (reference on p. 16); F. R. Lillie in Journ. Morph. xii. 1896, p- 239 ; Nussbaum in dren. mikr. Anat. xxvi. 1886, p. 485 ; Balbiani in Recueil Zool. Suisse, v. 1888, in Zool. Anz. 1891, pp. 312, 323, in Arch. Microgr. iv. v. 1892-3. For Higher Organisms especially see T. H. Morgan, Regeneration, 1901. 3 6 PROTOZOA CHAP. the word. In this sense, vegetal nutrition is the utilisation of nitrogenous substances that are more simple than proteids or peptones, together with suitable organic carbon compounds, etc., to build up proteids and protoplasm. The simplest of organisms with a vegetal nutrition are the Schizomycetes, often spoken of loosely as “bacteria” or “ microbes,’ in which the differentiation of cytoplasm and nucleus is not clearly recognisable. Some of these can build up their proteids from the free uncombined nitrogen of the atmosphere, carbon dioxide, and inorganic salts, such as sulphates and phosphates. But the majority of vegetal feeders require the nitrogen to be combined at least in the form of a nitrate or an ammonium salt—nay, for growth in the dark, they require the carbon also to be present in some organic combination, such as a tartrate, a carbohydrate, etc. Acetates and oxalates, “aromatic” compounds’ and nitriles are rarely capable of being utilised, and indeed are often prejudicial to life. In many vegetal feeders certain portions of the protoplasm are specialised, and have the power of forming a green, yellow, or brown pig- ment; these are called “ plastids” or “chromatophores.” They multiply by constriction - within the cell, displaying thereby a certain independent individuality. These plastids have in presence of light the extraordinary power of deoxidising carbon dioxide and water to form carbohydrates (or fats, ete.) and free oxygen; and from these carbohydrates or fats, together with ammonium salts or nitrates, etc., the vegetal protoplasm at large ‘an build up all necessary food matter. So that in presence of light of the right quality? and adequate intensity, such coloured vegetal beings have the capacity for building up their bodies and reserves from purely inorganic materials. Coloured vegetal nutrition, then, is a process involving the absorption of energy ; the source from which this is derived in the bacteria being very obscure at present. Nutrition by means of coloured plastids is 1 Whence the antiseptic powers of such aromatic alcohols as phenol and thymol, and acids as salicylic acid, ete., and their salts and esters. 2 The portion of the spectrum that is operative in ‘‘ holophytic” nutrition is the red or less refrangible half, and notably those rays in the true red, which are absorbed by the green pigment chlorophyll, and so give a dark band in the red of its absorption spectrum. The more refrangible half of the spectrum, so active on silver salts, that it is usually said to consist of ‘‘chemical rays,” is not only inoperative, but has a destructive action on the pigments themselves, and even on the protoplasm. Chlorophyll is present in all cases even when more -or less modified or masked by the accompaniment of other pigments. I ANIMALS AND PLANTS 37 distinguished as “holophytic,” and that from lower substances, which, however, contain organically combined carbon, as “ sapro- phytic,” for such are formed by the death and decomposition of living beings. The third mode of nutrition (found in some bacteria) from wholly inorganic substances, including free nitrogen, has received no technical name. All three modes are included in the term “autotrophic ” (self-nourishing). Vegetal feeders have a great tendency to accumulate reserves in insoluble forms, such as’starch, paramylum, and oil-globules on the one hand, and pyrenoids, proteid crystals, aleurone granules on the other. When an animal-feeding cell encysts or surrounds itself with a continuous membrane, this is always of nitrogenous composition, usually containing the glucosamide “chitin.” The vegetal cell-wall, on the contrary, usually consists, at least primarily, of the carbohydrate “ cellulose ”—the vegetal cell being richly supplied with carbohydrate reserves, and drawing on them to supply the material for its garment. This substance is what we are all familiar with in cotton or tissue-paper. Again, not only is the vegetal cell very ready to surround itself with a cell-wall, but its food-material, or rather, speaking accurately, the inorganic materials from which that food is to be manufactured, may diffuse through this wall with scarcely any difficulty. Such a cell can and does grow when encysted : it grows even more readily in this state, since none of its energies are absorbed by the necessities of locomotion, etc. Growth leads, of course, to division: there is often an economy of wall-material by the formation of a mere party-wall dividing the cavity of the old cell-wall at its limit of growth into two new cavities of equal size. Thus the division tends to form a colonial aggregate, which continues to grow in a motionless, and, so far, a “resting ” state. We may call this “vegetative rest,’ to distinguish it from “absolute rest,” when all other life-processes (as well as motion) are reduced to a minimum or absolutely suspended. The cells of a plant colony are usually connected by very fine threads of protoplasm, passing through minute pores where the new party-wall is left incomplete after cell-division.’ In a few plants, such as most Fungi, the cell - partitions are 1 Similarly, threads unite the cells of the colonial plant-Flagellate Volvoa, passing through the thick gelatinous cell-wall (pp. 126-127, Fig. 44). 38 PROTOZOA CHAP. in abeyance for the most part, and there is formed an apocyte with a continuous investment, sometimes, however, chambered at intervals by partitions between multinucleate units of protoplasm. We started with a purely physiological consideration, and we have now arrived at a morphological distinction, very valid among higher organisms. HIGHER PLANTS consist of cells for the most part each isolated in its own cell-cavity, sae Or the few slender threads of communication. HIGHER ANIMALS consist of cells that are rarely isolated in this way, but are mostly in mutual contact over the greater part of their surface. Again, Plants take in either food or else the material for food in solution through their surface, and only by diffusion through the cell-wall. Insectivorous Plants that have the power of capturing and digesting insects have no real internal cavity. Animal-feeding Protista take in their food into the interior of their protoplasm and digest it therein, and the Metazoa have an internal cavity or stomach for the same purpose. Here again there are exceptions in the case of certain internal parasites, such as the Tapeworms and Acanthocephala (Vol. II. pp. 74, 174), which have no stomachs, living as they do in the dissolved food-supplies of their hosts, but still possessing the general tissues and organs of Metazoa. Corresponding with the absence of mouth, and the absorption _ instead of the prehension of food, we find that the movements of plant-beings are limited. In the higher Plants, and many lower ones, the colonial organism is firmly fixed or attached, and the movements of its parts are confined to flexions. These are produced by inequalities of growth; or by inequalities of temporary distension of cell-masses, due to the absorption of liquid into their vacuoles, while relaxation is effected by the cytoplasm and cell-wall becoming pervious to the liquid. We find no case of a differentiation of the cytoplasm within the cell into definite muscular fibrils. In the lower Plants single naked motile cells dis- seminate the species; and the pairing-cells, or at least the males, have the same motile character. In higher Cryptogams, Cycads, and Ginkgo (the Maiden-hair Tree), the sperms alone are free- swimming; and as we pass to Flowering Plants, the migratory character of the male cells is restricted to the smallest limits, I ANIMALS AND PLANTS 39 though never wholly absent. Intracellular movements of the protoplasm are, however, found in all Plants. In Plants we find no distinct nervous system formed of cells and differentiated from other tissues with centres and branches and sense-organs. These are more or less obvious in all Metazoa, traces being even found in the Sponges. We may then define Plants as beings which have the power of manufacturing true food-stuffs from lower chemical substances than proteids, often with the absorption of energy. They have the power of surrounding themselves with a cell-wall, usually of cellulose, and of growing and dividing freely in this state, in which animal-like changes of form and locomotion are impossible ; their colonies are almost always fixed or floating; free locomotion is only possible in the case of their naked reproductive cells, and is transitory even in these. The movements of motile parts of complex plant-organisms are due to the changes in the osmotic powers of cells as a whole, and not to the contraction of ditferentiated fibrils in the cytoplasm of individual cells. Plants that can form carbohydrates with liberation of free oxygen have always definite plastids coloured with a lipochrome’ pigment, or else (in the Phycochromaceae) the whole plasma is so coloured. Solid food is never taken into the free plant-cell nor into an internal cavity in complex Plants. If, as in insectivorous Plants, it is digested and absorbed, it is always in contact with the morphological external surface. In the complex Plants apocytes and syneytes are rare—the cells being each invested with its own wall, and, at most, only communicating by minute threads with its neighbours. No trace of a central nervous system with differentiated connexions can be made out. Animals all require proteid food; their cyst-walls are never formed of cellulose; their cells usually divide in the naked condition only, or if encysted, no secondary party-walls are formed between the daughter-cells to unite them into a vegetative colony. Their colonies are usually locomotive, or, if fixed, their parts largely retain their powers of relative motion, and are often provided on their free surfaces with cilia or flagella; and many cells have differentiated in their cytoplasm contractile muscular fibrils. Their food (except in a few parasitic groups) is always taken 1 Pigments soluble in the ordinary solvents of fats, such as ether benzol, chloroform, ete. 40 PROTOZOA CHAP. into a distinct digestive cavity. A complex nervous system, of many special cells, with branched prolongations interlacing or anastomosing, and uniting superficial sense-organs with internal centres, is universally developed in Metazoa. All Metazoa fulfil the above conditions. 3ut when we turn to the Protozoa we find that many of the characters evade us. There are some Dinoflavellates (see p. 130) which have coloured plastids, but which differ in no other respect (even specific) from others that lack them: the former may have mouths which are functionless, the latter have functional mouths. Some colourless Flagellates are saprophytic and absorb nutritive liquids, such as decomposing infusions of organic matter, possibly free from all proteid constituents ; while others, scarcely different, take in food after the fashion of Amoeba. Sporozoa in the persistence of the encysted stage are very plant-like, though they are often intracellular and are parasitic in living Animals. On the other hand, the Infusoria for the most part answer to all the physiological characters of the Animal world, but are single cells, and by the very perfection of their structure, all due to plasmic not to cellular differentiation, show that they lhe quite off the possible track of the origin of Metazoa from Protozoa. Indeed, a strong natural line of demarcation hes between Metazoa and Protista. Of the Protozoa, certain groups, like the Foramini- fera and Radiolaria and the Ciliate and Suctorial Infusoria are distinctly animal in their chemical activities or metabolism, their mode of nutrition, and their locomotive powers. When we turn to the Proteomyxa, Mycetozoa, and the Flagellates we find that the distinction between these and the lower Fungi is by no means easy, the former passing, indeed, into true Fungi by the Chytridieae, which it is impossible to separate sharply from those Flagellates and Proteomyxa which Cienkowsky and Zopf have so accurately studied under the name of “ Monadineae.” Again, many of the coloured Flagellates can only (if at all) be dis- tinguished from Plants by the relatively greater prominence and duration of the mobile state, though classifiers are generally agreed in allotting to Plants those coloured Flagellates which in the resting state assume the form of multicellular or apocytial filaments or plates. On these grounds we should agree with Haeckel in distinguish- ing the living world into the Metazoa, or Higher Animals, which I METAZOA, METAPHYTA AND PROTISTA 41 are sharply marked off; the Metaphyta, or Higher Plants, which it is not so easy to characterise, but which unite at least two or more vegetal characters; and the Protista, or organisms, whose differentiation is limited to that within the cell (or apocyte), and does not involve the cells as units of tissues. These Protista, again, it is impossible to separate into animal and vegetal so sharply as to treat adequately of either group without including some of the other: thus it is that every text-book on Zoology, like the present work, treats of certain Protophyta. The most unmistakably animal group of the Protista, the Cilata, is, as we have seen, by the complex differentiation of its protoplasm, widely removed from the Metazoa with their relatively simple cells but differentiated cell-groups and tissues. The line of probable origin of the Metazoa is to be sought, for Sponges at least, among the Choanoflagellates (pp. 121 f. 181 f.). CHAPTER II PROTOZOA (CONTINUED): SPONTANEOUS GENERATION CHARACTERS OF PROTOZOA—CLASSIFICATION THE QUESTION OF SPONTANEOUS GENERATION From the first discovery of the Protozoa, their life-history has been the subject of the highest interest: yet it is only within our own times that we can say that the questions of their origin and development have been thoroughly worked out. If animal or vegetable matter of any kind be macerated in water, filtered, or even distilled, various forms of Protista make their appearance ; and frequently, as putrefaction advances, form after form makes its appearance, becomes abundant, and then disappears to be replaced by other species. The questions suggested by such phenomena are these: (1) Do the Protista arise spontaneously, that is, by the direct organisation into living beings of the chemical substances present, as a crystal is organised from a solution: (2) Are the forms of the Protista constant from one generation to another, as are ordinary. birds, beasts, and fishes ? The question of the “spontaneous generation ” of the Protista was readily answered in the affirmative by men who believed that Lice bred directly from the filth of human skins and clothes ;* and that Blow-flies, to say nothing of Honey-bees, arose in rotten flesh: but the bold aphorism of Harvey “ omne vivum ex ovo” at once gained the ear of the best-inspired men of science, and set them to work in search of the “eggs” that gave rise to the organisms of putrefaction. Redi (ob. 1699) showed that Blow- flies never arise save when other Blow-flies gain access to meat and deposit their very visible eggs thereon. Leeuwenhoek, his ' We have ourselves had hard work to persuade intelligent men of fair general education, even belonging to a learned profession, that this is not the case. 42 CHAP. II SPONTANEOUS GENERATION 43 contemporary, in the latter half of the seventeenth century adduced strong reasons for ascribing the origin of the organisms of putrefaction to invisible air-borne eggs. L. Joblot and H. Baker in the succeeding half-century investigated the matter, and showed that putrefaction was no necessary antecedent of the appearance of these beings: that, as well as being air-borne, the germs might sometimes have adhered to the materials used for making the infusion; and that no organisms were found if the infusions were boiled long enough, and corked when still boiling. These views were strenuously opposed by Needham in England, by Wrisberg in Germany, and by Buffon, the great French naturalist and philosopher, whose genius, unballasted by an adequate know- ledge of facts, often played him sad tricks. Spallanzani made a detailed study of what we should now term the “ bionomical” or “ oecological ” conditions of Protistic life and reproduction in a manner worthy of modern scientific research, and not attained by some who took the opposite side within living recollection. He showed that infusions kept sufficiently long at the boiling-point in hermetically sealed vessels developed no Protistic life. As he had shown that active Protists are killed at much lower temperatures, he inferred that the germs must have much higher powers of resistance ; and, by modifying the details of his experi- ments, he was able to meet various objections of Needham. Despite this good work, the advocates of spontaneous genera- tion were never really silenced; and the widespread belief in the inconstancy of species in Protista added a certain amount of credibility to their cause. In 1845 Pineau put forward these views most strongly; and from 1858 to 1864 they were supported by the elder Pouchet. Louis Pasteur, who began life as a chemist, was led from a study of alcoholic fermentation to that of the organisms of fermentation and of putrefaction and disease. He showed that in infusions boiled sufficiently long and sealed while boiling, or kept at the boiling-point in a sealed vessel, no life manifested itself: objections raised on the score of the lack of access of fresh air were met by the arrangement, so commonly used in “ pure cultures” at the present day, of a flask with a tube attached plugged with a little cotton-wool, or even merely bent repeatedly into a zigzag. The former attachment filtered off all germs or floating solid particles from the air, the latter brought about the settling of such particles in the elbows ro) 44 PROTOZOA CHAP. or on the sides of the tube: in neither case did living organisms appear, even after the lapse of months. Other observers suc- ceeded in showing that the forms and characters of species were as constant as in Higher Animals and Plants, allowing, of course, for such regular metamorphoses as occur in Insects, or alter- nations of generations paralleled in Tapeworms and Polypes. The regular sequences of such alternations and metamorphoses constitute, indeed, a strong support of the “ germ-theory’—the view that all Protista arise from pre-existing germs. It is to the Rev. W. H. Dallinger and the late Dr. Charles Drysdale that we owe the first complete records of such complex life- histories in the Protozoa as are presented by the minute Flagellates which infest putrefying liquids (see below, p. 116 f.). The still lower Schizomycetes, the “ microbes” of common speech, have also been proved by the labours of Ferdinand Cohn, von Koch, and their numerous disciples, to have the same specific constancy in consecutive generations, as we now know, thanks to the methods first devised by De Bary for the study of Fungi, and improved and elaborated by von Koch and his school of bacteriologists. And so to-day the principle “omne vivum ex vivo” is universally accepted by men of science. Of the ultimate origin of organic life from inorganic life we have not the faintest inkling. If it took place in the remote past, it has not been accomplished to the knowledge of man in the history of scientific experience, and does not seem likely to be fulfilled in the ‘immediate or even in the proximate future.' PROTOZOA Organisms of various metabolism, formed of a single cell or apocyte, or of a colony of scarcely differentiated cells, whose organs are formed by differentiations of the protoplasm and its secretions and accretions ; not composed of differentiated multicellular tissues or organs.” * Dr. H. Charlton Bastian has recently maintained a contrary thesis (The Nature and Origin of Living Matter, 1905), but has adduced no evidence likely to convince any one familiar with the continuous life-study of the lower organisms. * The terms ‘“organoid,” ‘‘organella,’’ have been introduced to designate a definite portion of a Protist specialised for a definite function ; the term “ organ” 11 HISTORY 45 This definition, as we have seen, excludes Metazoa (including Mesozoa, Vol. II. p. 92) sharply from Protozoa, but leaves an un- certain boundary on the botanical side; and, as systematists share with nations the desire to extend their sphere of influence, we shall here follow the lead of other zoologists and include many beings that every botanist would claim for his own realm. Our present knowledge of the Protozoa has indeed been largely extended by botanists,! while the study of protoplasmic physiology has only passed from their fostering care into the domain of General Biology within the last decade. The study of the Protozoa is little more than two centuries old, dating from the school of microscopists of whom the Dutchman Leeuwenhoek is the chief representative: and we English may feel a just pride in the fact that his most important publications are to be found in the early records of our own Royal Society. Baker, in the eighteenth century, and the younger Wallich, Carter, Dallinger and Drysdale, Archer, Saville Kent, Lankester, and Huxley, in the last half-century, are our most illustrious names. In France, Joblot, almost as an amateur, like our own Baker, flourished in the early part of the eighteenth century. Dujardin in the middle of the same century by his study of protoplasm, or sarcode as he termed it, did a great work in laying the founda- tions of our present ideas, while Balbiani, Georges Pouchet, Fabre-Domergue, Maupas, Léger, and Labbé in France, have worthily continued and extended the Gallic traditions of exact observation and careful deduction. Otto Friedrich Miiller, the Dane, in the eighteenth century, was a pioneer in the exact study and description of a large number of forms of these, as of other microscopic forms of life. The Swiss collaborators, Claparéde and Lachmann, in the middle of the nineteenth century, added many facts and many descriptions; and illus- trated them by most valuable figures of the highest merit from every point of view. Germany, with her large population of students and her numerous universities, has given many names to our list; among these, Ehrenberg and von Stein have added being reserved for a similarly specialised group of cells or tissues in a Metazoon or Metaphyte. We do not consider that this distinction warrants the introduction of new words into the terminology of general Zoology, however convenient these may be in an essay on the particular question involved. 1 This has been especially the case with the Flagellata, the Proteomyxa, and the Mycetozoa. 46 PROTOZOA CHAP. the largest number of species to the roll. Ehrenberg about 1840 described, indeed, an enormous number of forms with much care, and in detail far too elaborate for the powers of the microscope of that date: so that he was led into errors, many and grave, which he never admitted down to the close of a long and honoured life. Max Schultze did much good work on the Protozoa, as well as on the tissues of the Metazoa, and largely advanced our con- ceptions of protoplasm. His work was continued in Germany by Ernst Haeckel, who systematised our knowledge of the Radiolaria, Greeff, Richard Hertwig, Fritz Schaudinn, and especially Biitschli, who contributed to Bronn’s Zhier-Reich a monograph of monu- mental conception and scope, and of admirable execution, on which we have freely drawn. Cienkowsky, a Russian, and James- Clark and Leidy, both Americans, have made contributions of high quality. Lankester’s article in the Encyclopedia Britannica was of epoch-making quality in its philosophical breadth of thought. Delage and Hérouard have given a full account of the Protozoa in their Traité de Zoologie Concrete, vol, i. (1896); and A. Lang’s monograph in his Vergleichende Anatomie, 2nd ed. (1901), contains an admirable analysis of their general structure, habits, and life- cycles, together with full descriptions of well-selected types. Calkins has monographed “The Protozoa” in the Columbia University Biological series (1901). These works of Biitschh, Delage, Lang, and Calkins contain full bibliographies. Doflein has published a most valuable systematic review of the Protozoa parasitic on animals under the title Die Protozoen als Parasiten und Krankhettserreger (1901); and Schaudinn’s Archiv fiir Protistenkunde, commenced only four years ago, already forms an indispensable collection of facts and views. The protoplasm of the Protozoa (see p. 5 f.) varies greatly in consistency and in differentiation. Its outer layer may be granular and scarcely altered in Proteomyxa, the true Myxo- mycetes, Filosa, Heliozoa, Radiolaria, Foraminifera, etc.; it is Clear and glassy in the Lobose Rhizopods and the Acrasieae ; if 18 Continuous with a firm but delicate superficial pellicle of membranous character in most Flagellates and Infusoria ; and this pellicle may again be consolidated and locally thickened in some members of both groups so as to form a coat of mail, even with definite spines and hardened polygonal plates (Coleps, Fig. 54, II PROTOPLASM—GEOGRAPHICAL DISTRIBUTION 47 p- 150). Again, it may form transitory or more or less permanent pseudopodia,’ (1) blunt or tapering and distinct, with a hyaline outer layer, or (2) granular and pointed, radiating and more or less permanent, or (3) branching and fusing where they meet into networks or perforated membranes. Cilia or flagella are motile thread-lke processes of active protoplasia which perforate the pellicle; they may be combined into flattened platelets or firm rods, or transformed into coarse bristles or fine motionless sense- hairs. The skeletons of the Protozoa, foreign to the cytoplasm, will be treated of under the several groups. Most of the fresh-water and brackish forms (and some marine ones) possess one or more contractile vacuoles, often in relation to a more or less complex system of spaces or canals in Flagel- lates and Cihates. The Geographical Distribution of Protozoa is remarkable for the wide, nay cosmopolitan, distribution of the terrestrial and fresh-water forms;°* they owe this to their power of forming cysts, within which they resist drought, and can be disseminated as “dust.” Very few of them can multiply at a temperature approaching freezing-point ; the Dinoflagellates can, however, and therefore present Alpine and Arctic forms. The majority breed most freely at summer temperatures; and, occurring in small pools, can thus achieve their full development in such as are heated by the sun during the long Arctic day as readily as in the Tropics. In infusions of decaying matter, the first to appear are those that feed on bacteria, the essential organisms of putrefaction. These, again, are quickly followed and _ preyed upon by carnivorous species, which prefer liquids less highly charged with organic matters, and do not appear until the liquid, hitherto cloudy, has begun to clear. Thus we have rather to do with “habitat” than with “ geographical distri- ' Lang distinguishes ‘‘lobopodia,” ‘‘ filopodia,” and ‘‘pseudopodia” according to their form,—blunt, thread-like, or anastomosing. In some cases the protoplasm shows a gliding motion as a whole without any distinct pseudopodium, as in Amoeba limaz (Fig. 1, p. 5), and a pseudopodium may pass into a thin, active flagellum, which is, however, glutinous and serves for the capture of prey : such often occurs in the Lobosa Podostoma and Arcuothrix, which are possibly two names for one species or at least one genus; and in many cases a slender pseudopodium may be waved freely. 2 See Schewiakoff, ‘‘Ueb. d. Geograph. Verbreitung d. Siisswasserprotozoen,” in Mém. Acad. St. Pétersb. ser. 7, xli. 1893, No. 8. His views apply to most minute aquatic organisms—Animal, Vegetable, or Protistic. 4 8 PROTOZOA CHAP. bution,” just as with the fresh-water Turbellaria and the Rotifers (vol. ii. pp. 4 f£, 226 f). We can distinguish in fresh-water, as in inarine Protista, “littoral” species living near the bank, among the weeds; “plankton,” floating at or near the surface; “zonal” species dwelling at various depths ; and “ bottom-dwellers,” mostly “]imicolous” (or “ sapropelic,” as Lauterborn terms them), and to be found among the bottom ooze. Many species are “ epiphytic ” or “ epizoic,” dwelling on plants or animals, and sometimes choice enough in their preference of a single genus or species as host. Others again are “moss-dwellers,’ living among the root-hairs of mosses and the like, or even “terrestrial” and inhabiting damp earth. The Sporozoa are internal parasites of animals, and so are many Flagellates, while many Proteomyxa are parasitic in plant-cells. The Foraminifera (with the exception of most Allogromidiaceae) are marine, and so are the Radiolaria ; while most Heliozoa inhabit fresh water. Concerning the dis- tribution in time we shall speak under the last two groups, the only ones whose skeletons have left fossil remains. Classification—The classification of the Protozoa is no easy task. We omit here, for obvious reasons, the unmistakable Plant Protists that have a holophytic or saprophytic nutrition ; that are, with the exception of a short period of locomotion in the young reproductive cells, permanently surrounded with a wall of cellulose or fungus-cellulose, and that multiply and grow freely in this encysted state: to these consequently we relegate the CHYTRIDIEAE, which are so closely allied to the Proteomyxa and the Phycomycetous Fungi; and the Confervaceae, which in the resting state form tubular or flattened aggregates and are allied to the green Flagellates; besides the Schizophyta. At the opposite pole stand the INFUSORIA in the strict sense, with the most highly differentiated organisation found in our group, culminating in the possession of a nuclear apparatus with nuclei of two kinds, and exhibiting a peculiar form of conjugation, in which the nuclear apparatus is reorganised. The SPOROZOA are clearly marked off as parasites in living animals, which mostly begin life as sickle-shaped cells and have always at least two alternating modes of brood-formation, the first giving rise to aplanospores, wherein is formed the second brood of sickle- shaped, wriggling zoospores. The remainder, comprising the SARCODINA, or Ru1zopopa in the old wide sense (including all II CLASSIFICATION 49 that move by pseudopodia during the great part of their active life), and the FLAGELLATA in the widest sense, are not easy to split up; for many of the former have flagellate reproductive cells, and many of the latter can emit pseudopodia with or without the simultaneous retraction of their flagella. The RapIOLARIA are well defined by the presence in the body plasm of a central capsule marking it off into a central and a peripheral portion, the former containing the nucleus, the latter emitting the pseudopodia. Again, on the other hand, we find that we can separate as FLAGELLATA in the strict sense the not very natural assemblage of those Protista that have flagella as their principle organs of movement or nutri- tion during the greater part of their active life. The remaining eroups (which with the Radiolaria compose the Sarcodina of Biitschli), are the most difficult to treat. The Ruizopopa, as we shall limit them, are naked or possess a simple shell, never of calcium carbonate, have pseudopodia that never radiate abundantly nor branch freely, nor coalesce to form plasmatie networks, nor possess an axial rod of firmer substance. The FORAMINIFERA have a shell, usually of calcium carbonate, their pseudopodia are freely reticulated, at least towards the base; and (with the exception of a few simple forms) all are marine. The Mycrerozoa are clearly united by their tendency to aggregate more or less completely into complex resting-groups (fructifications), and by reproducing by unicellular zoospores, flagellate or amoeboid, which are not known to pair. The HeEttozoa resemble the Radiolaria in their fine radiating pseudopodia, but have an axial filament always present in each, and lack the central capsule; and are, for the most part, fresh-water forms. Finally, the PROTEOMYXA forms a sort of lumber-room for beings which are intermediate between the Heliozoa, Rhizopoda, and Flagellata, usually passing through an amoeboid stage, and for the most part reproducing by brood-formation. Zoospores that possess flagella are certainly known to occur in some forms of Foraminifera, Rhizopoda, Heliozoa, and Radiolaria, though not by any means in all of each group.’ 1 See E. R. Lankester, art. ‘‘ Protozoa” in Hncycl. Brit. 9th ed. (1885), reprinted with additions in ‘‘ Zoological Articles.” We cannot accept his primary division into Corticata and Gymnomyxa, which would split up the Flagellata and mark off the Gregarines from the other Sporozoa. VOL. ER 50 PROTOZOA ~ CHAP. II A. Pseudopodia the principal means of locomotion and feeding; flagella absent or transitory . : é . . I. SaRcopINna (1) Plastogamy only leading to an increase in size, never to the forma- tion of “ fructifications.” (a) Pseudopodia never freely coalescing into a network nor fine to the base : : RHIZOPODA. (*) Ectoplasm clear, free frac eraamnles pseudopodia, usually blunt . : : Ruizopopa LoBosa (**) Ectoplasm finely eranula; pseudopodia slender, branching, but not forming a network, passing into the body by basal dilatation . : RuHIZOPODA FILOSA (b) Pseudopodia branching freely ond coalescing to form networks ; ectoplasm granular ; test usually calenreous or sandy FORAMINIFERA (c) Pseudopodia fine to the very base ; radiating, rarely coalescing. (i.) Pseudopodia with a central filament ; HELIOZOA (ii.) Pseudopodia without a central filament. (*) eer divided into a central and a peripheral part by a “central capsule”. : RADIOLARIA (**) Body without a central capsule . PROTEOMYXA (2) Cells aggregating or fusing into plasmodia before forming a complex «« fructifieation? : : “Mycrrozoa B. Cells usually moving by “ euglenoid - Peciine’ or by excretion of a trail of viscid matter ; repeater by alternating modes of brood-forma- tion, rarely by Spencerian fission. ; . II. Sporozoa Flagella (rarely numerous) the chief or only means of motion and feeding : : III. FLuaGeLuatTa D. Cilia “iS chief organs ‘of motion, in the young state at least; nuclei of two kinds : : : ; . IV. InFusoRIa CHAPTER III PROTOZOA (CONTINUED): SARCODINA I. Sarcodina. PROTOZOA performing most of their life-processes by pseudopodia ; nucleus frequently gwing off fragments (chromidia) which may play a part in nuclear reconstitution on division ; sometimes with brood-cells, which may be at first flagellate ; but never reproducing in the flagellate state. 1. RHIZOPODA Sarcodina of simple form, whose pseudopodia never coalesce into networks (1), nor contain an axial filament (2), which commonly multiply by binary fission (3), though a brood-formation may occur ; which may temporarily aggregate, or undergo temporary or permanent plastogamic union, but never to form large plasmodia or complex fructifications as a prelude to spore-formation (4) ; test when present gelatinous, chitinous, sandy, or siliceous, simple and 1-chambered (5). Classification.° I. Ectoplasm distinct, clear ; pseudopodia blunt or tapering, but not branch- ing at the apex i : . : : . Loposa Amoeba, Auctt.; Pelomyxa, Greeff; Trichosphaerium, A. Schneid. ; 1 On this ground I have referred Puramocha, Greeff, to the Cryptomonadineae. * Differences (1) from Foraminifera ; (2) from Heliozoa ; (3) from Proteomyxa and Sporozoa ; (4) from Myxomycetes ; (5) from many Foraminifera. * T have not followed the usual classification into Gymnamoebaeand Thecamoebae, according to the absence or presence of a test (perforated by one or more openings) in the active state, as such a test occurs in isolated genera of Flagellata and Infusoria, and does not appear to have any great systematic importance. I On Ba PROTOZOA CHAP. Ehr.; Diflugia, Leclereq ; Lecquewreusia, Schlumberger; Hyalosphenia, Stein; Quadrula, F. E. Sch.; Heleopera, Leidy ; Podostoma, Cl. and L. ; Arcuothrix, Hallez. II. Ectoplasm undifferentiated, containing moving granules ; pseudopodia branching freely towards the tips , j 5 . FILOSA Euglypha, Duj.; Paulinella, Lauterb.; Cyphoderia, Schlumb. ;. Campascus, Leidy ; Chlamydophrys, Cienk. ; Gromia, Duj. = Hyalopus, M. Sch. We have defined this group mainly by negative characters, as such are the only means for their differentiation from the remain- ing Sarcodina; and indeed from Flagellata, since in this group zoospores are sometimes formed which possess flagella. More- over, indeed, in a few of this group (Podostoma, Avreuothrix), as in some Heliozoa, the flagellum or flagella may persist or be reproduced side by side with the pseudopodia. The subdivision of the Rhizopoda is again a matter of great difficulty, the characters presented being so mixed up that it is hard to choose: however, the character of the outer layer of the cytoplasm is perhaps the most obvious to select. In Loposa there is a clear layer of ectosarc, which appears to be of a greasy nature at its surface film, so that it 1s not wetted. In the FILosa, as in most other Sarcodina, this film is absent, and the ectoplasm is not marked off from the endoplasm, and may have a granular surface. Corre- sponding to this, the pseudopodia of the Lobosa are usually blunt, never branching and fraying out, as it were, at the tip, as in the Filosa; nay, in the normal movements of Amoeba limax (Fig. 1, p. 5) the front of the cell forms one gigantic pseudopodium, which constantly glides forward. Apart from this distinction the two groups are parallel in almost every respect. There may be a single contractile vacuole, or a plurality; or none, especially in marine and endoparasitic species. The nucleus may remain single or multiply without inducing fission, thus leading to apocytial forms. It often gives off “chromidial ” fragments, which may play an important part in reproduction.! In Amoeba binucleata there are constantly two nuclei, both of which divide as an antecedent to fission, each giving a separate nucleus to either daughter-cell. Pelomyxa palustris, the giant of the group, attaining a diameter of 1’” (2 mm.), has very blunt pseudopodia, an enormous number of nuclei, and no contractile vacuole, though 1 The significance of chromidia in Sarcodina (first noted by Schaudinn in Fora- minifera) was fully recognised and generalised by R. Hertwig in Arch. Protist. i, 1902, p. 1. MI SARCODIN A—RHIZOPODA se it is a fresh-water dweller, living in the bottom ooze of ponds, etc., richly charged with organic débris. It is remarkable also for containing symbiotic bacteria, and brilliant vesicles with a distinct membranous wall, containing a solution of glycogen.’ Few, if any, of the Filosa are recorded as plurinuclear. The simplest Lobosa have no investment, nor indeed any distinction of front or back. In some forms of Amoeha, how- ever, the hinder part is more adhesive, and may assume the form of a sucker-like disc, or be drawn into a tuft of short filaments or villi, to which particles adhere. Other species of Lobosa and all Filosa have a “ test,” or “theca,” 7c. an investment distinct from the outermost layer of the cell-body. The simplest cases are those of Amphizonella, Dinamoeba, and Trichosphaervum, where this is gelatinous, and in the two former allows the passage of food particles through it into the body by mere sinking in, like the protoplasm itself, closing again without a trace of per- foration over the rupture. In Zvrichosphaeriwm (Fig. 9) the test is perforated by numerous pores of constant position for the passaye of the pseudopodia, closing when these are retracted ; and in the “A” form of the species (see below) it is studded with radial spicules of magnesium carbonate. Elsewhere the test is more consistent and possesses at least one aperture for the emission of pseudopodia and the reception of food; to avoid con- fusion we call this opening not the mouth but the “pylome”: some Filosa have two symmetrically placed pylomes. When the test is a mere pellicle, it may be recognised by the limitation of the pseudopodia to the one pylomic area. But the shell is often hard. In Arcella (Fig. 10, C), a form common among Bog-mosses and Confervas, it is chitinous and shagreened, circular, with a shelf running in like that of a diving-bell around the pylome: there are two or more contractile vacuoles, and at least two nuclei. Like some other genera, it has the power of secreting carbonic acid gas In the form of minute bubbles in its cytoplasm, so as to enable it to float up to the surface of the water. The chitinous test shows minute hexagonal sculpturing, the expression of ver- tical partitions reaching from the inner to the outer layer. Several genera have tests of siliceous or chitinous plates, 1 Stoléin Z, wiss. Zool. \xviii. 1900, p. 625. Lilian Veley, however, gives reasons for regarding them as of proteid composition, J. Linn. Soc. (Zool.) xxix. 1905, p. 374 f They disappear when the Pelomyxa is starved or supplied with only proteid food. 54 PROTOZOA CHAP. formed in the cytoplasm in the neighbourhood of the nucleus, and connected by chitinous cement. Among these Quadrula (Fig. 10, A) is Lobose, with square plates, Huglypha (Fig. 8, Fia. 9.—Trichosphaerium sieboldii. 1, Adult of ‘‘A” form; 2, its multiplication by fission and gemmation; 3, resolution into 1-nucleate amoeboid zoospores; 4, development (from zoospores of ‘‘A”’) into ““B” form (5); 6, its multiplication by fission and gemmation; 7, its resolution after nuclear bipartition into minute 2-flagellate zoospores or (exogametes) ; 8, liberation of gametes ; 9, 10, more highly magnified pairing of gametes of different origin; 11, 12, zygote developing into “A” form. (After Schaudinn.) p- 29), and Paulinella! are Filose, with hexagonal plates. In. the latter they are in five longitudinal rows, with a pentagonal oral plate, perforated by the oval pylome. In other genera again, such as Cyphoderia (Filosa), the plates are merely chiti- 1 This genus contains two sausage-shaped, blueish-green plastids, possibly sym- biotic Cyanophyceous Algae. lI RHIZOPODA 55 nous. Again, the shell may be encrusted with sand-grains derived directly from without, or from ingested particles, as shown in Centropyxis, Diflugia (Fig. 10, D), Heleopera, and Campascus when supplied with powdered glass instead of sand. The cement in Difilugia is a sort of organic mortar, infiltrated with ferric oxide (more probably ferric hydrate). In Leequeu- reusia spiralis (formerly united with Difflugia) the test is formed of minute sausage-shaped granules, in which may be identified the partly dis- solved valves of Diatoms taken as food; it is spir- ally twisted at the apex, as if it had enlarged after its first formation, a very rare occurrence in this group. The most frequent mode of fission in the tes- taceous Rhizopods (Figs. 8, 10) is what Schaudinn aptly terms “bud-fission,” where half the protoplasm protrudes and accumu- lates at the mouth of the shell, and remains till a test has formed for it, while the other half re- Fic. 10.—Test-bearing Rhizopods. A, Quadrula tains the test of the symimetrica ; B, Hyalosphenia lata; ©, Arcella original animal. The eal >, Digugia ae (From Lang’s materials for the shell, whether sand-granules or plates, pass from the depths of the original shell outwards into the naked cell, and through its cyto- plasm to the surface, where they become connected by cementing matter into a continuous test. The nucleus now divides into two, one of which passes into the external animal; after this the two daughter-cells separate, the one with the old shell, the other, larger, with the new one. If two individuals of the shelled species undergo bud-fission in close proximity, the offspring may partially coalesce, so that a monstrous shell is produced having two pylomes. 56 PROTOZOA CHAP. Reproduction by fission has been clearly made out in most members of the group; some of the multinucleate species often abstrict a portion, sometimes at several points simultaneously, so that fission here passes into budding? (Fig. 9, 2, 6). Brood-division, either by resolution in the multinucleate species, or preceded by multiple nuclear division in the habitually 1-nucleate, though presumably a necessary incident in the life- history of every species, has only been seen, or at least thoroughly worked out, in a few cases, where it is usually preceded by encystment, and mostly by the extrusion into the cyst of any undigested matter.’ In Trichosphaerium (Fig. 9) the cycle described by Schaudinn is very complex, and may be divided into two phases, which we may term the A and the B subcycles. The members of the A cycle are distinguished by the gelatinous investment being armed with radial spicules, which are absent from the B form. The close of the A cycle is marked by the large multinucleate body resolving itself into amoeboid zoospores (3), which escape from the gelatinous test, and develop into the large multinucleate adults of the B form. These, like the A form, may reproduce by fission or budding. At the term of growth, however, they retract their pseudopodia, expel the excreta, and multiply their nuclei by mitosis (7). Then the body is resolved into minute 2-flagellate microzoospores (8), which are exogamous gametes, ie. they will only pair with similar zoospores from another cyst. The zygote (9-11) resulting from this conjugation is a minute amoeboid; its nucleus divides repeatedly, a gelatinous test is formed within which the spicules appear, and so the A form is reconstituted. In many of the test-bearing forms, whether Lobose or Filose, plastogamic unions occur, and the two nuclei may remain distinct, leading to plurinucleate monsters in their offspring by fission, or they may fuse and form a giant nucleus, a process which has here no relation to normal syngamy, as it is not associated with any marked change in the alternation of feeding and fission, ete. In Zvrichosphaeriwm also plastogamic unions between small individuals have for their only result the increase of size, enabling the produce to deal with 1 See Lauterborn in Z. wiss. Zool. lix. 1895, pp. 167, 537. 2 C. Scheel has seen » \ ie ASN ARAN KSA, 2, Rotalta 1 3 3 AY \ eS 5. Squamulina 4. Miliola (Quinqueloculina) Fic. 14.—Various forms of Foraminifera. In 4, Miliola, a, shows the living animal ; 4, the same killed and stained; «a, aperture of shell; 7, food particles; nu, nucleus ; sh, shell, (From Parker and Haswell, after other authors.) the species or of its stage of growth, so as to give rise to circular, spiral, or irregular complexes (see Fig. 13). In most VOL. I F 66 PROTOZOA CHAP. cases the part of the previously existing chamber next the pylome serves as the hinder part of the new chamber, and the old pylome becomes the pore of communication. But in some of the “ Perforata” each new chamber forms a complete wall of its own (“ proper wall,” Fig. 13, sb), and the space between the two adjacent walls is filled with an intermediate layer traversed by canals communicating with the cavities of the chambers (“intermediate skeleton”), while an external layer of the same character may form a continuous covering. The shell of the Perforata may be adorned with pittings or fine spines, which serve to increase the surface of support in such floating forms as Globigerina, Hastigerina, and the like (Fig. 17). In the “Tmperforata” the outer layer is often ornamented with regular patterns of pits, prominences, etc, which are probably formed by a thin: reflected external layer of protoplasm. In some of the “ Arenacea ” a “labyrinthine” complex of laminae is formed. A very remarkable point which has led to great confusion in the study of the Foraminifera, is the fact that the shell on which we base our characters of classification, may vary very much, even within the same individual. Thus in the genus Orbitolites the first few chambers of the shell have the character of a Milioline, in Orbiculina of a Peneroplis. The arrangements of the Milioline shell, known as Triloculine, Quinqueloculine, and Biloculine respectively, may succeed one another in the same shell (Figs. 14 4, 15). A shell may begin as a spiral and end by a straight continuation: again, the spherical Orbulina (Fig. 16 1) is formed as an investment to a shell indistinguish- able from Globigerina, which is ultimately absorbed. = In some cases, as Rhumbler has pointed out, the more recent and higher development shows itself in the first formed chambers, while the later, younger chambers remain at a lowher stage, as in the case of the spiral passing into a straight succession ; but the other cases we have cited show that this is not always the case. In ZLagena (Fig. 13 2) the pylome is pro- duced into a short tube, which may protrude from the shell or be turned into it, so that for the latter form the genus Hntosolenia was founded. Shells identical in minute sculpture are, however, found with either form of neck, and, moreover, the polythalamial shells (Nodosaria, Fig. 13 3), formed of a nearly straight succession of Lagena-like chambers, may have these chambers with their com- MI FORAMINIFERA 67 munications on either type. Rhumbler goes so far as to suggest that all so-called Zagena shells are either the first formed ehamber of a Nodosaria which has not yet become polythalamian by the formation of younger ones, or are produced by the separation of an adult Nodosaria into separate chambers. Many of the chambered species show a remarkable dimorphism, first noted by Schlumberger, and finally elucidated by J. J. Lister and Schaudinn. It reveals itself in the size of the B - CS eR Fic. 15.—A, Megalospheric; B, microspheric shell of Biloculina. c, The initial chamber. ‘he microspheric form begins on the Quinqueloculina type. (From Calkins’ Protozoa.) initial chamber ; accordingly, the two forms may be distinguished as “microspheric” and “ megalospheric” respectively (Fig. 15), the latter being much the commoner. The microspheric form has always a plurality of nuclei, the megalospheric a single one, except at the approach of reproduction. Chromidial masses are, however, present in both forms. The life-history has been fully worked out in Polystomella by Schaudinn, and in great part in Polystomella, Orbitolites, ete., by Lister; and the same scheme appears to be general in the class, at least where the dimorphism noted occurs. The microspheric form gives birth only to the megalospheric, but the latter may reproduce megalospheric broods, or give rise to swarmers, which by their (exogamous) O* (oe) PROTOZOA CHAP. conjugation produce the microspheric young. The microspherie forms early become multinucleate, and have also numerous chromidia detached from the nuclei, which they ultimately replace. These collect in the outer part of the shell and ageregate into new nuclei, around which the cytoplasm concentrates, to separate into as many amoeboid young “ pseudopodiospores ” as there are nuclei. These escape from the shell or are liberated by its 1 2 Fic. 16.—1, Orbulina universa. Highly magnified. 2, Globigerina bulloides. Highly magnified. (From Wyville Thomson, after d’Orbigny.) disintegration, and invest themselves with a shell to form the initial large central chamber or megalosphere. In the ordinary life of the megalospheric form the greater part of the chromatic matter is aggregated into a nucleus, some still remaining diffused. At the end of growth the nucleus itself disintegrates, and the chromidia concentrate into a number of small vesicular nuclei, each of which appropriates to itself a small surrounding zone of thick plasm and then divides by mitosis twice; and the 4-nucleate cells so formed are resolved into as many 1-nucleate, 2-flagellate swarmers, which. conjugate Il FORAMINIFERA 69 only exogamously.' The fusion of their nuclei takes place after some delay: ultimately the zygote nucleus divides into two, a shell is formed, and we have the microsphere, which is thus pluri-nucleate ab initio. As we have seen, the nuclei of the microsphere are ultimately replaced by chromidia, and the whole plasmic body divides into pseudopodiospores, which grow into the megalospheric form. In the Perforate genera, Patellina and Discorbina, plastogamy precedes brood formation, the cytoplasms of the 2-5 pairing individuals contracting a close union; and then the nuclei proceed to break up without fusion, while the cytoplasm Fic. 17.—Shell of Globigerina bulloides, from tow-net, showing investment of spines. (From Wyville Thomson. ) ageregates around the young nuclei to form amoebulae, which acquire a shell and separate. In both cases it is the forms with a single nucleus, corresponding to megalospheric forms that so pair, and the brood-formation is, mutatis mutandis, the same as in these forms. Similar individuals may reproduce in the same way, in both genera, without this plastogamic pairing, which is therefore, though probably advantageous, not essential. If pseudopodiospores form their shells while near one another, they may coalesce to form monsters, as often happens in Orbitolites.” The direct economic uses of the Foraminifera are perhaps greater than those of any other group of Protozoa. The Chalk is ' Which probably accounts for the earlier failure of Lister and of Schaudinn himself to note their conjugation. * Rhumbler, ‘‘ Die Doppelschalen v. Orbitolites u. and. Foraminiferen,” in Arch. Protist. i. 1902, p. 193. 70 PROTOZOA CHAP. composed largely of Zeavtularia and allied forms, mixed with the skeletons of Coccolithophoridae (pp. 113-114), known as Cocco- liths, etc. The Calcaire Grossier of Paris, used as a building stone, is mainly composed of the shells of Miliolines of Eocene age; the Nummulites of the same age of the Mediterranean basin are the chief constituent of the stone of which the Pyramids of Egypt are built. Our own Oolitic limestones are composed of concretions around a central nucleus, which is often found to be a minute Foraminiferous shell. The palaeontology of the individual genera is treated of in Chapman’s and Lister’s recent works. They range from the Lower Cambrian characterised by perforated hyaline genera, such as Lagena, to the present day. Gigantic arenaceous forms, such as Loftusia, are among the Tertiary representatives; but the limestones formed principally of their shells commence at the Carboniferous. The so-called Greensands contain greenish granules of “ glauconite,” containing a ferrous silicate, deposited as a cast in the chambers of Foraminifera, and often left exposed by the solution of the calcareous shell itself. Such granules occur in deep-sea deposits of the present day.’ 2: HRLIOZOA Sarcodina with radiate non-anastomosing pseudopodia of gran- ular protoplasm, each with a stiff axial rod passing into the body plasma; no central capsule, nor clear ectoplasm ; skeleton when present siliceous; nucleus single or multiple ; contractile vacuole (or vacuoles) in fresh-water species, superficial and prominent at the surface in diastole; reproduction by fission or budding in the active condition, or by brood-formation in a cyst, giving rise to resting spores ; conjugation isogamous in the only two species fully studied ; habitat floating or among weeds, mostly fresh water. 1. Naked or with an investment only when encysted. ApHRoTHORACA.—Actinolophus F.E. Sch. ; Myxastrum Haeck. ; Gymnosphaera Sassaki ; Dimorpha (Fig. 37,5, p. 112) Gruber ; Actinomonas Kent ; Actinophrys Ehrb. ; Actinosphaerium St. ; Camptonema Schaud ; Nuclearia Cienk. 1 The alleged Archaean genus Hozoon, founded by Carpenter and Dawson on structures found in the Lower Laurentian serpentines (ophicalcites), and referred to the close proximity of Nummulites, has been claimed as of purely mineral structure by the petrologists ; and recent biologists have admitted this claim. iI HELIOZOA FEM 2. Invested with a gelatinous layer, sometimes traversed by a firmer elastic network. CHLAMYDOPHORA. — Heterophrys Arch.; Mastigophrys Frenzel ; Acenthocystis, Carter, 3. Ectoplasm with distinct siliceous spicules. CHALAROTHORACA.—Raphidiophrys Arch. 4. Skeleton a continuous, fenestrated shell, sometimes stalked. DesmoTHoRACA.—Myriophrys Penard ; Clathrulina Cienk. ; Orbu- linella Entz. This class were at first regarded and described as fresh-water Radiolaria, but the differences were too great to escape the ereatest living specialist in this latter group, Ernst Haeckel, who in 1866 created the Heliozoa for their reception. We owe our knowledge of it mainly to the labours of Cienkowsky, the late William Archer, F. E. Schulze, R. Hertwig, Lesser, and latterly to Schaudinn, who has monographed it for the “Tierreich ” (1896); and Penard has published a more recent account. Actinophrys sol Ehrb. (Fig. 18) is a good and common type. It owes its name to its resemblance to a conventional drawing of the sun, with a spherical body and numerous close-set diverging rays. The cytoplasm shows a more coarsely vacuolated outer layer, sometimes called the ectosare, and a denser in- ternal layer the endosare. In the centre of the figure is the large nucleus, to which the continuations of the rays may be seen to converge ; the pseudopodia contain each a stiffish axial filament, which is covered by Fic. 18.—Actinophrys sol. a, Axial the fine granular plasm, showing nae ee ee eae Bo cans currents of the granules. The axial (From Lang’s Comparative Ana- filament disappears when the pseudo- 0” #"er Giaacies) podia are retracted or bent, and is regenerated afterwards. This bending oceurs when a living prey touches and adheres to a ray, all its neighbours bending in like the tentacles of a Sundew. The prey is carried down to the surface of the ectoplasm, and b 1 Possibly composed of the same proteid, “‘acanthin,” that forms spicules of greater permanence in the Acantharia among the Radiolaria (p. 75 f. Figs. 24, 25, A). 72 PROTOZOA CHAP. sinks into it with a little water, to form a nutritive vacuole. Fission is the commonest mode of reproduction, and temporary plastogamic unions are not uncommon. Arising from these true conjugations occur, two and two, as described by Schaudinn. n, aa . ae at | ie | N,N, n<-N N71, | N, | | } | Fic. 21.—Diagram illustrating the conjugation of Actinosphaerium. 1, Original cell ; 2, nucleus divides to form two, N,Ne; 3, each nucleus again divides to form two, N, and v3, the latter passing out with a little cytoplasm as an abortive cell; 4, repetition of the same process as in 3; 5, the two nuclei Ny have fused in syngamy to form the zygote nucleus N.. | ——: | i= (and 18 doubtful). None are known fossil. Their geographical distribution is cosmopolitan, as is the case with most of the minute fresh-water Protista ; 8 genera are exclusively marine, and Orbulinella has only been found in a salt-pond; Actinophrys sol is both fresh-water and marine, and Actinolophus has 1 species fresh-water, the other marine. One of the 14 species of Acantho- cystis is marine; the remaining genera and species are all inhabitants of fresh water.” 4, RADIOLARIA Sarcodina with the protoplasm divided by a perforated chitinous central capsule into a central mass surrounding the nucleus, and an outer layer ; the pseudopodia radiate, never anasto- mosing enough to form a marked network ; skeleton either siliceous, of spicules, or perforated ; or of definitely arranged spicules of proteid matter (acanthin), sometimes also coalescing into a latticed shell; reproduction by fission and by zoospores formed in the central capsule. Habitat marine, suspended at the surface (plankton), at varying depths (zonarial), or near the bottom (abyssal). 1 Such divisions into functional and abortive sister nuclei are termed ‘‘reduc- ing divisions,” and are not infrequent in the formation of pairing-cells, especially oospheres of Metazoa, where the process is termed the maturation of the ovum. * Besides these genera enumerated by Schaudinn, we include Dimorpha Gruber (Fig. 37 5, p. 112), Mastigophrys Frenzel, Ciliophrys Cienk., and Actinomonas usually referred to Flagellates. 76 PROTOZOA CHAP. The following is Haeckel’s classification of the Radiolaria : I. Porutosa (HoLorrypasta).—Homaxonie, or nearly so. Central capsule spherical in the first instance ;' pores numerous, minute, scattered ; mostly pelagic. A. SpuMELLARIA (PERIPYLAEA).—Pores evenly scattered ; skeleton of solid siliceous spicules, or continuous, and reticulate or latticed, rarely absent ; nucleus dividing late, as an antecedent to reproduction. B, AcANTHARIA (AcTIPYLAEA).—Pores aggregated into distinct areas ; skeleton of usually 20 centrogenous, regularly radiating spines of acanthin, whose branches may coalesce into a latticed shell ; nucleus dividing early. fe: k Be fe K: 5 es 9. & ee %. Fic. 22. —Collozoum inerme. A, B, C, three forms of colony ; D, small colony with central capsules (c.caps), containing nuclei, and alveoli (vac) in ectoplasm ; E, isospores, with crystals (c) ; F, anisospores ; nv, nucleus. (From Parker and Haswell. ) IL. Oscuosa (Moyorrypasta).—Monaxonice ; pores of central capsule limited to the basal area (osculum), sometimes accompanied by two (or more) smaller oscula at apical pole, mostly zonarial or abyssal. C. Nassennarta (Monopynara).—Central capsule ovoid, of a single layer ; pores numerous on the operculum or basal field ; skeleton siliceous, usually with a principal tripod or calthrop-shaped spicule passing, by branching, into a complex ring or a latticed bell-shaped shell; nucleus eccentric, near apical pole. D. PHABODARIA (CANNOPYLAEA, Haeck.; TRIPYLAEA, Hertw.).—Central capsule spheroidal, of two layers, in its outer layer an operculum, with radiate ribs and a single aperture, beyond which protrudes the outer layer; osculum basal, a dependent tube (proboscis) ; accessory oscula, when present, simpler, usually two placed sym- metrically about the apical pole ; skeleton siliceous, with a com- bination of organic matter, often of hollow spicules; nucleus sphaeroidal, eccentric; extracapsular protoplasm containing an accumulation of dusky pigment granules (“ phaeodium ”). 111 HELIOZOA—RADIOLARIA Ti A. SPUMELLARIA. Sublegion (1). Cornoparta.!'—Skeleton absent or of detached spicules ; colonial or simple. Order i, Cottoipra.—Skeleton absent. (Families 1, 2.) Thalassicolla Huxl.; Thalassophysa Haeck.; Collozowm Haeck.; Collosphaera J. Mull. ; Actissa Haeck. Order 11. BELoipEA.—Skeleton spicular. (Families 3, 4.) Sublegion (2). SPHAERELLARIA.—Skeleton continuous, latticed or spongy, reticulate. Certl. CALS Sree Fic. 23.—Actinumma asteracanthion. A, the shell with portions of the two outer spheres broken away; B, section showing the relations of the skeleton to the animal. cent. caps, Central capsule ; ex. caps.pr, extra-capsular protoplasm ; nu, nucleus ; sk. 1, outer, sk. 2, middle, sk. 3, inner sphere of skeleton. (From Parker and Haswell, after Haeckel and Hertwig.) Order iii. SPHAEROIDEA. — Skeleton of one or several concentric spherical shells; sometimes colonial. (Families 5-10.) Haliomma Ehrb. ; Actinomma Haeck. (Fig. 23). Order ivy. Prunorpra.— Skeleton a prolate sphaeroid or cylinder, sometimes constricted towards the middle, single or concentric. (Families 11-17.) Order vy. Discorpra.—Shell flattened, of circular plan, simple or con- centric, rarely spiral. (Families 18-23.) Order vi. LarcormpEa—Shell ellipsoidal, with all three axes unequal or irregular, sometimes becoming spiral. (Families 24-32.)* 1K. Brandt, in Arch. Prot. i. 1902, p. 59, regards the presence of spicules as not even of generic moment, and subdivides the Collodaria into two families —CoJllidu (solitary), and Sphaerozoea, colonial, i.e. with numerous central capsules. 2 Dreyer adds an additional order—Sphaeropylida, distinguished by a basal (or a basal and an apical) pylome. 78 PROTOZOA CHAP. B. ACANTHARIA. Order vii. AcTINELTDA.— Radial spines numerous, more than 29, usually grouped irregularly. (Families 33-35.) Avphacantha Haeck. Order viii. ACANTHONIDA.—Radial spines equal. (Families 36-38.) Order ix. SpHAEROPHRACTA. — Radial spines 20, with a latticed spherical shell, independent of, or formed from the reticulations of (Families 39-41.) Dorataspis Haeck. (Fig. 25, A). the spines. ; latticed shell, Order x. PRuNOPHRACTA.—Radial spines 20, unequal ellipsoidal, lenticular, or doubly conical. (Families 42-44.) | es Fig. 24.—NXiphacantha (Acantharia), From the surface. ‘The skeleton only, x 100. (From Wyville Thomson.) NASSELLARIA. Order xi. Nassorpra.—Skeleton absent. (Family 45.) Order xii, Piecrorpka.—Skeleton of a single branching spicule, the branches sometimes reticulate, but never forming a latticed shell or a sagittal ring. (Families 46-47.) Order xiii. StEPHOIDEA.—Skeleton with a with the branched spicule, and sometimes (Families 48-51.) Lithocereus Théel (Fig. 26, A). Order xiv. SpyrorpEA.—Skeleton with a lJatticed shell developed around the sagittal ring (cephalis), and constricted in the sagittal plane, with a lower chamber (thorax) sometimes added. (Families 52-55.) sagittal ring continuous other rings or branches. IlI RADIOLARIA 79) Order xv. BorryorpEa.—As in Spyroidea, but with the cephalis 3-4 lobed ; lower chambers, one or several successively formed. (Families 56-58.) Order xvi. CyrrorpEa.—Shell as in the preceding orders, but without lobing or constrictions. (Families 59-70.) Theoconus Haeck. (Fig. 25, B). D. PHAEODARIA. Order xvii. PHarkocystina.—Skeleton 0 or of distinct spicules; capsule centric. (Families 71-73.) Aulactiniwm Haeck. (Fig. 26, B). Order xviii. PHABOSPHAERIA.—Skeleton a simple or latticed sphere, with no oral opening (pylome) ; capsule central. (Families 74-77.) Order xix. PHAroGromta.—Skeleton a simple latticed shell with a pylome at one end of the principal axis ; capsule excentric, sub-apical. (Families 78-82.) Pharyngella Haeck.; Tuscarora Murr. ; Haeckel- tana Murr. (Fig. 28). Order xx. PHaroconcHta.—Shell of two valves, opening in the plane (“frontal”) of the three openings of the capsule. (Families 83-85.) We exclude Haeckel’s Dictyochida, with a skeleton recalling that of the Stephoidea, but of the impure hollow substance of the Phaeodaria (p. 84). They rank now as Silicoflagellates (p. 114). The Radiolarian is distinguished from all other Protozoa by the chitinous central capsule, so that its cytoplasm is separated into an outer layer, the extracapsular protoplasm (ectoplasm), and a central mass, the intracapsular, containing the nucleus.' The extracapsular layer forms in its substance a gelatinous mass, of variable reaction, through which the plasma itself ramifies as a network of threads (“sarcodictyum’’), uniting at the surface to constitute the foundation for the pseudopodia. This gelatinous matter constitutes the “calymma.” It is largely vacuolated, the vacuoles (“alveoli”), of exceptional size, lying in the nodes of the plasmic network, and containing a liquid probably of lower specific gravity than seawater; and they are especially abundant towards the surface, where they touch and become polygonal. On mechanical irritation they disappear, to be formed anew after an interval, a fact that may explain the sinking from the surface in disturbed water. This layer may con- tain minute pigment granules, but the droplets of oil and of albuminous matter frequent in the central layer are rare here. 1 Verworn has shown that Thalassicolla nucleata can, when the exoplasm is removed from the central capsule, regenerate it completely. First a delicate exo- plasm gives off numerous fine radiating pseudopodia, and the jelly is re-formed at their bases, and carries them farther out from the central capsule. See General Physiology (Engl. ed. 1899), p. 379. 80 PROTOZOA CHAP. The “ yellow cells” of a symbiotic Flagellate or Alga, Zoovan- thella, are embedded in the jelly of all except Phaeodaria, and the whole ectosare has the average consistency of a firm jelly. The pseudopodia are long and radiating, with a granular external layer, whose streaming movements are continuous with those of the inner network. In the Acantharia they contain a firm axial filament, like that of the Heliozoa, which is traceable to the central capsule; and occasionally a bundle of pseudopodia may coalesce to form a stout process like a flagellum (“sarco- B ( Fia, 25.—Skeletons of Radiolaria. A, Dorataspis ; B, Theoconus. (After Haeckel.) flagellum”). Here, too, each spine, at its exit from the jelly, is surrounded by a little cone of contractile filaments, the myophrisks, whose action seems to be to pull up the jelly and increase the volume of the spherical body so as to diminish its density. The intracapsular protoplasm is free from Zooxanthella except in the Acantharia. It is less abundantly vacuolated, and is finely granular. In the Porulosa it shows a radial arrange- ment, with pyramidal stretches of hyaline plasma separated by intervals rich in granules. Besides the alveoli with watery contents, others are present with albuminoid matter in solution. Oil-drops, often brilliantly coloured, occur either in the plasma or floating in either kind of vacuole; and they are often luminous at night. Added to these, the intracapsular plasm contains pigment-granules, most frequently red or orange, pass- 111 RADIOLARIA 81 ing into yellow or brown, though violet, blue, and green also occur. The “ phaeodium,” ' however, that gives its name to the Phaeodaria, is an ageregate of dark grey, green, or brown granules which are probably formed in the endoplasm, but accumulate in the extracapsular plasm of the oral side of the central capsule. Inorganic concretions and crystals are also found in the contents of the central capsule, as well as aggregates of unknown com- position, resembling starch-grains in structure. In the Monopylaea, or Nassellaria (Figs. 25, B, 26, A), the endoplasm is differentiated above the perforated area of the central capsule into a cone of radiating filaments termed the “porocone,’ which may be channels for the communication between the exoplasm and the endoplasm, or perhaps serve, as Haeckel suggests, to raise, by their contraction, the perforated area: he compares them to the myophane striae of Infusoria. In the Phaeodaria (Fig. 26, B), a radiating laminated cone is seen in the outermost layer of the endoplasm above the principal opening (“astropyle”), and a fibrillar one around the two accessory ones (“ parapyles ”); and in some cases, continuous with these, the whole outer layer of the endoplasm shows a meridional striation. The nucleus is contained in the endoplasm, and is always at first single, though it may divide again and again. The nuclear wall is a firm membrane, sometimes finely porous. If there are concentric shells it at first occupies the innermost, which it may actually come to enclose, protruding lobes which grow through the several perforations of the lattice-work, finally coalescing outside completely, so as to show no signs of the joins. In the Nassellaria a similar process usually results in the formation of a lobed nucleus, contained in an equally lobed central capsule. The chromatin of the nucleus may be concentrated into a central mass, or distributed into several “ nucleoli,” or it may assume the form of a twisted, gut-like filament, or, again, the nuclear plasm may be reticulated, with the chromatin deposited at the nodes of the network. The skeleton of this group varies, as shown in our conspectus, 1 The pigment is singularly resistant and insoluble, and shows no proteid reaction. Borgert states that it appears to be formed in the oral part of the endo- plasm, and to pass through the astropyle into the ectoplasm, where it accumulates. It is probably a product of excretion, and may serve, by its retention, indirectly to augment the surface. See Borgert, ‘‘ Ueb. die Fortpflanzung der tripyleen Radio- larien” in Zool. Jahrb. Anat. xiv. 1900, p. 203. VOT et G D to PROTOZOA CHAP. in the several divisions.| The Acantharia (Figs. 24, 25, A) have a skeleton of radiating spines meeting in the centre of figure of the endoplasm, and forcing the nucleus to one side. The spines are typically 20 in number, and emerge from the surface of the Fic. 26.—A, Lithocercus annularis, with sagittal ring (from Parker and Haswell). B, Awlactiniwm actinastrum. C,calymma ; cent. caps., km, central capsule ; re Ext. caps. pr., Extracapsular, cent caps and Int. caps. pr., intracapsular —— Int.caps. pr a1 protoplasm; 2, wu, nucleus ; f ie / op, operculum ; ph, phaeodium ; er psd, pSeudopodium ; Skel., eS e LLC .COpS. Pr skeleton ; 2, Zooxanthella. ee } : (From Lang’s Comparative z /- Anatomy, after Haeckel. ) regular spherical forms (from which the others may be readily derived) radially, in five sets of four in the regions corresponding to the equator and the tropics and polar circles of our world. ' Dreyer has shown that in many cases it may be explained by geometrical considerations. V. Hacker has written a most valuable account of the Biological relations of the skeleton of Radiolaria in Jen. Zeitschr. xxxix. 1904, p. 297. 111 RADIOLARIA a3 The four rays of adjacent circles alternate, so that the “ polar” and “ equatorial” rays are on one set of meridians 90° apart, and the “ tropical” spines are on the intermediate meridians, as shown in the figures. By tangential branching, and the meet- ing or coalescence of the branches, reticulate (Figs. 23, 24, 25) and latticed shells are formed in some families, with circles of openings or pylomes round the bases of the spines. In the Sphaerocapsidae the spines are absent, but their original sites are inferred from the 20 circles of pylomes. . In the Spumellaria the simplest form of the (siliceous) skeleton is that of detached spicules, simple or complex, or passing into a latticed shell, often with one or more larger openings (pylomes). Radiating spines often traverse the whole of the cavity, becoming continuous with its latticed wall, and bind firmly the successive zones when present (Fig. 23). Calearomma calearea was described by Wyville Thomson as having a shell of apposed calcareous discs, and MMJyxobrachia, by Haeckel, as having collections of the calcareous Coccoliths and Coccospheres. In both cases we have to do with a Radiolarian not possessing a skeleton, but retaining the undigested shells of its food, in the former case (Actissa) in a continuous layer, in the latter (7halassicolla) in accumulations that, by their weight, droop and pull out the lower hemisphere into distinct arms. The (siliceous) skeleton of the Nassellaria is absent only in the Nassoidea, and is never represented by distinct spicules. Its simplest form is a “tripod” with the legs downward, and the central capsule resting on its apex. The addition of a fourth limb converts the tripod into a “ calthrop,” the central capsule in this case resting between the upturned leg and two of the lower three regarded as the “anterolateral”; the odd lower leg, like the upturned one, being “ posterior.” Again, the skeleton may present a “ sagittal ring,” often branched and spiny (Fig. 26, A), or combined with the tripod or calthrop, or complicated by the addition of one or more horizontal rings. Another type is presented by the “ latticed chamber” surrounding the central capsule, with a wide mouth (“pylome”) below. This is termed the “cephalis”; it may be combined in various ways with the sagittal ring and the tripod or calthrop; and, again, it may be prolonged by the addition of one, two, or three chambers below, 84 PROTOZOA CHAP. the last one opening by a pylome (Fig. 25, B). These are termed “ thorax,’ “abdomen,” and “ post-abdomen ” respectively. In the Phaeodaria the skeleton may be absent, spicular (of loose or connected spicules) or latticed, continuous or bivalve. It is composed of silica combined with organic matter, so that it chars when heated, is more readily dissolved, and is not preserved in fossilisation. The spicules or lattice-work are hollow, often with a central filament running in the centre of the gelatinous contents. The latticed structure of the shell of the Challengeridae (Fig. 28) is so fine as to recall that of the Diatomaceae. In the Phaeoconchida the shell is in two halves, parted along the “frontal” plane of the three apertures of the capsule. Ave Ns : 7 Va Varta % ie ait te ' qo ¥ ar t z j ey u “sf, Saat raat pee i ‘ ‘ pottats Ute nea dr 1 ‘ ' ‘% tig ca H TOA fenntideg: (ei are Wate Page iy Pe aR ad chert ' Core tre elke j erat ti sis pao a | ° f "4 7h {i Eas g SAC Pe > Na ”, Fic, 27.—Scheme of various possible skeletal forms deposited in the meshes of an alveolar system, most of which are realised in the Radiolaria. (From Verworn, after Dreyer.) The central capsule (rarely inconspicuous and difficult, if not impossible to demonstrate) is of a substance which resembles chitin, though its chemical reactions have not been fully studied hitherto, and indeed vary from species to species. It is composed of a single layer, except in Phaeodaria, where it is double. The operculum in this group, 7.e. the area around the aperture, is composed of an outer layer, which is radially thickened, and a thin inner layer; the former is produced into the projecting tube (“ proboscis ”). Reproduction in the Radiolaria may be simple fission due to the binary fission of the nucleus, the capsule, and the ectoplasm in succession. If this last feature is omitted we have a colonial organism, composed of the common ectoplasm containing numerous central capsules; and the genera in which this occurs, all belonging to the Peripylaea, were formerly separated (as Polycyttaria) from TI RADIOLARIA 85 the remaining Radiolaria (Monocyttaria). They may either lack a skeleton (Collozoidae, Fig. 22), or have a skeleton of detached spicules (Sphaerozoidae), or possess latticed shells (Collosphaeridae) one for each capsule, and would seem therefore to belong, as only differentiated by their colonial habit, to the several groups having these respective characters. Fission has been well studied in Aulacantha (a Phaeodarian) by Borgert.’ He finds that in this case the skeleton is divided between the daughter-cells, and the missing part is regenerated. In cases where this is impossible one of the daughter-cells retains the old skeleton, and the other escapes as a bud to form a new’skeleton. Fic. 28.—Shells of Challengeridae: A, Tuscarora ; B, Pharyngella ; C, Haeckeliana. (From Wyville Thomson. ) Two modes of reproduction by flagellate zoospores have been described (Fig. 22). In the one mode all the zoospores are alike— isospores—and frequently contain a crystal of proteid nature as well as oil-globules. In the Polycyttaria alone has the second mode of spore-formation been seen, and that in the same Species in which the formation of isospores occurs. Here “amisospores” are formed, namely, large “mega-,’ and small “micro - zoospores.” They probably conjugate as male and female respectively ; but neither has the process been observed, nor has any product of such conjugation (zygote) been recognised. In every case the formation of the zoospores only involves the 1 Zool. Jahrb. Anat. xiv. 1900, p. 203. 86 PROTOZOA CHAP. endoplasm: the nucleus first undergoes brood division, and the plasma within the capsule becomes concentrated about its offspring, and segregates into the spores; the extracapsular plasm disintegrates.' The Yellow Cells (Zooxzanthella), so frequently found in the Radiolaria were long thought to be constituents of their body. Cienkowsky found that when the host died from being kept in unchanged water, the yellow cells survived and multiplied freely, often escaping from the gelatinised cell-wall as biflagellate zoospores. The cell-wall is of cellulose. The cell contains two chloroplastids, or plates coloured with the vegetal pigment “diatomin.” Besides ordinary transverse fission in the ordinary encysted state in the ectoplasm of the host, when free they may pass into what is. known as a “ Palmella-state,” the cell-walls gelatinising; in this condition they multiply freely, and constitute a jelly in which the individual cells are seen as rounded bodies. They contain starch in two forms—large hollow granules, not doubly refractive, and small solid granules which polarise light. We may regard them as Chrysomonadaceae (p. 113). Similar organisms occur in many Anthozoa (see pp. 261, 339, 373 f., 396). Diatomaceae (yellow Algae with silicified cell-walls) sometimes live in the jelly of certain Collosphaera. Both these forms live in the state known as “symbiosis” with their host; 7.e. they are in mutually helpfal association, the Radiolarian absorbing salts from the water for the nutrition of both, and the Alga or Flagellate taking up the CO, due to the respiration of the host, and building up organic material, the surplus of which is doubtless utilised, at least in part, for the nutrition of the host. A similar union between a Fungus and a coloured vegetal (“holophytic”) organism is known as a Lichen. The Suctorian Infusorian Amoebophrya is parasitic in the ectoplasm of certain Acantharia, and in the peculiar genus Sticho- lonche which appears to be intermediate between this group and Heliozoa. The Silicoflagellate family Dictyochidae are found temporarily 1 Porta has described reproduction by spores and by budding in Acantharia, Rend. R. Ist. Lomb. xxxiv. 1901 (ex Journ. R. Micr. Soc. 1903, p. 45). In Thalassophysa and its allies zoospore reproduction appears to be replaced by a process in which the central capsule loses its membrane, elongates, hecomes multinuclear, and ultimately breaks up into the nucleate portions, each annexing an envelope of ectoplasm to become a new individual (see Arch. Prot. vol. i. 1902). III RADIOLARIA 87 embedded in the ectoplasm of some of the Phaeocystina, and have a skeleton of similar nature. Their true nature was shown by Borgert. The Amphipod erustacean Hyperia' may enter the jelly of the colonial forms, and feed there at will on the host.’ Haeckel, in his Monograph of the Radiolaria of the Challenger enumerated 739 genera, comprising 4518 species ; and Dreyer has added 6 new genera, comprising 39 species, besides 7 belonging to known genera. Possibly, as we shall see, many of the species may be mere states of growth, for it is impossible to study the life- histories of this group; on the other hand, it is pretty certain that new forms are likely to be discovered and described. The Radiolaria are found living at all depths in the sea, by the superficial or deep tow-net; and some appear to live near the bottom, where the durable forms of the whole range also settle and accumulate. They thus form what is known as Radiolarian ooze, which is distinguished from other shallower deposits chiefly through the disappearance by solution of all calcareous skeletons, as they slowly fell through the waters whereon they originally floated at the same time with the siliceous remains of the Radiolaria. The greatest wealth of forms is found in tropical seas, though in some places in cold regions large numbers of individuals of a limited range of species have been found. Radiolaria of the groups with a pure siliceous skeleton can alone _be fossilised, even the impure siliceous skeleton of the Phaeodaria readily dissolving in the depths at which they live: they have been generally described by Ehrenberg’s name Polycystinece. Tripolis (Kieselguhr) of Tertiary ages have been found in many parts of the globe, consisting largely or mainly of Radiolaria, and representing a Radiolarian ooze. That of the Miocene of Barbados contains at least 400 species; that of Gruppe at least 130. In Secondary and Palaeozoic rocks such oozes pass into Radiolarian quartzites (some as recent as the Jurassic). They occur also in fossilised excrement (coprolites), and in flint or chert concretions, as far down as the lowest fossiliferous rocks, 1 Brandt, ‘‘ Die Koloniebildenden Radiolarien,” in Fawna wu. Flora des Golfes v. Neapel, xiii. 1885, gives a full account of the Zooxanthellae and Diatoms, and notes the parasitism of Hyperia. 2 See Koppen in Zool. Anz. xvii. 1894, p. 417. For Sticholonche, see R. Hertwig in Jena. Zeitsch. xi. 1877, p. 324; and Korotneff in Zeitsch. wiss. Zool. li. 1891, p. 613. Borgert’s paper on Dictyochidae is in the same volume, p. 629. 88 PROTOZOA CHAP. the Cambrian. The older forms are simple Sphaerellaria and Nassellaria. From a synopsis of the history of the order in Haeckel’s Monograph (pp. elxxxvi.-clxxxviii.) we learn that while a large number of skeletal forms had been described by Ehren- berg, Huxley in 1851 published the first account of the living animal. Since then our knowledge has been extended by the labours of Haeckel, Cienkowsky, R. Hertwig, Karl Brandt, and A. Borgert. 5. PROTEOMYXA Sarcodina without a clear ectoplasm, whose active forms are amoeboid or flagellate, or pass from the latter form to the former ; multiplying chiefly, if not exclusively, by brood-formation in a cyst. No complete cell-pairing (syngamy) known, though the cytoplasms may unite into plasmodia ; pseudopodia of the amoeboid forms usually radiate or filose, but without axial filaments. Sapro- phytic or parasitic in living animals or plants. This group is a sort of lumber-room for forms which it is hard to place under Rhizopoda or Flagellata, and which produce simple cysts for reproduction, not fructifications like the Mycetozoa. The cyst may be formed for protection under drought (“ hypno- cyst”), or as a preliminary to spore-formation (“sporocyst ”). The latter may have a simple wall (simple sporocyst), or else two or three formed in succession (“resting cyst”), so as to en- able it to resist prolonged desiccation, ete. : both differing from the hypnocyst in that their contents undergo brood formation, On encystment any indigestible food materials are extruded into the cyst, and in the “resting cysts,’ which are usually of at least two layers, this faecal mass lies in the space between them. The brood-cells escape, either as flagellate-cells, resembling the simpler Protomastigina, called “flagellulae,” and which often become amoeboid (Fig. 29); or already furnished with pseudopodia, and called “amoebulae,” though they usually recall Actinophrys rather than Amoeba. In Vampyrella and some others the amoebulae fuse, and so attain a greater size, which is most probably advanta- geous for feeding purposes. But usually it is as a uninucleate cell that the being encysts. They may feed either by ingestion by the pseudopodia, by the whole surface contained in a living host-cell, or by passing a pseudopodium into a_ host-cell (Fig. 29 5). They may be divided as follows :— III PROTEOMYXA 89 ee A. Myxorpra.—Flagella 1-3 ; zoospores separating at once. 1. ZoosporEAE.—Brood-cells escaping as flagellulae, even if they become amoeboid jater. Cilicphrys Cienk.; Pseudospora Cienk. (Fig. 29). 2. AzoosPOREAE.—Cells never flagellate. Protomyxa Haeckel ; Plasmo- diophora Woronin; Vampyrella Cienk.; Serwmsporidium L, Pfeiffer. B. Catattacra.—Brood-cells of cyst on liberation adhering at the centre to form a spherical colony, multiflagellate ; afterwards separating, and becoming amoeboid. Magosphwerw Haeckel (marine)." Plasmodiophora infests the roots of Crucifers, causing the disease known as “ Hanburies,” or “ fingers and toes,” in turnips, ete. Serumsporidium dwells in the body cavity of small Crustacea. (US \ - NI SF oO oS, COR Sy, Fic. 29.—Pseudospora lindstedtii. 1, 2, Flagellate zoospores: 3, young amoebula, with two contractile vacuoles, one being reconstituted by three minute formative vacuoles ; 4, 5, an amoebula migrating to a fungus hypha through the wall of which it has sent a long pseudopodium; 6, amoebula full-grown; 7, 8, mature cells rounded off, protruding a flagellum, before encysting ; 9, young sporocyst ; 10, the nucleus has divided into a brood of eight; 11-14, stages of formation of zoospores. cv, Contractile vacuole; e, mass of faecal granules ; j/, flagellum ; 2. nucleus. x about 72°. Many of this group were described by Cienkowsky under the name of “ Monadineae” (in Arch. Mikr. Anat. i. 1865, p. 203). Zopf has added more than anyone else since then to our know- ledge. He monographed them under Cienkowsky’s name, as a subordinate group of the Myxomycetes, “ Pilzthiere oder Schleim- pilze,’ in Schenk’s Handb. d. Bot. vol. iii. pt. ii. (1887). To Lankester (Hneycl. Brit., reprint 1891) we owe the name here adopted. Zopf has successfully pursued their study in recent 1 Most of Haeckel’s Monera, described as non-nucleate, belong here. Several have been proved to be nucleate, and to be rightly placed here ; and all require renewed study. gO PROTOZOA CHAP. papers in his Beitr. Nied. Org. The Chytridieae, usually ascribed to Fungi, are so closely allied to this group that Zopf proposes to include at least the Synchytrieae herein. This group is very closely allied to Sporozoa ; for the absence of cytogamy, and of sickle-germs,’ and of the complex spores and cysts of the Neosporidia, are the only absolute distinctions. 6. Mycrrozoa (MyxomMycETEs, MyXoGASTRES) Surcodina moving and feeding by pseudopodia, with no skeleton, aggregating more or less completely into complex “fructifications ~ before forming 1-nucleate resting spores; these may in the first instance liberate flagellate zoospores, which afterwards become amoeboid, or may be amoeboid from the first ; zoospores capable of forming hypnocysts from which the contents escape in the original form. 1. Aggregation taking place without plastogamy, zoospores amoeboid, with a clear ectosarc : : : : : ACRASIEAE. Copromyxa Zopt; Dictyostelium Brefeld. . Aggregation remaining lax, with merely thread-like connexions, except when encystment is to take place ; cytoplasm finely granular throughout ; complete fusion of the cytoplasm doubtful . . FILOPLASMODIEAE. Labyrinthula Cienk. ; Chlamydomyxa Archer ; Leydenia (?) Schaud. 3. Plasmodium formation complete, eventuating in the formation of a com- plex fructification often traversed by elastic, hygroscopic threads, which by their contraction scatter the spores; zoospores usually flagellate at first ; : 5 . : . MYXOMYCETES. Fuligo Hall. ; Chondrioderma Rostat. ; Didymiwm Schrad. (Fig. 30). to I. The Acrasieae are a small group of saprophytes, often in the most literal sense, though in some cases it has been proved that the actual food is the bacteria of putrefaction. In them, since no cell-division takes place in the fructification, it is certain that the multiplication of the species must be due to the fissions of*the amoeboid zoospores, which often have the habit of Amoeba limax (Fig. 1, p. 5). II. Filoplasmodieae.—Chlamydomyava” is a not uncommon inhabitant of the cells of bog-mosses and bog-pools, and its nutrition may be holophytic, as it contains chromoplasts ; but it 1 Even the Acystosporidiae have sickle-germs (blasts) in the insect host. 2 See Zopf, Beitr. Nied. Org. ii. 1892, p. 36, iv. 1894, p. 60, for the doubtful genus Chiamydomyza ; Hieronymus, abstracted by Jenkinson, in Quart. J. Mier. Sct. xiii. 1899 ; Penard, Arch. Protist. iv. 1904, p. 296. III MYCETOZOA—MYXOMYCETES Ol can also feed amoeba-fashion. Labyrinthula is marine, and in its fructification each of the component cells forms four spores. Leydenia has been found in the fluid of ascitic dropsy, associated with malignant tumour. Ill. Myxomycetes.—The fructification in this group is not formed by the mere aggregation of the zoospores, but these fuse by their cytoplasm to form a multinucleate body, the “ plas- modium,” which, after moving and growing (with nuclear division) for some time like a great multinucleate Reticularian, passes into rest, and develops a fructification by the formation of a complex outer wall; within this the contents, after multiplication of the nuclei, resolve themselves into uninucleate spores, each with its own cyst-wall. The fructifications of this group are often conspicuous, and resemble those of the Gasteromycetous fungi (eg., the Puff- balls), whence they were at first called MJyxogastres. De Bary first discovered their true nature in 1859, and ever since they have been claimed by botanist and zoologist alike. The spore on germination liberates its contents as a minute flagellate, with a single anterior lash and a contractile vacuole (Fig. 30, C). It soon loses the lash, becomes amoeboid, and feeds on bacteria, etc. (Fig. 30, D, E). In this state it can pass into hypnocysts, from which, as from the spores, it emerges as a flagellula. After a time the amoeboids, which may multiply by fission, fuse on meeting, so as to form the plasmodium (Fig. 30, F). This contains numerous nuclei, which multiply as it grows, and numerous contractile vacuoles. When it attains full size it becomes negatively hydrotactic, crawls to a dry place, and resolves itself into the fructification. The external wall, and sometimes a basal support to the fruit, are differentiated from the outer layer of protoplasm; while the nuclei within, after undergoing a final bipartition, concentrate each around an independent portion of plasma, which again is surrounded as a spore by a cyst-wall. Often the maturing plasmodium within the wall of the fruit is traversed by a network of anastomosing tubes filled with liquid, the walls of which become differentiated into membrane like the fruit-wall, and are continuous therewith. As the fruit ripens the liquid dries, and the tubes now form a network of hollow threads, the “ capillitium,” often with external spiral ridges (Fig. 30, A, B). These are very hygroscopic, and by their expansion and contraction 92 PROTOZOA CHAP. determine the rupture of the fruit-wall and the scattering of the spores. Again, in some cases the plasmodia themselves aggregate in the same way as the amoeboids do in the Acrasieae, and combine Fic. 30.—Didymium difforme. A, two sporangia (spy 1 and 2) ona fragmeut of leaf (Z) ; B, section of sporangium, with ruptured outer layer (a), and threads of capillitium (cp); ©, a flagellula with contractile vacuole (¢.vac) and nucleus (nw); D, the same after loss of flagellum ; 4, an ingested bacillus ; E, an amoebula; F, conjugation of amoebulae to form a small plasmodium ; G, a larger plasmodium accompanied by utmerous amoebulae ; sp, ingested spores. (After Lister.) to form a compound fruit termed an “aethalium,’! with the regions of the separate plasmodia more or less clearly marked off. The species formerly termed Aethaliuvm septicum is now known as Fuligo varians. It is a large and conspicuous species, common on tan, and is a pest in the tanpits. Its aethalia may reach a ' The name ‘‘ aethalium”’ is now always used in this sense. Il MYCETOZOA 93 diameter of a foot and more, and a thickness of two inches. Chondrioderma diffusum, often utilised as a convenient “ laboratory type,” is common on the decaying haulms of beans in the late autumn. The interest of this group is entirely biological, save for the “ flowers of tan.” ? 1 The group was monographed by Schroter in Engler and Prantl’s Pflanzen- Ffumilien, I. Teil, Abt. 1, 1897. See also A. Lister’s Monograph of the Mycetozoa, 1894; Massee, Monog. of the Myxogastres, 1893 ; Sir Edward and Agnes Fry, The Mycetozou, 1899 ; and Massee MacBride, The North Ainericun Slime Moulds, 1899. CHAPTER IV PROTOZOA (CONTINUED): SPOROZOA* IL. Sporozoa. Protozoa parasitic in Metazoa, usually intracellular for at least part of their cycle, rarely possessing pseudopodia, or flagella (save in the sperms), never cilia; reproduction by brood-formation, often of alternating types; syngamy leading up to resting spores in which minute sickle-germs are formed, or unknown (Myxo- sporidiaceae). This group, of which seven years ago no single species was known in its complete cycle, has recently become the subject of concentrated and successful study, owing to the fact that it has been recognised to contain the organisms which induce such scourges to animals as malarial fevers, and various destructive murrains. Our earliest accurate, if partial knowledge, was due to von Siebold, Kolliker, and van Beneden. Thirty years ago Ray Lankester in England commenced the study of species that dwell in the blood, destined to be of such moment for the well-being of man and the animals in his service ; and since then our knowledge has increased by the labours of Manson, Ross and Minchin at home, Laveran, Blanchard, Thélohan, Léger, Cuénot, Mesnil, Aimé Schneider in France, Grassi in Italy, Schaudinn, Siedlecki, L. and R. Pfeiffer, Doflein in Central Europe, and many others. ' Several monographs of the group have been published recently dealing with the group from a systematic point of view, including their relation to their hosts. Wasielewski, ‘‘Sporozoenkunde” (1896) ; Labbé, ‘‘Sporozoa” (in Tierreich, 1899). Doflein’s ‘‘ Protozoen als Parasiten und Krankheitserreger”’ (1901) contains most valuable information of the diseases produced by these and other Protozoic hosts. Minchin’s Monograph in Lankester’s Treatise on Zoology, pt. i. fasc. 2 (1903), is a full account of the class, and admirable in every way. 94 CHAP. IV SPOROZOA 95 As a type we will take a simple form of the highest group, the Gregarinidaceae, Monocystis, which inhabits the seminal vesicles of the earthworm. In its youngest state, the “sporozoite,”’ it is a naked, sickle-shaped cell, which probably makes its way from the eut into one of the large radial cells of the seminal funnel, where fe) epithelium cells of host ; d, e, growth stages ; 7, free gregarine ; g, association ; h, encystment; 7, j, brood-divisions in associated mates; /, pairing-cells ; 1, syngamy ; m, zygote; 7, 0, p, nuclear divisions in spores; g, cyst with adult spores, each containing 8 sickle-germs. (After Luhe, modified from Siedlecki.) Fig. 31.—Lankesteria ascidiae, showing life-cycle. «, 6, c, Sporozoites in digestive it attains its full size, and then passes out into the vesicles or reservoirs of the semen, to lie among the sperm morulae and young spermatozoa. The whole interior is formed of the opaque endosare, which contains a large central nucleus, and is full of refractive granules of paramylum or paraglycogen,' a carbohydrate allied to glycogen or animal starch, so common in the liver and 1 For its reactions see Biitschli, Arch. Protist. vii. 1906, p. 197. 96 PROTOZOA CHAP. muscles of Metazoa; besides these it contains proteid granules which stain with carmine, and oil-drops. The ectosare is formed of three layers: (1) the outer layer or “cuticle” * is, in many cases if not here, ribbed, with minute pores in the furrows, and is always porous enough to allow the diffusion of dissolved nutriment : (2) a clear plasmatic layer, the “ sarcocyte” ; (3) the “ myocyte,” formed of “myonemes,” muscular fibrils disposed in a network with transverse meshes, which effect the wriggling movements of the cell. The endosare contains the granules and the large central nucleus. The adult becomes free in the seminal vesicles ; here two approximate, and surround themselves with a common cyst: a process which has received the name of “association ” (Fig. 31, g-i). Within this, however, the protoplasms remain absolutely distinct. The nucleus undergoes pecuhar changes by which its volume is considerably reduced. When this process of “nuclear reduction” is completed, each of the mates undergoes brood-divisions (7), so as to give rise to a large number of rounded naked 1-nucleate cells—the true pairing-cells. These unite two and two, and so form the 1-nucleate spores (/-m), which become oat-shaped, form a dense cyst-wall, and have been termed “ pseudonavicellae”” from their likeness to the Diatoma- ceous genus Navicella. Some of the cytoplasm of the original cells remains over unused, as “ epipiasm,” and ultimately degene- rates, as do a certain number of the brood-cells which presum- ably have failed to pair. It is believed that the brood-cells from the same parent will not unite together. The contents of each spore have again undergone brood-division to form eight sickle-shaped zoospores, or “sporozoites” (n-g), and thus the developmental cycle is completed. Probably the spores, swallowed by birds, pass out in their excrement, and when eaten by an earthworm open in its gut; the freed sickle-germs can now migrate through the tissues to the seminal funnels, in the cells of which they grow, ultimately becoming free in the seminal vesicles.” 1 The cuticle in the allied genus Lankesteria, which is the form we figure on p. 95, is perforated by a terminal pore, through which the clear plasma of the sarcocyte may protrude as a pseudopodium. 2 This account is taken from Cucnot (in Arch. de Biol. 1900, p. 49), which con- firms Siedlecki’s account of the process in the allied genus Lankesteria in Bull. Acad. Cracow, 1899. Wolters’s previous description, assimilating the processes to those of Actinophrys, is by these authors explained as the result of imperfect preservation of his material. IV SPOROZOA— CLASSIFICATION Q7 We may now pass to the classification of the group. A. TELosporipEA.—Cells 1-nucleate until the onset of brood-formation, which is simultaneous. 1, GREGARINIDACEAE. —Cells early provided with a firm pellicle and possessing a complex ectosarc; at first intracellular, soon becoming free in the gut or coelom of Invertebrates, Pairing between adults, which simultaneously produce each its brood of gametes, isogamous or bisexual, which pair within the common cyst; zygotospores surrounded by a firm cyst, and producing within a brood of sickle-shaped zoospores. (iL) SCHIZOGREGARINIDAE.—Multiplying by simple fission in the free state as well as by brood-formation ; the brood-cells conjugating in a common cyst, but producing only one pairing nucleus in each mate (the rest aborting), and consequently only one spore. : : : . Ophryocystis A. Schn. (ii.) ACEPHALINLDAE, —Cell one-chambered, usually without an epimerite for attachment. Monocystis F. Stein ; Lankesteria Mingazzini. ii.) DicystrpazE.—Cell divided by a plasmic partition; epimerite usually present. Gregarina Dufour; Stylorhynchus A. Schn. ; Pterocephalus A. Schn. 2. CoccIpIACEAE. —Cells of simple structure, intracellular in Metazoa. Pairing between isolated cells usually sexually differentiated as oosphere and sperm, the latter often flagellate. Brood-formation of the adult cell giving rise to sickle-shaped zoospores (merozoites), or progamic and pro- ducing the gametes. Oosperm motile or motionless, finally producing a brood of spores, which again give rise to a brood of sickle-spores. (i.) CoccipupAr.—Cell permanently intracellular, or very rarely coelomic, encysting or not before division; zoospores always sickle-shaped ; oosperm encysting at once, producing spores with a dense cell-wall producing sickle-germs. (ii.) HAEMOSPORIDAE.—Cells parasitic in the blood corpuscles or free in the blood of cold-blooded animals, encysting before brood- formation ; zoospores sickle-shaped; oosperm at first motile. Lankeresterella Labbé ; (Drepanidiwm Lank.;) Karyolysus Labhé ; Haemogregarina Danilewski. (iiil.) ACYSTOSPORIDAE.—Cells parasitic in the blood and haemato- cytes of warm-blooded Vertebrates; never forming a cyst-wall before dividing ; zoospores formed in the corpuscles, amoeboid. Gametocytes only forming gametes when taken into the stomach of insects. Oosperm at first active, passing into the coelom, producing naked spores which again produce a large brood of sickle zoospores, which migrate to the salivary gland, and are injected with the saliva into the warm-blooded host. Haemamoeba Grassi and Feletti; Laverania Grassi and Feletti ; Haemoproteus Kruse ; Halteridium Labbé.4 B. Nerosporipra.—Cells becoming multinucleate apocytes before any brood- formation occurs. Brood-formation progressive through the apocyte, not simultaneous, 1 See p. 120. VOL. I H 98 PROTOZOA CHAP. 1. MyxosporIDIACEAE.—Naked parasites in cold-blooded animals. Spore- formation due to an aggregation of cytoplasm around a single nucleus to form an archespore, which then produces a complex of cells within which two daughter-cells form the spores and accessory nematocysts. Myaidium Biitsch.; Myzobolus Biitsch.; Henneguya Thelohan ; Nosema Nigeli (= Glugea Th.). 2, ACTINOMYXIDIACEAE.!— Y) ad é a Iwona ZL ead (2. SAAN = SIE f RAN GSS =— Sy Te yas qgggdoocsq0e0o0d Fic. 35.—Life-history of Malarial Parasites. A-G', Amoebula of quartan parasite to sporu- lation ; HW, its gametocyte; 7-47, amoebula of tertian parasite to sporulation; J. its gametocyte ; O, 7, “crescents” or gametocytes of Laverania ; P-S, sperm-forma- tion; U-W, maturation of oosphere ; -X, fertilisation ; VY, zygote. a, Zygote enlarging in gut of Mosquito; 6-e, passing into the coelom ; 7, the contents seg- mented into naked spores ; g, the spores forming sickle-germs or sporozoites ; h, sporozoites passing into the salivary glands. (From Calkins’s Protozoa, after Ross and Fielding Ould.) tertian (Hl. vivaz, Fig. 35, M). These brood-cells escape and behave for the most part as before. But after the disease has persisted for some time we find that in the genus Haemamoeba, IV SPOROZOA 105 which induces the common malarial fevers of temperate regions, certain of the full-grown germs, instead of behaving as schizonts, pass, as it were, to rest as round cells; while in the allied genus Laverania (Haemomenas, Ross) these resting-cells are crescentic, with blunt horns, and are usually termed half-moons (Fig. 35, O, T), characteristic of the bilious or pernicious remittent fevers of the tropics and of the warmer temperate regions in summer. These round or crescent-shaped cells are the gametocytes, which only develop further in the drawn blood, whether under the microscope, protected against evaporation, or in the stomach of the Anopheles: the crescents become round, and then they, lke the already round ones of Haemamoeba, differentiate in exactly the same way as the corresponding cells of Coceidium schubergi. The female cell only exhibits certain changes in its nucleus to convert it into an oosphere: the male emits a small number of sperms, long flagellum-like bodies,each with a nucleus; and these, by their wriggling, detach themselves from the central core, no longer nucleated. The male gametogonium with its protruded sperms was termed the “ Polymitus form,’ and was by some regarded as a degeneration-form, until MacCallum discovered that a “ flagellum ” regularly undergoes sexual fusion with an oosphere in Halteridium, as has since been found in the other genera. The oosperm (Y) so formed is at first motile (“ookinete”), as it is in Haemosporidae, and passes into the epithelium of the stomach of the gnat and then through the wall, acquiring a cyst-wall and finally projecting into the coelom (a-e). Here it segments into a number of spheres (“zygotomeres ” of Ross) corresponding to the Coccidian spores, but which never acquire a proper wall (7f). These by segmentation produce at their surface an immense quantity of elongated sporozoites (the “zygotoblasts” or “blasts” of Ross, Fig. 35, g), these are ultimately freed by the disappearance of the cyst-wall of the oosperm, pass through the coelom into the salivary gland (/), and are discharged with its secretion into the wound that the gnat inflicts in biting. In the blood the blasts follow the ordinary development of merozoites in the blood corpuscle, and the patient shows the corresponding signs of fever. This has been completely proved by rearing the insect from the egg, feeding it on the blood of a patient in whose blood there were ascertained to be the germs of a definite species of Haem- 106 PROTOZOA CHAP. amoeba, sending it to England, where it was made to bite Dr. Manson’s son, who had never had fever and whose blood on repeated examination had proved free from any germs. In the usual time he had a well-defined attack of the fever corresponding to that germ, and his blood on examination revealed - the Haemamoeba of the proper type. A few doses of quinine relieved him of the consequences of his mild martyrdom to science. Experiments of similar character but of less rigorous nature had been previously made in Italy with analogous results. Again, it has been shown that by mere precautions against the bites of Anopheles, and these only, all residents who adopted them during the malarious season in the most unhealthy districts of Italy escaped fever during a whole season; while those who did not adopt the precautions were badly attacked." Anopheles flourishes in shallow puddles, or small vessels such as tins, ete., the pools left by dried-up brooks and torrents, as well as larger masses of stagnant water, canals, and slow-flowing streams. Sticklebacks and minnows feed freely on the larvae and keep down the numbers of the species; where the fish are not found, the larvae may be destroyed by pouring paraffin oil on the surface of the water and by drainage. A combination of protective measures in Freetown (Sierra Leone) and other ports on the west coast of Africa, Ismailia, and elsewhere, has met with remarkable success during the short time for which it has been tried; and it seems not improbable, that as the relatively benign intermittent fevers have within the last century been banished from our own fen and marsh districts, so the Guinea coast may within the next decade lose its sad title of “The White Man’s Grave.” So closely allied to this group in form, habit, and life-cycle are some species of the Flagellate genus 7rypanosoma, that in their less active states they have been unhesitatingly placed here (see p. 119). Schaudinn has seen Trypanosomic characters in the “ blasts” of this group, which apparently is the most primi- tive of the Sporozoa and a direct offshoot of the Flagellates. The Myxosporidiaceae (Fig. 56) are parasitic in various 1 It would seem that resting-cells, 7.e. the crescents and corresponding spheres, of Laverania and Haemamocba may linger during months of apparent health in the spleen and red marrow of the bones; and that these by parthenogenesis produce sporozoites and determine relapses when, owing to a lowering of the general health, conditions favourable to new sporulation occur. iv SPOROZOA 107 cold-blooded animals. They are at least binucleate in the youngest free state, and become large and multinucleate apocytes, which may bud off outgrowths as well as reproduce by spores. The spores of the apocyte are not produced by simultaneous breaking up, but by successive differentiation. A single nucleus aggregates around itself a limited portion of the cytoplasm, and this again forms a membrane, becoming an archespore or a “ pansporoblast,” destined to produce two spores; within this, nuclear division takes place so as to form about eight nuclei, two of which are extruded as abortive, and of the other six, three are used up in the formation of each of the two spores. Of these three nuclei in each spore, two form nematocysts, hike those of a Coelen- terate (p. 246 f.), at the expense of the surrounding plasm ; while the third nu- cleus divides to form Fic. 36.—A, Myzxidium lieberkiihnii, amoeboid phase ; B, the two final nuclei Myzxobolus miilleri, spore with discharged nematocysts ee ae es (nte) ; ©, spores (psorosperms) of a Myxosporidian. of the reproductive ntc, nematocysts. (From Parker and Haswell.) body. The whole aggregate of the reproductive body and the two nematocysts 1s enveloped in a bivalve shell. In what we may eall germination, the nematocysts eject a thread that serves for attachment, the valves of the shell open, and the binucleate mass crawls out and grows afresh. Nosema bombycis Niigeli (the spore of which has a single nematocyst) is the organism of the “ Pébrine” of the silkworm, which was estimated to have caused a total loss in France of some £40,000,000 before Pasteur investigated the malady and prescribed the effectual cure, or rather precaution against its spread. This consisted in crushing each mother in water after it had laid its eggs and seeking for pébrine germs. If the mother proved to be infected, her eggs were destroyed, as the egos she had laid were certain to be also tainted. Balbiani com- pleted the study of the organism from a morphological standpoint. Some Myxosporidiaceae produce destructive epidemics in fish. 108 PROTOZOA CHAP. 1V The Dolichosporidia or Sarcosporidiaceae are, in the adult state, elongated sacs, often found in the substance of the volun- tary muscles, and known as “ Rainey’s” or “ Miescher’s Tubes” ; they are at first uninucleate, then multinucleate, and then break up successively into uninucleate cells, the spores, in each of which, by division, are formed the sickle-shaped zoospores.’ 1 Léger and Duboscq have found that Sarcocystis tenella, a parasite common in the muscles of the sheep (and rarely found in man), has a conjugation and sexual process recalling that of Stylorhynchus, save that the sperms are much smaller than the ova (C.R. 1902, i. p. 1148). CHAPTER V PROTOZOA (CONTINUED): FLAGELLATA III. Flagellata. PROTOZOA moving (and feeding in holozoie forms) by long flagella : pseudopodia when developed usually transitory : nucleus single or if multiple not biform: reproduction occurring in the active state and usually by longitudinal fission, sometimes alternating with brood- Jormation in the eyst or more rarely in the active state: form usually definite: a firm pellicle or distinct cell-wall often present. The Flagellates thus defined correspond to Biitschli’s group of the Mastigophora. The lowest and simplest forms, often loosely called “ Monads,” are only distinguishable from Sarcodina (especially Proteomyxa) and Sporozoa by the above characters: their artificial nature is obvious when we remember that many of the Sarcodina have a flagellate stage, and that the sperms of bisexual Sporozoa are flagellate (as are indeed those of all Metazoa except Nematodes and most Crustacea). Even as thus hmited the group is of enormous extent, and passes into the Chytridieae and Phycomycetes Zoosporeae on the one hand, and by its holophytic colonial members into the Algae, on the other. Classification. A. Fission usually longitudinal (transverse only in a cyst), or if multiple, radial and complete: pellicle absent, thin, or if armour-like, with not more than two valves. I. Food taken in at any part of the body by pseudopodia 1. PANTOSTOMATA Multicilia Cienk. ; Mastigamoeba F. E. Sch. (Fig. 37, 4). ! The alleged micronucleus of certain forms appears to be merely a ‘‘ blepharo- plast” (see p. 19); even when of nuclear origin, as in Zrypanosona, it has no function in reproduction like the micronucleus of Infusoria (see pp. 115, 120 f.). 109 Foo nut 1 PROTOZOA CHAP. d taken in at a definite point or points, or by absorption, or vition holophytie. No reticulate siliceous shell. Diameter under 500 p (1/50”). Contractile vacuole simple (one or more). (a) Colourless: reserves usually fat: holozoic, saprophytic or parasitic. . : 2. PROTOMASTIGACEAE (/3) Plastids yellow or brown: reserves fat or proteid: nutrition (€) (¢) variable : body naked, often amoeboid in active state (C. nudae), or with a_ test, sometimes containing calcareous discs (‘‘ coceoliths,” “rhabdoliths”) of peculiar form (C. loricatae) 3. CHRYSOMONADACEAE Chromulina Cienk. ; Chrysamoeba Klebs ; Hydrurus Ag. Dinobryon Ehrb. (Fig. 37, 11); Synerypte Ehrb. (Fig. 37, 12) ; Zooxanthella Brandt; Pontosphaera Lohm.; Coccolithophora Loh. ; Rhabdosphuera Haeck. Green, (more rarely yellow or brown) or colourless: reserves starch: fission longitudinal . . 4. CRYPTOMONADACEAE Cryptomonas Ehrb, (Fig. 37, 9); Paramoeba Greett. Green (rarely colourless): fission multiple, radial 5. VOLVOCACEAE System of contractile vacuoles complex, with accessory formative vacuoles or reservoir, or both. Pellicle delicate or absent: pseudopodia often emitted : excretory pore distinct from flagellar pit: reserves fat 6. CHLOROMONADACEAE Chloramoeba Lagerheim ; Thawmutomastiz, Lauterborn. Pellicle dense, tough or hard, often wrinkled or striate: con- tractile vacuole discharging by the flagellar pit. Nutrition variable. : : 5 . 7. EUGLENACEAE Euglena Ehrb.; Astasia Duj. (Fig. 37, 3); Anisonema Duj. ; Eutreptia Perty (Fig. 42, p. 124); Yrachelomonas Ehrb. (Fig. 37, 1); Cryptoglena Ehrb. Skeleton an open network of hollow siliceous spicules. Plastids yellow. Diameter under 500 p. : 8. SILICOFLAGELLATA Dictyocha Ehrb. Diameter over 500 pp. Mouth opening into a large reticulate endoplasm : flagella 1, or 2, very unequal. 9. CySTOrFLAGELLATA Noctiluca Suriray (Fig. 48); Leptodiscus R. Hertw. B. Fission oblique or transverse: flagella two, dissimilar, the one coiled round the base of the other or in a traverse groove ; pellicle often dense, of numerous armour-like plates ; : 10. DINOFLAGELLATA Ceratium Schrank; Gymnodinium Stein; Peridiniwm Ehrb. (Fig. 46) ; Pouchetia Schiitt ; Pyrocystis Murray (Fig. 47); Polykrikos Biitschli. The Protomastigaceae and Volvocaceae are so extensive as to require further subdivision. I. PROTOMASTIGACEAE Oral spots 2. Flagella distant in pairs. . : DISTOMATIDAE II. Oral spot 1 or 0. A FLAGELLATA—CLASSIFICATION Nga Flagellum 1. (a) No anterior process: often parasitic. : OIKOMONADIDAE Oikomonas K. (Figs. 37, 2, 8); Trypanosoma Gruby (Fig. 39, a-f) ; Treponema Vuill. (Fig. 39, g-t). (6) Anterior process unilateral or proboscidiform : cell often thecate BICOECIDAE Bicoeca Clark ; Poteriodendron St. (ce) Anterior process a funnel, surrounding the base of the flagellum : cells often thecate. (i.) Funnel free . ; : : CRASPEDOMONADIDAE Codosiga Clark; Monosiga Cl.; Polyoeca Kent; Proterospongia Kent ; Salpingoeca Cl. (ii.) Funnel not emerging from the general gelatinous investment PHALANSTERIDAE Flagella 2, unequal or dissimilar in function, the one sometimes short and thick. (a) Both flagella directed forwards — . : MONADIDAE Monas St. ; ; Anthophysa Bory (Fig. 37, 13). (b) One flagellum, usually the longer, turned backwards. BoDONIDAE Bodo St. (Fig. 38). Flagella 2, equal and similar ; ; AMPHIMONADIDAE Amphimonas Duj.; Diplonita K. (Fig. 37, 10); Rhipidodendron St. (Fig. 37, 14). Flagella 3. ; ; : : . ‘TRIMASTIGIDAE Dallingeria K. (Fig. 37, 6); Costia Leclercq. Flagella 4 or more: mostly parasitic in Metazoa. POLYMASTIGIDAE Trichomonas Donne; Tetramitus Perty (Fig. 37, 7); Hexamitus Duj. ; Lamblia Blanchard. Flagella numerous, sometimes constituting a complete ciliiform invest- ment, and occasionally accompanied by an undulating membrane : parasitic in Metazoa. (a) Flagella long: uucleus single: parasitic in insects TRICHONYMPHIDAE Dinenympha Leidy ; Joenia Grassi; Pyrsonympha Leidy ; Tricho- nympha Leidy ; Lophomonas St. ; Maupasia Schew. (6) Flagella short, ciliiform, uniformly distributed: nuclei very numerous, all similar: parasitic in Amphibia ; OPALINIDAE Opalina Purkinje and Valentin (Fig. 41). VOLVOCACEAE Cells usually isolated, separating after fission or brood-formation. Usually green (sometimes red), more rarely colourless saprophytes CHLAMYDOMONADIDAE Chlamydomonas Ehrb.; Phacotus Perty ; Polytoma Ehrb.; Sphaerella Sommerf. (Fig. 43); Zoochlorella. Cells multiplying in the active state by radial divisions in the same plane and usually incurving to form a spherical colony, united in a gelatinous investment, sometimes traversed hy plasmic threads VOLVOCIDAE Gonium O.F.M. ; Eudorina Ehrb.; Pandorina Bory (Fig. 45) ; Stephano- sphaera Cohn ; Volvow L. (Fig. 44). iZ PROTOZOA CHAP. Sere 4 9.Cryptomonas 10. Di plomita BOkomanas : 11. Dinobryon 12.Syncrypta 13.Anthophysa 14,Rhipidodendron Fia. 37.—Various forms of Flagellata. 2, 6-8, 10, 13, 14, Protomastigaceae ; pel Chrysomonadaceae ; 9, Cryptomonadaceae ; 1, 3, Euglenaceae ; 4, Pantostomata: note branched stalk in 13; branched tubular theca in 14; distinct thecae in 11; stalk and theca in 10. In Q2, flagellate (a) and amoeboid (+) phases are shown ; in ae flagellate (a) and Heliozoan (+) phases’; in 8 are shown two stages in the ingestion of a food particle (f) ; chr, plastoids ; c.vac, contractile vacuole ; 7, food particle ; g, gullet; 7, theca ; nw, nucleus ; p, protoplasm ; per, peristome ; 7.7, vacuole of ingestion. (From Parker and Haswell, mostly from Biitschli’s Protozoa. ) 1 Dimorpha is now referred to Heliozoa (p. 70). v FLAGELLATA 113 The modes of nutrition are threefold: the simplest forms live in liquids containing decaying organic matter which they absorb through their surface (“ saprophytic”): others take in food either Amoeba fashion, or into a vacuole formed for the purpose, or into a definite mouth (“ holozoic”): others again have coloured plastids, green or brown or yellow (“holophytic”), having the plant’s faculty of manufacturing their own food-supply. But we meet with species that show chromatophores at one time and lack them at another; or, again, the same individual (Luglena) may pass from holozoic life to saprophytic (Paramoeba, some Dinoflagellates) as conditions alter. Many secrete a stalk at the hinder end: by “ continuous ” formation of this, without rupture at fission, a branching colony is formed (Polyoeca). This stalk may have a varying consistency. In. Anthophysa (Fig. 37, 13) it appears to be due to the welding of excrementitious particles voided at the hinder end of the body with a gelatinous excretion; but the division of the stalk is here occasional or intermittent, so that the cells are found in tufts at the apex of the branches. A corresponding secretion, gelatinous or chitinous, around the body of the cell forms a cup or “theca,” within which the cell hes quite free or sticking to it by its surface, or attached to it by a rigid or contractile thread. The theca, again, may assume the form of a mere gelatinous mass in which the cell-bodies may be completely plunged, so that only the flagella protrude, as in Volvocidae, Proterospongia (Fig. 75, -p. 182), and Rhipidodendron (Fig. 37, 14). Often this jelly assumes the form of a fan (Phalansterium), the branching tubes of which it is composed lying for some way alongside, and ultimately diverging. In Hydrurus, the branching jelly assumes the form of a branching Confervoid.' The cell-body may be bounded by an ill-defined plasmatic layer in Chrysomonadaceae and some Protomastigaceae,” or it may form a plasmatic membrane or “ pellicle,” sometimes very firm and tough, or striated as in Euglenaceae, or it may have a separate “euticle” (in the holophytic species formed of cellulose), or even a bivalve or multivalve shell of distinct plates, hinged or over- lapping (Cryptoglena, Phacotus, Dinoflagellates). The wall of the ' T.e. resembling the thread-like water Algae. * Trichocysts (see p. 142) occur in some Chloromonadaceae.; and the Dino- flagellate Polykrilos possesses true nematocysts (see p. 131). VOL. I I DTA PROTOZOA CHAP. Coccolithophoridae, a family of Chrysomonadaceae, is strengthened by embedded calcareous spicules (“coccoliths,” “cyatholiths,” “vhabdoliths”), which in the most complex forms (cyatholiths) are like a shirt-stud, traversed by a tube passing through the stem and opening at both ends. These organisms’ constitute a large proportion of the plankton ; the spicules isolated, or in their original state of aggregation (“ coccospheres,” “ rhabdospheres ”), enter largely into the composition of deep-sea calcareous oozes. They occur fossil from Cambrian times (Potsdam sandstone of Michigan and Canada), and are in some strata extremely abundant, 800,000 occurring to the mm. cube in an Eocene marl. The Silicoflagellates have siliceous skeletons resembling that of many Radiolaria, to which they were referred until the living organism was described (see pp. 79, 86 f.). The flagellum has been shown by Fischer to have one of two forms: either it is whip-like, the stick, alone visible in the fresh specimen, being seen when stained to be continued into a long lash, hitherto invisible; or the whole length is fringed with fine ciliiform lateral outgrowths. If single it is almost always protruded as a tugging organ (“tractellum”);* the chief exceptions are the Craspedomonads, where it is posterior and acts as a scull (“pulsellum”), and some Dinoflagellates, where it is reversible in action or posterior, In addition to the anterior flagellum there may be one or more posterior ones, which trail behind as sense organs, or may anchor the cell by their tips. Dallingeria has two of these, and Lodo saltans a single anterior anchoring lash, by which they spring up and down against the organic débris among which they live, and disintegrate it. The numerous similar long flagella of the Trichonymphidae afford a transition in the genus Pyrsonympha to the short abundant cilia of Opalina, usually referred to the Ciliate Infusoria. 1 For a full monograph of this family see H. Lohmann, in Arch. f. Protisten- kunde, vol. i. 1902, p. 89. ? Delage has well explained the action of the single anterior flagellum which waves in a continuous spiral like a loaded string whirled round one’s head ; it thus induces a movement of the water, beyond its actual range, backwards and outwards, maintained by a constant influx from behind, which carries the cell onward at the same time that it necessarily rotates round its axis. If there is a pair of symmetrically placed flagella they co-operate like the arms of a swimmer ; when the second flagellum is unilateral the motion is most erratic, as seen in the Bodonidae (and the zoospores of many Chytridieae, which have most of the characters of the Flagellates, though habitually removed to the Fungi). Vv FLAGELLATA I15 An undulating membrane occurs, sometimes passing into the flagellum in certain genera, all parasitic, such as 7'rypanosoma (incl. Herpetomonas), Trichomonas, Hexamitus, and Dinenympha. In some cases the flagellum (or flagella) is inserted into a definite pit, which in allied forms is the mouth-opening. The contractile vacuole is present in the fresh-water forms, but not in all the marine ones, nor in the endoparasites. It may be single or surrounded by a ring of minute “formative” vacuoles or discharge into a permanently visible “reservoir.” This again may discharge directly to the surface or through the pit or canal in which the flagellum takes origin (Huglena). The “chromatophore” may be a single or double plate, or multiple.t In the peculiar form Paramoeba the chromatophore may degenerate and be reproduced anew. It often encloses rounded or polygonal granules of uncoloured plasma, very refractive, known as “ pyrenoids.” These, like the chromatophores, multiply by direct fission. The “reserves” may be (1) fat-globules; (2) granules of a possibly proteid substance termed “ leucosin”; (3) a carbohydrate termed “paramylum,” differing slightly from starch (see p. 95): (4) true starch, which is usually deposited in minute granules to form an investment for the pyrenoid when such is present. A strongly staining granule is usually present in the plasma near the base of the flagellum. This we may term a “ blepharo- plast ” or a “centrosome” in the wider sense. Fission is usually longitudinal in the active state; a few exceptions are recorded. Encystment is not uncommon; and in the coloured forms the cyst-wall is of cellulose. Division in the cyst is usually multiple;? in the coloured forms, however, vegetative growth often alternates with division, giving rise to plant-like bodies. Polytoma and other Chlamydomonadidae multiply by “brood-formation” in the active state; the blepharoplast, as Dangeard suggests, persist- ing to continue the motion of the flagella of the parent, while the rest of the plasm divides to form the brood. Conjugation has been observed in many species. In some species of Chlamydomonas it takes place after one or both of the two 1 The colouring matter is chlorophyll or some allied colouring matter. In the yellow and brown forms the additional pigment is termed loosely ‘‘ diatomin,” but its identity with that of Diatoms is in no case proved. ? Notably in the Craspedomonadidae, where transverse division also occurs. See Raoul Francé,. Die Craspedomonadineen (Buda-Pesth, 1897). I16 PROTOZOA CHAP: cells have come to rest, but in most cases it occurs between active cells. We find every transition between equal unions and differentiated sexual unions, as we shall see in discussing the Volvocaceae.| The “coupled-cell” differs in behaviour in the different groups, but almost always goes to rest and encysts at once, whatever it may do afterwards. The life-history of many Flagellates has been successfully studied by various observers, and has shed a flood of hght on many of the processes of living beings that were hitherto obscure. The first studies were carried through by the patient labours of Drysdale and Dallinger. A delicate mechanical stage enabled the observer to keep in the field of view a single Flagellate, and, when it divided into two, to follow up one of the products. A binocular eye-piece saved much fatigue, and enabled the observers to exchange places without losing sight of the special Flagellate under observation ; for the one who came to relieve would put one eye to the instrument and recognise the individual Flagellate under view as he passed his hand round to the mechanism of the stage before the first watcher finally relinquished his place at the end of the spell of work. Spoon- feeding by Mrs. Dallinger enabled such shifts to be prolonged, the longest being one of nine hours by Dr. Dallinger. The life- cycles varied considerably in length. It was in every case found that after a series of fissions the species ultimately underwent conjugation (more or less unequal or bisexual in character) ;* 1 And also in the ‘‘ Monads,” described by Dallinger and Drysdale, see above. 2 In Cercomonas dujardinii, Polytoma wvella, and Tetramitus rostratus the gametes resemble the ordinary forms and are isogamous. In Monas dallingeri and Bodo caudatus conjugation takes place between one of the ordinary form and size and another similar but smaller. In Dallingeria drysdali the one has the ordinary size and form, the other is equal in size, but has only one flagellum, not three ; in Lodo saltans they are unequal, the larger gamete arising in the ordinary way by longitudinal fission, the smaller by transverse division. Doubt has been thrown on the validity of our authors’ results by subsequent observers abroad ; but I can find no evidence that these have even attempted to repeat the English observations under the same severely critical conditions, and therefore consider the attacks so far unjustified. Schaudinn has observed conjugation between Z'richomonas indi- viduals which have lost their flagella and become amoeboid ; also in Lamblia intes- tinalis and in Trypanosoma (Halteridium %) noctuae (Fig. 39) ‘ Reduction-divisions ” (see p. 75, note 1) of the nuclei take place before fusion, and the nuclear pheno- mens are described as ‘‘complicated” (Arb. Kats. Gesundheitsamte, xx. 1904, p. 387). Paramocba ecilhardii in its adult state is colourless, amoeboid, multiciliate. It forms a brood cyst, from which are liberated flagellate zoospores, with a chromatophore, which reproduce by longitudinal fission in this state. They may also conjugate. Vv FLAGELLATA WF the zygote encysted ; and within the cyst the protoplasmic body Boies r+ Fic. 38.—Bodo saltans. A, the positions assumed in the springing movements of the anchored form ; B, longitudinal fission of anchored forms ; C, transverse fission of the same ; D, fission of free-swimming form ; E!-E?, conjugation of free-swimming with anchored form ; E®, zygote ; E®, emission of spores from zygote ; F, growth of spores: ¢.vac, contractile vacuole; ji.1, anterior; j/.2, ventral flagellum; mu, nucleus. (From Parker's Biology, after Dallinger. ) underwent brood-formation, the outcome of which was a mass of 118 PROTOZOA CHAP. spores discharged by the rupture of the cyst (Fig. 38). These spores grow from a size too minute for resolution by our microscopes into the ordinary flagellate form. They withstand the effects of drying, if this be effected immediately on their escape from the ruptured cyst; so that it is probable that each spore has itself a delicate cyst-wall and an aplanospore, from which a single zoospore escapes. The complex cycle, of course, comprises the whole course from spore-formation to spore-formation. Such complete and regular “ life-histories,” each characteristic of the species, were the final argument against those who held to the belief that spontaneous generation of living beings took place in infusions of decomposing organic matter. Previous to the work of these observers it had been almost universally beheved that the temperature of boiling water was adequate to kill all living germs, and that any life that appeared in a closed vessel after boiling must be due to spontaneous change in its contents. But they now showed that, while none of the species studied resisted exposure in the active condition to a temperature of 138°-140° F., the spores only succumbed, in liquid, to temperatures that might even reach 268° F., or when dry, even 300° F. or more. Such facts explain the constant occurrence of one or more such minute species in liquids putre- fying under ordinary conditions, the spores doubtless being present in the dust of the air. Very often several species may co- exist in one infusion; but they separate themselves into different zones, according to their respective need for air, when a drop of the liquid is placed on the slide and covered for examination. Dallinger! has made a series of experiments on the resistance of these organisms in their successive cycles to a gradual rise of temperature. Starting with a liquid containing three distinct species, which grew and multiplied normally at 60° F., he placed it under conditions in which he could slowly raise the teimpera- ture. While all the original inmates would have perished at 142° F., he succeeded in finally producing races that throve at 158° F., a scalding heat, when an accident put an end to that series of experiments. In no instance was the temperature raised so much as to kill off the beings, so that the increased tolerance of their descendants was due not, as might have been anticipated, to selection of those that best resisted, but to the inheritance of 1 In P.R.S. xxvii. 1878, p. 332. Vv FLAGELLATA I19 an increased toleration and resistance from one generation or cycle to another. As we noted above (p. 40), the study of the Flagellates has been largely in the hands of botanists. After the work of Biitschli in Bronn’s 7hier-Reich, Klebs * took up their study ; and the prin- cipal monographs during the last decade have appeared in Engler and Prantl’s Pflanzenfamilien, where Senn? treats the Flagellates generally, Wille the Volvocaceae, and Schiitt the “ Peridiniales ” or Dinoflagellata;* while only the Cystoflagellata, with but two genera, have been left to the undisputed sway of the zoologists.’ Among this group the majority are saprophytes, found in water containing putrefying matter or bacteria. The forms so earefully studied by Dallinger and Drysdale belong to the genera Bodo, Cercomonas, Tetramitus, Monas, and Dallingeria. Many others are parasites in the blood or internal cavities of higher animals, some apparently harmless, such as 7’richomonas vaginalis, parasitic in man, others of singular malignity. Costia necatrix, infesting the epithelial scales of fresh-water fish, often devastates hatcheries. The genus Zrypanosoma, Gruby, contributes a number of parasites, giving rise to deadly disease in man and beast. 7. lewisii is common in Rodents, but is relatively harm- less. 7. evansii is the cause of the Surra disease of Ruminants in India, and is apparently communicated by the bites of “ large brown flies” (almost certainly Breeze Flies or Tabanidae, Vol. VI. p-481). 7. brucei, transferred to cattle by the Tsetse Fly, Glossina morsitans (see Vol. VI. Fig. 244, p. 513) in Equatorial Africa, is the cause of the deadly Nagana disease, which renders whole tracts of country impassable to ox or horse. Other Trypanosomic diseases of animals are, in Algeria and the Punjab, “ dourine,” infecting horses and dogs; in South America, Mal de Caderas (falling-sickness), an epidemic paralysis of cattle. During the printing of this book, much additional knowledge has been gained on this genus and the diseases it engenders. - The Trypanosomic 1 In Z. wiss. Zool. lv. 1893, p. 353. 21. Teil, Abt: 1. a, 1900. 3 In the Chlorophyceac, 1. Teil, Abt. 2, 1897. 21) Neil, Abt... b;1896; 5 Besides the above, Dangeard, in various papers in his periodical Le Botaniste, has treated of most of the groups, and Raoul Francé has monographed the Poly- tomeae in the Jahrb. wiss, Bot. xxvi. 1894, p. 295, and Dill the genus Chlamy domonas, etc., its closest allies, in op. cit. xxviii. 1895, p. 323. ® For a detailed abstract of our knowledge of Trypanosoma and its allies up to Feh. 1, 1906, see Woodcock, ‘‘ The Haemoflagellates,’” in Quart. Journ. Mier, Sei. 1. 1906, p. 151. I20 PROTOZOA CHAP. fever recently recognised on the West Coast has been found to be the early stage of the sleeping-sickness, that well-known and most deadly epidemic of Tropical Africa. Through the researches of Castellani, Nabarro, and especially Colonel and Mrs. Bruce,we know now that the parasite 7. gambiense is transferred by an inter- mediate host, a kind of Tsetse Fly (Glossina palpalis). Schaudinn’s full study of a parasite of the blood corpuscles of the Owl has shown that while in its intracorpuscular state it resembles closely the malarial parasites in behaviour, and in its schizogenic multiplication, so that it was considered an Acystosporidian, under the name of Halteridium,it isreally a Trypanosoma ;' for the accomplishment of successful sexual re- production it requires transference to thi gut of a gnat (Culex). The germs may infect the ovary, and give the offspring of the insect the innate power of infecting Owls. Thus a new light is sh n th Fic. 39.—Morphology of Trypanosoma. a-f, Stages in ght is shed o : b development of Zrypanosoma noctuae from the OY1@1N of the Cocci- active Aygote (* OEE igh D; pat eM of diaceae, whose “blasts” nucleus into larger (trophic) and smaller (kineto-) — : nucleus; ¢, d, division of smaller nucleus and its In the insect host re- transformations to form ‘‘ blepharoplast”’ and myo- SeTnbl Dien sauete uemes; f, adult Trypanosoma; g, h, 1, Treponema sem Die PYPANosoma zeemannit of Owl; g, Trypanosome form; hk, 1n their morphology. Spirochaeta form; 7, rosette aggregate. (After TI l f TS de Schaudinn.) 1e 1umMalh 1Cle fever of the Western United States and the epizootic Texas fever are known to be due to blood parasites of the genus Piroplasma (Babesia), of which the free state is that of a Trypanosome. It appears certain that Texas fever, though due to Tick bites, is not transferred directly from one beast to another by the same Tick; but the offspring of a female Tick that has sucked an infected ox contains Trypanosome germs, and will by their bites infect other animals. 1 Doubts still subsist as to the interpretation of Schaudinn’s observations. Vv FLAGELLATA Iza It would seem probable that the virulence of the Persian Tick (Argas persica) is due to similar causes. The Indian maladies known as “ Kala Azar” and “ Oriental Sore” are characterised by blood parasites, at first called after their discoverer the “ Leishman bodies,” which have proved to be the effects of a Piroplasma. Trypanosoma is distinguished by the expansion of its flagellum into an undulating membrane, that runs down the edge of the body, and may project behind as a second lash. In this mem- brane run eight fine muscular filaments, or myonemes, four on either surface, within the undulating membrane; at their lower end they are all connected with a rounded body, the “ blepharo- plast,” which is here in its origin, as well as in its behaviour in reproductive processes, a true modified nucleus, comparable in some respects, as was first noted by Plimmer and Rose Bradford,’ with the micronucleus of the Infusoria. Part of the segmentation spindle persists in the form of a filament uniting the blepharoplast with the large true functional nucleus (Fig. 39, a-f). The blood of patients suffering from relapsing fever contains a fine wriggling parasite, which was described as a Schizomycete, allied to the bacteria, and hitherto termed Spirochaeta obermeiert. Schaudinn has shown that this and other similar blood parasites are closely allied to Z'rypanosoma; and since the original genus was founded on organisms of putrefaction which are undoubtedly Schizomycetes, Vuillemin has suggested the name 7Zvreponema. T. pallidum is found in syphilitic patients, and appears to be responsible for their illness.’ The Craspedomonadidae (often called Choanoflagellates, Fig. 40) are a group whose true nature was elucidated some forty years ago by the American zoologist, H. James-Clark. They are attached either to a substratum, by a stalk produced by the base of the cell, or to other members of the same colony; they are distinguished by the protrusion of the cytoplasm around the base of the single flagellum into a pellucid funnel,? in which the plasma is in constant motion, though the funnel retains its shape and size, except when, as sometimes happens, it is retracted. 1 Quart. Journ. Mier. Sci. xlvi. 1902. * A Zambezian Tick infects man with a Treponema, producing relapsing-fever ; another species is found in the tropical disease “framboesia”’ (“yaws” or “parangi’’). ’ Stated by Geza Entz and Raoul Francé to be due to the spiral twisting of a plasmic membrane, and to be like a cone formed by twisting paper, with the free edges overlapping. E22 PROTOZOA CHAP. The agitation of the flagellum determines a stream of water upwards along the outer walls of the funnel; and the food- particles brought along adhere to the outside of the funnel, and are carried by its streaming movement to the basal constriction, where they are swallowed by the plasma, which appears to form a swallowing vacuole at that point. Longitudinal fission is the ordinary mode of reproduction, extending up through the funnel. If the two so formed continue to produce a stalk, the result is 1.Monosiga. 2.Salpingoeca. 3.Polyoeca. 4.Proterospongia. Fic. 40.—Various forms of Craspedomonadidae. 2, a, Adult cell; 2, 6, longitudinal fission ; 2, c, the production of flagellulae by brood-formation ; ¢, collar ; c.vac, con- tractile vacuole ; jl, flagellum ; 7, theca ; nv, nucleus ; s, stalk. (After Saville Kent.) the formation of a tree-like stem, whose twigs bear at the ends the funnelled cells, or “collar-cells” as they are usually called. In Salpingoeca, as in so many other Flagellates, each cell forms a cup or theca, often of most graceful vase-like outline, the rim being elegantly turned back. Proterospongia (Fig. 75, p. 182) secretes a gelatinous investment for the colony, which is attached to solid bodies. In this species, according to Saville Kent, the central members of the colony retract their collar, lose their flagellum, become amoeboid, and finally undergo brood-formation to produce minute zoospores. This 1s the form which by its differentiation recalls the Sponges, and has been regarded as a ¢ FLAGELLATA ie transition towards them; for the flagellate, nutritive cells of the Sponges are provided with a collar, which exists in no other group of Metazoa (see pp. 171, 181, and Fig. 70, p. 176). The most recent monographer of the family is Raoul Francé, but James-Clark and Saville Kent did the pioneering work. Of the life-history of the Trichonymphidae,' all of which are parasitic in the alimentary canal of Insects, especially Termites or White Ants (Vol. V. p. 356), nothing is known. Some of them have a complete investment of motile flagella, like enormously — WG fl Fic. 41. — Opalina ranarum. A, liv- ing specimen ; B, stained specimen showing nuclei ; C, stages in nuc- lear division ; D-F, stages in fission; G, final product of fission ; H, encysted form; I, young form liberated from cyst ; K, the same after multi- plication of the nucleus has begun. NU, Nucleus. (From Parker’s Biology, after Saville Kent and Zeller.) long cilia, which in Dinenympha appear to coalesce into four longitudinal undulating membranes. Zophomonas inhabits the gut of the Cockroach and Mole-cricket. The Opalinidae have also a complete investment of cilia, which are short, and give the aspect of a Ciliate to the animal, which is common in the rectum of Amphibia, and dies when transferred to water. But despite the outward resemblance, the nuclei, of which there may be as many as 200, are all similar, and consequently this group cannot be placed among the Infusoria at all. Opalina has no mouth nor contractile vacuole. It multiplies by dividing ' Discovered by Leidy. For the most recent description of this group see Grassi and Sandias in Quart. Journ. Mier. Sci. xxxix. (figures) and x]. p. 1 (text), 1897. 124 PROTOZOA CHAP. irregularly and at intervals, resolving finally into 1-nucleate frag- ments, which encyst and pass into the water. When swallowed the cyst dissolves, its contents enlarge, and ultimately assume the adult form.! Maupasia has a partial investment of cilia, a single long flagellum and mouth, a contractile vesicle, and a single simple nucleus. It seems to find an appropriate place near the two above groups, though it is free, and possesses a mouth. Among the Euglenaceae, Huglena viridis is a very common Fic. 42,—Longitudinal Fission of Eulreptia viridis (Euglenaceae), showing chloroplasts, nucleus, and flagella arising from pharynx-tube. (After Steuer.) form, giving the green colour to stagnant or slow-flowing ditches and puddles in light places, especially when contaminated by a fair amount of dung, as by the overflow of a pig-sty, in company with a few hardy Rotifers, such as Hydatina senta (Vol. II. Fig. 106, p. 199) and Brachionus. Euglena is about 0:1 mm. in length when fully extended, oval, pointed behind, obliquely trun- cate in front, with a flagellum arising from the pharyngeal pit. It shows a peculiar wriggling motion, waves of transverse con- striction passing along the body from end to end, as well as flexures in different meridians. Such motions are termed “euglenoid.” The front part is colourless, but under a low Bezzenberger has given an analytical table of the eleven known species of the genus Opalina in Arch. Protist. iii. 1903, p. 138. Vv FLAGELLATA 125 power the rest of the cell is green, owing to the numerous chloro- phyll bodies or chloroplasts. The outermost layer of the cytoplasm shows a somewhat spiral longitudinal striation, possibly due to muscular fibrils. The interior contains many laminated plates of paramylum, and a large single nucleus. At the front of the body at the base of the flagellum is a red “ eye- spot” on the dorsal side of the pharynx-tube or pit, from which the flagellum protrudes. Wager has shown that this tube receives, also on its dorsal side, the opening of a large vacuole, sometimes called the reservoir, for into it discharges the contrac- tile vacuole (or vacuoles). The eye-spot is composed of numerous granules, containing the vegetal colouring matter “ haemato- chrome.” It embraces the lower or posterior side of the com- munication between the tube and the reservoir. The flagellum has been traced by Wager through the tube into the reservoir, branching into two roots where it enters the aperture of communication, and these are inserted on the wall of the reservoir at the side opposite the eye-spot. But on one of the roots near the bifurcation is a dilatation which lies close against the eye-spot, so that it can receive the lght reaction. Huglena is an extremely phototactic organism. It shows various wrig- glings along the longitudinal axis, and transverse waves of contraction and expansion may pass from pole to pole.’ Among the Chrysomonadaceae the genus Zooxanthella, Brandt, has already been described under the Radiolaria (p. 86), in the - jelly of which it is symbiotic. It also occurs in similar union in the marine Ciliates, Vorticella sertulariae and Scyphidia scorpaenae, and in Millepora (p. 261) and many Anthozoa (pp. 373 f., 596). Of the Chlamydomonadidae, Sphaerella (Haematococcus, Ag.) pluvialis (Fig. 43), and S. nivalis, in which the green is masked by red pigment, give rise to the phenomena of “red snow” and “bloody rain.” The type genus, Chlamydomonas, is remarkable for the variations from species to species in the character and behaviour of the gametes. Sometimes they are equal, at other times of two sizes. In some species they fuse immediately on approximation, in the naked active state; in others, they encyst on approaching, and unite by the emission of a fertilising tube, 1 Such movements, permissible by the perfectly flexible but firm pellicle, are termed ‘‘ metabolic ” or ‘‘euglenoid” in contradistinction to ‘‘amoeboid.” They also occur in many Sporozoa. ce 126 PROTOZOA CHAP. as in the Algal Conjugatae. Zoochlorella is symbiotic in green Ciliata (pp. 153 f., 158), Sponges (p. 175), Hydra (p. 256), and Turbellaria (Vol. II. p. 43). Of the Volvocidae, Volvox (Fig. 44) is the largest and most conspicuous genus. Its colony forms a globe the size of a pin’s head, floating on the surface of ponds, drains, or even puddles or water-barrels freely open to the light. It has what may be be called a skeleton of gelatinous matter,’ condensed towards the surface into a denser layer in which the minute cells are scattered. These have each an eye-spot, a contractile vacuole, Fie. 43. — Sphaerell pluvialis. A, motile stage; B, resting stage; C, D, two modes of fission ; E, Sphaerella lacustris, motile stage. chr, Chromatophores ; C.vae, contractile vacuole ; c.w, cell- wall; ji, flagella ; nu, nucleus ; nv’, nU- cleolus ; pyr, pyre- noids. (From Par- ker’s Biology.) and two flagella, by the combined action of which the colony is propelled. Delicate boundary lines in the colonial wall mark out the proper investment of each cell. The cells give off delicate plasmic threads which meet those of their neighbours, and form a bond between them. In that half of the hemi- sphere which is posterior in swimming, a few (five to eight) larger cells (“ macrogonidia” of older writers) are evenly distri- buted, protruding as they increase in size into the central jelly. These as they grow segment to form a new colony. The divisions are only in two planes at right angles, so that the young colony is at first a plate, but as the cells multiply the * Within which is often harboured the Rotifer, Proales parasita, Vol. II. p. 227. v FLAGELLATA Lam plate bends up (as in the gastrulation of the double cellular plate of the Nematode Cucullanus, Vol. II. p. 156), and finally forms a hollow sphere bounded by a single layer of cells: the site of the original orifice may be traced even in the adult as a blank space larger than exists elsewhere. Among the cells of the young colony some cease to divide, but continue to grow at an early period, and these are destined to become in turn the mothers Fic. 44.—Volvox globator. A, entire colony, enclosing several daughter-colonies ; B, the same during sexual maturity ; C, four zooids in optical section ; D!-D®, develop- ment of parthenogonidium ; E, ripe spermogonium ; F, sperm; G, ovum; H, oosperm. a, Parthenogonidia ; 71, flagellum ; ov, ovum ; ovy, ovaries ; pg, pigment spot ; sp, sperms; Spy; spermogonia dividing to form sperms. (From Parker's Biology, after Cohn and Kirchner.) (“ parthenogonidia”) of a new colony; they begin segmenting before the colony of which they are cells is freed. The young colonies are ultimately liberated by the rupture of the sphere as small-sized spheres, which henceforth only grow by enlargement of the sphere as a whole, and the wider separation of the vege- tative cells. Thus the vegetative cells soon cease to grow; all the supply of food material due to their living activities goes to the nourishment of the parthenogonidia, or the young colonies, as aS PROTOZOA CHAP. the case may be. ‘These vegetative cells have therefore surren- dered the power of fission elsewhere inherent in the Protist cell. Moreover, when the sphere ruptures for the liberation of the young colonies, it sinks and is doomed to death, whether because its light-loving cells are submerged in the ooze of the bottom, or because they have no further capacity for hfe. When conju- gation is about to take place, it is the cells that otherwise would be parthenogonidia that either act as oospheres or divide as “spermogonia” to form a flat brood of minute yellow male cells (“sperms”) These resemble vegetative cells, in the possession of an eye-spot and two contractile vacuoles, but differ in the enormously enlarged nucleus which determines a beaked process in front. After one of these has fused with the female cell (“oosphere”) the product (“oosperm”) encysts, passes into a stage of profound rest, and finally gives rise to a new colony. The oospheres and sperm-broods may arise in the same colony or in distinct ones, according to the species. Before we consider the bearings of the syngamic processes of Volvox, we will study those presented by its nearer allies, which have the same habitat, but are much more minute. Three of these are well known, Stephanosphaera, Pandorina, and Eudorina, all of which have spherical colonies of from eight to thirty-two cells embedded at the surface of a sphere, and no differentiation into vegetative cells and parthenogonidia (or reproductive cells). Stephanosphaera has its eight cells spindle shaped, and lying along equidistant meridians of its sphere; in vegetative repro- duction each of these breaks up in its place to form a young colony, and the eight daughter-colonies are then freed. In conjugation, each cell of the colony breaks up into broods of 4, 8, 16, or 32 small gametes, which swim about within the general envelope, and pair and fuse two and two: this is “isogamous,” “ endogamous ” conjugation. In Pandorina (Fig. 45) the cells are rounded, and are from 16 to 32 in each colony. The vegetative reproduction in this, as in Ludorina, is essentially the same as in Stephanosphaera. In conjugation the cells are set free, and are of three sizes in different colonies, small (S), medium (M), and large (L). The following fusions may oceur: Sx 8,8xM,SxL,MxM,Mx Li. Thus the large are always female, as it were, the medium may play the part of male to the large, female to the small; the small are males to the medium and to the large. The medium Vv FLAGELLATA 129 and small are capable, each with its like, of equal, undifferen- tiated conjugation; so that we have a differentiation of sex far other than that of ordinary, binary sex. Hudorina, however, has attained to “ binary sex,” for the female cells are the ordinary vegetative cells, at most a little enlarged, and the male cells are formed by ordinary cells producing a large flat colony of sixty-four minute males or sperms. In some cases four cells at the apex Fic. 45.—Pandorina morum. A, entire colony; B, asexual reproduction, each zooid dividing into a daughter-colony ; C, liberation of gametes; D-F, three stages in conjugation of gametes ; G, zygote ; H-K, development of zygote into a new colony. (From Parker’s Biology, after Goebel.) of a colony are spermogonia, producing each a brood of sperms, while the rest are the oospheres. The transition to Volvox must have arisen through the sterilisation of the majority of cells of a colony for the better nutrition of the few that are destined alone for reproduction. Volvox, as we have seen, has attained a specialisation entirely comparable to that of a Metazoon, where the segmentation of the fertilised ovum results in two classes of cells: those destined VOL. I K 139 PROTOZOA CHAP. to form tissues, and condemned to ultimate death with the body as a whole, and those that ultimately give rise to the repro- ductive cells, ova, and sperms. But this is a mere parallelism, not indicating any sort of relationship: the oospores of the Volvocaceae show that tendency to an encysted state, im which fission takes place, that is so characteristic of Algae, and these again show the way to Cryptogams of a higher status. Thus, Volvox, despite the fact that in its free life and cellular differen- tiation it is the most animal of all known Flagellates, is yet, with the rest of the Volvocaceae, inseparable from the Vegetable Kingdom, and is placed here only because of the impossibility of cleaving the Flagellates into two. The Dinoflagellata (Figs. 46, 47) are often of exceptionally large dimensions in this class, attaining a maximum diameter of 150 w(z do") and even 375 pw (,") in Pyrocystis noctiluca. The special character of the group is the presence of two flagella; the one, filiform, arises in a longitudinal groove, and extending its whole length projects behind the animal, and is the conspicuous organ of motion: the other, band-like, arises also in the longitudinal groove, but extends along a somewhat spiral transverse groove,’ and never protrudes from it in life, executing undulating move- ments that simulate those of a girdle of cilia, or a continuous undulating membrane (Fig. 46). This appearance led to the old name “ Cihoflagellata,’ which had of course to be abandoned when Klebs discovered the true structure.” There is a distinct cellulose membrane, sometimes silicified, to the ectoplasm, only interrupted by a bare space in the longitudinal groove, whence the flagella take origin. This cuticle is usually hard, sculptured, and divided into plates of definite form, bevelled and over- lapping at their junction; occasionally the cell has been seen to moult them. A large vacuolar space, traversed by plasmic strings, separates the peripheral cytoplasm from the central, within which is the large nucleus. There are in most species one or more chro- matophores, coloured by a yellowish or brownish pigment, which is a mixture of lipochromes, distinct from diatomin. In a few species the presence of these is not constant, and these species 1 In the Adinidae there is no groove ; the two lashes arise close together, and tle one is coiled round the base of the other. 2 In Unt. Inst. Tubingen, i. 1883, p. 233. * FLAGELLATA 13s show variability as to their nutrition, which is sometimes holozoic. Under these conditions the cell can take in food- particles as bulky as the eggs of Rotifers and Copepods, by the protrusion of a pseudopod at the junction of the two grooves. As in most coloured forms an eye-spot is often present, a cup- shaped aggregation of pigment, with a lenticular refractive body in its hollow. A contractile vacuole, here termed a “ pusule,” occurs in many species, communicating with the longitudinal groove by a canal. Nematocysts (see p. 246 f.) are present in Polykrikos, trichocysts (see p. 142) in several genera. Division is usually oblique, dividing the body into two dis- similar halves, each of which has to undergo a peculiar growth to reconstitute the missing portion, and complete the shell. The in- complete separation of the young cells leads to the formation of chains, notably in Ceratiwm and Fic. 46.—Peridinium divergens. a, Polykrikos, the latter dividing ; Se ee Se transversely and occurring in er.v, contractile vacuole surrounded : - by formative vacuoles ; 7, nucleus. chains of as many as eight. The (After seniitt.) process of division may take place when :the cell is active, or in a cyst, as in Pyrocystis (Fig. 47). Again, encystment may precede multiple fission, resulting in the formation of a brood of minute swarmers. It has been suggested that these are ae of playing the part of gametes, and conjugating in pairs.’ The Dinoflagellates are for the most part pelagic i in habit, float- ing at the surface, and when abundant tinge the water of fresh- water lakes or even ponds red or brown. Peridiniuvm (Fig. 46) and Ceratium (the latter remarkable for the horn-like backward prolongations of the lower end) are common genera both in the sea 1 Conjugation of adults has been observed by Zederbauer (Ber. Deutsch. Ges. xxii. 1904). A short connecting tube is formed by the meeting of outgrowths from either mate ; their protoplasmic contents meet and fuse herein to form a spherical resting-spore, as in the Conjugate Algae. re2 PROTOZOA CHAP. and fresh-waters. Gymnodinium pulvisculus is sometimes parasitic in Appendicularia (Vol. VIL. p. 68). Polykrikos* has four trans- verse grooves, each with its flagellum, besides the terminal one. Many of the marine species are phosphorescent, and play a large part in the luminosity of the sea, and some give it a red colour. Several fossil forms have been described. Peridiniwm is certainly found fossil in the firestone of Delitzet, be- longing to the Cretaceous. ’ t=) Oo Wyville Thomson, has a cellulose wall, no mouth, and in the zoospore state has the two flagella in longitudinal and transverse grooves of the Dinoflagellata. d FLAGELLATA 133 ences, of which one, a little firmer than the other, and trans- versely ridged, is called the tooth; at the junction of the two is a second, minute, flagellum, usually called the cilium. Behind these the oral groove has an oval space, the proper mouth ; behind this, again, the oral groove is continued for some way, with a distinct rod-like ridge in its furrow. The whole body, including the big flagellum, is coated by a strong cuticular pellicle, except at the oblong mouth, and the lps and rod are mere thickenings of this. The cytoplasm has a reticulate arrangement : the mouth opens into a central aggregate, from which strands diverge branching as they recede to the periphery, where they pass into a continuous lining for the cuticular wall, liquid fillmg the interspaces. The whole arrangement is not unlike that found in many plant- Fic. 48.—.Noctiluca miliaris, a marine Cysto- cells, but the only other flagellate. (From Verworn.) Protists in which it occurs are the Cihata 7rachelius (Fig. 56, p. 153) and Lowodes. The central mass contains the large nucleus. Noctiluea is an animal feeder, and expels its excreta through the mouth. The large flagellum is remarkable for the transverse striation of its plasma, especially on the ventral side. The cuticle may be moulted as in the Dinoflagellates. As a prelude to fission the external differentiations disappear, the nucleus divides in the plane of the oral groove, and a meridional constriction parts the two halves, the new external organs being regenerated. Conjugation occurs also, the two organisms fusing by their oral region; the loco- motive organs and pharynx disappear; the conjoined cytoplasms unite to form a sphere, and the nuclei fuse to form a zygote or fertilisation nucleus. This conjugation is followed by sporu- lation or brood-formation.' ' This process has the character of telolecithal segmentation in a Metazoan egg. 134 PROTOZOA CHAP. The nucleus passes towards the surface, undergoes successive fissions, and as division goes on the numerous daughter-nuclei occupy little prominences formed by the upgrowth of the cyto- plasm of the upper pole. The rest of the cytoplasm atrophies, and the hillocks formed by the plasmic outgrowths around the final daughter-nuclei become separate as so many zoospores (usually 256 or 512); each of these is oblong with a dorsal cap- like swelling, from the edge of which arises a flagellum pointing backwards; parallel to this the cap is prolonged on one side into a style also extending beyond the opposite pole of the animal." In this state the zoospore is, to all outward view, a naked Dino- flagellate, whence it seems that the Cystoflagellates are to be regarded as closely allied to that group. Leptodiseus is concayo- convex, circular, with the mouth central on the convex face, 1-flagellate, and attains the enormous size of 1:5 mm. (,),”) in diameter. The remarkable phosphorescence of Nocti/uca is not constant. It glows with a bluish or greenish light on any agitation, but rarely when undisturbed. A persistent stimulus causes a con- tinuous, but weak, light. This hght is so weak that several tea- spoonsful of the organism, collected on a filter and spread out, barely enable one to read the figures on a watch a foot away. As in other marine phosphorescence, no rise of temperature can be detected. The luminosity resides in minute points, mostly crowded in the central mass, but scattered all through the cyto- plasm. A slight irritation only produces luminosity at the point touched, a strong one causes the whole to flash. Any form of irritation, whether of heat, touch, or agitation, electricity or magnetism, is stated to induce the glow. By day, it is said, Noctiluca, when present in abundance, may give the sea the appearance of tomato soup. The earliest account of Noctiluca will be read with interest. Henry Baker writes in Employment for the Microscope :°—“ A curious Enquirer into Nature, dwelling at Wells upon the Coast of Norfolk, affirms from his own Observations that the Sparkling of Sea Water is occasioned by Insects. His Answer to a Letter wrote to him on that Subject runs thus, ‘In the Glass of Sea Water I send with this are some of the Animalcules which cause the Sparkling Light in Sea Water; they may be seen by holding 1 See Doflein, in Zool. Jahrb. Anat. xiv. 1900, p. 1. 2 London, 1753, 402-403. = FLAGELLATA 135 the Phial up against the Light, resembling very small Bladders or Air Bubbles, and are in all Places of it from Top to Bottom, but mostly towards the Top, where they assemble when the Water has stood still some Time, unless they have been killed by keep- ing them too long in the Phial. Placing one of these Animal- cules before a good Microscope, an exceeding minute Worm may be discovered, hanging with its Tail fixed to an opake Spot in a Kind of Bladder, which it has certainly a Power of contracting or distending, and thereby of being suspended at the Surface, or at any Depth it pleases in the including Water.’ ” “The above-mentioned Phial of Sea Water came safe, and some of the Animalcules were discovered in it, but they did not emit any Light, as my Friend says they do, upon the least Motion of the Phial when the Water is newly taken up. He lkewise adds, that at certain Times, if a Stone be thrown into the Sea, near the Shore, the Water will become luminous as far as the Motion reacheth: this chiefly happens when the Sea hath been ereatly agitated, or after a Storm.” Obviously what Mr. Sparshall, Baker’s correspondent, took for a worm was the large flagellum. The chief investigators of this group have been Huxley, Cienkowski, Allman, Biitschli, and G. Pouchet, while Ischikawa and Doftlein have elucidated the conjugation. CHAPTER VI PROTOZOA (CONTINUED): INFUSORIA (CILIATA AND SUCTORIA) IV. Infusoria. CoMPLEX Protozoa, never holophytic save by symbiosis with plant commensals, never amoeboid, with at some period numerous short cilia, of definite outline, with a double nuclear apparatus con- sisting of a large meganucleus and a small micronucleus (or several), the latter alone taking part in conjugation (karyo- gamy), and giving rise after conjugation to the new nuclear apparatus. The name Infusoria was formerly applied to the majority of the Protozoa, and included even the Rotifers. For the word signifies organisms found in “infusions” of organic materials, including macerations. Such were made with the most varied ingredients, pepper and hay being perhaps the favourites. They were left for varying periods exposed to the air, to allow the organisms to develop therein, and were then examined under the microscope.” With the progress of our knowledge, group after group was split off from the old assemblage until only the ciliate or flagellate forms were left. The recognition of the claims of the Flagellates to independent treatment left the group more natural ;* while it was enlarged by the admission of the Acinetans (Suctoria), which had for some time been regarded as a division of the Rhizopoda. 1 On this account Hickson has termed the group ‘“‘ Heterokaryota” in Lankester’s Treat. Zool. i. fase. 1, 1903. 2 See Baker, Employment for the Microscope, ed. 2, 1758. ° Saville Kent’s valuable Manual of the Infusoria (1880-1882), which gives figures of every genus and descriptions of every species known at that date, includes the Flagellates in its scope. 136 CHAP, VI CILIATA a7 I. Cimerara Infusoria, with a mouth, and cilia by which they move and feed; usually with undulating membranes, membranellae, cirrhi, or some of these. Genera about 144: 27 exclusively marine, 50 common to both sea and fresh water, 27 parasitic on or in Meta- zoa, the rest fresh water. Species about 500. We divide the Ciliata thus :'— (1.) Mouth habitually closed, opening by retraction of its circular or slit- like margin ; cilia uniform 3 Order 1. GYMNOSTOMACEAE. Lacrymaria, Ehrb.; Loxodes, Ehrb.; Loxophyllum, Duj.; Lionotus, Wrez.; Trachelius, Schrank ; Amphileptus, Ehrb. ; Actinobolus, St. ; Didinium, St. ; Scaphiodon, St.; Dysteria, Huxl.; Coleps, Nitzsch. ; Dileptus, Duj. ; Ileonema, Stokes ; Mesodinium, St. (IL) Mouth permanently open, usually equipped with one or more undu- lating membranes, receiving food by ciliary action (TRICHO- STOMATA, Biitschli) (a) Cilia nearly uniform, usually extending over the whole body, without any special adoral wreath of long cilia or membra- nellae ; mouth with one or two undulating membranes at its margin or extending into the short pharynx. Order 2. ASPIROTRICHACEAE. Paramecium, Hill; Colpoda, O. F. Mill. ; Colpidiwm, St. ; Leuco- phrys, Ehrb.; Cyclidium, Cl. and L.; Lembadion, Perty ; Cinetochilum, Perty; Plewronema, Duj.; Ancistrum, Maup.; Glaucoma, Ehrb. ; Uronema, Duj. ; Lembus, Cohn ; Urocentrum, Nitzsch ; Icthyophtheirius, Fouquet. (b) Strong cilia or membranellae forming an adoral wreath, and bounding a more or less enclosed area, the “peristome,” at one point of which the mouth lies. (i.) Body more or less equally covered with fine cilia ; adoral wreath an open spiral Order 3. HmrTEROTRICHACEAE Spirostomum, Ehrb. ; Bursaria, O. F. Mull. ; Stentor, Oken; Folliculina, Lamk.; Conchophtheirus, St.; Balan- tidium, Cl. and L.; Nyctotherus, Leidy ; Metopus, Cl. and L.; Caenomorpha, Perty; Discomorpha, Levander ; Blepharisma, Perty. (ii.) Body cilia limited in distribution or absent ; peristome anterior, nearly circular, sinistrorse. Order 4. OLIGOTRICHACEAE. Halteria, Duj.; Maryna, Gruber; Tintinnus, Schrank ; Dictyocystis, Ehrb. ; Strombidiwm, Cl. and L. (= Tor- quatella, Lank.). (iii.) Peristome extending backwards along the ventral face, which alone is provided with motile cirrhi, ete. ; dorsal cilia fine, motionless. . Order 5. HyporTRICcHACEAE. 1 Orders 1 and 2 constitute together the Holotricha of Stein ; Bitschli regards 3 to 6 as sections of Spirotrocha. 138 PROTOZOA CHAP. Stylonychia, Ehrb.; Kerona, O. F. Mull.; Oxytricha, Ehrb. ; Euplotes, Ehrb.; Stichotricha, Perty ; Schazo- tricha, Gruber. (iv.) Body cilia reduced to a posterior: girdle, or temporarily or permanently absent; peristome anterior, nearly circular, edged by the adoral wreath,! bounded by a gutter edged by an elevated rim or collar. Order 6. PERITRICHACEAE. Lichnophora, Cl.; Trichodina, Ehrb.; Vorticella, L. ; Zoothamnium, Bory; Carchesium, Ehrb.; Epistylis, Ehrb.; Opercularia, Lamk.; Vaginicola, Lamk.; Pysicola, Kent; Cothurnia, Ehrb.; Scyphidia, Lachmann ; Ophrydium, Bory ; Spirochona, St. The Ciliata have so complex an organisation that, as with the Metazoa, it is well to begin with the description of a definite type. For this purpose we select Stylonychia mytilus, Ehrb. (Fig. 49), a species common in water rich in organic matter, and relatively large (1/75”=4 mm.). It is broadly oval in outline, with the wide end anterior, truncate, and sloping to the left side behind ; the back is convex, thinning greatly in front; the belly flat. It moves through the water either by continuous swimming or by jerks, and can either crawl steadily over the surface of a solid or an air surface such as an air bubble, or advance by springs, which recall those of a hunting spider. The boundary is every- where a thin plasmic pellicle, very tender, and readily undergoing diftluence like the rest of the cell. From the pellicle pass the cilia, which are organically connected with it, though they may be traced a little deeper; they are arranged in slanting longitu- dinal rows, and are much and variously modified, according to their place and function. On the edge of the dorsal surface they are fine and motionless, probably only sensory (s.h.); except three, which protrude well over the hinder end (c.p.), stout, pointed, and frayed out at the ends, and possibly serving as oars or rudders for the darting movements. These are distinguished from simple cilia as “ cirrhi.” At the right hand of the frontal area there begins, just within the dorsal edge, a row of strong cilium-like organs (Fig. 49, per) ; these, on careful examination, prove to be transverse triangular plates, which after death may fray into cilia.” They are the Dextrorse in all but Lichnophora and Spirochona. 2 Each membranella is a transversely elongated oval in reality, and below it is a double row of basal granules, corresponding to the individual cilia that consti- tute it. Similarly, the undulating membranes have a single row of basal granules. So. vI CILIATA 139 “ adoral membranellae.” and there crosses over the edge of the body to the ventral aspect, and then curves inwards towards the median lne, which it reaches about half-way back, where it passes into the pharynx (m). It forms the front and left-hand boundary of a wedge-shaped ‘de- pression, the “ peri- stomial area,” the right- hand boundary being the “preoral ridge” or lip (/), which runs nearly on the median line, projecting down- ward and over the de- pression. This ridge bears on its inner and upper side a row of fine “preoral cilia” (poc) and a wide “preoral undulating membrane ” (p.om), which extends horizontally across, be- low the peristomial area. The roof of this area bears along its right- hand edge an “ internal undulating membrane ” (g), and then, as we pass across to the left, first an “endoral mem- brane” and then an “endoral” row of cilia. This row passes to the left blunt angle, zz os = Fic. 49.—Ventral view of Stylonychia inytilus. a.c, Abdominal cirrhi; av, anus discharging the shell of a Diatom ; ¢.c, caudal cirrhi ; c.p, dorsal cirrhi ; cv, contractile vacuole ; e, part of its replenishing canal ; f.c, frontal cirrhi; f.v, food vacuoles ; 4, internal undulating membrane ; 7, lip; m, mouth or pharynx ; mc, marginal cirrhi; NV, 4, lobes of meganucleus ; 7, 7, micronuclei ; 0, anterior end ; per, adoral membranellae ; poc, preoral cilia ; p.om, preoral undulating membrane; s./, sense hairs. (Modified from Lang. ) In some allied genera (not in Stylonychia), at the base and on the inner side of each adoral membranella, is a “ paroral ’ cilium. 140 PROTOZOA CHAP. All these motile organs, with the exception of the preoral cilia, pass into the pharynx; but the adoral membranellae soon stop short for want of room. There are some seventy membranellae in the adoral wreath. The rest of the ventral surface is marked by longitudinal lines, along which the remaining appendages are disposed. On either side is a row of “marginal cirrhi” (me.), which, like the membranellae, may fray out into cilia, but are habitually stiff spine-like, and straight in these rows; these are the chief swim- ming organs. Other cirrhi, also arranged along longitudinal rows, with so many blank spaces that the arrangement has to be carefully looked for, occur in groups along the ventral surface. On the right of the peristome are a group which are all curved —the “frontal cirrhi” (fc.). Behind the mouth is a second group—the “abdominal cirrhi” (a.c.), also curved hooks; and behind these again the straight spine-like “caudal” or “anal” cirrhi (¢.c), which point backwards. These three sets of ventral cirrhi are the organs by which the animal executes its crawling and darting movements. Besides the mouth there are two other openings, both indistinguishable save at the very moment of discharge ; the anus (an) which is dorsal, and the pore of the contractile vacuole, which is ventral. The protoplasm of the body is sharply marked off into a soft, semi-fluid “endoplasm ” or “ endosare,” and a firmer “ ectoplasm ” or “ ectosare.” The former is rich in granules of various kinds, and in food-vacuoles wherein the food is digested. The mode of ingestion, ete., is described below (p. 145). The ectoplasm is honeycombed with alveoli of definite arrangement, the majority being radial to the surface or elongated channels running length- wise ; inside each of these lies a contractile plasmic streak or myoneme. The contractile vacuole (cv) lies in this layer, a little behind the mouth, and is in connexion with two canals, an anterior (¢) and a posterior, from which it is replenished. The nuclear apparatus lies on the inner boundary of the ecto- plasm; it consists of (1) a large “meganucleus” formed of two ovoid lobes (V, V), united by a slender thread ; and (2) two minute “micronuclei” (n, 7), one against either lobe of the meganucleus. Stylonychia multiplies by transverse fission, the details of which are considered on pp. 144, 147. The protoplasm of Ciliata is the most differentiated that we vI CILIATA 141 find in the Protista, and we can speak without exaggeration of the “organs” formed thereby. The form of the body, determined by the firm pellicle or plasmic membrane, is fairly constant for each species, though it may be subject to temporary flexures and contractions. The pellicle varies in rigidity ; where the cilia are abundant it is pro- portionately delicate, and scarcely differs from the ectoplasm proper, save for not being alveolate. In the Peritrichaceae it is especially resistant and proof against decay. In Coleps (Gymnostomaceae) it is hardened and sculptured into the semblance of plate-armour, and the prominent points of the plates around the mouth serve as teeth to lacerate other active Protista, its prey; but, like the rest of the protoplasm, this disappears by decay soon after the death of the Coleps. Where, as in certain Oligotrichaceae, cilia are absent over part of the body, the pellicle is hardened ; and on the dorsal face and sides of Dysteria it even assumes the character of a bivalve shell, and forms a tooth-like armature about the mouth. From the pellicle protrude the cilia, each of which is con- tinued inwards by a slender basal filament to end in a “basal granule” or “ blepharoplast.” The body-cila are fine, and often reversible in action, which is exceptional in the organic world. They may be modified or combined in various ways. We have seen that in Stylonychia some are motionless sensory hairs. The cirrhi and. setae sometimes fray out during hfe, and often after death, into a brush at the tip, and have a number of blepharo- plasts at their base. The same holds good for the membranellae and undulating membranes. They are thus comparable to the “vibratile styles” of Rotifers (Vol. II. p. 202) and the “combs ” or “ Ctenophoral plates” of the Ctenophora (p. 412 f.).’ The ectosarc has a very complex structure. Like other 1 Tail-like appendages are found in Scaphiodon and in Dysteria and its allies (Gymnostomaceae), Urocentrwm (Aspirotrichaceae), Discomorpha and Caenomorpha (Heterotrichaceae). In the first two and last two cases they are prolongations of the body ; in the third an aggregate of cilia. One or more long caudal setiform cilia are present in the genera Lembadion, Plewronema, Cyclidium, Lembus, Cinetochilum, Ancistrum, and Uronema ; all these are addicted to making spring- ing darts. Tufts of cilia of exceptional character often serve for temporary attach- ment. The stalk (or at least its external tube) of the Peritrichaceae appears to be the chitinous excretion of a zone of such cilia. Fauré-Fremiet terms such a zone or annular brush a ‘‘scopula” (‘‘Struct. de l’'app. fixateur chez les Vorticellides,” Arch. Protist. vi. 1905, p. 207). For a discussion of the finer structure of the cilia in Ciliata, and the mechanism of their action, see Schuberg, Arch. Protist. vi. 1905, p. 61. =< 142 PROTOZOA CHAP. protoplasm it has a honeycombed or alveolate structure, but in this case the alveoli are permanent in their arrangement and position. Rows of these alveoli run under the surface; and the cilia are given off from their nodal points where the vertical walls of several unite, and wherein the basal granule or blepharo- plast is contained. Longitudinal threads running along the inner walls of the alveoli of the superficial layer are differen- tiated into muscular fibrils or “ myonemes,” to which structures TT iarspa teat Samra haba ee as Re): sian int] acd OR = E=} = F—| I =F SS = = 4 te Fig. 50.—Kcetosare of Ciliata. «-7, from Stentor coeruleus ; g, Holophrya discolor. a, Transverse section, showing cilia, pellicle, canals, and imyonemes; 6, surface view below pellicle, showing inyonemes alternating with blue granular streaks ; c, more superficial view, showing rows of cilia adjacent to myonemes ; d, myoneme, highly magnified, showing longitudinal and transverse striation ; e, two rows of cilia; 4, 9g, optical sections of ectosarc, showing pellicle, alveolar layer (@), myonemes (m), and canals in ectosare. (From Calkins, after Metschnikoff, Biitschli, and Johnson.) so many owe their marked longitudinal striation on the one hand, and their power of sudden contraction on the other. The appearance of transverse striation may be either due to transverse imyonemes, or produced by the folds into which the contraction of longitudinal fibrils habitually wrinkles the pellicles, when it is fairly dense (Peritrichaceae); circular muscular fibrils, however, undoubtedly exist in the peristomial collar of this group. Embedded in the ectosare are often found trichocysts,’ analogous ' See Mitrophanow ‘‘Sur les Trichocystes . . . du Paramoeciwm,” Arch. Protist. v. 1904, p. 78. VI CIETAWA 143 to the nematocysts of the Coelenterata (p. 247), and doubtless fulfilling a similar purpose, offensive and defensive. A trichocyst is an oblong sac (4 w long in Parameciwm) at right angles to the surface, which on irritation, chemical (by tannin, acids, ete.) or mechanical, emits or is converted into a thread several times the length of the cilia (33 yz), often barbed at the tip. In the predaceous Gymnostomaceae, such as Didiniwm, the trichocysts around (or even within) the mouth are of exceptional size, and are ejected to paralyse, and ultimately to kill, the active Infusoria on which they feed. In most of the Peritrichaceae they are, when present, limited to the rim around the peristome, while in the majority of species of Cillata they have not been described. Fibrils, possibly nervous,’ have been described in the deepest layer of the ectosare in Heterotrichaceae. The innermost layer of the ectosarc is often channelled by a system of canals,” usually inconspicuous, as they discharge con- tinuously into the contractile vacuole; but by inducing partial asphyxia (e.g. by not renewing the limited supply of air dissolved in the drop of water on the slide under the cover-glass), the action of the vacuole is slackened, and these canals may be more readily demonstrated. The vacuole, after disappearance, forms anew either by the coalescence of minute formative vacuoles, or by the enlargement of the severed end of the canal or canals. The pore of discharge to the surface is visible in several species, even in the intervals of contraction.’ The pore is sometimes near that of the anus, but is only associated with it in Peritrichaceae, where it opens beside it into the vestibule or first part of the long pharynx, often through a rounded reservoir (Fig. 60, 7) or elongated canal. The endosare, in most Ciliates well differentiated from the ectosarce, is very soft; though it is not in constant rotation like that of a Rhizopod, it is the seat of circulatory movements alternating with long periods of rest. Thus it is that the food- vacuoles, after describing a more or less erratic course, come to discharge their undigested products at the one point, the anus. 1 The ‘‘neurophane”’ fibrils of Neresheimer, Arch. Protist. ii. 1903, p. 305 f. * Sometimes the number of afferent canals is limited to five (Paramecium), or even one. There may be one or more contractile vacuoles, and in the latter case the different ones have an independent rhythm. ° Tt is from such conclusive cases that the universal character of a discharge to the surface has been inferred in the rest of Protista possessing this organ. 144 PROTOZOA CHAP. In a few genera (Didinium, for instance) the course from mouth to anus is a direct straight line, and one may almost speak of a digestive tract. In Lowodes and Trachelius (Fig. 56) the endo- sare, as in the Flagellate Noctiluca (Fig. 48, p. 133), has a central mass into which the food is taken, and which sends out lobes, which branch as they approach and join the ectoplasm. The endosare contains excretory granules, probably calcium phos- phate, droplets of oil or dissolved glycogen, proteid spherules, paraglycogen grains, ete. The nuclear apparatus lies at the inner boundary of the ectoplasm. The “meganucleus” may be ovoid, elongated, or composed of two or more rounded lobes connected by slender bridges (Stentor, Stylonychia). The “micronucleus” may be single; but even when the meganuclens is not lobed it may be . accompanied by more than one micronucleus, and when it is lobed there is at least one micronucleus to each of its lobes. The meganucleus often presents distinct granules of more deeply staining material, varying with the state of nutrition; these are especially visible in the band-like meganuclei of the Peritrichaceae (Figs. 51,60). At the approach of fission it is in many cases dis- tinetly fibrillated.” But all other internal differentiation, as well as any constriction, then disappears; and the ovoid or rounded figure becomes elongated and hour-glass shaped, and finally con- stricts into two ovoid daughter-meganuclei, which, during and after the fission of the cell, gradually assume the form charac- teristic of the species. The micronuclei (each and all when they are multiple) divide by modification of karyokinesis (or “ mitosis ”) as a prelude to fission: 1n this process the chromatin is resolved into threads which divide longitudinally, but the nuclear wall 1 Gruber (Ber. Ges. Freib. 1888) has shown that in several marine Ciliata the meganucleus is represented by an enormous number of minute granules dis- seminated through the endosare, which, on the approach of fission, unite into a single meganucleus. As an adjacent micronucleus makes its appearance at this stage, he infers that the micronucleus must be also resolved in the intermediate life of the cell into granules too small for recognition under the highest magnifica- tion attainable, and that they must then coalesce. 2 In the peculiar Peritrichan Spirochona the division of the meganucleus is a much more complex process than usual, and recalls that of the undifferentiated nuclei of many Rhizopods (see Rompel in Z. wiss. Zool. viii. 1894, p. 618). Opalina has neither mouth nor anus, nor contractile vacuole, but a large number of similar nuclei, that divide by a true mitotic process, like micronuclei. We have referred it (pp. 114, 123) to the Flagellates, next to the Trichonymphidae. VI CILIATA 145 remains intact. If an Infusorian be divided into small parts, only such as possess a micronucleus and a fragment of the mega- nucleus are capable of survival. We shall see how important a part the micronuclei play in conjugation, a process in which the old meganuclei are completely disorganised and broken up and their débris expelled or digested. The mouth of the Gymnostomaceae is habitually closed, opening only for the ingestion of the living Protista that form their prey. It usually opens into a funnel-shaped pharynx, strengthened with a circle of firm longitudinal bars, recalling the mouth of an eel-trap or lobster-pot (“ Reusenapparat ” of the Germans); and this is sometimes protrusible. In Dysteria the rods are replaced by a complicated arrangement of jaw- or tooth- like thickenings, which are not yet adequately described. We have above noted the strong adoral trichocysts in this group. In all other Ciliates’ the “mouth” is a permanent depression lined by a prolongation of the pellicle, and containing cilia and one or more undulating membranes, and when adoral membranellae are present, a continuation of these. In some species, such as Pleuronema (Fig. 57), one or two large membranes border the mouth right and left. In Peritrichaceae the first part of the pharynx is distinguished as the “ vestibule,” since it receives the openings of the contractile vacuole or its reservoir and the anus. The pharynx at its lower end (after a course exceptionally long and devious in the Peritrichaceae ; Figs. 51,60) ends against the soft endosare, where the food-particles accumulate into a rounded pellet ; this grows by accretion of fresh material until it passes into the endosare, which closes up behind it with a sort of lurch. Around the pellet liquid is secreted to form the food-vacuole. If the material supplied be coloured and insoluble, like indigo or carmine, the vacuoles may be traced in a sort of irregular, discontinuous circulation through the endosarc until their remains are finally discharged as faeces through the anus. No prettier sight can be watched under the microscope than that of a colony of the social Bell-animaleule (Carchesium) in coloured water—all producing food-currents brilliantly shown up by the wild eddies of the pigment granules, and the vivid blue or crimson colour of 1 Save the Opalinopsidae, which are usually termed ‘ Opalinidae” ; but which cannot retain the latter name on the removal of the genus Opalina to the Flagellates. VOL, I L 146 PROTOZOA CHAP. the food-vacuoles, the whole combining to present a most attrac- tive picture. Ehrenberg fancied that a continuous tube joined up the vacuoles, and interpreted them as so many stomachs threaded, as it were, along a slender gut; whence he named the group “ Polygastrica.” ¥ic. 51. — Carchesium polypinum. Scheme of the path taken by the ingested food in digestion and expul- sion of the excreta. The food enters through the pharynx and is transported downward (small cir- cles), where it is stored in the concavity of the sausage - shaped meganucleus (the latter is recognised by its containing darker bodies). It remains here for some time at rest (small crosses). Then it passes upward upon the other side (dots) and returns to the middle of the cell, where it undergoes solution. The excreta are removed to the outside, through the vestibule and cell mouth. The black line with arrows indi- cates the direction of the path. (From Ver- worn, after Green- wood.) We owe to Miss Greenwood * a full account of the formation and changes of the food-vacuoles in Carchesium polypinum. The vacuole passes steadily along the endosare for a certain time after its sudden admission into it, and then enters on a phase of quiescence. Zeitschr. wiss. Zool. xxxi. 1878, p. 262. - 168 PORIFERA CHAP. Then Biitschli' (1884) and Sollas? on combined morphological and embryological evidence (1884) concluded that sponges were remote from all the Metazoa, showing bonds only with Choano- flagellate Protozoa (p. 121). This the exact embryological work of Maas, Minchin, and Delage has done much to prove, but it has to be admitted that unanimity on the exact position of the phylum has not yet been attained, some authorities, such as Haeckel, Schulze, and Maas still wishing to include sponges in the Metazoa. In this short history we have been obliged to refer only to work helping directly to solve the problem of the nature of a sponge, hence many names are absent which we should have wished to mention. Halichondria panicea. One of the commonest of British sponges, which may be picked up on almost any of our beaches, and which has also a cosmopolitan distribution, is known by the clumsy popular name of the “crumb of bread sponge,” alluding to its consistency ; or by the above technical name, with which even more serious fault may be found.’ In its outward form H. panicea affords an excellent case of a peculiarity common among sponges. Its appearance varies ac- cording to the position in which it has lived. In fact, Bowerbank remarks that it has no specific form. It may grow in sheets of varying thickness closely attached to a rock, when it is “encrusting,” or it is frequently massive and lying free on the sea bottom ; again, it may be fistular, consisting of a single long tube, or it may be ridge-like, apparently in this case consisting of a row of long tubes fused laterally. In this last form it used to be called the “ cockscomb sponge,” having been taken for a distinct species. Bidder has proposed to call the different forms of the same species “metamps” of the species. Figures of the metamps of HZ. panicea will be found in Bowerbank’s useful Monograph.* 1 Ann. Mag. Nat. Hist. (5) xiii. 1884, p. 381. 2 Quart. Journ. Mier. Sei. xxiv. 1884, p. 612. 8 The name was coined by Dr. Fleming from ydaé ‘‘silex”’ and xévdpos ‘‘ car- tilage,”’ and as these roots could only give Chalic-chondria it is not surprising that those who have not referred to Dr. Fleming’s statements give the derivation as as ‘‘ sea” and xévdpos. 4 Monograph of British Sponges, vol. iii. pl. xxxix.-xl. For revision of nomen- clature in this Monograph, see Hanitsch, 77. Liverp. Biol. Soc. viii. 1894, p. 173. vil STRUCTURE OF HALICHONDRIA 169 The colour of the species is as inconstant as its form, ranging from green to light brown and orange. MacMunn concludes from spectroscopic work that HH. panicea contains at lease three pigments, a chlorophyll, a lipochrome, and a histohaematin.’ Lipochromes vary from red to yellow, chlorophyll is always associated with one or more of them. MHistohaematin is a respiratory pigment. Proof has not yet been adduced that the chlorophyll is proper to the sponge and is not contained in symbiotic algae. In spite of all this inconstancy HH. panicea is one of the most easily determined species. It is only necessary to dry a small fragment, including the upper sur- face; a beautiful honeycomb- like structure is then visible on this surface, and among British sponges this 1s a property peculiar to the species (Bowerbank). Whatever the form of the sponge, one or more large rounded apertures are always present on the exterior; these are the “oscula.” In the encrusting metamp the oscula are flush with the general surface, while in the other cases they are raised on conical projections ; fistular specimens carry the osculum at the distal end, and the cocks- eee a eo Lal pone ae comb has a row of them along its A, natural size; B, magnified. upper edge. Much more numerous are eendcdy mevebes are than the oscula are smaller apertures scattered over the general surface of the sponge, and known as “ostia.” If the sponge be placed in a shallow glass dish of sea water the function of the orifices can be made out with the naked eye, especially if a little powdered chalk or carmine be added to the water. If the specimen has been gathered after the retreating tide has left it exposed for some time, this addition is unnecessary, for as soon as it is plunged into water its current bursts vigor- ously forth, and is rendered visible by the particles of detritus that have accumulated in the interior during the period of 1 Journ. Physiol. ix. 1888, p. 1. 170 PORIFERA CHAP. exposure and consequent suspended activity. “The oscula then serve for the exit of currents of water carrying particles of solid matter, while the entrance of water is effected through the ostia. Sections show that the ostia lead into spaces below the thin superficial layer or “dermal membrane”; these are continued down into the deeper parts of the sponge as the “ incurrent canals,” irregular winding passages of lumen continually dimin- ishing as they descend. They all sooner or later open by numerous small pores—* prosopyles ”—into certain subspherical sacs termed flagellated chambers. Each chamber discharges by one wide aperture—‘ apopyle ”—into an “excurrent canal.” This latter is Fic. 64.—H. panicea ; the arrows indicate the direction of the current, which is made visible by coloured particles. (After Grant.) only distinguishable from an incurrent canal by the difference in its mode of communication with the chambers. The excurrent canals convey to the osculum the water which has passed through the ostia and chambers. All the peri- pheral parts of the sponge from which chambers are absent are termed the “ ectosome,” while the chamber-bearing regions are the “ choanosome.” The peculiar crumb-of-bread consistency is due to the nature of the skeleton, which is formed of irregular bundles and strands of minute needles or spicules composed of silica hydrate, a substance familiar to us in another form as opal: they are clear and transparent like glass. They are scattered through the tissues in great abundance. The classes of cellular elements in the sponge are as follows : Flattened cells termed “ pinacocytes ” cover all the free surfaces, that is to say, the external surface and the walls of the excur- VII CBHELS AND SPICULES AN rent and incurrent canals. The flagellated chambers are lined by “choanocytes ” (cf. Fig. 70, p. 176); these are cells provided at their inner end with a flagellum and a collar surrounding it. They resemble individuals of the Protozoan sub-class Choanoflagellata, and the likeness is the more remarkable because no other organisms are known to possess such cells. Taken together the choanocytes constitute the “ gastral layer,” and they are the active elements in producing the current. The tissue surrounding the chambers thus lying between the excurrent and incurrent canals consists of a gelatinous matrix colonised by cells drawn from two distinct sources. In the first place, it contains cells which have a common origin with the pina- cocytes, and which together with them make up the “ dermal layer”; these are the “collencytes” and “scleroblasts”; secondly, it contains “archaeocytes,” cells of independent origin. Collencytes are cells with clear protoplasm and thread-like =~ _ (Oars pseudopodial processes; they are T*j,05., issrammatc section of distinguished as stellate or bipolar, dermal ostia ; ex.c, excurrent, or ex- A : halant canal; iz.c, incurrent canal ; according as these processes are o, osculum. (Modified from Wilson.) many or only two. Scleroblasts or spicule cells are at first rounded, but become elongated with the growth of the spicule they secrete, and when fully grown are consequently fusiform. Each spicule consists of an organic filamentar axis or axial fibre around which sheaths of silica hydrate are deposited succes- sively by the scleroblast. Over the greater length of the spicule the sheaths are cylindrical, but at each end they taper to.a point. The axial canal in which the axial fibre lies is open at both ends, and the fibre is continuous at these two points with an organic sheath, which invests the entire spicule. From this structure we may conclude that the spicule grows at both ends—z.e. it grows in two opposite directions along one line—it has two rays lying in one axis, and is classed among uniaxial diactinal spicules. Being 172 PORIFERA CHAP. pointed at both ends it receives the special name oxea. The lamination of the spicule is rendered much more distinct by heat- ing or treatment with caustic potash.’ Fic. 66.—Cut end of a length of a siliceous spicule from HWyalonema sieboldii, with the lamellar structure revealed by solution. 104. (After Sollas.) The archaeocytes are rounded amoeboid cells early set apart in the larva; they are practically undifferentiated blastomeres. Some of them become reproductive elements, and thus afford a good instance of “continuity of germ plasm,” others probably perform excretory functions.” The reproductive elements are ova and spermatozoa, and are to be found in all stages in the dermal jelly. Dendy states that the eggs are fertilised in the inhalant canals, to which position they migrate by amoeboid movements, and there become suspended by a peduncle. The larva has unfortunately not been described, but as the course of development among the near relatives of H. panicea is known to be fairly constant, it will be con- venient to give a description of a “ Hali- chondrine type” of larva based on Maas’ account of the development of Gellius varius.* The free-swimming larvae escape by the Fic. 67.—Free-swimming osculum; they are minute oval bodies moving iat epimers | rapidly by means of a covering of cilia. Outer epithelium ; vi, The greater part of the body is a dazzling pigment ; «, hinder : : é A pole. (After Maas.) White, while the hinder pole is of a brown violet colour. This coloured patch is non- ciliate, the general covering of cilia ending at its edge in a ring of cilia twice the length of the others. Forward move- 1 Sollas, Ann. Mag. Nat. Hist. (4) xx. 1877, p. 285; Biitschli, Zeitschr. f. wiss. Zool. xix. 1901, p. 256. 2 Minchin, ‘‘Sponges” in Jreatise on Zoology, edited by E. Ray Lankester, p. 87. See also Bidder, Proc. Roy. Soc. li. 1892, p. 474. 3 Zool. Jahrb. Anat. vii. 1894. vil DEVELOPMENT 173 ment takes place in a screw line; when this ceases the larva rests on its hinder pole, and the cilia cause it to turn round on its axis, Sections show that the larva is built up of two layers :— 1. “The inner mass,” consisting of various kinds of cells in a gelatinous matrix. 2. A high flagellated epithelium, which entirely covers the larva with the exception of the hinder pole. The cells in the inner mass are classified into (1) undifferenti- ated cells, recognised by their nucleus, which possesses a nucleolus ; these are the archaeo- eytes; (2). differentiated cells, of which the nucleus contains a chromatin net ; these give rise to pinaco- cytes, collencytes, and scleroblasts. Some of them de form a flat epithelium Fic. 68.—Longitudinal section through the hinder Zz : g pole of the larva of G. varius. a, Flagellated which covers the hinder cells ; ma}, undifferentiated cell ; ma”, differen- pole. Some of the sclero- ed ue x, surface of hinder blasts already contain spicules. Fixation occurs very early. The front pole is used for attachment, the pigmented pole becoming the distal end (Fig. 69). The larva flattens out, the margin of the attached end is produced into radiating pseudopodial processes. The flagellated cells retreat to the interior, leaving the inner mass exposed, and some of its cells thereupon form a flat outer epithelium. This is the most important process of the meta- morphosis; it 1s followed by a pause in the outward changes, coinciding in time with rearrangements of the internal cells to give rise to the canal system; that is to say, lacunae arise in the inner mass, pinacocytes pass to the surface of the lacunae, and form their lining; the flagellated cells, which have lain in con- fusion, become grouped in small clusters. These become flagellated chambers, communications are established between the various portions of the canal system, and its external apertures arise. There is at first only one osculum. The larvae may be obtained by keeping the parent sponge in a dish of sea, water, shielded from too bright a light, and surrounded by a second dish of water to keep the temperature constant. They will undergo meta- maz ma? L774 PORIFERA CHAP. morphosis in sea water which is constantly changed, and will live for some days. We have said that the young sponge has only one osculum. This is the only organ which is present in unit number, and it is natural to ask whether perhaps the osculum may not be taken as a mark of the individual; whether the fistular specimens, for example, of H. panicea may not be solitary individuals, and the cockscomb and other forms colonies in which the individuals are merged to different degrees. Into the metaphysics of such a view we cannot enter here. We must be content to refer to the views of Huxley and of Spencer on Individuality. Fic. 69.—Larva of Gellius varius shortly after But it is advisable to cane is daniel Lae he alee avoid speaking of a multi- Neocon mena suc Mewdemedas % ogoulate sponge as a colony of many individuals, even in the sense in which it is usual to speak of a colony of polyps as formed of individuals. The repetition of oscula is probably to be regarded as an example of the phenomenon of repetition of parts, the almost universal occurrence of which has been emphasised by Bateson. Delage* has shown that when two sponge larvae fixed side by side fuse together, the resulting product has but one osculum. This, though seeming to bear out our point of view, loses weight in this connexion, when it is recalled that two Echinoderm larvae fused together give rise in a later stage to but one individual. Ephydatia fluviatilis. In the fresh water of our rivers, ponds, and lakes, sponges are represented very commonly by Ephydatia (Spongilla) fluviatilis, a cosmopolitan species. The search for specimens is most likely 1 Materials for the Study of Variation, 1894, p. 30. 2 Arch. de Zool. Exp. (2) x. 1892, pp. 345-498. On the general subject of adhesion of species, see Bowerbank, Brit. Ass. Rep. 1857, p. 11, who quotes Grant as the first to observe the phenomenon. VII STRUCTURE OF EPHYDAT/A 175 to be suecessful if perpendicular timbers such as lock-gates are examined, or the underside of floating logs or barges, or over- hanging branches of trees which dip beneath the surface of the water. The sponge is sessile and massive, seldom forming branches, and is often to be found in great luxuriance of growth, masses of many pounds weight having been taken off barges in the Thames. The colour ranges from flesh-tint to green, according to the exposure to hght. This fact is dealt with in a most interesting paper by Professor Lankester,' who has shown not only that the green colour is due to the presence of chlorophyll, but that the colouring matter is contained in corpuscles similar to the chlorophyll corpuscles of green plants, and, further, that the flesh- coloured specimens contain colourless corpuscles. which, though differing in shape from those which contain the green pigment, are in all probability converted into these latter under the influence of sufficient light. The corpuscles, both green and colourless, are contained in amoeboid cells of the dermal layer ;* and in the same cells but not in the corpuscles are to be found amyloid substances. The anatomy of Hphydatia fluviatilis is very similar to that of Halichondria panicea, differing only in one or two points of importance. The ectosome is an aspiculous membrane of dermal tissue covering the whole exterior of the sponge and forming the roof of a continuous subdermal space. This dermal membrane is perforated by innumerable ostia, and is supported above the ‘subdermal cavity by means of skeletal strands, which traverse the subdermal cavity and raise the dermal membrane into tent- like elevations, termed conuli. The inhalant canals which arise from the floor of the subdermal cavity are as irregular as in HT, panicea, and interdigitate with equally irregular exhalant canals; these latter communicate with the oscular tubes. Be- tween the two sets of canals are the thin folds of the choanosome with its small subspherical chambers provided with widely open apopyles (Fig. 70). The soft parts are supported on a siliceous skeleton of oxeas, which may have a quite smooth surface or may ' Quart. Journ. Mier. Sci. xxii. 1882, p. 229. * But see Gamble and Keeble, Quart. Journ. Micr. Set. xlvii. 1904, p. 363, who show that various green animals really owe their colour to ‘‘algae,” though the infection with the ‘‘ alga” is difficult to detect because it takes place by means of a colourless cell. See also Zoochloredia, on p. 126. 176 PORIFERA CHAP. be covered in various degrees with minute conical spines (Fig. 72, a, b). These spicules are connected by means of a substance termed spongin deposited around their overlapping ends, so as to form an irregular network of strands, of which some may be distinguished as main strands or fibres, others as connecting fibres. In the main fibres several spicules le side by side, while in the connecting fibres fewer or frequently single spicules form the thickness of the fibre. The fibres are continuous at the base with a plate or skin of spongin, which is secreted over the lower surface of the sponge and intervenes between it and the sub- Fic. 70.—Ephydatia fluviatilis. Section of flagellated chamber, showing the choanocytes passing through the apopyle. (After Vosmaer and Pekelharing. ) stratum. Of the chemical composition of spongin we shall speak later (see p. 237). It is a substance which reaches a great im- portance in some of the higher sponges, and forms the entire skeleton of certain kinds of bath sponge. Lying loose in the soft parts and hence termed flesh spicules, or microscleres, are minute spicules of peculiar form. These are the amphidiscs, consisting of a shaft with a many-rayed disc at each end (Fig. 72). In addition to its habitat the fresh-water sponge is worthy of attention on account of its methods of reproduction, which have arisen in adaptation to the habitat. A similar adaptation is widespread among fresh-water members of most aquatic in- vertebrates.! 1 Sollas, Tr. Dublin Soc. (2) iii. 1884, p. 87. VII GEMMULES OF £PHYDATIA WIL 76 Ephydatia fluviatilis normally produces not only free-swim- ming larvae of sexual origin, but also internal gemmules arising asexually. These bodies appear in autumn, distributed through- out the sponge, often more densely in the deeper layers, and they come into activity only after the death of the parent, an event which happens in this climate at the approach of winter. Weltner’ has shown that on the death and disintegration of the mother sponge some of the gemmules remain attached to the old skeleton, some sink and some float. Those which remain Fic. 71.—Portion of the skeletal frame- Fic. 72.—Spicules of H. fluviatilis. a.b.c, work of #. jluviatilis. a, Main Oxeas, spined and smooth ; d.e, amphi- fibres ; 6, connecting fibres. (After dises, side and end views. (After Weltner.) Potts.) attached are well known to reclothe the dead fibres with living tissue. They inherit, as it were, the advantages of position which contributed to the survival of the parent, as one of the selected fittest. The gemmules which sink are doubtless rolled short distances along the bottom, while those which float have the opportunity of widely distributing the species with the risk of being washed out to sea. But even these floating gemmules are exposed to far less dangers than the delicate free- swimming larvae, for their soft parts are protected from shocks by a thick coat armed with amphidiscs. The gemmules are likewise remarkable for their powers of ' Arch. Naturg. lix. 1893, p. 246. VOU; N 17s PORIFERA CHAP. resistance to climatic conditions, powers which must contribute in no small way to the survival of a species exposed to the variable temperatures of fresh water. Thus, if the floating gemmules or the parent skeleton with its attached and dormant offspring should chance to be included in the surface layer of ice during the winter, so far from suffering any evil consequences they appear to benefit by these conditions. Both Potts and Weltner have contirmed the truth of this statement by ex- periments. Weltner succeeded in rearing young from gemmules which had suffered a total exposure of 17 days to a temperature “under 0" C2 Of important bearing on the question of the utility of the gemmules are certain instances in which #. fluviatilis has been recorded as existing in a perennial con- dition." The perennial individuals may or may not bear gemmules, which makes it evident that, with the acquisition of the power to survive the winter cold, the prime necessity of forming these bodies vanishes. The perennial specimens are described as exhibiting a diminished vegetative Fic. 73.—Gemmule of &. activity in winter, the flagellated chambers Oe ee may be absent (Lieberkiihn), or present in unusually small numbers (Weltner), the entire canal system may be absent (Metschnikoff), or, on the other hand, it may be complete except for the osculum. In tropical countries gemmulation occurs as a defence against the ravages caused by the dry season when the waters recede down their banks, exposing all or most of their sponge inhabit- ants to the direct rays of the sun. The sponges are at once killed, but the contained gemmules being thoroughly dried, become efficient distributing agents of the species; they are light enough to be carried on the wind. It is probable that those individual sponges which escape desiccation survive the dry season without forming gemmules. It has been shown experimentally that gemmules are not injured by drying—Zykoff found that gemmules kept dry for a period of two years had not lost the power of germination. 1 Weltner, Blatt. Aquar. Fr. vii. 1896, p. 277, and ‘‘ Spongillidenstudien,” Arch. Naturg. ii. 1893, p. 271. aes GEMMULES OF £PHYDATIA 179 The mature gemmules consist of a more or less spherical mass of cells, which we shall refer to as yolk cells, and of a complex coat. The latter is provided with a pore or pore tube (Fig. 74) which is closed in winter by an organic membrane. There are three layers in the coat: an inner chitinous layer surrounded by an air-chamber layer, which is finely vesicular, showing a structure recalling plant tissue, and con- taining amphidises arranged along radii passing through the centre of the gemmule. One of the dises of each amphidisc lies in the inner chitinous coat, while the other les in a similar membrane which envelopes the air-chamber layer and is termed the outer chitinous coat. Marshall has suggested that one function of the amphidiscs is to weight the gemmules and thus protect them against the force of the river current; and no doubt the sinking or floating of individual gemmules depends on the relative degree of development of the air- chambers and of the amphidiscs. A study of the development of Ephydatia gemmules vividly illus- trates various characters of the inner rye. 74.—Part of a longitudinal processes of sponges. Specially note- ee cima asin a worthy are the migrations of cells pore (a). (After Potts.) and the slight extent to which divi- sion of labour is carried: one and the same cell will be found to perform various functions. The beginning of a gemmule is first recognisable * as a small cluster of amoeboid archaeocytes in the dermal membrane. These move into the deeper parts of the sponge to form larger groups. They are the essential part of the gemmule, the yolk cells, which, when germination takes place, give rise to a new sponge. They are followed by two distinct troops of actively moving cells. Those forming the first troop arrange themselves round the yolk cells and ultimately assume a columnar form so that they make an epithelioid layer. They then secrete the inner chitinous coat. The cells of the second troop are entrusted with the nutrition of the gemmule. Consequently they pass in among the yolk cells, distribute their food supplies, and make their escape 1 Evans, Quart. Journ. Micr. Sci. xliv. 1900, p. 72. 180 PORIFERA CHAP. by returning into the tissues of the mother sponge, before the columnar cells have completed the chitinous coat. Yet another migration now occurs, the cells— “ scleroblasts ”—which have been occupied in secreting amphidiscs at various stations in the sponge, carry the fully formed spicules to the gemmules and place them radially round the yolk cells between the radially lying cells of the columnar layer. The scleroblasts themselves remain with the amphidiscs, and becoming modified, contribute to the formation of the air-chamber layer. The columnar cells now creep out between the amphidises till their inner ends rest on the outer ends of these spicules. They then secrete the outer chitinous coat and return to the mother sponge. Carter gives directions’ for obtaining young sponges from the gemmules. The latter should be removed from the’ parent, cleaned by rolling in a handkerchief, and then placed in water in a watch-glass, protected with a glass cover and exposed to sunlight. In a few days the contents of the gemmule issue from the foramen and can be seen as a white speck. A few hours later the young sponge is already active and may be watched producing aqueous currents. At this age the sponge is an excellent object for studying in the living condition: being both small and transparent it affords us an opportunity of watching the movements of particles of carmine as they are carried by the current through the chambers. Potts? describes how he has followed the transportal of spicules by dermal cells, the end of each spicule multiplying the motion, swaying like an oscillating rod. In £. fluviatilis reproduction also occurs during the warmer months in this climate by means of sexual larvae. These are interesting for certain aberrant features in their metamorphosis.” While some of the flagellated chambers are formed in the normal way from the flagellated cells of the larva, others arise each by division of a single archaeocyte. This, it is suggested, is cor- related with the acquisition of the method of reproduction by gemmules, the peculiarities (i.e. development of organs from archaeocytes) of which are appearing in the larvae. Definition —We may now define sponges as multicellular, 1 Ann. Mag. Nat. Hist. (2), x. 1882, p. 365. 2 P. Ac. Philad. 1887, pp. 158-278. 3 Evans, Quart. Journ. Micr. Sci. xlii. 1899, p. 363. VII SYSTEMATIC POSITION 181 two-layered animals; with pores perforating the body-walls and admitting a current of water, which is set up by the collared cells of the “ gastral” layer. Position in the Animal Kingdom.—Sponges are the only multicellular animals which possess choanocytes, and their mode of feeding is unique. Since they are two-layered it has been sought to associate them with the Metazoan phylum Coelen- terata, but they are destitute of nematocysts or any other form of stinging cell, and their generative cells arise from a class of embryonic cells set apart from the first, while the generative cells of Coelenterata are derived from the ectoderm, or in other eases from the endoderm. These weighty differences between sponges and that group of Metazoa to which they would, if of Metazoan nature at all, be most hkely to show resemblance, suggest that we should seek a separate origin for sponges and Metazoa. We naturally turn to the Choanoflagellate Infusorian stock (see p. 121) as the source of Porifera, leaving the Ciliate stock as the progenitors of Metazoa. That both Porifera and Metazoa are reproduced by ova and spermatozoa is no objection to this view, seeing that the occur- rence of similar reproductive cells has been demonstrated in certain Protozoa (see pp. 100, 128). Let us now see which view is borne out by facts of embryo- logy. Suppose, for the moment, we regard sponges as Metazoa, then if the sponge larva be compared with the Metazoan larva we must assign the large granular cells to the endoderm; the flagellated cells to the ectoderm ; and we are led to the anomalous statement that the digestive cells in the adult are ectodermal, the covering, outer cells endodermal; or conversely, if we start our comparisons with the adults, then it follows that the larval ectoderm has the characters of an endoderm, and the larval endoderm those of an ectoderm. Thus both embryology and morphology lead us to the same point, they both show that in the absence of any fundamental agreement between Porifera and Metazoa it is necessary to regard the two stocks as independent from the very first, and hence the name ParAzOA (Sollas) has been given to the group which contains the Porifera as its only known phylum. Interesting in connexion with the phylogeny of Parazoa is co the Choanoflagellate genus Proterospongia (Fig. 75), described by 182 PORIFERA CHAP. VII Saville Kent, and since rediscovered both in England and abroad. This is a colony of unicellular individuals embedded in a common jelly. The individuals at the surface are choanoflagellate, while in the interior the cells are rounded Fic. 75.—Proterospongia haeckeli. a, Amoeboid cell; 6, a cell dividing ; ¢, cell with small collar; z, jelly. x-800. (After 8. Kent.) or amoeboid, and some of them undergo multiple fission to form reproductive cells. This is just such a creature as we might imagine that ancestral stage to have been of which the free- swimming sponge larva is a reminiscence: for we have seen that the flagellated cells of the larva are potential choanocytes. 1 Francé, Organismus der Craspedomonaden, Budapest, 1897, p. 217. CHAPTER VIII PORIFERA (CONTINUED) : FORMS OF SPICULES——CALCAREA— HOMOCOELA—— HETEROCOELA — HEXACTINELLIDA — DEMOSPON- GIAE — TETRACTINELLIDA— MONA XONIDA :-— CERATOSA— KEY TO BRITISH GENERA OF SPONGES SponGeEs fall naturally into two branches differing in the size of their choanocytes: in the MEGAMASTICTORA ee cells are rela- tively large, varying from dy to 9 in diameter; in MIcromas- TICTORA they are about 3 in diameter.’ For further subdivision of the group the spicules are such important weapons in the hands of the systematist that it is convenient to name them according to a common scheme. This has been arrived at by considering first the number of axes along which the main branches of the spicules are distributed, and secondly whether growth has oceurred in each of these axes in one or both directions from a point of origin.” I. Monaxons.—Spicules of rod-like form, in which growth is directed from a single origin in one or both directions along a single axis. The axis of any spicule is not necessarily straight, it may be curved or undulating. The ray or rays are known as actines. Biradiate monaxon spicules are termed “ rhabdi” (Fig. 76, @). A rhabdus pointed at both ends is an “oxea,” rounded at both ends a “strongyle,’ knobbed at both ends a “tylote.” By branching a rhabdus may become a “ triaene” (Fig. 110, &, /). Uniradiate monaxon spicules are termed “ styli.” II. Zetraxons—Spicules in which growth proceeds from an ! Sollas, Encyclopedia Britannica, art. ‘‘Sponges,” 1887. 2 Sollas, Ann. Mag. Nat. Hist. (5) iii. 1879, p. 23 ; Challenger Report, vol. xxv. pt. Ixiii. 1888, p. lii. 183 184 PORIFERA——-MEGAMASTICTORA CHAP. origin in one direction only, along four axes arranged as normals to the faces of a regular tetrahedron. Forms produced by growth from an origin in one direction along three axes lying in one plane are classed with tetraxons- IIL. 7riaxons.—Spicules in which growth is directed from an origin in both directions along three rectangular axes. One or more actines or one or 7 ce Es c two axes may be suppressed. IV. Polyaxons.—Spicules in which radiate growth from a centre proceeds in several Fic. 76.—Types of megascleres. a, Rhabdus directions. : : (monaxon diactine) ; 4, stylus (monaxon NE Sph CCS a Spicules in monactine) ; c, triod (tetraxon triactine) ; which verowth is concentric d, calthrop (tetraxon tetractine); e, 2 ee triaxon hexactine ; f, euaster. about the origin. A distinction more funda- mental than that of form is afforded by the chemical composition : all sponges having spicules composed of calcium carbonate belong to a single class, CALCAREA, which stands alone in the branch Megamastictora. BRANCH If. MEGAMASTICTORA CLASS CALCAREA Calcarea are marine shallow-water forms attached for the most part directly by the basal part of the body or occasionally by the intervention of a stalk formed of dermal tissue. They are almost all white or pale grey brown in colour. Their spicules are either monaxon or tetraxon or both. The tetraxons are either quadriradiate and then called “calthrops,” or triradiate when the fourth actine is absent. The triradiates always lie more or less tangentially in the body-wall; similarly three rays of a calthrop are tangentially placed, the fourth lying across the thickness of the wall. It is convenient to include the triradiate and the three tangentially placed rays of a calthrop under the common 28 VIII CALCAREA—HOMOCOELA 185 term “ triradiate system” (Minchin). The three rays of one of these systems may all be equal in length and meet at equal angles: in this case the system is “regular.” Or one ray or one angle may differ in size from the other rays or angles re- spectively, which are equal: in either of these two cases the system is bilaterally symmetrical and is termed “sagittal.” A special name “alate” is given to those systems which are sagittal in consequence of the inequality in the angles. Thus all equiangular systems whether sagittal or not are opposed to those which are alate. This is the natural classification.’ Sub-Class I. Homocoela. The Homocoela or Ascons possess the simplest known type of canal system, and by this they are defined. The body is a sac, branched in the adult, but simple in the young; its continu- ous cavity is everywhere lined with choanocytes, its wall is traversed by inhalant pores, and its cavity opens to the exterior at the distal end by an osculum. The simple sac-like young is the well-known Olynthus of Haeckel—the starting-point from which all sponges seem to have set out. Two processes are in- volved in the passage from the young to the adult, namely, multi- plication of oscula and branching of the original Olynthus tube or sac. If the formation of a new osculum is accompanied by fission of the sac, and the branching of the latter is slight, there arises an adult formed of a number of erect, well separated main tubes, each with one osculum and lateral branches. Such is the case in the Leucosoleniidae. In the Clathrinidae, on the other hand, branching of the Olynthus is complicated, giving rise to what is termed reticulate body form, that is, a sponge body con- sisting of a network of tubules with several oscula, but with no external indication of the limits between the portions drained by each osculum. These outward characters form a safe basis for classification, because they are correlated with other fundamental differences in structure and development.” As in Halichondria, and in fact all sponges, the body-wall is formed of two layers; the gastral layer, as we have said, forming a continuous lining to the Ascon tube and its branches. The 1 Minchin, Lankester’s 7’reatise on Zoology, pt. ti. 1900. * Minchin, Joc. cit. p. 110. 186 PORIFERA CHAP. dermal layer includes a complete outer covering of pinacocytes, which is reflected over the oscular rim to meet the gastral layer at the distal end of the tube; a deeper gelatinous stratum in which lie scleroblasts and their secreted products—calcareous spicules ; and finally porocytes.’ These last are cells which traverse the whole thickness of the thin body-wall, and are perforated by a duct or pore. The porocytes are contractile, and so the pores may be opened or closed; they are a type of cell which is known only in Calcarea. It will be noticed that the fusiform or stellate “connective tissue cells” are absent. The layer of pinacocytes as a whole is highly contractile, and is capable of diminishing the size of p the sponge to such an extent as quite to obliterate temporarily the gastral cavity.” The choanocytes show certain con- B stant differences in structure in the FG 772 the ro tyes of Aecaraa families Clathrinidae and Leucoso- collar cells. A, of Clathrina, leniidae respectively. In the former, nucleus basal; B, of Leuco the nucleus of the choanocyte is solenia, nucleus not basal, : tates ‘ flagellum arising from the basal; in the latter, it is apical, and Sa EAU eI Tk the flagellum can be traced down to Ub CE Sia): . The tetraxon spicules have “ equiangular ” triradiate systems in the Clathrinidae, while in Leucosoleniidae they are “alate.” Finally, the larva of Clathrinidae is a “parenchymula” (see p. 226), that of Leucosolenidae an “ amphiblastula.” The fact that it is possible to classify the Calearea Homocoela largely by means of histological characters is in accordance with the importance of the individual cell as opposed to the cell-layers generally throughout the Porifera, and is interesting in serving to emphasise the low grade of organisation of the Phylum. The organs of sponges are often unicellular (pores), or the products of the activity of a single cell (many skeletal elements); and even in the gastral layer, which approaches nearly to an epithelium, comparable with the epithelia of Metazoa, the component cells 1 Bidder, Quart. Journ. Micr. Sci. xxxii. 1891, p. 631, and Minchin, Quart. Journ. Micr. Sci. xxxiii. 1892, p. 266. * Minchin, Lankester’s Z’reatise on Zoology, p. 30. ee a —--- ~~ Pe = ae « VIII CALCAREA—HETEROCOELA 187 still seem to assert their independence, the flagella not lashing in concert, but each in its own time and direction. Sub-Class II. Heterocoela. The Heterocoela present a series of forms of successive grades of complexity, all derivable from the Ascons, from which they differ in having a discontinuous gastral layer. The simplest Heterocoela are included in the family Sycet- tidae, of which the British repre- sentative is Sycon (Fig. 79). In Sycon numerous tubular flagellated chambers are arranged radially round a central cavity, the “ para- gaster,” into which they open (Figs. ‘78, 79). The chambers, which are here often called radial tubes, are Fic. 78.—Transverse section of the body-wall Fie. 79.— Sycon coronatum. At a of Sycon carteri, showing articulate tubar a portion of the wall is removed, skeleton, gastric ostia (a.p), tufts of oxeas at exposing the paragaster and the the distal ends of the chambers (jl.ch), and gastric ostia of the chambers pores (p). (After Dendy.) opening into it. close set, leaving more or less quadrangular tubular spaces, the 1 Vosmaer and Pekelharing, Verh. Ak. Amsterdam, (2) vi. 3, 1898, p. 1. 188 PORIFERA CHAP. inhalant canals, between them; and where the walls of adjacent chambers come in contact, fusion may take place. Pores guarded by porocytes put the inhalant canals into communication with the flagellated chambers. The paragaster is lined by pinaco- cytes; choanocytes are confined to the flagellated chambers. The skeleton is partly defensive, partly supporting; one set of spicules strengthens the walls of the radial tubes and forms collectively the “ tubar skeleton.” It is characteristic of Sycettidae that the tubar skeleton is of the type known as “ articulate ”—7.e. it is formed of a number of successive rings of spicules, in- stead of consisting of a single ring of large spicules which run the whole length of the tube. The walls of the paragaster are known as the “gastral cortex” ; they contain quadriradiate spi- cules, of which the triradiate systems he tangentially in the gastral cortex, while the apical ay projects into the paragaster, and is no doubt defensive. The distal ends of the chambers Fic. 80.—Sycon setosum. Young Sponge. bristle with tufts of oxeate x 200. ad, Dermal cell; g, gastral ; cell; 0, osculum; p, pore cell; sp, Spicules, and the separate cham- monaxon ; sp; triradiate spicule. Jers: are distincuishable in sur- (After Maas.) ; 2aoe : face view. It is interesting to notice that in some species of Sycon, the gaps between the distal ends of the chambers are covered over by a delicate perforated membrane, thus leading on, as we shall see presently, to the next stage of advance’ The larva of Sycon is an amphiblastula (see p. 227). Fig. 80 is a drawing of the young sponge soon after fixation; it would pass equally well for an ideally simple Ascon or, neglecting the arrangement of the spicules, for an isolated radial tube of Sycon. Figs. 81, 82 show the same sponge, somewhat older. From them it is seen that the Sycon type is produced from the young individual, in what 1 Dendy, Quart. Journ. Micr. Sci. xxxv. 1894, p. 230. a a VII CALCAREA—HETEROCOELA 189 may be called its Ascon stage, by a process of outgrowth of tubes from its walls, followed by restriction of choanocytes to the flagellated chambers. Minute observation has shown 1 that this latter event is brought about by immigration of pinacocytes from the exterior. These cells creep through the jelly of the dermal Fic, 81.—S. setosum. Young Sponge, with one whorl of radial tubes. 0, Osculum ; p, pore ; sp,, monaxon ; spy, quadriradiate spicule. (After Maas.) layer and line the paragaster as fast as its original covering of choanocytes retreats into the newly formed chambers. With a canal system precisely similar to that of Sycon, Ute (Fig. 83) shows an advance in structure in the thickening of the dermal layers over the distal ends of the chambers. The dermal thickenings above neighbouring chambers extend laterally and 1 Maas, Zeitschr. wiss. Zool. \xvii. 1899-1900, p. 215. 190 PORIFERA CHAP. meet; and there results a sheet of dermal tissue perforated by dermal ostia, which open into the inhalant canals, and strengthened by stout spicules running longitudinally. This layer is termed a cortex ; it covers the whole sponge, compacting the radial tubes so that they form, together with the cortex, a secondary wall to the sponge, which is once more a simple sac, but with a complex wall. The cortex may be enormously developed, so as to form more than half the thickness of the do Tillis: "% Px 7 & * 3 E E oeseey Weaaes Bich E 4 be? 5 e 3 : : dp Fia. 82.—Sycon raphanus. A, Longitudinal Fic, 83.—Transverse section of the section of young decalcified Sponge at a body-wall of Ute, passing longi- stage somewhat later than that shown in tudinally through two chambers. Fig. 81. B, Transverse section of the a.p, Apopyle ; d.o, dermal ostium ; same through a whorl of tubes. d, Dermal ji.ch, flagellated chamber or radial membrane; g, gastral membrane; J/, tube ; z.c, inhalant canal ; p, pro- paragaster ; sp%, tetraradiate spicule ; 7, sopyle. (After Dendy.) radial tube. (After Maas.) wall (Fig. 84). The chambers taken together are spoken of as the chamber layer. We have already alluded to the resemblance between a young Ascon person and a radial tube of Sycon—a comparison which calls to mind the somewhat strange view of certain earlier authors, that the flagellated chambers are really the sponge individuals. If now we suppose each Ascon-like radial tube of Sycon to undergo that same process of growth by which the VIII CALCAREA——-HETEROCOELA Ig! Sycon itself was derived from the Ascon, we shall then have a sponge with a canal system of the type seen in Leucandra among British forms, but more diagrammatically shown in the foreign genus Leucilla (Fig. 85). The foregoing remarks do not pretend to give an account of the transition from Sycon to Leucilla as it occurred in phylogeny. For some in- dication of this we must await embryological research. In Leucandra the funda- mental structure is obscured by the irregularity of its canal system. It shows a further and most important difference from Leucilla in the smaller size and rounded form of its chambers. This change of form marks an advance in efficiency ; for now the flagella converge to a centre, so that Fic. 84. —Transverse section through the body-wall of Grantiopsis. d.o, Dermal ostium ; jl.ch, flagellated chamber ; 7.c, long incurrent canal traversing the thick cortex to reach the chamber layer; p, apopyle. (After Dendy.) they all act on the same drop of water, while in the tubular chamber their action is more widely — distributed and proportionately less intense (see p. 236). Above are de- scribed three main types of canal system —that of Homocoela, of Sycon, and of Leucandra and Leu- cilla. These are con- veniently termed the Fic. 85.—Transverse section through the body -wall of first, second, and Leucilla. d.o, Derma] ostium ; ez.c, Jl.ch, chamber ; %.c, inhalant canal. exhalant canal ; (Alter Dendy.) third types respec- tively, and may be briefly described as related to one another somewhat in the same way as a scape, umbel, and compound umbel among 192 PORIFERA CHAP. inflorescences. These types formed the basis of Haeckel’s famous classification. It has, however, been concluded? that the skeleton is a safer guide in taxonomy, at any rate for the smaller subdivisions; and in modern classifications genera with canal systems of the third type will be found distributed among various families; while in the Grantiidae, Ute and Leucandra stand side by side. This treatment imphes a belief that the third type of canal system has been independently and repeatedly evolved within the Calcarea—an example of a pheno- menon, homoplasy, strikingly displayed throughout the group. It is, remarkably enough, the case that all the canal systems found in the remainder of the Porifera are more or less modified forms of one or other of the second two types of canal system above described. The families Grantiidae, Heteropidae, and Amphoriscidae, all possessing a dermal cortex, are distinguished as follows :—The Grantiidae by the absence of subdermal sagittal triradiate spicules and of conspictous subgastral quadriradiates; the Heteropidae by the presence of sagittal triradiates; the Amphoriscidae by the presence of conspicuous subgastral quadri- radiates. Two families of Calcarea, possibly allied, remain for special mention—the Pharetronidae, a family rich in genera, and con- taining almost all the fossil forms of the group, and the Astro- scleridae. The Pharetronidae are with one, or perhaps two exceptions, fossil forms, having in common the arrangement of the spicules of their main skeletal framework in fibres. The family is divided into two sub-families :— I. Dialytinae—The spicules are not fused to one another; the exact mode of their union into fibres is unknown, but an organic cement may be present. Lelapia australis, a recent species, should probably be placed here as the sole living representative. Dendy has shown * that this remarkable species has a skeleton of the same fibrous character as is found in typical Dialytinae, and that the trivadiate spicules in the fibres undergo a modification into the “ tuning-fork” type (Fig. 86, C), to enable them to be compacted into smooth fibres. 1 «Die Kalkschwimme,” 1871. 2 Dendy, Joc. cit. p. 159. ° Quart. Journ. Micr. Sci. xxxvi. 1894, p. 127. VIII CALCAREA—PHARETRONIDAE 193 “ Tuning-forks,” though not exclusively confined to Pharetronids, are yet very characteristic of them. Fic. 86.—Portions of the skeleton of Petrostroma schulzei. A, Framework with en- sheathing pellicle ; B, quadriradiate spicules with laterally fused rays ; C, a ‘‘ tuning- fork.” (After Doederlein.) II. Lithoninae.——The main skeletal framework is formed of spicules fused together, and is covered by a cortex containing free spicules. The sub-family contains only one living genus and a few recently described fossil forms. Petrostroma schulzei! lives in shallow water near Japan; Plectro- ninia halli® and Bactronelia were found in Eocene beds of Victoria; Porosphaera, long known from the Chalk of England and of the Con- tinent, has recently been shown by Hinde® to be nearly allied to Plectro- ninia; finally, Plectinia* is a genus erected by Pocta for a sponge from Cenomanian beds of Bohemia. Doederlein, in 1896, expressed his opinion that fossil representatives of Lithoninae would most surely be Fia. 87.—A spicule from the skeleton discovered. The fused spicules are framework of Plectroninia, show- equiangular quadriradiates ; they are Ueda Se re united in Petrostroma by lateral fusion of the rays, in Plectroninia (Fig. 87) and Porosphaera by 1 Doederlein, Zool. Jahrb. Abth. Anat. x. 1896, p. 15, pl. ii. and iii. * Hinde, Quart. Journ. Geol. Soc. lvi. 1900, p. 50. % Hinde, Tr. R. Mier. Soc. 1904, p. 3. 4 Potta, Bull. Acad. Bohime, 1903. VOL. I O 194 PORIFERA CHaP. fusion of apposed terminal flat expansions of the rays, and in some, possibly all, genera a continuous deposit of calcium carbonate ensheaths the spicular reticulum. ‘Thus they recall the forma- tion of the skeleton on the one hand of the Lithistida and on the other of the Dictyonine Hexactinellida (see pp. 202, 211). “ Tuning-forks”” may occur in the dermal membrane. The Astroscleridae, as known at present, contain a single genus and species, apparently the most isolated in the phylum. Fic. 88.—Astrosclera wil- leyana, Lister. A, the Sponge. x abouts. p, The ostia on its distal surface. B, a portion of the skeleton show- ing four polyhedra with radiating erystal- line fibres. ©, an ostium ; the surround- ing tissue contains young stages of poly- hedra. (After Lister.) Astrosclera willeyana’ was brought back from the Loyalty Islands, and from Funafuti of the Ellice group. Its skeleton is both chemically and structurally aberrant. In other Calcarea the calcium carbonate of the skeleton is present as calcite, in Astrosclera as aragonite, and the elements are solid polyhedra, 1 J. J. Lister in Willey’s Zoological Lesults, pt. iv. 1900, p. 459. es) ee VIII CALCAREA—ASTROSCLERIDAE 195 united by their surfaces to the total exclusion of soft parts (Fig. 88). Each element consists of crystalline fibres radially disposed around a few central granules, and terminating peri- pherally in contact with the fibres of adjacent elements. Young polyhedra are to be found free in the soft parts at the surface. The chambers are exceptionally minute, especially for a calcareous sponge, comparing with those of other sponges as follows :— Astrosclera chambers, 10u xX 8u to 18ux 11yp. Smallest chambers'in Silicea, 154 x 18 to 24u x 31. Smallest chambers in Calearea, 604 x 40. In its outward form Astrosclera resembles certain Pharetronids. The minute dimensions of the ciliated chambers relegate Astro- sclera to the Micromastictora, and the fortunate fact that the calcium carbonate of its skeleton possesses the mineral characters not of calcite, but of aragonite, renders it less difficult to conceive that its relations may be rather with the non-calcareous than the calcareous sponges. BRANCH II. MICROMASTICTORA All sponges which do not possess calcareous skeletons are characterised by choanocytes, which, when compared with those of Calcarea, are conspicuous for their smaller size. The great majority (Silicispongiae) of the non-calcareous sponges either secrete siliceous skeletons or are connected with siliceous sponges by a nicely graded series of forms. The small remainder are entirely askeletal. All these non-calcareous sponges are included, under the title Micromastictora, in a natural group, opposed to the Megasmastictora as of equal value. The subdivision of the Micromastictora is a matter of some difficulty. The Hexactinellida alone are a well circumscribed group. After their separation there remains, besides the askeletal genera, an assemblage of forms, the Demospongiae, which fall into two main tribes. These betray their relationship by series of intermediate types, but a clue is wanting which shall determine decisively the direction in which the series are to be read. The askeletal genera are the c7vuwa of the systematist. It is perhaps safest, while recognising that many of them bear a likeness of 196 PORIFERA——MICROMASTICTORA CHAP. one kind or another to various Micromastictora, to retain them together in a temporary class, the Myxospongiae. CLASS I. MYXOSPONGIAE The class Myxospongiae is a purely artificial one, containing widely divergent forms, which possess a common negative char- acter, namely, the absence of a skeleton. As a result of this absence they are all encrusting in habit. One genus, Hexadella, has been regarded by its discoverer Topsent’ as an Hexactinellid. The same authority places Oscarella with the Tetractinellida ; it is more difficult to suggest the direction in which we are to seek the relations of the remaining type, Halisarca. Hexadella, from the coast of France, is a remarkable little rose- coloured or bright yellow sponge, with large sac-like flagellated chambers and a very lacunar ectosome. Oscarella is a brightly coloured sponge, with a characteristic velvety surface; it is a British genus, but by no means confined to our shores. Its canal system has been described by some authors as diplodal, by others as eurypylous. Topsent” has shown, and we can confirm his statement, that though the chambers have usually the narrow afferent and _ efferent ductules of a diplodal system, yet since each one may com- municate with two or three canals, the canal system cannot be described as diplodal. The hypophare attains a_ great development, and in it the generative products mature. The pinacocytes, like those of Plakinidae, and perhaps of Canalaria ay Dermalia Autoderm. A Bs i | Hypoderm — Prostalia basalia Fig. 93.—Scheme to show the arrangement of spicules in the Hexactinellid skeleton. Canalaria, microscleres in the walls of the excurrent canals; Dermalia Ft >} ‘ . A Be 7K that the Japanese name means “ Together unto old age and unto the same grave,” while by a slight alteration it becomes “ Lobsters in the same cell,” and remarks that the Japanese find this an amusing pun. The same Spongicola lives in pairs in Hyalonema sieboldi. Another case of Fic. 100.—Skeletal lattice apparently constant association is that of oe Ge the Hydroid stocks which inhabit Walteria. F. E. Schulze describes Stephanoscyphus mirabilis (see p. 318) in a specimen of Walteria jflemmingi; the presence of the polyp causes the sponge to grow out into little dome-shaped elevations, each of which shelters one polyp; while in W. leuckarti Ijima finds a similar association in every specimen examined. vA Vu! FOSSIL HEXACTINELLIDA 207 Fossil Hexactinellida. This group has the distinction of including among its Lyssacine members the oldest known sponge, Protospongia fenes- trata, of Cambrian age (Salter). As preserved it consists of a single layer of quadriradiate, or possibly quinqueradiate spicules, which, arranged as a _ square meshed lattice, supported the superficial layer of the sponge (Fig. 101). Whether or not the fossil represents the whole of the sponge-skeleton does not appear.’ The extraordinary Recepta- culitidae are probably early Lyssacine forms: they are cup- or saucer-shaped fossils, abundant in Silurian and above all in Devonian strata, and have been “assigned in turn to pine cones, Foramini- Fic. 101.—Part of the speciiuen of Pro- tospongia fenestrata in the Sedgwick Museum, Cambridge. Nat. size. (After Sollas. ) Fic. 102.—A portion of the outer surface of a Recepta- eulitid, Acanthoconia bar- randei, in which the ex- panded outer rays of the spicules are partially de- stroyed, revealing the four tangential rays beneath. x 3. (After Hinde.) fera, Sponges, Corals, Cystideans,’ and Tunicata. Hinde” brings forward im- portant arguments for retaining them among Hexactinellida. The only elements in the skeleton of the simpler genera, e.g. Ischadites, are structures comparable to Hexactinellid spicules. The surface of the fossil presents a series of lozenges forming a regular mosaic. Each lozenge is the expanded end of one of the rays of a spicule ; it conceals four rays in one plane, tangential to the wall of the cup- shaped fossil, while the sixth ray pro- jects vertically to the wall into the cavity of the cup. In the genus Receptaculites itself there is an inner layer of plates abutting against the inner ' Sollas, Quart. Journ. Geol. Soc. 1880, p. 362. * Quart. Journ. Geol. Soc, xl. 1884, p. 795. 208 PORIFERA CHAP. ends of the sixth rays, and at present problematic. An axial canal is present in each of the rays—the six canals meeting at the centre of the spicule. Special chinks between the spicules appear to have provided a passage for the water current. The beautiful Ventriculites, so common in the Chalk and present in the Cambridge Greensand, are historically interesting, for the fact that they are fossil Hexactinellida of which the general and skeletal characters were very minutely described by Toulmin Smith long before recent representatives of the group were known. In common with a num- they are distinguished by the per- foration of the nodes, a character due to the fact that the siliceous investment which unites the spicules together stops short before reaching the centre of each spicule, and bridges across the rays so as to form a_ skeleton octahedron. This character is rare in recent Fig. 103.—A node of the skeleton of Hexactinellids, but, as first poimted ee nine ite out by Carter, it is presented by one or two forms, of which Aw/o- cystis gray Bwk is best known. The majority of the fossil Hexactinellida belong to the Dictyonine section, a fact attribut- able to the greater coherence of their skeleton. The “ Dictyonina ” are to be reckoned among the rock-builders of Jurassic and Cretaceous times. The Octactinellida and Heteractinellida are two classes created by Hinde’ to contain certain little-known Devonian and Carboniferous sponges, possessing in the one case 8-rayed spicules, of which 6 rays lie in one plane and 2 are perpendicular to this plane; in the other case, spicules with a number of rays varying from 6 to 30. Bearing in mind the manner in which octactine spicules are known to arise in recent Hexactinellida (p. 200), it is clearly possible to derive these 8-rayed spicules from hexactines by some similar method; while the typical ‘ “Monograph British Fossil Sponges,” Palaeont. Soc. xl. and xli. 1887 and 188 CO ber of fossil Dictyonine species’ VIII DEMOSPONGIAE 209 spicule of the Heteractinellida is a euaster. Hence we may refer the Octactinellid fossils to the class Hexactinellida, and the Heter- actinellid forms either to the Monaxonida or Tetractinellida. CLASS III. DEMOSPONGIAE Silicispongiae in which triaxonid spicules are absent. This class has attained the highest level of organisation known among Porifera; the most efficient current-producing apparatus is met with here, so, too, are protective coverings, stout coherent skeletons, and the highest degree of histological differentiation found in the phylun. Correspondingly it is the most successful group, the majority of existing sponges coming within its boundaries. A few genera and species are exceedingly specialised, for example, Disyringa dissimilis (p. 215). These, however, contribute only a very small contingent to the Demosponge population, those species which are really prolific and abundant being, as we should expect, the less exaggerated types. Canal System.—With a few exceptions the representatives of the Demospongiae may be said to have taken up the evolution of the canal system at the stage where it was left in Leweandra aspera—a stage which the ancestral Demosponges must have reached quite independently of the Calcarea. These commoner members are thus already gifted with the advantages pertaining to a spherical form of ciliated chamber, and so, too, is the Rhagon (Fig. 105), an immature stage noteworthy as the simplest form of Demosponge, and thus the starting-point for the higher types of canal system. The exceptions above alluded to are not with- out interest: they are the Dendroceratina, of doubtful affinities, (p. 220), which possess small tubular Syconate chambers. They may be regarded either as of independent origin from other Demospongiae, thus making the group polyphyletic, or more simply as representing the ancestral condition, and in this case we must look on the possession of spherical chambers by the Rhagon as a secondary feature. Occupying as it does the important position above indicated, the Rhagon merits a brief description. It is a small discoid or hemispherical body attached by a flat base. It contains a central paragaster, with a single osculum at the free end. Into the paragaster open directly a VOL. I P 21.0 PORIFERA CHAP. few spherical flagellated chambers, which lie in the lateral walls of the body. The basal wall of the paragaster, the parts of its lateral walls between the openings of neighbouring chambers, and the entire outer surface of the body are covered with pina- cocytes. It is convenient to call the basal part of the sponge from which chambers are absent the hypophare, the upper chamber-bearing part the spongophare. In some of the deeper dermal cells spicules may be already present. In the Rhagon, then, the canal system is of the second type, but all the adult Demosponges have advanced to the third type, and the further evolution in this system is in the direction of improving the mode of communication of the chambers with the canal system. The Fic. 104.—Diagram of (A) eurypylous and (B) aphodal canal systems. a, Apopyle; a’, aphodus ; #, excurrent canal; J, incurrent canal; p, prosopyle ; p’, short pro- sodus. (After Sollas.) ? changes involved go hand in hand with increasing bulk of the dermal layer. A glance at the accompanying figures will show at once the connexion between the phenomena. The increase in the dermal layer (1) greatly reduces the extent of the lumen of the excurrent canals; and (2) results in the intervention of a narrow tube or aphodus between the mouth of each chamber and the excurrent canal. The chamber system is then converted from an “eurypylous” to an “aphodal” type. When the incurrent canal also opens into the chamber by way of narrow tubes, one proper to each chamber and termed “ prosodus,” the canal system is of the “ diplodal” type. Cortex.—aAll the stages in the formation of a cortex are to be seen among the adult members of the group. Certain species (e.g. Plakina monolopha, ¥.K.S.) are destitute even of an ectosome, VIII DEMOSPONGIAE PAM others have a simple dermal membrane (//alichondria panicea, Tetilla pedifera) and various others are provided with a cortex, either of simple structure or showing elaboration in one or more particulars. Thus a protective armature of special spicules may be present in the cortex, eg. in Geodia, or to a less extent in Tethya, or there may be an abundance of contractile elements, and these may be arranged in very definite ways, forming valve- like apparatus that will respond to stimuli. Everywhere among sponges the goal of the skeleton appears to have been coherence. We have seen how in Calcarea and in Hexactinellida this has been attained by the secretion around the separate elements of a continuous mineral sheath, calcareous in the one case and siliceous in the other. Here we had an excellent instance of the attainment of one end by similar means in two different groups, after their separation from the common stock, and therefore independently. In Demospongiae, on the other hand, the same end—coherence—has been secured by two new methods, each distinct from the former: first the spicules may be united in strands by an organic deposit, spongin ; secondly, the spicules may assume irregular shapes and interlock closely with one another, forming dense and stout skeletons. The latter method is that characteristic of the Lithistid Tetractinellida. Classification.—It is not of great moment which scheme of classification We maintain, seeing that all hitherto proposed are confessedly more or less artificial, and sufficient data for framing a natural one are not yet forthcoming. For convenience, we accept three subdivisions and define them thus :— I. TerRacTINELLIDA.—Demospongiae possessing tetraxon or triaene spicules or Lithistid desmas. II. Monaxontpa.—Demospongiae possessing monaxon but~-not tetraxon spicules. III. Cerarosa.—Demospongiae in which the main skeleton is formed of fibres of spongin. ‘The fibres may have a core of sand-grains or of foreign spicules, but not of spicules proper to the sponge. But at the same time we admit that some of the Ceratosa are probably descended from some of the families of Monaxonida, so that we should perhaps be justified in separating these families of Monaxonida from the rest, and associating them with the allied families of Ceratosa—a method of classification due to DIVA PORIFERA CHAP. Vosmaer. Again, some Monaxonida approximate to Tetractinel- lida, and we might, with Vosmaer, unite them under the title Spiculispongiae. This proceeding, though it has the advantage of being at least an attempt to secure a natural classification, involves too much assumption when carried out in detail to be wholly satisfactory. Sub-Class I. Tetractinellida.' Tetractinellida appear to flourish best in moderate depths from 50 to 200 fathoms, but they are found to be fairly abundant also in shallower water right up to the coast line, and in deep water up to and beyond the 1000 fathom line. Occasionally they he free on the bottom, but are far more commonly attached; fixation may be direct or by means of rooting spicules; the occurrence of a stalk is rare. There is great variety in the root tuft, which may be a long loose wisp of grapnel-headed spicules, as in many species of Zetilla, or a massive tangle, as in Cinachyra barbata ; in these cases the sponge is merely anchored, so that it rests at the level of the surface of the ooze; in other cases, eg. Thenea wyvillei, the root tuft consists of a number of pillars of spicules which raise the sponge above the level of the ooze, into which they descend and there become continuous with a large dense and confused mass of spicules. The parachute-like base of Tetilla casula invites comparison with the “ Crinorhiza” forms of some Monaxonids (p. 216). Two Orders are distinguished thus :— I. Cuortstipa.—Tetractinellida with quadriradiate spicules, which are never articulated together into a rigid network. Il. Lirurstipa.—Tetractinellida with branching scleres (desmas), which may or may not be modified tetrad spicules, articulated together to form a rigid network. Triaene spicules may or may not be present in addition. Order I. Choristida. Plakina monolopha, from the Adriatic and Mediterranean, furnishes a connecting link between the Rhagon stage and other Tetractinellida. The choanosome is simply folded; there is no distinet ectosome ; the chambers are eurypylous. The skeleton 1 Sollas, Challenger Monograph, xxv. 1888. Vuil TETRACTINELLIDA 213 consists of microcalthrops and their derivatives. The hypophare is well developed. Plakina thus shows a certain amount of resemblance to Oscarella (p. 196), with which it shares the very remarkable possession of flagellated pinacocytes. One of the species of Vetilla, T. pedifera, continues the series. The folds of its choanosome are more complicated than in P. monolopha, and their outer ends are bridged together by a thin layer of ectosome (cf. species of Sycon among Calcarea); the chambers are still eurypylous. The skeleton reaches a high level: it includes oxeas and triaenes radiately disposed and microscleres (sigmata) scattered throughout the dermal layer. The British Poecillastra com- pressa from the north of Scot- land and Orkney and Shetland is at about the same stage of C development, being without Fic. 105.— Diagrammatic vertical sections cortex and having eurypylous ee B, Plakina: C, Tetilia chambers, but it is not so good an example, as the folds of its choanosome are confused. From 7. pedifera we pass to the other species of Tetilla and all the higher genera of Choristida; these possess a cortex not of homologous origin in the various cases, but probably to Fic. 106.—A, Craniella type; B, Stellettid type. ch, Chone ; co, collenchyma; d.0, dermal ostia ; 7b, fibrous tissue ; 7.c, intercortical cavity ; sd, subdermal cavity ; sp, sphincter. (After Sollas.) be classified under one of two heads, typified by Stelletta and Craniella respectively (Fig. 106). 214 PORIFERA CHAP. In the Stellettids the cortex arises by the centrifugal growth of a dermal membrane such as that of TZetilla pedifera; in Craniella directly from the dermal tissue of the distal ends of the choanosomal folds. In both cases the end result, after completion of cell differentia- tion, is a cortex either fibrous throughout or collenchymatous in its outer portion and fibrous in the deeper layers. In the Stellettid type the centrifugal growth of the dermal membrane involves — the addition of secondary distal portions to the ends of the inhalant passages. These are the intercortical cavities or canals. Their most specialised form is the “chone.” A.-chone is @ passage through the cortex opening to the exterior by one or more ostia, and communicating with the deeper parts of the inhalant system by a single aperture provided with a sphincter (Fig. 106, B). In the Craniella type the inter- cortical cavities are parts of the primary inhalant system. They communicate with its deeper parts by sphinctrate apertures. Without Fic. 107.— Disyringa dissimilis. any knowledge of the development Se ae Meera eg ce one would certainly have supposed Transverse sections at the levels that the subdermal cavity, pore-sieve indicated to show subdivision of and sphinctrate passages of Craniella the lumina of the excurrent and incurrent tubes; ¢.¢, excurrent represented a number of chones, of Re | eeasnee ae ® °S which the outer portions had_ be- come fused (Fig. 106, A). In both Craniella and Stelletta the chamber system is aphodal, and these genera may fairly be taken as representatives of the average level reached by Tetractinellida. The skeleton is of the radiate type: the type which prevails in the Choristida, but which has an erratic distribution, appearing in some genera of VIII TETRACTINELLIDA 215 each family but not in others. The genus Pachymatisma, of which we have the species P. johnstonia and P. normani in these islands, exemplifies this; it belongs to the highly differentiated family Geodiidae, possesses an elaborate cortex with chones, but its main skeleton is non-radiate. Disyringa dissimilis is remarkable for the perfection of its symmetry, and for the absence of that multiplication of parts which is so common among sponges. It possesses a single inhalant tube and a single osculum (Fig. 107). Until quite recently it stood alone in the restriction of its inhalant apertures to a single area. Kirkpatrick, however, has now described a sponge—NSpongocardium gilchristi \—from Cape Colony, in which the dermal ostia are concentrated in one sieve-lke patch at the opposite pole to the single osculum. Disyringa is still without companions in the possession of an inhalant tube. The concentration of ostia into sieve areas occurs again in Cinachyra, each sponge possessing in this case several inhalant areas with or without scattered ostia also. Order II. Lithistida. The characteristic spicule of Lithistida—the desma—may be a modified calthrop (tetracrepid desma), or it may be produced by the growth of silica over a uniaxial spicule (rhabdocrepid desma) (Fig. 110, q), or it may be of the polyaxon type. It is probable that the group is polyphyletic, and that some of its members should remain associated with Tetractinellida, while others should be removed to Monaxonida. Forms with tetracrepid desmas, and those forms with rhabdocrepid desmas which possess triaenes, have Tetractinellid affinities, while forms possessing rhabdocrepid desmas but lacking triaenes, and again those in which the desmas are polyaxon, are probably descendants of Monaxonida. Owing to the consistency of the skeleton Lithistida are frequently found as fossils. The commonest known example is Siphonia. As in the case of so many other fossil sponges the skeleton is often replaced by carbonate of lime, a fact which 1 Marine Investigations in South Africa, i. 1902, p. 224. 2 Cf. Sollas, Eneyclopedia Britannica, 1887, art. ‘‘ Sponges,” and Schrammen, Mitth. Mus. Hildesheim, 14, 1901. % Sollas, Quart. Jowrn. Geol. Soc. xxxiii. 1877, p. 790. 216 PORIFERA CHAP. misled some of the earlier investigators but was established by the researches of Sollas and Zittel. Sub-Class II. Monaxonida.' The Monaxonida inhabit for the most part shallow water, but they also extend through deep water into the abysses, thirteen species having been dredged from depths of over 2000 fathoms by the “Challenger” Expedition alone. In some cases, e.g. Cladorhiza, Chondrocladia, all the species of a genus may live in deep water, while in others the genus, or in others, again, the species, may have a wide bathymetrical range. Thus Azxinella spp. occur in shallow water and in various depths down to 2385 fathoms, Aainella erecta ranges from 90 to 1600 fathoms, Stylocordyla stipitata from 7 to 1600,and so on. The symmetry of the deep-water forms contrasts strikingly with the more irregular shape of their shallow-water allies. The shallow-water species are almost always directly attached, some few are stalked ; those from deep water have either a long stalk or some special device to save them from sinking in the soft ooze or mud. Thus the deep-sea genus Zvrichostemma has the form of a low inverted cone, round the base of which a long marginal fringe of spicules projects, continuing the direction of the somal spicules, and so forming a supporting rim. The same form has been independently evolved in Halicnemia patera, and an approach to it in Xenospongia patelliformis. A similar and more striking case of homoplasy is afforded by the Crinorhiza form, which has been attained in certain species of the deep-sea genera Chondro- cladia, Axoniderma, and Cladorhiza; here the sub-globular body is supported by a vertical axis or root, and by a whorl of stout processes radiating outwards and downwards from it, and formed of spicular bundles together with some soft tissue. There is recognisable in the order Monaxonida a cleft between one set of genera, typically corticate, and suggesting by their structure a relationship, whether of descent or parentage, with the Tetractinellida, and a second set typically non-corticate : these latter are the Halichondrina, the former are the Spintharophora. 1 Ridley and Dendy, Challenger Monograph, lix. 1887. 2 Ibid. p. 262; cf. also p. 197. VIII MONAXONIDA 217 Order I. Halichondrina. We have already seen typical examples of the Halichondrina in Halichondria panicea and Ephydatia fluviatilis. Within the Halichondrina the development of spongin reaches its maximum among spiculiferous sponges, and accordingly the Ceratosa take their multiple origin here (p. 220). Among Halichondrina spongin co-operates with spicules to form a skeleton in various ways, but always so as to leave some spicules bare or free in the flesh. It may bind the spicules end to end in delicate networks (as in Reniera or Gellius), or into strands, sometimes reaching a con- siderable thickness (as in Chalina and others). In a few cases there appears to be a kind of division of labour between the spicules and spongin, the latter forming the bulk of the fibre, ae. fulfilling the functions of support, while the spicules merely beset its surface as defensive organs, rendering the sponge unfit for food. Fibres formed on this pattern are called plumose, and are typical of Axinellidae. The distinctive fibre of the Ectyoninae is as it were a combination of the Axinellid and Chalinine types: a horny fibre both cored with spicules and beset with them. Spicules besetting the surface of a fibre are termed “echinating.” Whenever its origin has been investigated, spongin has proved to be the product of secretion of cells; in the great majority of cases it is poured out at the surface of the cell, and Evans showed,' at any rate in one species of Spongilla, that the spongin fibres are continuous with a delicate cuticle at the surface of the sponge. In Reniera spp. occurs a curious case of formation of spongin as an intracellular secretion. A number of spherical cells each secrete within themselves a short length of fibre ; they then place themselves in rows, so orientated that their contained rods lie end to end in one line. The rods then fuse and make up continuous threads; the cells diminish in breadth, ultimately leaving the fibre free.” Order II. Spintharophora. These corticate forms are further characterised by the arrange- ment of their megascleres, which is usually, like that of most 1 Quart. J. Mier. Sci. xli. 1901, p. 477. 2 Loisel, J. de l’ Anat. et Phys. xxxiv. 1898, p. 1. Mo) PORIFERA CHAP. Tetractinellida, radial, or approximating to radial. The micro- scleres are, when present, some form of aster. The cortex resembles that of Tetractinellida, and v. Lendenfeld has described chones in Tethya lyneurium." The existence of the above points of resemblance between Spintharophora and Tetractinellida suggests a relationship between the two groups as its cause. In judging this possibility the follow- ing reflections occur to us. A cortex exists in various independent branches of Tetractinellida. It has in all probability had a different phylogenetic history in each—why not then in these Monaxonida also? Within single genera of Tetractinellida some species are corticate, others not, witness Zeti/la. The value of a cortex for purposes of classification may easily be overestimated. If we are to uphold the relationship between these two groups, we must base our argument on the conjunction of similar characters in each. The genus Proteleia” is interesting for its slender grapnel- like spicules, which project beyond the radially disposed cortical spicules, and simulate true anatriaenes of minute proportions. That they are not anatriaenes is shown by the absence of an axial thread in their cladi. It is not surprising that a form of spicule of such obvious utility as the anatriaene should arise more than once. Of exceptional interest, on account of their boring habit, are the Clionidae. How the process of boring is effected is not known; the presence of an acid in the tissues was suspected, but has been searched for in vain. The pieces of hard substance removed by the activity of the sponge take their exit through the osculum and have a fixed shape ® (Fig. 108). As borers into oyster shells, Clonidae may be reckoned as pests of practical importance, and in some coasts they even devastate the rocks, penetrating to a depth of some feet, and causing them to crumble away." Sponges, however, as agents in altering the face of the earth do not figure as destroyers merely. On the contrary, it has 1 R. v. Lendenfeld, Acta Ac. German. lxix. 1896, p. 22. 2 Challenger Report, lix. 1887, p. 214. 3 Topsent, Zoologie Descriptive, i. ; also Cotte, C. R. Soc. Biol. Paris, 1902, pp. 638-639. 4 Topsent, Arch. Zool. Exp. (3) viii. 1900, p. 36. VIII MONAXONIDA 219 been calculated’ that sponge skeletons may give rise with considerable rapidity to beds of flint nodules; in fact, it appears that a period so short as fifty years is sufficient for the formation of a bed of flints out of the skeletons of sponges alone. Suberites domuncula is well known for its constant symbiosis with the Hermit crab. The young sponge settles on a Whelk or other shell inhabited by a Pagurus, and gradually envelops it, becoming very massive, and completely concealing the shell, without however closing its mouth. The aperture of this always remains open to the exterior, however great the growth of the sponge, a tubular passage being left in front of it, which Fic. 108.—A, calcareous corpuscle detached by Cliona ; B, view of the galleries excavated by the Sponge. (After Topsent. ) continues the lumen of the shell and maintains its spiral direction. When the crab has grown too big for the shell, it merely advances a little down this passage. The shell is never absorbed, as was once supposed.” The crab, besides being provided with a continually growing house, and being thus spared the ereat dangers attending a shift of lodgings, benefits continually by the concealment and protection afforded by the massive sponge; the latter in return is conveyed to new places by the crab. Ficulina jficus is sometimes, like S. domuncula, found in symbiosis with Pagurus, but the constancy of the association is wanting in this case. The sponge has several metamps, one of which, from its fig-like shape, gives it its name. 1 Sollas, Challenger Monograph, xxv. pt. lxili. 1888, p. Ixxxix. 2 Topsent, Arch. Zool. Exp. (3) viii. 1900, p. 226. For an account of certain very remarkable structures termed diaphragms in Cliona mucronata and C. ensifera, see Sollas, 4nn. Mag. Nat. Hist. (5) i. 1878, p. 54. 220 PORIFERA CHAP. Sub-Class III. Ceratosa. The Ceratosa are an assemblage of ultimate twigs shorn from the branches of the Monaxonid tree. They are therefore related forms, but many of them are more closely connected with their Monaxonid relatives than with their associates in their own sub- class, The genera Aulena and Phoriospongia, placed by v. Lendenfeld among Ceratosa, by Minchin among Monaxonida, show each in its own way how close is the link between these two sub-classes. Aulena possesses in its deeper parts a skeleton of areniferous spongin fibres, in fact a typical Ceratose skeleton; but this is continuous with a skeleton in the more superficial parts, which is composed of spongin fibres echinated by spicules proper to the sponge, and precisely comparable to the ectyonine fibres of some Monaxonida. Phoriospongia, as far as its main skeleton is concerned, is a typical Ceratose sponge, with fibres of the areniferous type, but it possesses sigmata free in the flesh. The sub-class is confined to shallow water, no horny sponge having been dredged from depths greater than 410 fathoms.’ The greatest number occur at depths between 10 and 26 fathoms. In the majority of the Ceratosa the skeletal fibres are homo- geneous, formed of concentric lamellae of spongin, deposited by a sheath of spongoblasts around a filiform axis. In others, however, the axis attains a considerable diameter, so as to form a kind of pith to the fibre, which is then distinguished as heterogeneous. In one or two cases some of the spongo- blasts of a heterogeneous fibre are included in the fibre between the spongin lamellae. Janthella is the best-known example in which this occurs. Ceratosa are divided into Dictyoceratina and Dendroceratina, distinguished, as their names express, by the nature of the skeleton—net-like, with many anastomoses, in the one; tree-like, without anastomoses between its branches, in the other. The Dictyoceratina comprise by far the larger number of Ceratosa. They fall into two main families, the Spongidae and Spongelidae, both represented in British waters. The Spongidae 1 R. von Lendenfeld, Monograph of Horny Sponges, 1889, p. 831. VIII CERATOSA—KEY TO BRITISH GENERA 221 are characterised by a granular ground substance and aphodal chamber system; the Spongelidae by a clear ground substance and sac-like eurypylous chambers. The bath sponge, Huspongia officinalis, belongs to the Spongidae. The finest varieties come from the Adriatic, the coarser ones from the Dalmatian and North African coasts of the Mediterranean, from the Grecian Archipelago, from the West Indies, and from Australian seas. The softer species of the genus Hippospongia also form a source of somewhat inferior bath sponges. Among Dendroceratina, Darwinella is unique and tempts to speculation, in that it possesses isolated spongin elements, resemb- ling in their forms triaxon spicules. Key to British Genera of Sponges. Skeleton calcareous. ; é : : : L. Skeleton siliceous : : : : 6 Skeleton horny, or without free spicules ; : $853 Skeleton absent : A : ; : . 55 9 / Gastral layer continuous ‘ i 5S * \ Gastral lay er discontinuous, peut to demas : ; 4 3 f Equiangular triradiate systems present . : . Clathrina ' | Triradiate systems all alate. : . Leucosolenia 4 Chambers tubular, radially arranged —. : : ita * | Chambers spherical, irregularly scattered ; . Leucandra 5 ( Tufts of oxeate spicules at the ends of the chambers : Sycon * \Oxeate spicules lying longitudinally in the cortex : Ute All the spicules hexradiate or eas easily derived from hexradiate 6 type ; : : . ‘ 7 * | Some of the spicules calthrops or triaenes : ; yes Megascleres uniaxial. ; : : ee - {Amphidises present. : : : “4 eae) i. 32 \ Amphidiscs absent , : : ; erg Rooting spicules a well-defined wisp; four apertures lead into the 8 gastric cavity é : : . Hyalonema thomsont " | Rooting tuft diffuse ; sponge oval; osculum single Pheronema carpentert ( Sponge tubular, dermal and gastral pinuli absent Hwuplectella suberea 9. ~ Sponge a widely open cup ; dermal and gastral pinuli present | Asconema setubalense [/Heteactine spicule, a calthrop or triaene with short rhabdome ; 10. - microsclere a spined microxea : . Dercitus bucklandi | Triaenes with fully developed rhabdome : : eh 222 PORIFERA CHAP. t i se. x F1s. 109.—Microscleres of Demospongiae. a, b, Sigmaspires viewed in different directions ; c,d, bipocilli viewed in different directions ; e,toxaspire ; 7,7’, spiraster ; 7, sanidaster ; h, amphiaster ; 7, sigma; 7, diancistra; k, isochela; Jd, m, anisochelae viewed in different directions ; 7, cladotyle ; 0, toxa; p, forceps ; gy, oxyaster ; 7, spheraster ; s, oxyaster with 6 actines ; ¢, another with 4 actines ; wu, another with rays reduced to two (centrotylote microxea) ; v, tylote microrhabdus; w, trichodragmata ; r, oxeate microrhabdus or microxea. ‘ 7 { Microscleres sigmata . s : . Craniella cranium \Sigmata absent, asters present . - . 5 ~ ee i Microscleres include spirasters . : Poecillastra compressa 12. ~ Microscleres include sterrasters . : : : one es ibe icroscleres include euasters: spirasters and sterrasters absent . 13 Two kinds of euaster present. 5 Stelletta 13. - Microscleres include a euaster and a sanidaster or r aniphiaster i Stryphnus ponderosus 14. { Microscleres include microrhabdi : Pachymatisma johnstonia \ Microseleres include many-rayed euasters : Cydonium millert 15 {Some of the microscleres asters. : : : AG “| Microscleres absent, or not asters : ; . a.) alae ib Skeleton radiate ; asters of more than one kind ; Tethya 16. - Sponge encrusting ; asters of one kind only : . Hymedesmia \aieteton fibrous ; : : : . Axinella spp. | Megascleres all diactinal ; chelae present : . Desmacidon 17. ~ Megascleres all diactinal ; chelae absent : 5 - 18 \ Some or all of the megascleres monactinal : . ee VIII KEY TO BRITISH GENERA 223 18 {Habitat fresh water. : : ; ‘ . 86 * | Habitat marine ; : : : 5 wy 22 ‘Megascleres include cladotyles . ; 4 Acarnus Megascleres include dumb-bell or sausage- shaped spicules forming the main reticulum. 3 ; : : incanin 19, | Microscleres include bipocilli. : us 20 "| Microscleres include diancistra . : : ice ntha Megascleres include forceps ‘ ; Forcepia Skeleton formed of isolated monactines vertically placed . Hymeraphia None of the above peculiarities present : ; sped 20 {Skeleton fibre not echinated . ; ; : Tophon ~~" \Skeleton fibre echinated : : : . Pocillon 21 {Skeleton with echinating spicules : : : . 28 ~"* (Skeleton without echinating spicules. d : | 30 99 J Spongin abundant : : : : “28 “~~ | Spongin scanty : ; : : : oS 93 {Fibre not echinated —. , : : ‘ 24 “*" | Fibre echinated ; : : Dh plodemia 24 {Fibre with a single axial series of spicules d : Chalina ~~ | Fibres with numerous spicules arranged polyserially —. Pachychalina Microscleres absent : , ; : . 26 25. - Microscleres sigmata and) = : toxa . : : ; peel Microscleres sigmata or f 26 {Skeleton confused : ; : : Halichondria ~~" | Skeleton reticulate : : : : : Reniera ( Rind and fistulous appendages present ; microscleres sigmata Oceanapia 27. - No rind; skeleton reticulate ; microscleres sigmata and | eee eae ae : ; ; ze e No rind ; skeleton reticulate ; microscleres sigmata or y Skeleton confused or formed of bundles of spicules with echinating spined styles : Me) 28. \ Skeleton fibrous or reticulate, or ane? of ener galhmasns . 45 |Steeton formed of a dense deme axis, and columns radiating from it to the surface ‘ , : : ; ; | oe, (Spicules of the ectosome styles . ; A : Pytheas 29. « Spicules of the ectosome oxeas or absent . Clathrissa Main skeleton confused. Special ectosomal skeleton absent Spanioplon east of the choanosome not differing from those of the 30 ectosome . - : . 5 i! Megascleres of the choangsome differing from those of the ecto- some : : : H r : . 32 1. {Chelae absent . : ; ; , ; Seo \ Chelae present ; ‘ ‘ : : . 44 { Trichodragmata present ‘ ; : . Tedania Be ee \ Trichodragmata absent ; : : . 42 to bo a PORIFERA CHAP. Fic. 110.—Megascleres. a-/ and q-s, Modifications of monaxon type. 4, Stron- gyle; 0b, tylote; c, oxea; d, tylotoxea ; e, tylostyle ; J, style; g, spined tylo- style ; h, sagittal triod (a triaxon form derived from monaxon) ; j,oxytylote ; &, anatriaene ; /, protriaene ; m, sterraster (polyaxon) ; n, radial section through the outer part of m, show- ing two actines soldered together by intervening silica; 0, desma of an Anomocladine —_Lithistid (polyaxon); g, crepidial strongyle, basis of rhab- docrepid Lithistid desma ; 7, young form of rhab- docrepid desma, showing crepidial strongyle coated with successive layers of silica; s, rhabdocrepid desma. Skeleton reticulate or fibrous. : ; : Bei! 33 Skeleton radiate or diffuse : ; : 2 sew | Skeleton with radiating fibres forming a renee with others crossing them at right sels I 5 : : Oui No microscleres : : : : : oho + Microscleres sigmata and : ; ; 34. : ioxe with or without trichodragmata Microscleres sigmata or J Desmacella 35, {Sponge fan- or funnel-shaped . 5 ; : . 36 ov . . | Sponge not fan- or funnel-shaped : : Hymeniacidon 36 { Megascleres slender and twisted 5 save . Phakellia oD. . . | Megascleres somewhat stout, not twisted ; ; Tragosia 37 {Sigmata present, skeleton diffuse : ‘ : Biemma ol. 4 : \Sigmata absent : : : : : - 38 38 (Skeleton more or less radiate. : ; : sso ~* \Skeleton diffuse ; sponge boring : : : Cliona 39 fSponge discoid with marginal fringe _. . Halicnemia * (Sponge massive or stipitate without marginal fringe : 1 AO I I Sponge body prolonged into mammiform projections . Polymastia Aopen epee ee s : eee ~" \Sponge body without mammiform projections . : . 44 ( No microscleres. Megascleres tylostyles with or without styles 41. Suberites Viiteeneal ores centrotylote. Megascleres styles or tylostyles — Ficulina 49 { Choanosomal megascleres smooth : . = 743 ~ \ Choanosomal megascleres spined ; : . _ Dendoryx 8 I 43 { Microscleres chelae and sigmata of about the same size .Lissodendoryx | Chelae, if present, smaller than the sigmata , ; Yvesia VIII REY TOO BRITISH “GENERA Zeb 44 { Isochelae : : . Esperiopsis ‘ \Anisochelae. : : Esperella 45 { Fibres or columns plumose é : . . 46 * | Fibres or columns ectyonine —. ; ; es 7 46 { Microscleres toxa , ; 4 Casponan * \Microscleres absent ; : Avinella 47 {Skeleton reticulate : : . 48 ‘" \Skeleton not reticulate , . 49 48 { Microscleres present. Spicules of the fibre core spined . Myzxilla * | Microscleres absent. Spicules of the fibre core smooth . Lissomyxilla Main skeleton formed of plume-like columns. : ce, 49. - Main skeleton formed of horny fibres (ectyonine). Special dermal skeleton wanting . : : ; ‘ Clathria 50 { Dermal skeleton contains styles only. : . Microciona * | Dermal skeleton contains diactine spicules with or without styli 51 51 { Main skeleton columns with a core of smooth oxeas Plumohalichondria ‘| Main skeleton columns with a core of spined styles . Stylostichon Central axis contains much spongin. Echinating spined styl 52 present. : ‘ Raspailia ~ | Central axis with little or no sponein: ‘Spined styles absent. Pillars radiating from the axis support dermal skeleton. Ciocalypta ( Ground substance between chambers clear; chambers pear-shaped or 53. - oval; eurypylous. ; Spongelia | Ground substance granular. Chambers spherical with aphodi . 54 BA { Fibres not pithed ; sponge fan-shaped . : : Leiosella ’ \ Fibres pithed ; sponge massive : ; ‘ Aplysina BS f Chambers long, tubular, eeehed : . Halisarca “* (Chambers not much longer than broad ; not branolied , Oscarella 5G fAmphidises present —. : ; . Ephydatia * | Amphidises absent ; : : : . Spongilla VOL. I Q COAP TERY 1X PORIFERA (CONTI TUED) : REPRODUCTION, SEXUAL AND ASEXUAL— PHYSIOLOGY—DISTRIBUTION—FLINTS THE reproductive processes of Sponges are of such great import- ance in leading us to a true conception of the nature of a sponge that we propose to treat them here in a special section. Both sexual and asexual methods are common; the multiplication of oscula we do not regard as an act of reproduction (p. 174). Fria. 111.—A, amphiblastula larva of Sycon raphanus ; B, later stage, showing invagina- tion of the flagellated cells. c.s, Segmentation cavity ; ec, ectoderm ; en, endoderm. (After F. E. Schulze, from Balfour.) A cursory glance at a collection of sponge larvae from different groups would suggest the conclusion that they are divisible into two wholly distinct types. One of these is the amphiblastula, and the other the parenchymula, This was the conclusion accepted by zoologists not long ago. We are indebted to Delage, Maas, and Minchin for dispelling it, and showing that 226 CHAP. IX DEVELOPMENT 227 these types are but the extreme terms of a continuous series of forms which have all the same essential constitution and undergo the same metamorphosis. The amphiblastula of Sycon raphanus (Fig. 111) consists of an anterior half, formed of slender flagellated cells, and a posterior half, of which the cells are large, non-flagellate, and rounded. These two kinds of cell are arranged around a small internal vavity which is largely filled up with amoebocytes. The flagellated cells are invaginated into the dome of rounded cells during metamorphosis, in fact, become the choanocytes or gastral cells; the rounded cells, on the other hand, become the dermal cells—an astonishing fact to any one acquainted only with Metazoan larvae. A typical parenchymula is that of Clathrina blanca (Fig. 112). When hatched it consists of a wall surround- ing a large central cavity and built up of flagellated cells interrupted at the hinder pole by two cells (p.g.c)—the mother-cells of archaeocytes. Before the metamorphosis, certain of the flagel- lated cells leave the wall and sink into the central cavity, and undergoing Fic. 112.—Median longitudinal certain changes establish an inner mass cH Pens ieee eth hes larva of Clathrina blanca. of future dermal cells. By subsequent —= p.g.c, Posterior granular metamorphosis the remaining flagellated ae ee cells become internal, not this time by invagination, but by the included dermal cells breaking through the wall of the larva, and forming themselves into a layer at the outside. In the larva of C. blanca, after a period of free-swimming existence, the same three elements are thus recognisable as in that of Sycon at the time of hatching; in the newly hatched larva of C. blanca, however, one set of elements, the dermal cells, are not distinguishable. The difference, then, between the two newly hatched larvae is due to the earlier cell differentiation of the Sycon larva.’ Now consider the larva of Leucosolenia. It is hatched as a Sift ies WO Ss ” SEY \, Wana ya by oy 1 Cf. Minchin in E. Ray Lankester’s Treatise, p. 77. 228 PORIFERA CHAP. - completely flagellated larva; its archaeocytes are internal (as In Sycon); future dermal cells, recognisable as such, are absent. They arise, as in C. blanea, by transformation of flagellated cells ; but (1) this process is confined to the posterior pole, and (2) the internal cavity 1s small and filled up with archaeocytes. Con- sequently the cells which have lost their flagella and become converted into dermal cells cannot sink in as in C. blanca: they accumulate at the hinder pole, and thus arises a larva half flagellated, half not; in fact, an amphiblastula. Or, briefly, in Leucosolenia the larva at hatching is a parenchymula, and when ready to fix is an amphiblastula; and, again, the differ- ence between the newly hatched larva and that of Sycon is due to the earlier occurrence of cell differentiation in the latter. What completer transitional series could be desired ? Turning to the Micromastictora, the developinental history already sketched is fairly typical (p. 172). The differences between Mega- and Micro-mastictoran larvae are referable mainly to the fact that the dermal cells in the latter become at once differentiated among themselves to form the main types of. dermal cell of the adult.’ The metamorphosis is comparable to that of C. blanca. Among Tetractinellida and Hexactinellida sexually produced larvae have not been certainly identified. Asexual reproduction takes place according to one of three types, which may be alluded to as (1) “ budding,” (2) “ gemmula- tion,” (3) formation of “ asexual larvae.” By budding (Fig. 113) is meant the formation of reproductive bodies, each of which contains differentiated elements of the various classes found in the parent. A simple example of this is described by Miklucho Maclay in Ascons, where the bud is merely the end of one of the Ascon tubes which becomes pinched off and so set free. In Leucosolenia botryoides * Vasseur describes a similar process ; in this, however, a strikingly distinctive feature is present (Fig. 114), namely, the buds have an inverse orientation with respect to that of the parent,so that the budding sponge presents a contrast to a sponge in which multiplication of oscula has occurred. In fact, the free distal end of the bud becomes the base of the young sponge, and the osculum is formed at the opposite extremity, co) where the bud is constricted from the parent. Such a reversal 1 Maas, Zool. Centralbl. vy. 1898, p. 581. 2 Arch. Zool. Exp. viii. 1879, p. 59. i BUDDING 229 of the position of the bud is noteworthy in view of its rarity, and the case is worth reinvestigating, for in other animal groups a Pia. 113.—Lophocalyx philippensis. The specimen bears several buds attached to it by long tufts of spicules. (After F. E. Schulze.) A Ey Fic. 114.—Leucosolenia botryoides. A, a piece of the Sponge laden with buds, a-f; 7, the spicules of the buds directed away from their free ends ; h, the spicules of the parent directed towards the osculum, 7. 3B, a bud which has been set free and has become fixed by the extremity which was free or distal in A. (After Vasseur.) bud or a regenerated part retains so constantly the same orien- tation as the parent that Loeb,’ after experimenting on the * ** Biological Lectures, Wood's Holl,” 1894, p. 43. 230 PORIFERA CHAP. regeneration of Coelenterata and other forms, concluded that a kind of “ polarity ” existed in the tissues of certain animals. In Osearella lobularis' the buds are transparent floating bladders, derived from little prominences on the surface of the sponge. Scattered in the walls of the bladders are flagellated chambers, which open into the central cavity. The vesicular nature of the buds is doubtless an adaptation, lessening their specific gravity and so enabling them to float to a distance from the parent. Gemmulation.— Spongilla has already afforded us a typical example of this process. Gemmules very similar to those of ; Spongilla are known in a few marine sponges, especi- ally in Suwberites and in Ficulina. They form a layer attached to the surface of support of the sponge —a_ layer which may be single or double, or even three or four tiers deep. A ‘micropyle is sometimes present in the spongin coat, sometimes absent; possibly its absence Fic. 115.—Gemmules of Ficulina. A, vertical ay. be correlated with section of gemmules in site ; B, vertical see- the piling of one layer of Sheer is portion of one gemmule. mm, gemmules on. another, as this, by covering up the micropyle, would of course render it useless. Presumably when a micropyle is present the living contents escape through it and leave the sponge by way of the canal system (Fig. 115). The only case besides Spongilla in which the details of development from gemmules have been traced is that of Zethya.” Mere microscopic examination of a Zethya in active reproduction would suggest that the process was simple budding, but Maas has shown that the offspring arise from groups of archaeocytes in the cortex, that is to say, they are typical gemmules. As they develop they migrate outwards along the radial spicule-bundles 1 F. E. Schulze, Zool. Anz. ii. 1879, p. 636. 2 Maas, Zeitschr. wiss. Zool. xx. 1901, p. 268. IX GEMMULATION and are finally freed, like the buds of the Hexactinellid Lopho- calyx (Fig. 113). The comparison of the process of development on the one hand by gemmules, and on the other by larval development, is of some interest.. In both cases two cell layers—a dermal and a gastral—are established before the young sponge has reached a functional state. Dif- ferences of detail in the formation of the chambers occur in the gemmule; these find parallels in the differences in the same process exhibited by the larvae of various groups of sponges. On the other hand, the order of tissue differentiation is not the same in the gemmule as in the larva. Of the reproduction of Tetrac- tinellida extremely little is known. Spermatozoa occur in the tissues in profusion and are doubtless functional, but larvae have been Fra. 116.—Development of the tri- radiate and quadriradiate spicules of Clathrina. (1) Three sclero- blasts ; (2) each has divided: the spicule is seen in their midst ; (3) addition of the fourth ray by a porocyte. p, Dermal aperture of pore; 7, fourth ray. (After Minchin.) seldom observed. In Hexactinellida the place of Fic. spicules of Sycon setosum. 1200. 117.—Three development of the triradiate stages (After Maas. ) in the Xx sexually produced larvae is taken by bodies of similar origin to gemmules but with the appearance of paren- chymulae. Ijima has indeed seen a few ege-cells in Hexactinellids” He finds, however, that archaeocyte con- geries occur In abundance, and there is good reason to believe with him that these are responsible for the numerous parenchymula-like asexually pro- duced larvae he has observed. The discovery of “asexual larvae” was first made by Wilson in the Monaxonid Esperella ; in this case the asexual larva is, as far as can be detected, identical with that developed A similar phenomenon, the production from the fertilised ege. 1 Maas, loc. cif. p. 284. 2 J. Coll. Japan, xv. 1901, p. 180. 232 PORIFERA CHAP. of apparently identical larvae by both sexual and asexual methods, has been observed in the Coelenterate Gonionema murbachit. Artificially, sponges may be reproduced with great advantage to commerce by means of cuttings. Cuttings of the bath sponge are fit to gather after a seven years’ growth. The development of the various forms of spicules is a subject about which little is yet known. Most spicules of which the development has been traced originate in a single dermal cell. The triradiate and quadriradiate spicules of Homocoela (Clathrinidae), as Minchin * has most beautifully shown, form an excep- tion. Three cells co-operate to form the triradiate; these three divide to give six before the growth of the spicule is complete. A quadriradiate is formed from a triradiate spicule by addition of the fourth ray, which, again, has a separate origin in an independent cell, in fact a porocyte. Fic. 118.—Development of monaxon Whe eT pune ont Cy spicules. A, from Spongilla tidae, on the other hand, originate oats ae, ie Set in a single cell? but the quadi- very large monaxon, from Leuco- radiate spicules are formed from aa ae ee (Atter te these by the addition of a fourth ray in a manner similar to that which has just been described for Clathrinidae. Monaxon spicules if not of large size undergo their entire development within a single scleroblast (Fig. 118, A). In some cases if their dimensions exceed certain limits, several cells take part in their completion; some of these are derived from the ' Perkins, Johns Hopkins Univ. Circ. xxi. 1902, p. 87. * For details of this interesting process see Minchin, Quart. J. Micr. Sci. xl. 1898, p. 469. * Maas, Zeitschr. wiss. Zool. xvii. 1900, p. 225. po. ae — ee ee ee eee es bo IX DEVELOPMENT OF SPICULES division of the original scleroblast, others are drawn from the surrounding tissue. In 7'ethya, for example, and in Leucosolenia * the scleroblasts round the large monaxon spicules are so numerous as to have an almost epithelioid arrangement. The large oxeas of Yetilla, Stelletta, and Geodia, however, are formed each within a single scleroblast.” Fic. 119.—Development of spheraster. A, of Tethya, from union of two quadriradiate spicules. (After Maas.) B (a-e), of Chondrilla, from a spherical globule. (After Keller.) Triaenes have been shown® to originate as monaxons with one swollen termination, from which later the cladi grow out. Information as to the scleroblasts in this case is needed. The value of a knowledge of the ontogeny of microscleres might be great. Maas believes that he has shown that the spherasters of Zethya are formed by the union of nunute tetractine cal- » throps (Fig.119,A). If 3 this view should be con- firmed, it would afford a very strong argument for the Tetractinellid _ affinities of Tethya, fa ene heme ite keene Keller; on the other hand, finds that the spherasters of the Tetractinellid Chondrilla WMAAA AENAR RANA G SOREN wis RAS hag S “er 1 Maas, SB. Ak. Miinchen, xxx. 1900, p. 553, and Zeitschr. wiss. Zool. 1xx. 1901, p. 265 ; see also Sollas, dan. Mag. Nat. Hist. (5) ix. 1880, p. 401. ? Sollas, Challenger Monograph, xxv. 1888, p. xlv. 5 Sollas, ibid. pp. 18 and 34, pl. vy. + Zeitschr. wiss. Zool. lii. 1891, p. 294. 234 PORIFERA CHAP. originate as spheres (Fig. 119, B); and spheres have been observéd in the gemmule of a Zethya; no spherasters were as yet present in the gemmule, and spheres were absent in the adult.' In the genus Placospongia certain spicules are present which outwardly closely resemble the sterrasters so characteristic of certain Tetractinellidae. Their development, however, as will be seen from Fig. 120, shows that they are not polyaxon but spiny monaxon spicules. Placo- spongia 18 consequently trans- ferred to the Monaxonida Spin- tharaphora. Sterrasters originate within Fic. 121.—Three stages in the development ita ge oe $7 5 HUMES : ae of an anisochela. al, Ala; al’, lower hairlike fibres* (trichites), which ala; f, falx ; 7’, lower falx ; 7, rostrum; aye united at their inner ends. 7’, lower rostrum. (After Vosmaer anid : Pekelharing.) The outer ends become thickened and further modified. The position occupied by the nucleus of the scleroblast is marked in the adult spicule by a hilum. The anisochela has been shown repeatedly to originate from a C-shaped spicule.® What little is known of the development of Hexactinellid spicules we owe to Ijima.*|| Numerous cells are concerned in certain later developmental stages of the hexaster; a hexaster passes through a hexactin stage, and —a fact “possibly of importance for the phylogeny of spicules in Hexactinellida °— in two species the first formed spicules are a kind of hexactin, known as a “ stauractin,” and possessing only four rays all in one plane (cf. Protospongia, p. 207). PHYSIOLOGY Production of the Current.—It is not at first sight obvious that the lashing of flagella in chambers arranged as above 1 J. Sollas, P. Zool. Soc. London, ii. 1902, p. 215. 2 Sollas, Ann. Mag. Nat. Hist. (5) ix. 1880, p. 402. 8 Bowerbank, and also Vosmaer and Pekelharing, Verh. Ak. Amsterdam (2) vi. 3, 1898. 4 J. Coll. Japan, xv. 1901, p. 193. — ee eee ee eee ee ee eT IX PHYSIOLOGY ty Lo») tm described, between an inhalant and an exhalant system of canals, will necessarily produce a current passing inwards at the ostia and outwards at the osculum. And the difficulty seems to be increased when it is found? that the flagella in any one chamber do not vibrate in concert, but that each keeps its own time. This, however, is of less consequence than might seem to be the case. Two conditions are essential to produce the observed results: (1) in order that the water should escape at the mouth of the chamber there must be a pressure within the chamber higher than that in the exhalant passages; (2) in order that water may enter the chamber there must be within it a pressure less than that in the inhalant passages. But the pressure in the inhalant and exhalant passages is presumably the same, at any rate before the current is started, therefore there must be a difference of pressure within the chamber itself, and the less pressure must be round the periphery. Such a distribution of pressures would be set up if each flagellum caused a flow of water directed away from its own cell and towards the centre of the chamber; and this would be true whether the flagellum beats synchronously with its fellows or not. The comparative study of the canal systems of sponges ~*~ acquires a greater interest in proportion as the hope of correlat- ing modifications with increase of efficiency seems to be realised. In a few main issues this hope may be said to have been realised. The points, so to speak, of a good canal system are (1) high oscular velocity, which ensures rapid removal of waste products to a wholesome distance; (2) a slow current without eddies in the flagellated chambers, to allow of the choanocytes picking up food particles (see below), and moreover to prevent injury to the delicate collars of those cells; (3) a small area of choanocytes, and consequent small expenditure of energy in current production. It is then at once clear at what a disadvantage the Ascons are placed as compared with other sponges having canal systems of the second or third types. Their chamber and_ oscular currents can differ but slightly, the difference being obtained merely by narrowing the lumen of the distal extremity of the body to form the oscular rim. Further, the choanocytes are 1 Vosmaer and Pekelharing, Verh. Ak. Amsterdam, 1898. 2 See Bidder, P. Camb. Soc. vi. 1888, p. 183; Sollas, Challenger Monograph, Xxv. 1883, pp. xvili.-xxi.; and Vosmaer and Pekelharing, loc. cit. 236 PORIFERA CHAP. acting on a volume of water which they can only imperfectly control, and it is no doubt due to the necessity of limiting the volume of water which the choanocytes have to set in motion that the members of the Ascon family are so restricted in size. The oscular rim is only a special case of a device adopted by sponges at the very outset of their career, and retained and perfected when they have reached their greatest heights; the volume of water passing per second over every cross-section of the path of the current is of course the same, therefore by narrowing the cross-sectional area of the path at any point, the velocity of the current is proportionally increased at that point. The lining of the oscular rim 1s of pinacocytes ; they determine a smooth surface, offering little frictional resistance to the current, while choanocytes in the same position would have been a hindrance, not only by setting up friction, but by causing irregularities in the motion. Canal systems of the second type show a double advance upon that of the Ascons, namely, subdivision of the gastral cavity and much greater length of the smooth walled exhalant passage. The choanocytes have now a task more equal to their strength, and, further, there is now a very great inequality between the total sec- tional areas of the flagellated chambers and that of the oscular tube. Canal systems of the third type with tubular chambers are an improvement on those of the second, in that the area of choanocytes is increased by the pouching of the chamber-layer without corresponding increase in the size of the sponge. How- ever, the area of choanocytes represents expenditure of energy, and the next problem to be solved is how to retain the improved current and at the same time to cut down expense. The first step is to change the form of the chamber from tubular to spherical. Now the energy of all the choanocytes is concentrated on the same small volume of water. The area of choanocytes is less, but the end result is as good as before. At the wide mouth of the spherical chamber there is nevertheless still a cause of loss of energy in the form of eddies, and it is as an obviation of these that one must regard the aphodi and prosodi with which higher members of the Demospongiae are provided. The correctness of this view receives support, apart from mechanical principles, from the fact that the mass of the body of any one of these sponges is greater relatively to the total flagellated area than in those sponges with eurypylous chambers; that is to say, a few IX CANAL SYSTEMS—FOOD 2477 aphodal and diplodal chambers are as efficient as many of the eurypylous type. It is manifest that the current is the bearer of the supply of food; but it requires more care to discover (1) what is the nature of the food; (2) by which of the cells bathed by the current the food is captured and by which digested. The answer to the latter question has long been sought by experi- menters,, who supplied the living sponge with finely powdered coloured matters, such as carmine, indigo, charcoal, suspended in water. The results received conflicting interpretations until it became recognised that it was essential to take into account the length of time during which the sponge had been fed before its tissues were subjected to microscopic examination. Vosmaer and Pekelharing obtained the following facts: Spongilla lacustris and Sycon ciliatum, when killed after feeding for from half an hour to two hours with milk or carmine, contain these substances in abundance in the bodies of the choanocytes and to a slight degree in the deeper cells of the dermal tissue; after feeding for twenty-four hours the proportions are reversed, and if a period of existence in water uncharged with carmine intervenes between the long feed and death then the chambers are completely free from carmine. These are perhaps the most conclusive experi- ments yet described, and they show that the choanocytes ingest solid particles and that the amoeboid cells of the dermal layer receive the ingested matter from them. In all probability it is fair to argue from these facts that solid particles of matter suitable to form food for the sponge are similarly dealt with by it and undergo digestion in the dermal cells. Choanocytes are the feeding organs par excellence ; but the pinacocytes perform a small share of the function of ingestion, and in the higher sponges where the dermal tissue has acquired a great bulk the share is perhaps increased. In the above experiments is implied the tacit assumption that sponges take their food in the form of finely divided solids. Haeckel” states his opinion that they feed on solid particles derived from decaying organisms, but that possibly decaying substances in solution may eke out their diet. Loisel, in 1898,° 1 Carter and Lieberkiihn in 1856, Haeckel in 1872, Metschnikoff in 1879, and many later workers. 2 Die Kalkschwimme, 1872, i. p. 372. * J. Anat. Physiol. 1898, pp. 1, 6, 234. PORIFERA CHAP. bo ios) ioe) made a new departure in the field of experiment by feeding sponges with coloured solutions, and obtained valuable results. Thus solutions, if presented to the sponge in a state of extreme dilution, are subjected to choice, some being absorbed, some rejected. When absorbed they are accumulated in vacuoles within both dermal and gastral cells, mixed solutions are separ- ated into their constituents and collected into separate vacuoles. In the vacuoles the solutions may undergo change; Congo red becomes violet, the colour which it assumes when treated with acid, and similarly blue litmus turns red. The contents of the vacuoles, sometimes modified, sometimes not, are poured out into the intercellular gelatinous matrix of the dermal layer, whence they are removed partly by amoeboid cells, partly, so Loisel thinks, by the action of the matrix itself. It adds to the value of these observations to learn that Loisel kept a Spongilla supplied with filtered spring-water, to which was added the filtered juice obtained from another crushed sponge. This Spongilla lived and budded, and was in good health at the end of ten days. Movement.—Sponges are capable of locomotion only in the young stage; in the adult the only signs of movement are the exhalant current, and in some cases movements of contraction sufficiently marked to be visible to the naked eye. Meresjkowsky was one of the early observers of these movements. He mentions that he stimulated a certain corticate Monaxonid sponge by means of a needle point: a definite response to each prick inside the oscular rim was given by the speedy contraction of the osculum.* Pigments and Spicules.—Various reasons lead one to con- clude that the spicules have some function other than that of support and defence, probably connected with metabolism, For the spicules are cast off, sometimes in large numbers, to be replaced rapidly by new ones, a process for which it is difficult to find an adequate explanation if the spicules are regarded as merely skeletal and defensive.” Potts remarks upon the strik- ing profusion with which spicules are secreted by developing Spongillids from water in which the percentage of silica present must have been exceedingly small. The young sponges climbed 1 Mém. Ac. St. Pétersb. (7) xxvi. 1878, p. 10. * Sollas, Challenger Report, xxv. pt. |xili. p. 1xxxviii. , | | IX PHYSIOLOGY——_DISTRIBUTION to Ss) © up the strands of spicules as they formed them, leaving the lower parts behind and adding to the upper ends. Of the physiology of the pigments of sponges not much is yet known: a useful summary of facts will be found in Von Fiirth’s text-book.’ Spongin.—Von Fiirth ' points out that this term is really a collective one, seeing that the identity of the organic skeletal substance of all sponge species is hardly to be assumed. Spongin is remarkable for containing lodine. The amount of iodine present in different sponges varies widely, reaching in certain tropical species of the Aplysinidae and Spongidae the high figure 8 to 14 per cent. Seaweeds which are specially rich in iodine contain only 1:5 to 1°6 per cent. In view of the fact that iodine is a specific for croup, it is of interest to observe that the old herb doctors for many centuries recognised the bath sponge as a cure for that disease. Distribution in Space.—All the larger groups of Sponges are cosmopolitan. Hach group has, however, its characteristic bathy- metrical range: the facts are best displayed by means of curves, as in Fig. 122, which is based wholly on the results obtained by the “Challenger” Expedition. The in- formation as to littoral species is con- sequently inadequate, and we have not the data requisite for their discussion. Sponges generally (a) and Monaxonida in particular (4) are more generally dis- tributed in water of depths of 51 to 200 fathoms than in depths of less than 50 fathoms; but localities in shallow water are Fiq. 122.—The ordinals mea- sure (i.) the number of species, a-7, and (ii.) the number of stations, @’-7’, at which successful hauls were made. The abscissae measure the depth: thus at I. the depth is from 0 to 50 fathoms ; at IT. from 51 to 200; at III. from 201 to 1000 ; at LV. from 1001 upwards. a,a’, are the curves for Sponges generally ; 6, 6’, for Mon- axonida; ¢,¢’, for Hexacti- nellida ; d, d@’, for Tetrac- tinellida ; e, e’, for Cal- carea; f, 7’, for Ceratosa. 1 Vergl. Physioiogie d. niederen Thiere, 1903, p. 441. 240 PORIFERA CHAP. richer, for the station curve (a’) rises abruptly from I. to IL., while the species curve (a) in the same region is almost horizontal. The Hexactinellid curve (c) culminates on JII., showing that the group is characteristically deep water. That for Tetracti- nellida (d@) reaches its greatest height on IL, 7.e. between 51 and 200 fathoms. Even here, in their characteristic depths, the Tetractinellida fall below the Hexactinellida, and far below the Monaxonida in numbers. Again, the Monaxonida are commoner than Hexactinellida in deep water of 201 to 1000 fathoms, and it is not till depths of 1000 fathoms are passed that Hexactinellida prevail, finally preponderating over the Monaxonida in the ratio of 2:1. The Calcarea and Ceratosa are strictly shallow-water forms. It is a fact well worth consideration that the stations at which sponges have been found are situated, quite irrespective of depth, more or less in the neighbourhood of land. In the case of Cal- carea and Ceratosa this is to be expected, seeing that shallow water is commonest near land, but it is surprising that it should be true also of the Hexactinellida and of the deep-water species of Tetractinellida and of Monaxonida. While the family groups are cosmopohtan, this is not true of genera and species. The distribution of genera and _ species makes it possible to define certain geographical provinces for sponges as for other animals. That this is so,is due to the existence of ocean tracts bare of islands; for ocean currents can act as distributing agents with success only if they flow along a coast or across an ocean studded with islands. It is, of course, the larval forms which will be transported; whether they will ever develop to the adult condition depends on whether the current carrying them passes over a bottom suitable to their species before metamorphosis occurs and the young sponge sinks. If such a bottom is passed over, and if the depth is one which can be supported by the particular species in question, then a new station may thus be established for that species. The distance over which a larva may be carried depends on the speed of the current by which it is borne, and on the length of time occupied by its metamorphosis. Certain of the ocean currents accomplish 500 miles in six days; this gives some idea of the distance which may intervene between the birthplace and ) | | 4 ry IX DISTRIBUTION IN SPACE AND TIME 241 the final station of a sponge; for six days is not an excessive interval to allow for the larval period of at any rate some species. Distribution in Time.— All that space permits us to say on the palaeontology of sponges has been said under the headings of the respective classes. We can here merely refer to the chrono- logical table shown in Fig. 123 :’— PALEOZOIC MESOZOIC CAINOZOIC NVIDIAOGHO snouz4inosuvg sno30v13489.7 SNO39WL3Y9 sn INIDOLSINd 4N303y4 dISSVUNP aiW dissvanp an NVINBWYD NVINNTIS NWINOA3GQ 3N3009119 3N3290I1g NWINU3d 3N3901W SvId sviq MEGAMASTICTORA CALCAREA HOMOCOELA CALCAREA HETEROCOELA SYCETTIDAE GRANTIIDAE PHARETRONES DIALYTINAE LITHONINAE sci hsctel ecg een ess hoses taser MSs} MICROMASTICTORA HEXACTINELLIDA RECEPTACULITIDAE HETERACTINELLIDA OCTACTINELLIDA TETRACTINELLIDA | CHORISTIDA es oe oe aa LitHistiDA MONAXONIDA wanah=- - es =e pahoes she 4 ced Ss ae as ee BSS CERATOSA we le ey aed ieee eat Hee heal lb SN le tee | = Fig. 123.—Table to indicate distribution of Sponges in time. Flints.—The ultimate source of all the silica in the sea and fresh-water areas is to be found in the decomposition of igneous rocks such as granite. The quantity of silica present in solution in sea water is exceedingly small, amounting to about one-and- a-half parts in 100,000; it certainly is not much more in average fresh water. This is no doubt due to its extraction by diatoms, which begin to extract it almost as soon as it is set free from the parent rock. It is from this small quantity that the siliceous sponges derive the supply from which they form their spicules. Hence it would appear that for the formation of one 1 For further details see Zittel, Lehrbuch der Palaeontologie, and Felix Bernard, Eléments de Palaeontolcgie, 1894. VOL. I R 242 PORIFERA CHAP. IX ounce of spicules at least one ton of sea water must pass through the body of the sponge. Obviously from such a weak solution the deposition of silica will not occur by ordinary physical agencies ; 1t requires the unexplained action of living organisms. This may account for the fact that deposits of flint and chert are always associated with organic remains, such as Sponges and Radiolaria. By some process, the details of which are not yet understood, the silica of the skeleton passes into solution. In Calcareous deposits, a replacement of the carbonate of hme by the silica takes place, so that in the case of chalk the shells of Foraminifera, such as Globigerina and Teaxtularia and those of Coccoliths, are converted into a siliceous chalk. Thus a siliceous chalk is the first stage in the formation of a flint. A further deposition of silica then follows, cementing this pulverulent material into a hard white porous flint. It is white for the same reason that snow is white. The deposition of silica continues, and the flint becomes at first grey and at last apparently black (black as ice is black ona pond). Frequently flints are found in all stages of formation: siliceous chalk with the corroded remains of sponge spicules may be found in the interior, black flint blotched with grey forming the mass of the nodule, while the exterior is completed by a thin layer of white porous flint. This layer must not be confused with the white layer which is frequently met with on the surface of weathered flints, which is due to a sub- sequent solution of some of the silica, so that by a process of unbuilding, the flint is brought back to the incompleted flint in its second stage. In the chalk adjacent to the flints, hollow casts of large sponge spicules may sometimes be observed, proving the fact, which is however unexplained, of the solution of the spicular silica. The formation of the flints appears to have taken place, to some extent at least, long after the death of the sponge, and even subsequent to the elevation of the chalk far above the sea-level, as is shown by the occurrence of layers of flints in the joints of the solid chalk." ' For further details see Sollas, ‘‘The Formation of Flints,” in The Age of the Earth, 1905, p. 181. ‘ COELENTERATA AND CTENOPHORA BY & 0. HICKSON, M.A., ERS. Formerly Fellow and now Honorary Fellow of Downing College, Beyer Professor of Zoology in the Victoria University of Manchester. CHAPTER: X COELENTERATA INTRODUCTION—CLASSIFICATION——HY DROZOA——ELEUTHEROBLASTEA —MILLEPORINA— GYMNOBLASTEA——CALYPTOBLASTEA GRAP- TOLITOIDEA—-STYLASTERINA THE great division of the animal kingdom called CoELEN- TERATA was constituted in 1847 by R. Leuckart for those animals which are commonly known as polyps and _jelly-fishes. Cuvier had previously included these forms in his division Radiata or Zoophyta, when they were associated with the Star- fishes, Brittle-stars, and the other Echinodermata. The splitting up of the Cuvierian division was rendered necessary by the progress of anatomical discovery, for whereas the Echinodermata possess an alimentary canal distinct from the other cavities of the body, in the polyps and jelly-fishes there is only one cavity to serve the purposes of digestion and the cir- culation of fluids. The name Coelenterata (xoidos = hollow, évtepov =the alimentary canal) was therefore introduced, and it may be taken to signify the important anatomical feature that the body-cavity (or coelom) and the cavity of the alimentary canal (or enteron) of these animals are not separate and distinct as they are in Echinoderms and most other animals. Many Coelenterata have a pronounced radial symmetry, the body being star-like, with the organs arranged symmetrically on lines radiating from a common centre. In this respect they have a superficial resemblance to many of the Echinodermata, which are also radially symmetrical in the adult stage. But it cannot be insisted upon too strongly that this superficial resemblance of the Coelenterata and Echinodermata has no genetic significance. 245 246 COELENTERATA CHAP. The radial symmetry has been acquired in the two divisions along different lines of descent, and has no further significance than the adaptation of different animals to somewhat similar conditions of life. It is not only in the animals formerly classed by Cuvier as Radiata, but in sedentary worms, Polyzoa, Brachiopoda, and even Cephalopoda among the Mollusca, that we find a radial arrangement of some of the organs. It is interest- ing in this connexion to note that the word “ polyp,” so frequently applied to the individual Coelenterate animal or zooid, was originally introduced on a fancied resemblance of a Hydra to a small Cuttle-fish (#7. Poulpe, Zat. Polypus). The body of the Coelenterate, then, consists of a bedy- wall enclosing a single cavity (“coelenteron”). The body-wall consists of an inner and an outer layer of cells, originally called by Allman the “endoderm” and “ectoderm” respectively. Between the two layers there is a substance chemically allied to mucin and usually of a jelly-like consistency, for which the convenient term “mesogloea,’ introduced by G. C. Bourne, is used (Fig. 125). The mesogloea may be very thin and inconspicuous, as it 1s in Hydra and many other sedentary forms, or it may become very thick, as in the jelly-fishes and some of the sedentary Alcyonaria. When it is very thick it is penetrated by wandering isolated cells from the ectoderm or endoderm, by strings of cells or by cell-lined canals; but even when it is cellular it must not be confounded with the third germinal layer or mesoblast which characterises the higher groups of animals, from which it differs essentially in origin and other characters. The Coelenterata are two-layered animals (DIPLOBLASTICA), in contrast to the Metazoa with three layers of cells (TRIPLoBLASTICA). The growth of the mesogloea in many Coelenterata leads to modifications of the shape of the coelenteric cavity in various directions. In the Anthozoa, for example, the growth of vertical bands of mesogloea covered by endoderm divides the peripheral parts of the cavity into a series of intermesenterial compartments in open com- munication with the axial part of the cavity; and in the jeily- fishes the growth of the mesogloea reduces the cavity of the outer regions of the disc to a series of vessel-like canals. Another character, of great importance, possessed by all Coelenterata is the “nematocyst” or “ thread-cell” (Fig. 124). = NEMATOCYSTS 247 This is an organ produced within the body of a cell called the “cnidoblast,’ and it consists of a vesicular wall or capsule, surrounding a cavity filled with fluid containing a long and usually spirally coiled thread continuous with the wall of the vesicle. When the nematocyst is fully developed and receives a stimulus of a certain character, the thread is shot out with great velocity and causes a sting on any part of an animal that is sufficiently delicate to be wounded by it. The morphology and physiology of the nematocysts are subjects of very great difficulty and complication, and cannot be discussed in these pages. It may, however, be said that by some authorities the cnidoblast is supposed to be an extremely modified form of mucous or gland cell, and that the discharge of the nematocyst is subject to the control of a primitive nervous system that is continuous through the body of the zooid. There is a considerable range of structure in the nemato- cysts of the Coelenterata. In of cenidoblast. After thorns in the middle of the thread, but Schneider.) none at the base. In some of the Siphono- phora the undischarged nematocysts reach their maximum size, nearly 0°05 mm. in length. When a nematocyst has once been discharged it is usually 248 COELENTERATA CHAP. rejected from the body, and its place in the tissue is taken by a new nematocyst formed by a new ecnidoblast; but in the thread of the large kind of nematocyst of Millepora there is a very delicate band, which appears to be similar to the myophan thread in the stalk of a Vorticella. Dr. Willey’ has made the important observation that in this coral the nematocyst threads can be withdrawn after discharge, the retraction being effected with great rapidity. The “cnidoblast” is a specially modified cell. It sometimes bears at its free extremity a delicate process, the “ cnidocil,’ which is supposed to be adapted to the reception of the special stimuli that determine the discharge of the nema- tocyst. In many species delicate contractile fibres (Fig. 124, Mf) can be seen in the substance of the cnidoblast, and in others its basal part is drawn out into a long and probably contractile stalk (“enidopod”), attached to the mesogloea below. There can be little doubt that new nematocysts are constantly formed during life to replace those that have been discharged and lost. Each nematocyst is developed within the cell-sub- stance of a enidoblast which is derived from the undifferentiated interstitial cell-groups. During this process the cnidoblast does not necessarily remain stationary, but may wander some considerable distance from its place of origin.” This habit of migration of the cnidoblast renders it difficult to determine whether the ectoderm alone, or both ectoderm and endoderm, can give rise to nematocysts. In the majority of Coelenterates the nematocysts are confined to the ectoderm, but in many Anthozoa, Seyphozoa, and Siphonophora they are found in tissues that are certainly or probably endodermic in origin. It has not been definitely proved in any case that the cnidoblast cells that form these nematocysts have originally been formed in the endoderm, and it is possible that they are always derived from ectoderm cells which migrate into the endoderm. It is probably true that all Coelenterata have nematocysts, and that, in the few cases in which it has been stated that they are absent (eg. Sarcophytum), they have been overlooked. It cannot, however, be definitely stated that similar structures do not occur in other animals. The nematocysts of the Mollusc Aeolis are not the product of its own tissues, but are introduced 1 Willey’s Zool. Results, pt. ii. 1899, p. 127. 2 Murbach, Archiv f. Naturg. lx. Bd. i. 1894, p. 217. x CLASSIFICATION 249 into the body with its food.’ The nematocysts that occur in the Infusorian Lpistylis wmbellaria and in the Dinoflagellate Polykrikos (p. 131) require reinvestigation, but if it should prove that they are the product of the Protozoa they cannot be regarded as strictly homologous with those of Coelenterata. In many of the Turbellaria, however, and in some of the Nemertine worms, nematocysts occur in the epidermis which appear to be undoubtedly the products of these animals. The Coelenterata are divided into three classes :— 1. Hyprozoa.—Without stomodaeum and mesenteries. Sexual cells discharged directly to the exterior. 2. ScypHozoa.— Without stomodaeum and mesenteries. Sexual cells discharged into the coelenteric cavity. 3. ANTHOZOA = ACTINOZOA.—With stomodaeum and mesen- teries. Sexual cells discharged into the coelenteric cavity. The full meaning of the brief statements concerning the structure of the three classes given above cannot be explained until the general anatomy of the classes has been described. It may be stated, however, in this place that many authors believe that structures corresponding with the stomodaeum and mes- enteries of Anthozoa do occur in the Scyphozoa, which they therefore include in the class Anthozoa. Among the more familiar animals included in the class Hydrozoa may be mentioned the fresh-water polyp Hydra, the Hydroid zoophytes, many of the smaller Medusae or jelly-fish, the Portuguese Man-of-war (Physalia), and a few of the corals. Included in the Scyphozoa are the large jelly-fish found floating on the sea or cast up on the beach on the British shores. The Anthozoa include the Sea-anemones, nearly all the Stony Corals, the Sea-fans, the Black Corals, the Dead-men’s fingers (Aleyonium), the Sea-pens, and the Precious Coral of commerce. CLASS I. HYDROZOA In this Class of Coelenterata two types of body-form may be found. In such a genus as Obelia there is a fixed branching colony of zooids, and each zooid consists of a simple tubular body- wall composed of the two layers of cells, the ectoderm and the 1 G. H. Grosvenor, Proc. Roy. Soc. 1xxii. 1903, p. 462. 250 COELENTERATA—HYDROZOA CHAP. endoderm (Fig. 125), terminating distally in a conical mound—the “ hypostome ”—which is perforated by the mouth and surrounded by a crown of tentacles. This fixed colony, the “hydrosome,” feeds and increases in size by gemmation, but does not produce sexual cells. The hydrosome produces at a certain season of the year a number of buds, which develop into small bell-lke jelly- fish called the “ Medusae,” which swim away from the parent stock and produce the sexual cells. The Medusa (Fig. 126) consists of a delicate dome-shaped contractile bell, perforated by radial canals and fringed with tentacles; and from its centre there depends, like the clapper of a bell, a tubular process, the manubrium, which bears the mouth at its extremity. This free-swimming sexual stage in the life-history of Obelia is called the “medusome.” It is difficult to determine whether, in the evolution of the Hydrozoa, the hydrosome preceded the medusome or vice versd. By some authors the medusome is regarded as-a specially modified sexual individual of the hydrosome colony. By others the medusome is regarded as the typical adult Hydrozoon form, and the zooids of the hydrosome as nutritive individuals arrested in their development to give support to it. Whatever may be the right interpretation of the facts, however, it is found that in some forms the medusome stage is more or less degenerate and the hydrosome is predominant, whereas in others the hydrosome is degenerate or inconspicuous and the medusome is predominant. Finally, in some cases there are no traces, even in development, of a medusome stage, and the life-history is completed in the hydrosome, while in others the hydrosome stages are lost and the life-history is completed in the medusome. If a conspicuous hydrosome stage is represented by H, a conspicuous medusome stage by M, an inconspicuous or degenerate hydrosome stage by h, an inconspicuous or degenerate medusome stage by m, and the fertilised ovum by O, the life-histories of the Hydrozoa may be represented by the following formule :— i; O -—-H -—- O (Hydra) 2. O—H—m—O (Sertularia) a O-H—M—O (Obelia) 4. O-—h—-M—O (Liriope) D. O —- M — O (Geryonia) The structure of the hydrosome is usually very simple. It se HYDROSOME AND MEDUSOME ANAS A consists of a branched tube opening by mouths at the ends of the branches and closed at the base. The body-wall is built up of ectoderm and endoderm. Between these layers there is a thin non-cellular lamella, the mesogloea. In a great many Hydrozoa the ectoderm secretes a chitinous protective tube called the “perisarc.” The mouth is usually a small round aperture situated on the summit of the hypostome, and at the base of the hypostome there may be one or two crowns of tentacles or an area bearing irregularly scattered tentacles. The tentacles may be hollow, containing a cavity continuous with the coelenteric cavity of the body; or solid, the endo- derm cells arranged in a single row forming an axial support for the ecto- derm. The ectoderm of the tentacles is provided with numerous nematocysts, usually arranged in groups or clusters on the distal two-thirds of their length, but sometimes confined to a cap-like swelling at the extremity (capitate ten- tacles). The hydrosome may be a single zooid producing others asexually by gemmation (or more rarely by fission), Fie. 125.—Diagram of a ver- tical section through a which become free from the parent, or — hydrosome. Coel, Coelen- : aes : 1 ip . . whys teron ; ct, ectoderm ; Lind, it may be a colony of zooids in organic Bra eH a ME Between ths connexion with one another formed by ectoderm and the endoderm . : ey ee there is a thin mesogloea the continuous gemmation of the original not represented in the zooid derived from the fertilised ovum ‘iagram. MM, mouth; 7, E tentacle. and its asexually produced offspring. When the hydrosome is a colony of zooids, specialisation of certain individuals for particular functions may occur, and the colony becomes dimorphic or polymorphic. The medusome is more complicated in structure than the hydrosome, as it is adapted to the more varied conditions of a free-swimming existence. The body is expanded to form a disc, “umbrella,” or bell, which bears at the edge or margin a number of tentacles. The mouth is situated on the end of a hypostome, called the “manubrium,” situated in the centre of the radially symmetrical body. The surface that bears the manubrium is 252 COELENTERATA—HYDROZOA CHAP. called oral, and the opposite surface is called aboral. The cavity partly enclosed by the oral aspect of the body when it is cup- or bell-shaped is called the “sub-umbrellar cavity.” In the medusome of nearly all Hydrozoa there is a narrow shelf projecting inwards from the margin of the disc and guard- ing the opening of the sub-umbrellar cavity, called the “ velum.” The mouth leads through the manubrium into a flattened part of the coelenteric cavity, which is usually called the gastric cavity, and from this a number of canals pass radially through the meso- gloea to join a circular canal or ring- canal at the margin of the umbrella. A special and important feature of the medusome is the presence of sense- organs called the “ ocelli” and “ stato- Frc, 126,—Diagram of a vertical CYSts,’ situated at the margin of the section through a medusome. ymbrella or at the base of the coel, Coelenteron ; J/, mouth ; Man, manubrium; R, radial tentacles. Pe de pen er : The ocelli may usually be recog- nised as opaque red or blue spots on the bases of the tentacles, in marked contrast to their trans- parent surroundings. The ocellus may consist simply of a cluster of pigmented cells, or may be further differentiated as a cup of pigmented cells filled with a spherical thickening of the cuticle to form a lens. The exact function of the ocelli may not be fully understood, but there can be little doubt that they are lght- perceiving organs. The function of the sense-organs known as statocysts, how- ever, has not yet been so satisfactorily determined. They were formerly thought to be auditory organs, and were called “ otocysts,” but it appears now that it is impossible on physical grounds for these organs to be used for the perception of the waves of sound in water. It is more probable that they are organs of the static function, that is, the function of the per- ception of the position of the body in space, and they are consequently called statocysts. In the Leptomedusae each statocyst consists of a small vesicle in the mesogloea at the margin of the umbrella, containing a hard, stony body called the “statolith.” In Geryonia and some other Trachomedusae the statolith is carried by a short tentacular process, the “statorhab,” x BLEUTHEROBLASTBA—AVDRA 253 projecting into the vesicle; in other Trachomedusae, however, the vesicle is open, but forms a hood for the protection of the statorhab; and in others, but especially in the younger stages of development, the statorhab is not sunk into the margin of the umbrella, and resembles a short but loaded tentacle. Recent researches have shown that there is a complete series of connect- ing links between the vesiculate statocyst of the Leptomedusae and the free tentaculate statorhab of the Trachomedusae, and there can be little doubt of their general homology. In the free-swimming or “ Phanerocodonic” medusome the sexual cells are borne by the ectoderm of the sub-umbrellar cavity either on the walls of the manubrium or subjacent to the course of the radial canals. Order I. Eleutheroblastea. This order is constituted mainly for the well-known genus Hydra. By some authors Hydra is regarded as an aberrant member of the order Gymnoblastea, to which it is undoubtedly in many respects allied, but it presents so many features of special interest that it is better to keep it in a distinct group. Hydra is one of the few examples of exclusively fresh-water Coelenterates, and hke so many of the smaller fresh-water animals its distribution is almost cosmopolitan. It occurs not only in Europe and North America, but in New Zealand, Australia, tropical central Africa, and tropical central America. Hydra is found in this country in clear, still fresh water attached to the stalks or leaves of weeds. When fully expanded it may be 25 mm. in length, but when completely retracted the same individual may be not more than 3 mm. long. The tubular body-wall is built up of ectoderm and endoderm, enclosing a simple undivided coelenteric cavity. The mouth is situated on the summit of the conical hypostome, and at the base of this there is a crown of long, delicate, but hollow tentacles. The number of tentacles is usually six in Hf. vulgaris and H. oligactis} and eight in H. viridis, but it is variable in all species. During the greater part of the summer the number of indi- viduals is rapidly increased by gemmation. The young Hydras produced by gemmation are usually detached from their parents 1H. Jung, Morph. Jahrb. viii. 1881, p. 339. 254 COELENTERATA——HYDROZOA CHAP. before they themselves produce buds, but in /. oligactis the buds often remain attached to the parent after they themselves have formed buds, and thus a small colony is produced. Sexual reproduction usually commences in this country in the summer and autumn, but as the statements of trustworthy authors are conflicting, it 1s probable that the time of appearance of the sexual organs varies according to the conditions of the environ- ment. Individual specimens may be male, female, or hermaphrodite. Nussbaum? has published the interesting observation that when the Hydras have been well fed the majority become female, when the food supply has been greatly restricted the majority become male, and when the food-supply is moderate in amount the majority become hermaphrodite. The gonads are simply clusters of sexual cells situated in the ectoderm. There is no evidence, derived from either their structure or their development, to show that they represent reduced medusiform gonophores. The testis produces a number of minute spermatozoa. In the ovary, however, only one large yolk-laden egg-cell reaches maturity by the absorption of the other eggs. The ovum is fertilised while still within the gonad, and undergoes the early stages of its development in that position. With the differentia- tion of an outer layer of cells a chitinous protecting membrane is formed, and the escape from the parent takes place.” It seems probable that at this stage, namely, that of a protected embryo, there is often a prolonged period of rest, during which it may be carried by wind and other agencies for long distances without injury. The remarkable power that Hydra possesses of recovery from injury and of regenerating lost parts was first pointed out by Trembley in his Slain memoir.® A Hydra can be cut into a considerable number of pieces, and each piece, provided both ectoderm and endoderm are re- presented in it, will give rise by growth and regeneration to a complete zooid. There is, however, a limit of size below which fragments of Hydra will not regenerate, even if they contain 1 Verh. Ver. Rheinland, xlix. 1893, pp. 13, 14, 40, 41. 2 For an account of the development and of the chitinous membrane see A. Brauer, Zeitschr. f. wiss. Zool. lii. 1891, p. 9. 3 Trembley, Mémoires pour servir a Histoire d’un genre de Polypes d'eau douce, 1744. x ELEUTHEROBLASTEA—-HYDRA 255 cells of both layers. The statement made by Trembley, that when a Hydra is turned inside out it will continue to live in the introverted condition has not been confirmed, and it seems probable that after the experiment has been made the polyp remains in a paralysed condition for some time, and later reverts, somewhat suddenly, to the normal condition by a reversal of the process. There is certainly no substantial reason to believe that under any circumstances the ectoderm can undertake the function of the endoderm or the endoderm the functions of the ectoderm. One of the characteristic features of Hydra is the slightly expanded, disc-shaped aboral extremity usually called the “ foot,” an unfortunate term for which the word “sucker ” should be sub- stituted. There are no root-like tendrils or processes for attach- Fia. 127.—A series of drawings of Iydra, showing the atti- tudes it assumes during one of the more rapid movements = from place to place. 1, The 2 Hydra bending over to one = y side; 2, attaching itself to = the support by the mouth and tentacles; 3, drawing the sucker up to the mouth ; 4, inverted ; 5, refixing the sucker ; 6, reassuming the erect posture. (After Trem- FSS Tare Tess bley. ) 5 6 ? i! 2 ment to the support such as are found in most of the solitary Gymnoblastea. The attachment of the body to the stem or weed or surface-film by this sucker enables the animal to change its position at will. It may either progress slowly by gliding along its support without the assistance of the tentacles, in a manner similar to that observed in many Sea-anemones; or more rapidly by a series of somersaults, as originally described by Trembley. The latter mode of locomotion has been recently described as follows :—* The body, expanded and with expanded tentacles, bends over to one side. As soon as the tentacles touch the bottom they attach themselves and contract. Now one of two things happens. The foot may loosen its hold on the bottom and the body contract. In this manner the animal comes to stand on its tentacles with the foot pointing upward. The body now bends over again until the foot attaches itself close to the attached tentacles. These loosen in their turn, and so the Hydra is again 256 COELENTERATA—HYDROZOA CHAP. in itsnormal position. In the other case the foot is not detached, but glides along the support until it stands close to the tentacles, which now loosen their hold.” ? Hydra appears to be purely carnivorous. It will seize and swallow Entomostraca of relatively great size, so that the body- wall bulges to more than twice its normal diameter. But smaller Crustacea, Annelid worms, and pieces of flesh are readily seized and swallowed by a hungry Hydra. In A. viridis the chlorophyll corpuscles * of the endoderm may possibly assist in the nourish- ment of the body by the formation of starch in direct sunlight. Three species of Hydra are usually recognised, but others which may be merely local varieties or are comparatively rare have been named.’ Hf, viridis. — Colour, grass-green. Average number of tentacles, eight. Tentacles shorter than the body. Embryonic chitinous membrane spherical and almost smooth. Hf, vulgaris, Pallas (4. grisea, Linn.).—Colour, orange-brown. Tentacles rather longer than the body, average number, six. Embryonic chitinous membrane spherical, and covered - with numerous pointed branched spines. Hf. oligactis, Pallas (H. fusea, Linn.).— Colour, brown. Tentacles capable of great extension; sometimes, when fully expanded, several times the length of the body. Average number, six. Embryonic chitinous membrane plano-convex, its convex side only covered with spines. The genera Microhydra (Ryder) and Protohydra (Greeff) are probably allied to Hydra, but as their sexual organs have not been observed their real affinities are not yet determined. Microhydra resembles Hydra in its general form and habits, and in its method of reproduction by gemmation, but it has no tentacles. It was found in fresh water in North America. Protohydra* was found in the oyster-beds off Ostend, and resembles MWicrohydra in the absence of tentacles. It multiplies by transverse fission, but neither gemmation nor sexual repro- duction has been observed. Haleremita is a minute hydriform zooid which is also marine. 1G. Wagner, Quart. Journ. Mier. Sci. xlviii. 1905, p. 589. 2 See p. 126. 3 Hydra pallida, Beardsley, has been found to be very destructive to the fry of the Black-spotted Trout in Colorado, U.S. Fish. Rep. Bull. 1902, p. 158. * For figures of Protohydra see Chun, Bronn’s Thier-Reich, ‘‘ Coelenterata,” 1894, Bd. ii. pl. ii. i MILLEPORINA 257 It was found by Schaudinn* in the marine aquarium at Berlin in water from Rovigno, on the Adriatic. It reproduces by gemina- tion, but sexual organs have not been found. Another very remarkable genus usually associated with the Eleutheroblastea is Polypodium. At one stage of its life-history it has the form of a spiral ribbon or stolon which is parasitic on the eggs of the sturgeon (Acipenser ruthenus) in the river Volga.” This stolon gives rise to a number of small Hydra-like zooids with twenty tentacles, of which sixteen are filamentous and eight club-shaped. These zooids multiply by longitudinal fission, and feed independently on Infusoria, Rotifers, and other minute organisms. The stages between these hydriform individuals and the parasitic stolon have not been discovered. Order II. Milleporina. Millepora was formerly united with the Stylasterina to form the order Hydrocorallina; but the increase of our knowledge of these Hydroid corals tends rather to emphasise than to minimise the distinction of Midlepora from the Stylasterina. Millepora resembles the Stylasterina in the production of a massive calcareous skeleton and in the dimorphism of the zooids, but in the characters of the sexual reproduction and in many minor anatomical and histological peculiarities it is distinct. As there is only one genus, Millepora, the account of its anatomy will serve as a description of the order. The skeleton (Fig. 128) consists of large lobate, plicate, ramified, or encrusting masses of calcium carbonate, reaching a size of one or two or more feet in height and breadth. The surface is perforated by numerous pores of two distinct sizes; the larger—gastropores’—are about 0°25 mm. in diameter, and the smaller and more numerous “ dactylopores” about 0°15 mm. in diameter. In many specimens the pores are arranged in definite cycles, each gastropore being surrounded by a circle of 5-7 dactylopores; but more generally the two kinds appear to be irregularly scattered on the surface. When a branch or lobe of a Millepore is broken across and examined in section, it is found that each pore is continued as a 1 Sitzber. Ges. naturf. Freunde Berlin, ix. 1894, p. 226. 2M. Ussov, Morph. Jahrb. xii. 1887, p. 137. VOL. I s 25 8 COELENTERATA—HYDROZOA CHAP. vertical tube divided into sections by horizontal calcareous plates (Fig. 129, Zab). These plates are the “tabulae,’ and constitute the character upon which Jfillepora was formerly placed in the now discarded group of Tabulate corals. The coral skeleton is also perforated by a very fine reticulum of canals, by which the pore-tubes are brought into communica- Fic, 128.—A portion of a dried colony of Millepora, showing the larger pores (gastro- pores) surrounded by cycles of smaller pores (dactylopores). At the edges the cycles are not well defined. tion with one another. In the axis of the larger branches and in the centre of the larger plates a considerable quantity of the skeleton is of an irregular spongy character, caused by the disintegrating influence of a boring filamentous Alga.’ The discovery that Jfillepora belongs to the Hydrozoa was made by Agassiz” in 1859, but Moseley * was the first to give 1 This organism is usually described as a fungus (Ach/ya), but it is probably a green Alga. See J. E. Duerden, Bull. Amer. Mus. Nat. Hist. xvi. 1902, p. 323. * Bibl. Univ. de Genéve, Arch. des Sciences, vy. 1859, p. 80. * Phil. Trans. exlvii. 1876, p. 117. x MILLEPORINA 259 an adequate account of the general anatomy. The colony consists of two kinds of zooids—the short, thick gastrozooids (Fig. 129, G@) provided with a mouth and digestive endoderm, and the longer and more slender mouthless dactylozooids ()))—united together by a network of canals running in the porous channels of the superficial layer of the corallum. The living tissues of the zooids extend down the pore-tubes as far as the first tabulae, and below this level the canal-system is degenerate and function- less. It is only a very thin superficial stratum of the coral, therefore, that contains living tissues. The zooids of Jfi/lepora are very contractile, and can be with- drawn below the general surface of the coral into the shelter of the pore-tubes. When a specimen is examined in its natural position on the reef, the zooids are usually found to be thus con- tracted; but several observers have seen the zooids expanded in the living condition. It is probable that, as is the case with other corals, the expansion occurs principally during the night. The colony is provided with two kinds of nematocysts—the small kind and the large. In some colonies they are powerful enough to penetrate the human skin, and Millepora has there- fore received locally the name of “stinging coral.” On each of the dactylozooids there are six or seven short capitate tentacles (Fig. 129, ¢), each head being packed with nematocysts of the small kind; similar batteries of these nematocysts are found in the four short capitate tentacles of the gastrozooids. The nemato- eysts of the larger kind are found in the superficial ectoderm, some distributed irregularly on the surface, others in clusters round the pores. The small nematocysts are about 0:°013 mm. in length before they are exploded, and exhibit four spines at the base of the thread; the large kind are oval in outline, 0°02 x 0°025 mm. in size, and exhibit no spines at the base, but a spiral band of minute spines in the middle of the filament. There is some reason to believe that the filament of the large kind of nematocysts can be retracted.! At certain seasons the colonies of Afillepora produce a great number of male or female Medusae. The genus is probably dioecious, no instances of hermaphrodite colonies having yet been found. Each Medusa is formed in a cavity situated above the last-formed tabula in a pore-tube, and this cavity, the “ampulla,” 1S. J. Hickson, Willey’s Zool. Results, pt. ii. 1899, p. 127. 260 COELENTERATA—HYDROZOA CHAP. having a greater diameter than that of the gastrozooid tubes, can ; Can.1, canal system ; Cor, corallum ; J, an expanded dactylo- (Cor) ; G, a gastrozooid, seen in (Partly after Moseley.) I SS — g¢ the corallum Amp, an ampulla containing a medusa of Millepora. edusae ; ¢, tentacle ; Zab, tabula in the pore-tubes, generating in the lower layers of the coralluim ct, the continuous sheet of ectoderm coverin 7 4) , free-swimming M Diagrammatic sketch to show the structure at the surface ; Can.2, canal system de zooid with its capitate tentacles ; # vertical section ; Med 129% Fic. be recognised even in the dried skeleton. It is not known how frequently the sexual seasons occur, but from the rarity in the x MILLEPORINA 201 collections of our museums of Millepore skeletons which exhibit the ampullae, it may be inferred that the intervals between successive seasons are of considerable duration. The Medusae of Millepora are extremely simple in character. There is a short mouthless manubrium bearing the sexual cells, an umbrella without radial canals, while four or five knobs at the margin, each supporting a battery of nematocysts, represent all that there is of the marginal tentacles. The male Medusae have not yet been observed to escape from the parent, but from the fact that the spermatozoa are not ripe while they are in the ampullae, it may be assumed that the Medusae are set free. Duerden, however, has observed the escape of the female Medusae, and it seems probable from his observations that their independent life is a short one, the ova being discharged very soon after liberation. Millepora appears to be essentially a shallow-water reef coral. It may be found on the coral reefs of the Western Atlantic ex- tending as far north as Bermuda, in the Red Sea, the Indian and Pacific Oceans. The greatest depth at which it has hitherto been found is 15 fathoms on the Macclesfield Bank, and it flourishes at a depth of 7 fathoms off Funafuti in the Pacific Ocean. Millepora, like many other corals, bears in its canals and zooids a great number of the symbiotic unicellular “ Algae” (Chrysomonadaceae, see pp. 86, 125) known as Zooxanthellae. All specimens that have been examined contain these organisms in abundance, and it has been suggested that the coral is largely dependent upon the activity of the “Algae” for its supply of nourishment. There can be no doubt that the dactylozooids do paralyse and catch living animals, which are ingested and digested by the gastrozooids, but this normal food-supply may require to be supplemented by the carbohydrates formed by the plant-cells. But as the carbohydrates can only be formed by the “ Algae” in sunlight, this supplementary food-supply can only be provided in corals that live in shallow water. It must not be supposed that this is the only cause that limits the distribution of J/iJlepora in depth, but it may be an important one. The generic name Jillepora has been applied to a great many fossils from different strata, but a critical examination of their structure fails to show any sufficient reason for including many of them in the genus or even in the order. Fossils that are 262 COELENTERATA—HYDROZOA CHAP. undoubtedly AMillepora occur in the raised coral reefs of relatively recent date, but do not extend back into Tertiary times. There seems to be no doubt, therefore, that the genus is of comparatively recent origin. Among the extinct fossils the genus that comes nearest to it is Avopora from the Eocene of France, but this genus differs from J/idlepora in having monomorphic, not dimorphic, pores, and in the presence of a minute spine or columella in the centre of each tube. The resemblances are to be observed in the general disposition of the canal system and of the tabulation. Whether Azopora is or is not a true Milleporine, however, cannot at present be determined, but it is the only extinct coral that merits consideration in this place. Order III. Gymnoblastea—Anthomedusae. This order was formerly united with the Calyptoblastea to form the order Hydromedusae, but the differences between the two are sufficiently pronounced to merit their treatment as distinct orders. In many of the Gymnoblastea the sexual cells are borne by free Medusae, which may be recognised as the Medusae of Gymnoblastea by the possession of certain distinct characters. The name given to such Medusae, whether their hydrosome stage is known or not, is Anthomedusae. The Gymnoblastea are solitary or colonial Hydrozoa, in which the free (oral) extremity of the zooids, including the crown of tentacles, is not protected by a skeletal cup. The sexual cells may be borne by free Anthomedusae, or by more or less degenerate Anthomedusae that are never detached from the parent hydrosome. The Anthomedusae are small or minute Medusae provided with a velum, with the ovaries or sperm-sacs borne by the manubrium and with sense-organs in the form of ocelli or pigment-spots situated on the margin of the umbrella. The solitary Gymnoblastea present so many important differ- ences in anatomical structure that they cannot be united in a single family. They are usually fixed to some solid object by root-like processes from the aboral extremity, the “ hydrorhiza,” or are partly embedded in the sand (Corymorpha), to which long filamentous processes project for the support of the zooid. The remarkable species Hypolytus peregrinus' from Wood’s Holl, 1 Quart. Journ. Mier, Sci. xlii. 1899, p. 341. x GYMNOBLASTEA—ANTHOMEDUSAE 263 however, has no aboral processes, and appears to be only temporarily attached to foreign objects by the secretion of the perisare. Among the solitary Gymnoblastea several species reach a gigantic size. Corymorpha is 50—75 mm. in length, but Monocaulus from deep water in the Pacific and Atlantic Oceans is nearly 8 feet in length. Among the solitary forms atten- tion must be called to the interesting pelagic Pelagohydra (see p. 274). The method of colony formation in the Gymnoblastea is very varied. In some cases (Clava squamata) a number of zooids arise from a plexus of canals which corresponds with the system of root-like processes of the solitary forms. In Hydractinia this plexus is very dense, and the ectoderm forms a continuous sheet of tissue both above and below. The colony is increased in size in these cases by the gemmation of zooids from the hydrorhiza. In other forms, such as Tubularia larynx, new zooids arise not only from the canals of the hydrorhiza, but also from the body- walls of the upstanding zooids, and thus a bushy or shrubby colony is formed. In another group the first-formed zooid produces a hydrorhiza of considerable proportions, which fixes the colony firmly to a stone or shell and increases in size with the growth of the colony. This zooid itself by considerable growth in length forms the axis of the colony, and by gemmation gives rise to lateral zooids, which in their turn grow to form the lateral branches and give rise to the secondary branches, and these to the tertiary branches, and so one; each branch terminating in a mouth, hypostome and crown of tentacles. Such a method of colony formation is seen in Bougainvillia (Fig. 150). A still more complicated form of colony formation is seen in Ceratella, in which not a single but a considerable number of zooids form the axis of the colony and of its branches. As each axis is covered with a continuous coat of ectoderm, and each zooid of such an axis secretes a chitinous fenes- trated tube, the whole colony is far more rigid and compact than is usual in the Gymnoblastea, and has a certain superficial resemblance to a Gorgoniid Alcyonarian (Fig. 133, p. 271). The branches of the colony and a considerable portion of the body-wall of each zooid in the Gymnoblastea are usually protected by a thin, unjointed “perisare”” of chitin secreted by the ecto- derm; but this skeletal structure does not expand distally to 26 COELENTERATA—HYDROZOA CHAP, A form a cup-lke receptacle in which the oral extremity of the zooid can be retracted for protection. The zooids of the Gymnoblastea present considerable diversity of form and structure. The tentacles may be reduced to one (in Monobrachium) or two (in Lar sabellarum), but usually the number is variable in each individual colony. In many cases, such as Cordylophora, Clava, and many others, the tentacles are irregularly scattered on the sides of the zooids. In others there may be a single circlet of about ten or twelve tentacles round the base of the hypo- stome. In some genera the tentacles are arranged in two series (Lubularia, Cory- morpha, Monocaulus), a distal series round the margin of the mouth which may be arranged in a single circlet or seattered irregularly on the hyposome, and a proximal series arranged in a single circlet some little distance from the Fic. 130.—Diagrammatic sketch to show the method yy oyth. In Branchio- of branching of Bougainvillia. gon, Gonophores ; . ; Hr, hydrorhiza ; t.z, terminal zooid. cerianthus imperator the number of tentacles is very great, each of the two circlets consisting of about two hundred tentacles. The zooids of the hydrosome are usually monomorphic, but there are cases in which different forms of zooid occur in the same colony. In Hydractinia, for example, no less than four different kinds of zooids have been described. These are called gastrozooids, dactylozooids, tentaculozooids, and _ blastostyles respectively. The “gastrozooids” are provided with a conical hypostome bearing the mouth and two closely-set circlets of some ten to thirty tentacles. The “ dactylozooids” are longer than the gastrozooids and have the habit of actively coiling and x GYMNOBLASTEA—ANTHOMEDUSAE 265 uncoiling themselves; they have a small mouth and a single circlet of rudimentary tentacles. The “tentaculozooids” are situated at the outskirts of the colony, and are very long and slender, with rudimentary tentacles and no mouth. The “)lastostyles,” usually shorter than the gastrozooids, have two circlets of rudimentary tentacles and a mouth. They bear on their sides the spherical or oval gonophores. The medusome stage in the life-history of these Hydrozoa is produced by gemmation from the hydrosome, or, in some cases, by gemmation from the medusome as well as from the hydro- some. In many genera and species the medusome is set free as a minute jelly-fish or Medusa, which grows and develops as an independent organism until the time when the sexual cells are ripe, and then apparently it dies. In other Gymnoblastea the medusome either in the female or the male or in both sexes does not become detached from the parent hydrosome, but bears the ripe sexual cells, discharges them into the water, and degenerates withcut leading an independent life at all. In these cases the principal organs of the medusome are almost or entirely function- less, and they exhibit more or less imperfect development, or they may be so rudimentary that the medusoid characters are no longer obvious. Both the free and the undetached medusomes are gonophores, that is to say, the bearers of the sexual cells, but the former were described by Allman as the “ phanerocodonic ” gonophores, @.e. “with manifest bells,” and the latter as the “adelocodonic ” gonophores. The gonophores may arise either from an ordinary zooid of the colony (Syncoryne), from a specially modified zooid—the blastostyle—as in Hydractinia, or from the hydrorhiza as in certain species of Perigonimus. The free- swimming Medusa may itself produce Medusae by gemmation from the manubrium (Sarsia, Lizzia, Rathkea, and others), from the base of the tentacles (Sarsia, Corymorpha, Hybocodon), or from the margin of the umbrella (Zleutheria). The free-swimming Medusae or phanerocodonic gonophores of the Gymnoblastea are usually of small size (1 or 2 mm. in diameter) when first liberated, and rarely attain a great size even when fully mature. They consist of a circular, bell-shaped or flattened disc—the umbrella—provided at its margin with a few or numerous tentacles, and a tubular manubrium bearing the mouth depending from the exact centre of the under (oral) 266 COELENTERATA—HYDROZOA CHAP. side of the umbrella (Fig. 132, A). The mouth leads into a shallow digestive cavity, from which radial canals pass through the substance of the umbrella to join a ring-canal at the margin (Fig. 131). The sense-organs of the Medusae of the Gymnoblastea are in the form of pigment-spots or very simple eyes (ocelli), situated at the bases of the tentacles. The orifice of the umbrella is guarded by a thin shelf or mem- brane, as in the Calyptoblastea, called the velum. The sexual cells are borne by the manubrium (Figs. 131 and 132, A). There are many modifications observed in the different genera as regards the number of tentacles, the number and character of the radial canals, the minute structure of the sense-organs, and some other characters, but they agree in having a velum, ocellar sense-organs, and Fic. 131.—Medusa of Cladonema, from Manubrial sexual organs. The ie atatas showing pent” tentacles are rudimentary in Amal- the ocelli at the base of the ten- thea; in Corymorpha there is only toes the svelitgs on the MAI" one tentacle; in Perigonimus there the gonads, and the radial and ring- are two ; and in Bougainvillia they canals of the umbrella. (After Peoria) are numerous; but the usual number is four or six. The radial canals are usually simple and four in number, but there are six in Lar sabellarum, which branch twice or three times before reach- ing the margin of the umbrella (Fig. 132, B). There can be no doubt that the Medusae of many Gymno- blastea undergo several important changes in their anatomical features during the period of the ripening of the sexual cells. Thus in Lar sabellarwm the six radial canals are simple in the first stage of development (A); but in the second stage (B) each radial canal bifurcates before reaching the margin, and in the adult stage shows a double bifurcation. The life-history has, however, been worked out in very few of the Antho- medusae, and there can be little doubt that as our knowledge grows several forms which are now known as distinct species x GYMNOBLASTEA—ANTHOMEDUSAE 207 will be found to be different stages of growth of the same species. The movements of the Medusae are well described by Allman ' in his account of Cladonema radiatum :—“It is impossible to grow tired of watching this beautiful medusa; sometimes while dashing through the water with vigorous diastole and systole, it will all at once attach its grapples to the side of the vessel, and become suddenly arrested in its career, and then after a period of repose, during which its branched tentacles are thrown back over its umbrella and extended into long filaments which float, like Fic. 132.—Two stages in the development of the Medusa of Lar sabellarum (Willsia stellata). A, first stage with six canals without branches ; B, third stage with six canals each with two lateral branches. The developing gonads may be seen on the manubrium in A. (After Browne.) some microscopic sea-weed in the water, it will once more free itself from its moorings and start off with renewed energy.” The Medusa of Clavatella, “in its movements and mode of life, presents a marked contrast to the medusiform zooid of other Hydrozoa. The latter is active and mercurial, dancing gaily through the water by means of the vigorous strokes of its crystalline swimming-bell. The former strides leisurely along, or, using the adhesive discs as hands, climbs amongst the branches of the weed. In the latter stage of its existence it becomes stationary, fixing itself by means of its suckers; and 1 “*Gymnoblastic Hydroids,” Ray Society, 1871, p. 359. 268 COELENTERATA—HYDROZOA CHAP. thus it remains, the capitate arms standing out rigidly, like the rays of a starfish, until the embryos are ready to escape.” * Among the Gymnoblastea there are many examples of a curious association of the Hydroid with some other living animals. Thus Hydractinia is very often found on the shells carried by living Hermit crabs, Dicoryne on the shells of various Molluscs, Tubularia has been found on a Cephalopod, and Eetopleura (a Corymorphid) on the carapace of a crab. There is but little evidence, however, that in these cases the association is anything more than accidental. The occurrence of the curious species, Lar sabellarum, on the tubes of Sabella, of Campaniclava cleodorae on the living shells of the pelagic Molluse Cleodora cuspidata, and of a Gorgonia on the tubes of Tubularia parasitica, appear to be cases in which there is some mutual relationship between the two comrades. The genus Stylactis, however, affords some of the most interesting examples of mutualism. Thus Stylactis vermicola is found only on the back of an Aphrodite that lives at the great depth of 2900 fathoms. 8S. spongicola and S. abyssicola are found associated with certain deep-sea Horny Sponges. S. minot is spread over the skin of the little rock perch Minows inermis, which is found at depths of from 45 to 150 fathoms in the Indian seas. In many cases it is difficult to understand what is the ad- vantage of the Hydroid to the animal that carries it, but in this last case Alcock ? suggests that the Stylactis assists in giving the fish a deceitful resemblance to the incrusted rocks of its environ- ment, in order to allure, or at any rate not to scare, its prey. Whether this is the real explanation or not, the fact that in the Bay of Bengal and in the Laccadive and Malabar seas the fish is never found without this Hydroid, nor the Hydroid without this species of fish, suggests very strongly that there is a mutual advantage in the association. Cases of undoubted parasitism are very rare in this order. The remarkable form Hydrichthys mirus, supposed to be a Gymnoblastic Hydroid, but of very uncertain position in the system, appears to be somewhat modified in its structure by its parasitic habits on the fish Seriola zonata. Corydendrium ! Hincks, British Hydroid Zoophytes, 1868, p. 74. 2 Ann. Mag. Nat. Hist. (6) x. 1892, p. 207. 3 Fewkes, Bull. Mus. Comp. Zool. xiii. 1887, p. 224. x GYMNOBLASTEA—ANTHOMEDUSAE 269 parasiticum is said to be a parasite living at the expense of Hudendrium racemosum. Mnestra is a little Medusa which attaches itself by its manubrium to the Molluse Phyllirhoe, and may possibly feed upon the skin or secretions of its host. Nearly all the species of the order are found in shallow sea water. Stylactis vermicola and the “Challenger” specimen of Mono- caulus imperator occur at a depth of 2900 fathoms, and some species of the genera Hudendrium and Myriothela descend in some localities to a depth of a few hundred fathoms. Cordylo- phora is the only genus known to occur in fresh water. From its habit of attaching itself to wooden piers and probably to the bottom of barges, and from its occurrence in navigable rivers and canals, it has been suggested that Cordylophora is but a recent immigrant into our fresh-water system. It has been found in England in the Victoria docks of London, in the Norfolk Broads, and in the Bridgewater Canal. It has ascended the Seine in France, and may now be found in the ponds of the Jardin des Plantes at Paris. It also occurs in the Elbe and in some of the rivers of Denmark. The classification of the Gymnoblastea is not yet on a satis- factory basis. At present the hydrosome stage of some genera alone has been described, of others the free-swimming Medusa only is known. Until the full life-history of any one genus has been ascertained its position in the families mentioned below may be regarded as only provisional. The principal families are :— Fam. Bougainvilliidae—The zooids of the hydrosome have a single circlet of filiform tentacles at the base of the hypostome. In Bougainvillia belonging to this family the gonophores are liberated in the form of free-swimming Medusae formerly known by the generic name Hippocrene. In the fully grown Medusa there are numerous tentacles arranged in clusters opposite the terminations of the four radial canals. There are usually in addition tentacular processes (labial tentacles) on the lps of the manubrium. Sougainvillia is a common British zoophyte of branching habit, found in shallow water all round the coast. The medusome of Bougainvillia ramosa is said to be the common little medusa Margelis ramosa.' Like most of the Hydroids it has a wide geographical distribution. Other genera are Peri- gonimus, which has a Medusa with only two tentacles; and 1 Hartlaub, Wiss. Meeresunt. deutsch. Meere in Kiel N.F.I. 1894, p. 1. 270 COELEN TERATA—HYDROZOA CHAP. Dicoryne, which forms spreading colonies on Gasteropod shells and has free gonophores provided with two simple tentacles, while the other organs of the medusome are remarkably degenerate. In Garveia and Hudendrium the gonophores are adelocodonic, in the former genus arising from the body-wall of the axial zooids of the colony, and in the latter from the hydrorhiza. Stylactis is sometimes epizoic (p. 268). Among the genera that are usually placed in this family, of which the medusome stage only is known, are Lizzia (a very common British Medusa) and Rathkea. In Margelopsis the hydrosome stage consists of a single free- swimming zooid which produces Medusae by gemmation. Fam. Podocorynidae.—The zooids have the same general features as those of the Bougainvilliidae, but the perisare does not extend beyond the hydrorhiza. In Podocoryne and Hydractinia belonging to this family the hydrorhiza forms an encrusting stolon which is usually found on Gasteropod shells containing a living Hermit crab. In Podo- coryne the gonophores are free-swimming Medusae with a short manubrium provided with labial tentacles. Mydractinia differs from Podocoryne in having polymorphic zooids and adelocodonic gonophores. A fossil encrusting a Nassa shell from the Pliocene deposit of Italy has been placed in the genus Hydractinia, and four species of the same genus have been described from the Miocene and Upper Greensand deposits of this country.’ These are the only fossils known at present that can be regarded as Gymnoblastic Hydroids. The Medusa Zhamnostylus, which has only two marginal ten- tacles and four very long and profusely ramified labial tentacles, is placed in this family. Its hydrosome stage is not known. Fam. Clavatellidae.—This family contains the genus Clava- tella, in which the zooids of the hydrosome have a single circlet of capitate tentacles. The gonophore is a free Medusa provided with six bifurcated capitate tentacles. Fam. Cladonemidae.—This family contains the genus Clado- nema, in which the zooids have two circlets of four tentacles, the labial tentacles being capitate and the aboral filiform. The gonophore is a free Medusa with eight tentacles, each provided with a number of curious capitate tentacular processes (Fig. 131). 1 Carter, Ann. Mag. Nat. Hist. (4) xix. 1877, p. 44; (5) i. 1878, p. 298. x GYMNOBLASTEA—ANTHOMEDUSAE Zyl Fam. Tubulariidae.—This important and cosmopolitan family is represented in the British seas by several common species. The zooids of the hydrosome of Zubularia have two circlets of numerous filiform tentacles. The gonophores are adelocodonic, and are situated on long peduncles attached to the zooid on the upper side of the aboral circlet of tentacles. The larva escapes from the gonophore and acquires two tentacles, with which it beats the water and, assisted by the cilia, keeps itself afloat for some time. In this stage it is known as an “ Actinula.” ' Fam. Ceratellidae.—The colony of Ceratella may be five inches in height. The stem and main branches are substantial, Fic. 183.—Ceratella fusca, About nat. size. (After Baldwin Spencer.”) and consist of a network of branching anastomosing tubes supported by a thick and fenestrated chitinous perisare. The 1 The aberrant genus Hypolytus (p. 262) may belong to this family. 2 Spencer, Zrans. Roy. Soc. Vict. 1892, p. 8. 272 COELENTERATA—HYDROZOA CHAP. whole branch is enclosed in a common layer of ectoderm. The zooids have scattered capitate tentacles. The Ceratellidae occur in shallow water off the coast of New South Wales, extend up the coast of East Africa as far as Zanzibar, and have also been described from Japan. Fam. Pennariidae.—In the hydrosome stage the zooids have numerous oral capitate tentacles scattered on the hypostome, and a single circlet of basilar filiform tentacles. The medusa of Pennaria, a common genus of wide distribution, is known under the name Globiceps. Fam. Corynidae.—In the hydrosome stage the zooids of this family possess numerous capitate tentacles arranged in several circlets or scattered. In Cladocoryne the tentacles are branched. Syneoryne is a common and widely distributed genus with numerous unbranched capitate tentacles irregularly distributed over a considerable length of the body-wall of the zooid. In many of the species the gonophores are liberated as Medusae, known by the name Sarsia, provided with four filiform tentacles and a very long manubrium. In some species (S. prolifera and S. siphonophora) the Medusae are reproduced asexually by gemmation from the long manubrium. A common British Anthomedusa of this family is Dipurena, but its hydrosome stage is not known. In the closely related genus Coryne the gonophores are adelocodonic, and exhibit very rudimentary medusoid characters. Fam. Clavidae.—This is a large family containing many genera, some with free-swimming Medusae, others with adelo- codonic gonophores. In the former group are included a number of oceanic Medusae of which the hydrosome stage has not yet been discovered. The zooids of the hydrosome have numerous scattered filiform tentacles. The free-swimming Medusae have hollow tentacles. Clava contains a common British species with a creeping hydrorhiza frequently attached to shells, and with adelocodonic gonophores. Cordylophora is the genus which has migrated into fresh water in certain European localities (see p. 269). It forms well-developed branching colonies attached to wooden gates and piers or to the brickwork banks of canals. Several Anthomedusae, of which the hydrosome stage is not known, appear to be related to the Medusae of this family, but are sometimes separated as x GYMNOBLASTEA—ANTHOMEDUSAE bo the family Tiaridae. Of these Ziara, a very brightly coloured jelly-fish sometimes attaining a height of 40 mm., is found on the British coasts, and Amphinema is found in considerable numbers at Plymouth in September. Zwrritopsis is a Medusa with a hydrosome stage like Dendroclava. For Stomatoca, see p. 415. Fam. Corymorphidae.—This family contains the interesting British species Corymorpha nutans. The hydrosome stage con- sists of a solitary zooid of great size, 50-75 mm. in length, provided with two circlets of numerous long filiform tentacles. The free-swimming Medusae are produced in great numbers on the region between the two circlets of tentacles. These Medusae were formerly known by the name Steenstrupia, and are note- worthy in having only one long moniliform tentacle, opposite to one of the radial canals. The gigantic Monocaulus imperator of Allman was obtained by the “ Challenger” at the great depth of 2900 fathoms off the coast of Japan. It was nearly eight feet in length. More recently Miyajima? has described a specimen from 250 fathoms in the same seas which was 700 mm. (27°5 in.) in length. Miyajima’s specimen resembles those described by Mark from 800 fathoms off the Pacific coast of North America as Branchiocerianthus urceolus in the remarkable feature of a distinct bilateral arrange- ment of the circlets of tentacles. Owing to the imperfect state of preservation of the only specimen of Allman’s species it is difficult to determine whether it is also bilaterally symmetrical and belongs to the same species as the specimens described by Mark and Miyajima. These deep-sea giant species, however, appear to differ from Corymorpha in having adelocodonic gonophores. Fam. Hydrolaridae.—This family contains the remarkable genus Lar, which was discovered by Gosse attached to the margin of the tubes of the marine Polychaete worm Sabella. The zooids have only two tentacles, and exhibit during life curious bowing and bending movements which have been compared with the exercises of a gymnast. The Medusae (Fig. 132, A and B) have been known for a long time by the name Willsia, but their life-history has only recently been worked out by Browne. 1 Journ. Coll. Sci. Tokyo, xiii. 1900, p. 235 (with a beautiful coloured illustration). 2 Proc. Zool. Soc. 1897, p. 818. VOL. I T 274. COELENTERATA—HYDROZOA CHAP. Fam. Monobrachiidae.—J/onobrachium, found in the White Sea by Mereschkowsky, forms a creeping stolon on the shells of Tellina. The zooids of the hydrosome have only one tentacle. Fam. Myriothelidae.—This family contains the single genus Myriothela, The zooid of the hydrosome stage is solitary and is provided, as in the Corynidae, with numerous scattered capitate tentacles. The gonophores are borne by blastostyles situated above the region of the tentacles. In addition to these blastostyles producing gonophores there are, in JZ phrygia, supplementary blastostyles which capture the eggs as they escape from the gonophores and hold them until the time when the larva is ready to escape. They were called “claspers” by Allman. In some of the Arctic species Frl. Bonnevie’ has shown that they are absent. Each zooid of JZ phrygia is hermaphrodite. Fam. Pelagohydridae.—This family was constituted by Dendy * for the reception of Pelagohydra mirabilis, a remarkable new species discovered by him on the east coast of the South Island of New Zealand. The hydrosome is solitary and _ free- : swimming, the proximal \_.zen.71, portion of the body being modified to form a float, the distal portion form- ing a flexible proboscis terminated by the mouth and a group of scattered manubrial tentacles. The tentacles are filiform and Fia. 134.—Pelagohydra mirabilis. Fl, The float ; scattered over the surface Be ation oa mouth | ot) fim: iat athe, sine ae are developed on stolons between the tentacles of the float. They have tentacles arranged in four radial groups of five each, at the margin of the umbrella. As pointed out by Hartlaub,? Pelagohydra is not the only genus in which the hydrosome floats. Three species of the genus Margelopsis have been found that have pelagic habits, and two 1 Zeitschr. f. wiss. Zool. xiii. 1898, p. 489. * Quart. Journ. Mier, Sct. xlvi. 1902, p. 1. % Zool. Zentralbl. x. 1908, p. 27. x CALYPTOBLASTEA—LEPTOMEDUSAE 275 of then have been shown to produce numerous free-swimming Medusae by gemmation; but at present there is no reason to suppose that in these forms there is any extensive modification of the aboral extremity of the zooid to form such a highly specialised organ as the float of Pelagohydra. The affinities of Pelagohydra are not clear, as our knowledge of the characters of the Medusa is imperfect; but according to Dendy it is most closely related to the Corymorphidae. JJar- gelopsis belongs to the Bougainvilliidae. Order IV. Calyptoblastea—Leptomedusae. The hydrosome stage is characterised by the perisarc, which not only envelops the stem and branches, as in many of the Gymnoblastea, but is continued into a trumpet-shaped or tubular cup or collar called the “ hydrotheca,’ that usually affords an efficient pro- tection for the zooids when retracted. No solitary Calyptoblastea have been discovered. In the simpler forms the colony consists of a creeping hydro- rhiza, from which the zooids arise singly (Clytia johnston), but these zooids may give rise to a lateral bud which grows longer than the parent zooid. The larger colonies are usually formed by alternate right and left budding from the last-formed zooid, so that in contrast to the Gymnoblast colony the apical zooid of the stem is the youngest, and not the oldest, zooid Fic. 135.—Part of a hydrocladium : of a dried specimen of Plumu- of the colony. In the branching joria profunda. Gt, Gono- colonies the axis is frequently com- theca; Hc, the stem of the : phe hydrocladium with joints (J) ; posed of a single tube of perisarc, Ht, a single hydrotheca; , which may be lined inf€rnally by = vematophores. Greatly en- : larged. (After Nutting.) the ectoderm and endoderm tissues formed by the succession of zooids that have given rise to the branches by gemmation. Such a stem is said to be monosiphonic. 276 COBLEN TERATA——HY DROZOK CHAP. In some of the more compheated colonies, however, the stem is composed of several tubes, which may or may not be surrounded by a common sheath of ectoderm and perisarc, as they are in Ceratella among the Gymnoblastea. Such stems are said to be “ polysiphonic ” or “ fascicled.” The polysiphonic stem may arise in more than one way, and in some cases it is not quite clear in what manner it has arisen.’ In many colonies the zootds are only borne by the terminal monosiphonic branches, which receive the special name “ hydro- cladia.” The gonophores of the Calyptoblastea are usually borne by rudimentary zooids, devoid of mouth and tentacles (the “ blastostyles ”), protected by a specially dilated cup of perisare known as the “ gonotheca” or “ gonangium.” The shape and size of the gonothecae vary a good deal in the order. They may be simply oval in shape, or globular (Schizotricha dichotoma), or greatly elongated, with the distal ends produced into slender necks (Plumularia setacea). They are spinulose in P. echinulata, and annulated in P. halecioides, Clytia, etc. In some genera there are special modifications of the branches and hydrocladia, for the protection of the gonothecae. The name “ Phylactocarp ” is used to designate structures that are obviously intended to serve this purpose. The phylactocarp of the genera Aglaophenia and Thecocarpus is the largest and most remarkable of this group of structures, and has received the special name “corbula.” The corbula consists of an axial stem or rachis, and of a number of corbula-leaves arising alternately from the rachis, bending upwards and then inwards to meet those of the other side above, the whole forming a pod-shaped receptacle. The gonangia are borne at the base of each of the corbula-leaves. There is some difference of opinion as to the homologies of the parts of the corbula, but the rachis seems to be that of a modified hydrocladium, as it usually bears at its base one or more hydrothecae of the normal type. The corbula-leaves are usually described as modified nematophores (vide infra), but according to Nutting’ there is no more reason to regard them as modified nematophores than as modified hydrothecae, and he regards them as “simply the modification of a structure originally intended to 1 For a discussion of the origin of the polysiphonic stem in Calyptoblastea see Nutting, “American Hydroids,” Smithsonian Institution Special Bulletin, pt. 1. 1900, p. 4. 2 Loc. cit. p. 38. x CALYPTOBLAST EA—LEPTOMEDUSAE PAG LG protect an indefinite person, an individual that may become either a sarcostyle! or a hydranth.’ The other forms of phylactocarps are modified branches as in Lytocarpus, and those which are morphologically appendages to branches as in Cladocarpus, Aglaophenopsis, and Streptocaulus. The structures known as “ nematophores ” in the Calyptoblastea are the theeae of modified zooids, comparable with the dactylo- zooids of Millepora. They form a well-marked character of the very large family Plumulariidae, but they are also found in species of the genera Ophiodes, Lafoéina, Oplorhiza, Perisiphonia, Diplo- cyathus, Halecium, and Clathrozoon among the other Calyptoblastea. The dactylozooids are usually capitate or filiform zooids, without tentacles or a mouth, and with a solid or occasionally a perforated core of endoderm. They bear either a battery of nematocysts (Plumularia, ete.), or of peculiar adhesive cells (Aglaophenia and some species of Plumularia). The functions of the dactylozooids are to capture the prey and to serve as a defence to the colony. In the growth of the corbula of Aglaophenia the dactylozooids appear to serve another purpose, and that is, as a temporary attachment to hold the leaves together while the edges themselves are being connected by trabeculae of coenosare. In a very large number of Calyptoblastea the gonophore is a reduced Medusa which never escapes from the gonotheca, but in the family Eucopidae the gonophores escape as free-swimming Medusae, exhibiting certain very definite characters. The gonads are situated not on the manubrium, as in the Anthomedusae, but on the sub-umbrellar aspect of the radial canals. The marginal sense-organs may be ocelli or vesiculate statocysts. The bell is usually more flattened, and the velum smaller than it is in the Anthomedusae, and the manubrium short and quadrangular. Such Medusae are called Leptomedusae. Leptomedusae of many specific forms are found abundantly at the surface of the sea in nearly all parts of the world, but with the exception of some genera of the Eucopidae and a few others, their connexion with a definite Calyptoblastic hydrosome has not been definitely ascertained. It may be an assumption that time will prove to be unwarranted that all the Leptomedusae pass through a Calyptoblastic hydrosome stage. 1 The term ‘‘sarcostyle” is usually applied to the dactylozooid of the Calypto- blastea. COELENTERATA——HYDROZOA CHAP. to N ioe) Fam. Aequoreidae.—In this family the hydrosome stage is not known except in the genus Polycanna, in which it resembles a Campanulariid. The sense-organs of the Medusae are statocysts. The radial canals are very numerous, and the genital glands are in the form of ropes of cells extending along the whole of their oral surfaces. Aeguorea is a fairly common genus, with a flattened umbrella and a very rudimentary manubrium, which may attain a size of 40 mm. in diameter. Fam. Thaumantiidae.—The Medusae of this family are dis- tinguished from the Aequoreidae by having marginal ocelli in place of statocysts. The hydrosome of Zhauwmantias alone is known, and this is very similar to an Obelia. Fam. Cannotidae.—The hydrosome is quite unknown. The Medusae are ocellate, but the radial canals, instead of being undivided, as in the Thaumantidae, are four in number, and very much ramified before reaching the ring canal. The tentacles are very numerous. In the genus Polyorchis, from the Pacific coast of North America, the four radial canals give rise to numerous lateral short blind branches, and have therefore a remarkable pinnate appearance. Fam. Sertulariidae.—In this family the hydrothecae are sessile, and arranged bilaterally on the stem and branches. The general form of the colony is pinnate, the branches being usually on opposite sides of the main stem. The gonophores are adelo- codonic. Sertularia forms more or less arborescent colonies, springing from a creeping stolon attached to stones and shells. There are many species, several of which are very common upon the British coast. Many specimens are torn from their attach- ments by storms or by the trawls of fishermen and cast up on the sand or beach with other zoophytes. The popular name for one of the commonest species (S. abietina) is the “sea-fir.” The genus has a wide geographical and bathymetrical range. Another common British species frequently thrown up by the tide in great quantities is Hydrallmania faleata. It has slender spirally- twisted stems and branches, and the hydrothecae are arranged unilaterally. The genus Grammaria, sometimes placed in a separate family, is distinguished from Sertularia by several characters. The stem and branches are composed of a number of tubes which are con- siderably compressed. The genus is confined to the southern seas. % CALYPTOBLASTEA——LEPTOMEDUSAE 279 Fam. Plumulariidae.— The hydrothecae are sessile, and arranged in a single row on the stem and branches. Nemato- phores are always present. Gonophores adelocodonic. This family is the largest and most widely distributed of all the families of the Hydrozoa. Nutting calculates that it contains more than one-fourth of all the Hydroids of the world. Over 300 species have been described, and more than half of these are found in the West Indian and Australian regions. Repre- sentatives of the family occur in abundance in depths down to 300 fathoms, and not unfrequently to 500 fathoms. Only a few species have occasionally been found in depths of over 1000 fathoms. The presence of nematophores may be taken as the most characteristic feature of the family, but similar structures are also found in some species belonging to other families (p. 277). The family is divided into two groups of genera, the ELEUTHEROPLEA and the SrTaTopLea. In the former the nemato- phores are mounted on a slender pedicel, which admits of more or less movement, and in the latter the nematophores are sessile. The genera Plumularia and Antennularia belong to the Eleu- theroplea. The former is a very large genus, with several common British species, distinguished by the terminal branches being pinnately disposed, and the latter, represented by