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Full text of "Protozoa"


lllllli!lllilimil!llllltiilillilillllll!llilllllllll}llll!lllilllllllll!lhMII!i:i!i!!!!!l:|!i!i-ii;ll!!lilHlillll!lllllllli^^ 



^-.b'^r^ ^^ 



y:h 



THE 

CAMBRIDGE NATURAL HISTORY 



EDITED BY 



S. F. HARMER, Sc.D., F.R.S.. Fellow of King's College, Cambridge 
Superintendent of the University Museum of Zoology 



A. E. SHIPLEY, M.A., F.R.S., Fellow of Christ's College, Cambridge 
University Lecturer on the Morphology of Invertebrates 



-f ROTOZOA/ 

By Marcus Hartoc;, M.A., Trinity College (D.Sc. 
Lond.), Professor of Natural History in the Ouccn's 
College, Cork 

PORIFERA (SPONGES) 

By Igerna B. J. SOLLAS, B.Sc. (Lond.), Lecturer on 
Zoology at Nevvnham College, Cambridge 

COELENTERATA & CTENOPHORA 

By S. J. HiCKSON, M.A., F.R.S., formerly Fellow and 
now Honorary Fellow of Downing College, Cambridge ; 
Beyer Professor of Zoology in the Victoria University of 
Manchester 

EGHINODERMATA 

B>' E. W. MacBride, M.A., F.R.S., formerly Fellow of 
St. John's College, Cambridge ; Professor of Zoology in 
McGiir University, Montreal 




iLoutioH 
MA CM ILL AX AND CO., Li.mited 

XKW YORK: THK .\I.\tMIIJ..\X COMl'A.W 
I 906 

.'i U rights resoTted 



Aud pitch down his basket before us, 

All tremljling alive 
With pink aud grey jellies, your sea-fruit ; 

You touch the strange lumps, 
And mouths gape there, eyes open, all manner 

Of horns and of humps. 

BsowNiNG, The EmjUshmim in Italy 



CONTENTS 



Scheme of the Classification adopted in this Book 



PEOTOZOA 

CHAPTER I 

Protozoa — Introduction — Functions of Protoplasm — Cell-division— 

Animals and Plants 3 



CHAPTER II 

PpvOTOzoa {contisued) : Spontaneous Generation— Characters of Pro- 
tozoa — Classification 4^ 



CHAPTER III 
Protozoa [coxtinved) : Sarcodina 51 

CHAPTER IV 
1'rotozoa {coxtixued) : Sporozoa Ol 

CHAPTER V 
Protozoa {coxtixued) -. FLAfiELi.AiA . 109 

CHAPTER VI 
Protozoa (coxtixced) : Infusoria (Ciliata and Suctoria) . . .136 



CONTENTS 



PORIFEPtA (SPONGES) 
CHAPTER VII 

PACE 

PoRiFERA (Sponges) — Introduction — Hisionv — Descuiption of Hali- 

CHOXDRIA PAXWEA AS AN EXAMPLE OF BRITISH MARINE SPONGF.S AND 
OF EPHYDATIA FLUVIATILIS FROM FrESH WaTER — DEFINITION — POSI- 
TION IN THE Animal Kingdom 16;" 



CHAPTER VIII 

PORIFERA {continued): FORMS OF SPICULES — CaLCAREA HoMOCOELA — 

Heterocoela — Hexactinellida— Demospongiae— Tetractinellida 

— Monaxonida — Ceratosa — Key to British Genera of Sponges 183 



CHAPTER IX 

PORIFERA (COXTIXUED) : REPRODUCTION, SkXUAL AND AsEXUAL — PHYSIO- 
LOGY — Distribution — Flints 226 



COELENTEPATA 
CHAPTER X 

COELENTERATA — INTRODUCTION — CLASSIFICATION — HyDROZOA — ElEUTHERO- 
BLAS IE A — Ml LLEPORI NA — GyMNOBL ASTEA — C ALYPTOBL ASTEA — GRAPTO- 
LiTOiDEA— Stylasterina 245 

CHAPTER XT 

HyDROZOA {COXTIWED) : TrACHOMEDUSAE — XaIUOMEDUSAE— SiPHONOPHORA 288 

CHAPTER XII 

CoELENTERATA (C'O.VT/ATK/j) : SCYPHOZOA = SCYPIIOMEDUSAE . . . 310 

CHAPTER XIII 

CoELENTERATA (COXTIXUED) : AnTHOZOA = ACTINOZOA — GENERAL ChARAC- 

TKRS — Alcyonari.v 326 

CHAPTER XIV 
Anthozoa (coxtixued) : Zoantharia . . 365 



COiNTKX 1> 



CTENOI'HOIJA 
CHAPTER XV 

PACE 

Ctexophora 412 



ECHIXODERMATA 

CHAPTER XYI 

ECHIXODERMATA — iNTiioDUCTioN— Classification— Anatomy of a Star- 
fish-Systematic Account of Asteiioipea 



CHAPTER XVIT 

EcHiNOPERMATA (co.vr/.vrs^) : Oi'Hiuroii)EA=1'>iuttij-. Stars . . . 477 

CHAPTER XVIII 
EcHiNDDERMATA (coAT/.vrBi^) : Echinoidea = Sea-Urchins . . . . 503 

CHAPTER XIX 

ECHIXODERM ATA (CO AT/ ATEB) : HoLOTHUROIDEA = Sea -CrCUMBERS . . 560 

CHAPTER XX 

Echinodermata {coxtixued) : Pelmatozoa — Crinoidea = Sea - Lilies — 

Thecoidea — Carpoidea — Cystoidea— Blastoidea .... 579 

CHAPTER XXI 
Echinodermata (coxtixued) : Development and Phylogeny . . .601 

IXDEX 625 



SCHEME OF THE CLASSIFICATION" ADOPTED 
IX THIS BOOK 

The names af extinct (jroirps^ arc printed in itedics. 
PROTOZOA (pp. 1, 48). 



SARCO- 
DINA 

ip. 51 



r Rhizopoda 


f Lobosa (p. 51) 






a-. 51) 


^ 


Filosa (p. 52). 
' AUogi-omidiaceae (p. 58). 
Asti-orliizidaceae (p. 59). 
Lituolidaceae (p. 59). 
Miliolidaceae (p. 59). 




Foraminifera 


Texnilaviaceae (p. 59). 




(p. 58) 




Cheilostoniellaceae (p. 59). 

Lagenaceae (p. 59). 

Globit^erinidae (p. 59). 

Kotaliaceae (p. 59). 
, Nummulitaceae (p. 59). 
' Aphrothoraca (p. 70). 

Clilamydophora (p. 71). 




Heliozoa 






(,P. 70) 




Chalarothoraca (p. 71). 
, Desmothoraca (t). 71). 










r Colloidea 

(p. 77). 








Collodaria 








(p. 77) 


Beloidea 

. (p. 77). 
' Spliaeroidea 






Si)nmellaria 
=^Peripylaea- 
(PP. 76, 77) 




Piuiioidea 






Sphaerellaria 


(p. 77V 




Porulosa 




(P-77) ' 


DiscoidL-a 




= Holo- 






(p. 77). 




trypasta 






LaivDidca 


Radiolaria 


(p. 76) 






'(p. 77). 


(p. 75) 






Actinelida 






(p. 78). 








Acanthoiiida 






Acantharia 


(p. 78). 
Sphaerophract 

(p. 78). 






= Actipvlaea 
'pp. 76, 78) 








Prunoidiracta 






L 


i (p. 78). 




Osculosa 
= Mono- 


Xassollaria 

^t 1 


' Nassoidea 

(p. 78). 


I 


trypasta 

. (p. 7Gi 


= .\lonop}da 
(pp. 76, 78) 


ea 


Plfctaidca 
I U'. 78). 



{Continued on the next liage.) 



SCHEME OF CLASSIFICATION 





, 


f 




■ Stephoidea 












(p. 78). 








Xassellaria 




Spyroidea 

(p. 78). 

Botryoidea 








= ^lonopyl 

(coiitd.) 


lea 












(p. 79). 






Osculosa 






Cyrtoidea 




Radiolaria 


= Moiio- 






. (P- 79). 




(contd.) 


trypasta 

{contd. ) 






Phaeocystina 

(p. 79). 


SARCO- 






Phaeodaria 




Pliaeosphaeria 


DINA 






= Ganuopy] 


aea 


(p. 79j. 


(contd.) 






= Tripylaea 
(pp. 76, 79) 




Phaeogromia 

(p. 79). 
Phaeoconchia 

V (P- 79). 








^ i\Iyxoidea 
'(p. 89) 


/" Zoosporeae (p. 89). 




Proteomyxa 




( Azoosporeae (p. 89). 




(p. 88) 


" 


Catallacta 

I (p. 89). 














Mycetozoa 

^ (p. 90) 






' Acrasieae (p. 90). 
- Filoplasmodicae (p. 90). 
^Myxomycetes (pp. 90, 91). 



SPORO 
ZOA 

(p. 94) 



Telosporidia 

(p. 97) 



Neosporidia 



r Schizogregarinidae (j). 97). 
-j Acephalinidae (p. 97). 
(Dicystidae (p. 97), 



Gregarini- 
daceae 
(PP- 97, ! . . 
Oopcidiaoeae i Coccidiidae (pp. 97, 99). 
Ooccidiaceae J Haemosporidae (pp. 97, 102). 
a)p. »/, y»j ^ Acystosporidae (pp. 97, 102). 
r Myxosporidiaceae (pp. 98, 106). 
-! Actinomyxidiaceae (p. 98). 
I^Sarcosporidiaceae (pp. 98, 108). 



FLAGEL- 
LATA 

(p. lO'J; 



( I'autostomata (]i. 109). 

j^ Distoniatidae (p. 110). 
Oikomonadidae (p. 111). 
Bicoecidae (p. 111). 
Craspedomonadidae (pp. Ill, 
121). 
Protomasti- Phalansteridae (p. 111), 
gaceae -. Monadidae (p. 111). 
(p. 110) 15()(loiiidae (p. 111). 

Ampliimonadidae (p. 111). 
Trimastigidae (p. 111). 
Polvniastigidae (p. 111). 
Tnclionvnipliidac" (pp. Ill, 12.3'i. 
l.Opaliindae (pp. Ill, 12:j). 
Chryso- [ 

nionadaceae-^ Coccolitlio[ilu)ridae (p. 114). 
(pp. 110, 125) [ 
Cryptomonadaceae (p. 110) 
Volvocaceac ( Chlamydomoiiadidao (pp. Ill, 
(pp. 110, - 125). 
Ill) ( Volvocidae (pp. Ill, 126). 

Chloromonadaceae (p. 110). 
Euglenaceae (pp. 110, 124). 
Silicoflagellata (pp. 110, 114). ' 
Cvstoflagellata (pp. 110, 132). 
.Dinoflagellata fpp. 110, 130). 



SCHEME OF CLASSIFICATION 



r Gymnostomaceae (pp. 137, 152). 
I Aspirotrichaceae (pp. 137, ir)3). 
I HL'tcrotrichaceae (pp. 137, lo3). 

Oligolrieliaceae (pp. 13", 155). 

Hypotrieliaceae (pp. 137, 1.38). 

Poritricliaceae (pp. 138, 155). 
Suctoria = Tentaculifera (p. 158). 



INFUS- 
ORIA 



Ciliata 

ip. 137) 



PORIFERA (p. 163). 



MEGA 
MASTIC 
TORA 

ipp. 1S3, 
18-4 



Calcarea 

(p. 184) 



Homocoela 

(p. 185) 



Heterocoela 

(p. 187j 



Family. 
Leucosoleniidae 

(p. 185). 
Clathriiiidae 

(p. 185). 
'Sycettidae (p. 187). 
Grantiidae (p. 192). 
Heteiopidae 

(p. 192). 
Amphoriscidae 

(p. 192). 



Sub-Fainily. 



Pharetronidae 

(p. 192) 

Astroscleridae 
(p. 194). 



(' Dialytinae 
J (p. 192). 
I Litlioninae 
L (p. 193). 



MICRO 
MASTIC- 
TORA 

(pp. 183. 

195) 



f Myxospongiae 

(p. 196). 

Hexactin- f Amphidiscophora 

ellida ^1'' ■^^'^)- 
, ,^P I Hexasterophora 



I" 



203). 



OCTACTIXELLID, 

(p. 208). 
Uetera ctinellwa 
(p. 208). 

Tetractin- 
ellida 
(pp. 211, 

212) 
Monaxon- 

ida 
(pp.211, 

216) 



Demo- 
spongiae 

(p. 209) 



Receptaculi- 
tidac (p. 207). 



Ceratosa 

(pp. 211, 

220) 



' Clioristida 
(p. 212). 
Litliistida 
. (pp. 212, 215); 
Halichondrina 

(p. 217). 
Spintliavophora 
(,.. 217). 

!)eii(lroceratina 
(pp. 220, 221). 



■I. 



220). 



SCHEME OF CLASSIFICATION 



COELENTERATA (p 243). 



Class. Order. Sub 

f Eleutheroblastea 

(p. 2:,-i). 

Milleporina 

(p. 2r,7). 



Gymnoblastea 
(Anthomedusae) 

(p. 262) 



Sub-Family. 



HYDRO- 

ZOA 

IP- 249) 



Calyptoblastea 
(Leptomedusae) 



Graptolitoidea 

(p. 281) 



Stylasterina 

(p. 283) 



Trachomedusae 

(p. 288) 



Narcomedusae 

(p. 295) 

Siphono- I Calyco- 

phora- phorae- 

^ (p. 297) [ (p. 305) 



Bougainvilliidae 
(p. 269). 

Podocorynidae (p. 270). 

Clavatellidae (p. 270). 

Cladonemidae (p. 270). 

Tubulariidae (p. 271). 

Ceratellidae (p. 271). 

Pennariidae (p. 272). 

Coryuidae (p. 272). 

Clavidae (p. 272). 

Tiaridae (p. 273). 

Corymorphidae (p. 273). 

Hydrolai'idae (p. 273). 

Monobrachiidae (p. 274). 

Myriotlielidae (p. 274). 
LPelagohydridae (p. 274). 
f Aequoreidae (p. 278). 

Thauinantiidae (p. 278). 

Cannotidae (p. 278). 

Sertulariidae (p. 278). 

Plumulariidae (p. 279) 



Hydroceratinidae 

(p. 279). 
Campanulariidae (p. 280). 
Eucopidae (p. 280). 
Dcndroijra'pt idae 

(p. 281). 
Muiio-prionidac (p. 282). 
Dqirionidae (p. 282). 
_ Retiolitidac (p. 282). 

Stromatoporidae (p. 283), 

Stylasteridae (p. 285). 

Olindiidae (p. 291). 
Petasidae (p. 294). 
Trachynomidae (p. 294). 
Pectyllidae (p. 294). 
Aglauridae (p. 294). 
Geryoniidau (p. 295). 
'Cunanthidaft (p. 296). 
Pegantliidae (j). 296). 
Aegiiiidau (j). 296). 
Sohaaridae (p. 296). 

Mouophyidae (p. 306) 



f Eleutlieroplea (p. 279). 
\ Statoplea (p. 279). 



{Continued on the next 2mge.) 



( Sphaeronectinae 
J (p. 306). _ 
\ Cyinboiicctinae 
I (p. 306). 



SCHEME OF CLASSIFICATION 



HYDRO Siphono 

ZOA I phora 

{conhL) (contd.) 



Calyoo- 

phorae 
[contd. ) 



Family. 



Dipliyiilao (p. 306) 



(p. 307) 



Cubomedusae 

(p. 318) 

Stauromedusae 

(p. 320) 



SCYPHO- 

ZOA -: 
SCYPHO 
MEDUSAE 

(pp. -iil', 

310 1 



Coronata 

(p. 3-1) 



Discophora 

(p. 323) 



^ I'olyphyidae (p. 307). 
Pliysonectidae (p. 307) 

^'''^''^horae. Auronectidae (p. 308). 
^ ' Knizopliysaludae 

(p. 308). 
Chondrophoridae 

(p. 308). 

rCliarvluleidae (p. 318). 
- Cliirodroj.idae (p. 319). 
I Trii.edaliidae (p. 319). 
[ Luceniariidae (]i. 320). 
■ I)fl>astridae (p. 321). 
I Steiioscypliidae (p. 321). 
( Periphyllidae (j>. 322). 

Ephyro])sidae (p. 322). 
I Atollidae (j). 322). 
( Pelagiidae (p. 323). 

Cyanaeidae (p. 324). 
I Ulmaridae (p. 324). 

Ca.ssiopeidae (p. 324) 

Gepheidae (p. 324) 

Rhizostomatidae (p. 325) 
Lyclmovliizidae (j). 325) 
Lei)tobrachiidae (p. 325) 
[ Catostylidae (p. 325) 



' Seinaeo- 
stomata 
(p. 323) 



Rl.izo- 
stoniata 
(p. 324) 



Aiiipluearyoiiiiiac 

().. 306) 
Prayiiiae (p. 306) 
Desiiio))liyiiiae 
^ (p. 307) 
Steplianophyiiiac 

(p. 307) 

Galeolarinae "i 

(p. 307) 

Diphyo])siiia(3 I 

(p. 307) I 
Abylinae 

(p. 307) j 



■ Agalmiiiae (]). 307). 

Apoleminae (p. 307). 

Pliysophoiiiiae 
. (p. 308). 



So 



"I = Arcadoniyari; 
/ (p. 324). 
^ =Radioiiiyana 
i (p. 324). 

I =Cycloiiivaria 
r (p. 325): 



ANTHOZOA 
ACTINO- 
ZOA 

(pp. 249, 326) 



Alcyonaria 

(!>. 32!tj 



Grade. 

Protoalcyonacea 

(p. 342) 



Synal- 

cyonacea 

ip. 342) 



Stolonifera 

(p. 342) 



Coenothucal 
(p. 344) 



(Coiifinued vii- tlic next pinjc.) 



Family. 

I Haimcidae (p. 342). 

I" Cornulariidae (p. 344). 
I Clavulaiiidae (p. 344). 
'1 Tiil.iporidae (p. 344). 
I F(>v<,sitid',e (p. 344). 
■ HrHolitidae (]). 346). 

Helioi.oridae (p. 346). 

Ciiiroscridnc (p 346). 
'hccidae (p. 346). 

Chactetidac (p. 346). 






SCHEME OF CLASSIFICATION 



Class. Sub-Class. Grade. Order. Sub-Order. 


Fauiily. 










f Xeuiidae (i>. 348). 
Telestidae (p. 348). 
Coelogorgiidae 








Alcyonacea 
(p. 346) 


(p. 349). 
{ Alcyoniidae (p. 349). 








Nephthyidae 










(p. 349). 










Siphonogorgiidae 










L (p. 349). 










' 


' Briareidae (p. 350). 










Pseudaxonia 


Sclerogorgiidae 

(p. 351). 
Melitodidae.(p. 351). 










(p. 350) ■ 










.,. 


Coralliidae (p. 352). 












■Lsidae (p. 353). 








Gorgonacea 




Primnoidae (j). 354). 








(p. 350) ~ 


Axifera 
(p. 353) 


Chryjsogorgiidae 

(p. 355). 
Muriceidae (p. 355). 










Plexauridae(p.356). 






Synal- 
cyonacea 

{contd. ) 






Gorgoniidae (p. 356). 




Alcyonaria 

{contd.) 




' 


Gorgonellidae 
I (p. 357). 
' Pteroeididae 












(p. 361). 










Pennatuleae 


Pennatulidae 










(p. 361) - 


(p. 361). 
^'il•gulal•iidae 


ANTHO- 










I ^ (p. 362). 


ZOA 










' Funiculinidae 


{cuntd.) 










(p. 362). 
Anthoptilidac 








Penna- 


Spicatae 


(p. 362). 








tiilacea - 


(p. 362) ^ 


Kophobelenmoiiidae 








(p. 358) 




(p. 362). 
Uinbellnlidae 






















, (p. 362). 










Verticilladeae 












(p. 363) 












Kenilleae 
(p. 363) 1 


Renillidae (p. 363). 










A'eretilleae 












(p. 364) 










■ Edwardsiidae 

(p. 377). 






Echvardsiidea 






(p. 375) 


Protantlieidae 






. (p. 377). 










' Halcaiiipidae 

(p. 380). 




Zoantharia 






Actiniidae (p. 381). 




(].p. .-j-jg, 






Sagartiidae 




365) 


Actiiiiaria 
(p. 377) 


Actiniina 

(p. 380) 


(p. 381). 
Aliciidae (p. 382). 
Phyllactidae 

(p. 382). 
Buiiodidae (p. 382). 
Minyadidae 












(p. 383). 



{Lodtinued on the next 2>(t</e.] 



SCHEME OF CLASSIFICATION 



Class. SulHCbss. Oitler. 


Sub-Older. 


Family. 










foralliinorpliidae 






Acliiiiaiia 


.Stiehodact}'- 


(p. 383). 
Disiosoinatidae (j). 383), 






{could.) 


Una 
(p. 383) 

Eiitocnemaria ) 
(p. 394) \ 


Rhodartidac (p. 383). 
Thalassiaiithidae 
(p. 383). 

Cyatho2)hylHdae (p. 394). 
Cynthaxoniidac (p. 394). 
CyHtiphiillidae (p. 394). 

.Aladrepoiidae [y. 395). 








Poritidac {\>. 396). 










Turbinoliidae(p.398)^ 












Oculiiiidae (p. 399) 












A.straeidae (p. 399) 


,A, 










A. Geminaiitt's 


05 










(p. 400) 


CO 










A. Fissiparaiitcs 


< 


ANTHOZOA 

iyonld.) 


Zoantharia 

{coatd.) 


^ladreporaria 

(p. 384) 


Cyclocnemaria 

(p. 397) 


(p. 400) 
Trochosniiliacea 

[Sub-Fani.] (p. 

401) 
Pocillo])oridai! 

(p. 401) J 










Plcsiofimgiidae 


^ 










(p. 403) 


o 










Fiuigiidae (p. 403) 












Cycloseridae 


^ 










(p. 404) 


■ ^ 










PlcsioporUidae 










(p. 404) 


bo 










Eupsanuinidae 


3 








L 


I (p. 404) 


^ 






/'oanthidea 




Zoanthidae (p. 404). 






(p. 404) 


' 


Zaphrcntidnc (p. 406). 






Antipatliidea 




' Antipathidae (p. 408). 
Leiopathidae (p. 409). 






= Aiiti- 








patliaria 


' 


Dendrobracliiidae 






(p. 407) 
C"i>riaiithi(lea 




. (p. 409). 





409). 



OTENOPHORA (p. 412). 



TENTACULATA (p. 417) 



NUDA (p. 423) 



Cydippidea 



Lobata (p. 418) 



Cestoidea (i-. 420) 
Platyctenea i p. 421) 



Family, 
f Merteiisii<lay (p. 417). 

Calliaiiiridac (],. 417). 
I Pleurobracddidae (p. 418). 

Lcsueuriidae (p. 419). 

Bolinidae (p. 419). 

Deiopeidae (p. 419). 

Euiliainphaeidai! (j). 419) 

iMicharidae (p. 420). 

.Miiciiiiidae (p. 420). 

Calyinniidae (p. 420). 

Ocyroidae (p. 420). 

Ce.stidae (p. 420). 
f Ctennplaliidae (p. 421). 
\ Coeloiilanidae (p. 422). 

P>eioidae (ji. 423). 



SCHEME OF CLASSIFICATION 



ECHINODERMATA (p. 425). 



SLib-Pliyluiu. 



ELEU- 

THERO 

ZOA 

(p. 430) 



Aster- 
oidea 

(pp. 430, 
431) 



Spinulosa 

(pp. 4(_;i, 

462) 

Velata 

(pp. 461, 
464) 

Paxillosa 

(pp. 461, 
466) 



Valvata 

(pp. 461, 
471) 



Ophiur- 
oidea 

(pp.431. 

477) 



Forcipulata 

(pp. 462, 473) 



Streptophiurae 

(p. 41)4) 

Zygophiurae 

(pp. 494, 495) 

Cladophiurae 

pp. 494, 500) 



Endocyclica 

(pp. 529, 530) 



Echin- 
oidea , 

(pp. 431, 
503) 



Family. 

IEchinasteridae (p. 462). 
Solastcridae (p. 462). 
Asteriiiidae (p. 463). 
Poraniidae (p. 464). 
Gaiieriidae (p. 464). 
j\Iitlirodidae (p. 464). 
( l'ytli()iiasteridae(p. 464). 
J My.xasteridae (p. 464). 
{ Pterasteridae (ji. 466). 
r Archasteridae (p. 466). 
I Astropectinidau (p. 467). 
1 Poreellanasteridae 
I (p. 470). 

ILinfkiidae (p. 471). 
Peiitagonasteridae 
(p. 471). 
Gymnasteridae (p. 471). 
Aiitheiieidae (p. 471). 
Pfiilacerotidae (p. 471). 
j-Astcriidae (p. 473). 
Hcliasteridae (p. 474). 
Zornasteridae (p. 474). 
Stichasteridae (p. 474). 
Podicellastoridao 
(p. 474). 
^ Brisingidae (p. 474). 



■ Ophiolepididae (p. 495). 
Aiupliiuridae (p. 497). 
Ophiocomidae (]>. 499). 
Oj.liintliricidae (p. 499). 
Astros.'li.Miiiil.u- (p. 501). 
Trichastcii.lau {]>. 501). 
Euryalidae (p. 501). 
Cidaridae (]i. 533). 
Efhinothuriidae (]>. 535). 
Salcniidae (p. 537). 
Arliaciidae (p. 538). 
Diadeiuatidae (p. 538). 



Echinidae (p. 539) 



Clype- 
asbroidea 

(],p. 529, 
542) 



' Protoclypea; 

(p. 548). 

Euclype- 
astroide; 
(p. 549) 



-.19). 



troidea 

Filnilaridae (]i 
Ecliiuantliidae 

= Clypea.stridao 

(p. 549). 
Laganidae (]). 549). 
Sciitellidae (p. 549). 



f Temno- 
I pleiirinae 

- (p. 539). 
Ecliininae 
I, (p. 539). 



(Continued o)i the, next page.) 



SCHEME OF CLASSIFICATION 



Sub-riiyluni. Class. 



Echinoidea 

[c.on/d.) 



ELEU- 
THEROZOAl 

{coatd.) 



Holothuroidea 

(pp. 431, 560) 



PELMATO- 
ZOA 

(pp. 430, o79) 



Spatangoidea 

il>p.529,549) 



Crinoidea 

(p. 580) 



Thecoidea = 
Edrioaster- 

OIDEA 

(pp. 580, 596). 
Cakpoidea 
(pp. 580, 596). 

C'rSTOlDEA 

(pp. 580, 597). 
Blastoidea 
L (pp. 580, 599). 



Aspidochirota 

(p. 570). 
Elasipoda 

(p. 571). 
Pelagothuriida 

(p. 572). 
Dendrochirota 

(p. 572). 
Molpadiida 

(p. 575). 
Synaptida 

(p. 575). 



LvADUiYATA 

(p. 595). 
Articulata 

(p. 595). 

Cam ER ATA 

(p. 595). 



Family. 
[ I'A'liinonidae (p. 553) 
Nucleolidae (p. 554) 
Cassidulidae (p. 554) 
Ananchytidae (p. 554) 
Palaeostoniatidae 

(p. 554) 
Spataiigidae (p. 554) 
^ Brissidae (ji. 556) 
Archaeocii/oridac 

(p. 557). 
Mr/,uu/i,/,ir (p. 557). 
7V,„-,r/,/„/,/„r(p. 557). 
lIolediji>i>idra (p. 558). 
Echinocuiiidae (p. 558). 
CoUyriiidac (p. 559). 



AFternata 

(p. 554). 



Sternata 

(p. 554). 



Hyocrinidae (p. 590). 
Rhizocrinidae (p. 590). 
Pentacrinidae (]). 591). 
Holopodidae (p. 592). 
Comatulidae (p. 594). 



PROTOZOA 



MAECUS HARTOCr, M.A., Trinity College (D.Sc. Lond.) 

Professor of Natural History in the Queen's College, Cork. 



CHAPTEE I 

rnoTOzoA — introduction — functions of protoplasm — 

CELL-DIVISION ANIMALS AND PLANTS 

The Free Amoeboid Cell.— It' 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 ca^•ity was at first called a 
" cell " ; and this term was then applied to the bounding wall, 
and finally to the unit of living matter within, the envelope 
receiving the name of " cell-wall." In this modern sense tlie 
" cell " consists of a viscid substance, called first in animals 
" sarcode " by Dujardin (1835), and later in plants " protoplasm " ^ 
by Yon Molil (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, HirediU, 2nd ed. 190:3 ; 
Heniieguy, Lc(;ons sicr la Cellule, 1896 ; Yerworn, General Physiology, English 
ed. 1899 ; Wilson, The Cell in Development and Inheritance, 2nd ed. 1900. All 
these books contain full Inbliographies. 

- As we shall see later, it is l>y no means easj- to separate sharjily I'rotozoa and 
Protoiihyta, the lowest animals and the lowest plants ; and therefore in our pre- 



PROTOZOA 



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 
tliat of the others ; and this co-operation has so trained and 
specially moilified 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, in 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 Amoeba may 
measure in its most contracted state l/lOO in. or 250 /it in 
diameter,^ and some closely allied species {Pelomyxa, see p. 5 2) 
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 ])ecomes 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- 

liniinarv survey to designate lowly forms of lifi-, not formed of the aggregation of 
dilFerentiated 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 jilants (see also p. 35 f.). 

^ The " micron," re])rcsented by the Greek letter /u, is 1/1000 mm., very nearly 
1/2.'), 000 of an inch, and is the unit of length commonly ado]>ted for niieroscojiic 
measurements. 

- A solid substratum is required, to whicili the lower surface adiiercs slightly : that 
movement is complicated b\- a sort of rolling over of tlie upper surface, constantly 



PROTOPLASM 



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-tiuid, and may well be compared 
to very soft dough which has already begun to rise. It resembles 






Fk;. 1. — Amoeba, showing clear ectoplasm, granular endoplasm, dark nucleus, and lighter 
contractile vacuole. The changes of form, a-f, are of the A. Umax type ; <j, h. of 
the .1. 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 {i.e. kill it by 



prolonging tlie front of the jiseudopodiuni, while the material of the lower surface is 
brought up behind. H. S. Jennings, Contr. to the Study and Bchnxiour of the Lower 
Oriianisiiis, 1904, pt. vi. p. 129 f., "The Jfovements 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 a.xis 
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 
pseudopodiuni is put forth, and ceases when it has attained full dimensions. 

"^ "We use as a corresponding adjective the term "plasmic." 



PROTOZOA 



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 /x 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," " endosarc ") 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 alveoli, that is, the points 
where two or three boundaries meet.^ Tlie 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 tlie 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 l)e applied to fixed specimens, for natural death is followed bj" 
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 SchewiakotF, in Z. v-iss. 
Zool. Ivii. 1893, p. 32, to consist of a calcium phosphate, probably CasPoOg. 

'■'■ It is not always possible to tell how much of these structures represents 
what existed in life (see p. 11). 



RESF'ONSE TO STIMULI 



..^0m&!^ 



iisuiiUy arranged in a disliiict network, eontluent into a "parietal 
layer" within the nuclear wall; tlie meshes traversing a. eaA-ity 
full of li(|ui(l, the nueloar sap, and containing in their course the 
granules; while in the t-avity are usually found one or two droplets 
of a denser suhstance 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 
" optinumi." 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 al)ove 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 
a still higher point they will not 
recommence under any circumstances 
whatever. 

Again, a slight electric shock will 
determine the retraction of all pro- 
cesses, and a period of rest in a 
spherical condition. A milder shock 
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 l)y larger 
creatures, etc. (see also p. 21). 

If substances solul)le in water be introduced the xVmoeba will, 




. 2. — Ovum of a Sea-Urchiu, 
showing the radially striated cell- 
membrane, the cytoplasm con- 
taining yolk-granules, the large 
nucleus (germinal vesicle), with 
its network of linin containing 
chromatin granules, and a large 
nucleole (germinal s])ot). (From 
Balfour's Embrt/olog)/, after 
Hertwig.) 



^ The chromatin and nucleoles are especially rich in phospliorus, ]ir()lialily in the 
combination micleinic acid. 



PROTOZOA 



US ii 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, l)ut 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 w4th oxygen.^ Such 
of these changes as involve the excretion of carbonic acid are 
termed " respiratory." 

This liberation of energy is the " response " to an action (jf 
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 
H(j often means an obvious contraction, but is better termed 

' In i.-lieiuical phrase the process is " exotlieriaic." 



ASSIMILATION 



"motility"": and irritability evinced l>y 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. 3), 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 — i.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. — Amoeba devouring a ])lant cell ; lour successive stages of ingestion 
(From Verworu.) 



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 bvdk due to nutrition is tlius twofold : part is the 
increase of the protoplasm itself — " assimilative growth," part is 
the storage of reserves — " accumulative growth " : these reserves 
being availal)le in ttirn by digestion, whether for future true 
growtli 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 sliot ; but not 
that it could make provision for an increase of its own bulk, so 
as to irain in calibre and strenutli, nor even iur tlie restoration 



PROTOZOA 



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 







Fro. 4. — Amoeba poli/jjuilia in successive stages of equal tission ; nucleus dark, con- 
tractile vacuole clear. (From Verworn, after F. E. Scliulze.) 



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 xirotoplasniic growtli. 



VITAL PROCESSES 



" sisters " to one another. We must l)ear in mind that in this 
self-sacriticiug maternity the mother is resolved into her children, 
and her very existence is lost in their production. The above 
phenomena, iekitability, motility, digestion, nutPxItion, growth, 
KEriiODUCTiON, 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 violently 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 alcohol 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 f?e-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 solid 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 al)solute alcohol, and is attended with the same optical 
results. The study of the behaviour of coagulable colloids has 
been recently studied l)y 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 MicrotomisV s Vade Mccum, 1st ed. (1885), pointed out 
that "Clearing reagents are liquids whose primary function is to make microscopic 
preparations transparent by penetrating amongst the higlily refractive elements of 
wliich the tissues are composed, having an index of refraction not greatly inferior 
to that of the tissues to be cleared " (j). 213). "We showed later ("The State in 
•which Water exists in Live Protoplasm," in Ecp. Brit. Ass. 1889, p. 645, and 
Journ. Boy. Micr. Soc. 1890, p. 441) that since the refractivity of living proto- 
jilasm is only 1'363-1*368, it follows that the water in the living protoplasm is in 
a state of j)erfpct )tliysical conil)ination, like the water of a solution of gum [read a 



1 2 PROTOZOA 



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, like 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 impossiljle to state 
them all in such terms than it would Ije 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 
Hn[)position, and for these cases we must admit that living protoplasm is a viscid 
li(iuid 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, Fixlrumj u. 
Fdrbung, 1900. 

' In its original use "automatism" designates the continuous sequence and 
combination of actions, without external interference, ])erformed 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 jiroteids with nucleinic acid, which in addition to the above elements 
contain phosphorus. 



METABOLISM I 3 



lias 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,'' 
wdiere 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 (1) the mere breaking of 
complex substances into simY)ler 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- 

' The specific gravity oF living protoplasm has been estimated liy detci'miniiig 
tlie density of a solution of gum in which certain Infusoria Hoat freely at any 
depth. It Avas found by the concurrent results of Julia B. Piatt and Stephen R. 
Williams (see Amcr. Natural, xxxiii. 1899, p. 31, xxxiv. 1900, p. 95) to be from 
1-014 to 1"019, while the Metazoon Hiidra was found to give a density of only 1-0095 
to 1 -0115. The difference of about '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, etc. Jensen obtained a much higher 
result for Paramccimn, using a solution of the crystalloid substance, ])otassium 
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 



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, etc.). 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 must 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. 2. '5 f). 

The Protista that live in water undergo a death by " diffiu- 
ence " or " granular disintegration " on being wounded, cruslied, 
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 v/hich themselves finally dis- 
solve. If the injury be a local rupture of the external pellicle or 

^ Energy may be derived from the mere S2)littimj up of comjilex substances 
within the cell : when such a splitting involves the liberation of CO2 the process 
is (mis-)called " intramolecular respiration." 

- A similar organ, but with cellular walls, is the bladder of the Rotifers and 
certain Platyhelminthes, in connexion with their renal system (vol. ii. pp. 53, 199, 
and e.sjiccially pp. 2l:3-.">\ 



RESPIRATION — DIGESTION I 5 



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 liable to this disintegration process, often termed 
" diliiuenee," 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 possiljle. 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 tlie 
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 resoh'ed into two or 
more new substances, often taking up the elements of w^ater 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 
simple 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 
simple sugars), that are really taken up liy the protoplasm, 

1 In Rej}. Brit. Ass. 1888, p. 714 ; Ann. Mag. Nat. Hist. (6), iil. 1889, p. 64, 
This view has been fully worked out, mainly on Ciliates, by Degen in Bot. Zeit. 
kiii. Abt. 1. 1905. 



1 6 PROTOZOA 



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 " {Fulign 
varians,-p. 92), and by Professor Augustus Dixon and the author 
from the gigantic multinucleate Amoeba, Pelomyxa ^palustins 
(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- 

1 See Hartog, "On Multiple Cell-division, as compared with Bi-partition as 
Herbert Spencer's limit of growth," in Kcp. 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. 

'■^ "On the Digestive Ferment of a large Protozoon." Ec2i. Brit. Ass. 1893, p. 801. 

■' See for studies of the movements of Protoplasm, Berthold, Frof.oplasmn- 
i)ieclmnik (1886) ; Biitschli, Investigations on Microscojnc Foams and on Proto- 
plasm, English ed. 1894 ; Verworn, General Physiology, 1899 ; Le Dantec, La Maiierc 
Vivante, 1893 1 ; and Jensen, " Unters. ueb. Protoplasmamechanik," in Arcli. Cles. 
Phys. Ixxxvii. 1901, p. 361 ; Davenport, Experimental Morpiliology, i. 1897 ; H. S. 
Jennings, Contr. etc. 1904. 



MOVEMENTS I J 



growths, and " coutraction," leading to their diminution and dis- 
appearance within the general surface.^ Expansion is prohahly 
due to the lessening of the surface-tension at the point of out- 
crrowth, contraction to the increase of surface-tension. Yerworn 
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 Eadiolaria, 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 nifile 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 
" fiagella," 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 roimd, bend sharply 

^ The terms " expansion " and " contraction " refer only to the suj)erficial area : 
it is very doubtful •whetlier the volume alters during these changes. 

VOL. I C 



1 8 PROTOZOA 



down to the surface and slowly recover ; tlie movement atfects 
the cilia successively in a definite direction in waves, and pro- 
duces, like that of flagella, either locomotion of tlie cell or 
currents in the medium. We can best realise their action by 
recalling the waves of bending and recovery of the cornstalks 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 flagella are probably also due to 
changes of surface tension — alternately on one side and the other 

Fk;. 5. — Motion of a I'ow of cilia, iu profile. (From Verworn.) 

in the cilium, but passing round in circular succession in the 
flagellum,- giving rise to a conical rotation like 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. AVhen the organism is free, the 
flagellum is usually in advance, and the cell folLjws, rotating at 
the same time round its longitudinal axis ; such an anterior 
flagellum, called a " tractellum," is the common form in l^rotista 
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, 

' For discnssions on the mechanism of ciliary action, see Schiifer, Anat. Anz. 
xxiv. 1934, p. 497, xxvi. 190.'., p. 517 ; Schuberg, Arcli. ProtxH. vi. 190."), ji. 8;'.. 
- T.ilvo tlio line of most rapid <;ro\vth iu a eircunmutating plant-stem. 



MOTILE REACTIONS 1 9 



reiidily-staiiiing plasm, which corresponds to a " eeutrosoiue " or 
centre of plasniic forces (see below, pp. 11"), 121, 1-11); it lias 
lu'en termed a " lilepliaroplast." ^ 

.\.gain, the cytoplasm may have differentiated in it delinite 
streaks of specially contractile character ; sucli streaks within its 
substance are called " myonemes " ; they are, in tact, muscular 
fihrih. 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 tliicker. It seems probable tliat 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, i.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 
(tsmotically active substances which induced expansion."^ 

The Motile Reactions of the l*rotozoa ^ 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 follow'S : — (i.) mechanical : such as agitation and 
contact ; (ii.) force of GRAVITY, or centrifugal force ; (iii.) 
CURRENTS in the water; (iv.) radiant energy (light); (v.) 
changes in the temperature of the medium ; (vi.) electric 
cuRitENTS through the medium ; (vii.) 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. 

' A similar body lies at the centre to which the axial filaments of the radiating 
liseudo[)odia of the Heliozoa converge, and might be termed by parity a 
" podoplast" ; but " centrosome " is a convenient general term to include all such 
bodies. It is clearly of nuclear origin in Trypanosoma (Fig. 39, p. 120). 

^ See for development of this view AV. M'Dougall in Juurn. 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 
Murphology, 1897. 



PROTOZOA 



(i.) Mechanical stlmuli. — 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 Ehizopods 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 tlie 
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 ddhris 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. 

(ii.) Most living beings are able to maintain their le^•el 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, 
Euglena and Chlamydomonas, Ijegin 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 Sec Jenniuirs in Woods HoU. Biol. Led. 1S99, v. 93. 



REACTIONS TO STIMULI 



(iii.) PiHEOTAxy. — This is the tendency to move against 
the stream in flowing water. It is shown hy 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 Piotifers, 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 
Light. These movements have been distinguished into " photo- 
pathic," i.e. 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 Paramecium 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 
I)art, 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 Paramcdnm, the response, instead of carrying it away, 
brings it into the region of greater concentration, and may thus kill it. 



2 2 PROTOZOA 



then are re])elled 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 /a/ 10 and 
49 ft/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° P.); that of Paramecium is 28° C. (82' P.). 

(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 TracJielomonas, 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 
" galvanotaxy," and this particular form is " negative." Opalina 
(Fig. 41, p. 123), however, and most Flagellates are "positively 
galvanotactic," and 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 P!i>/sioI. vol. xxvi. 1900-190], p. 291. 



REPRODUCTION 2 3 



witli that of '• chemiotaxy " for siil)stances that in weak sulution 
are attractive or repellent to the being. Parameciiun, wliich 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 stimuli, such as we have just studied, or to 
iriternal stimuli, the outcome of internal changes, such as fatigue, 
hunger, and the like. Of the latter kind are the movements that 
result in p.ErRODUCTiox. 

Reproduction. — We have noted above that the growth of an 
organism which retains its shaj^e 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 

^ 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 cm. cube measures 6 square centimetres, and 
its bulk is 1 cubic centimetre. The sui)erficial area of the 2-centimetre cube 
measures 24 square centimetres, while its volume measures 8 cubic centimetres. 
Thus the larger cube has only 3 cm. sq. of surface to every cubic cm. 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 culie will divide it into eight 
separate 1 -centimetre cubes, each now possessing the original ratio of surface to 
volume. 



PROTOZOA 



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 
cataholic 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 must 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 life 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 

^ 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 
HO 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 cliaracters of the internal structures of such a nucleus 
are constantly changing with the vital activities and functions of the cell. 



CELL-DIVISION 



25 



suspended in the linin network (long regarded us a mere 




Fig. 6. — Changes in nucleus and cell in indirect (mitotic) nuclear division. A, resting 
nucleus with two centrioles ^ in single centrosphere (c) ; B, ceutrosphere divided, 
spindle and two asters («) forming ; C, ceutrospheres separated, nuclear wall 
disappearing ; D, resolution of nucleus into chromosomes ; E, mature plasmic 
spindle, with longitudinal fission of chromosomes ; F, chromosomes forming 
equatorial plate (cjj) of spindle. (From Wilson.) 



niicleole). Such a nucleus is often termed 
nucleus.^ 



vesicular 



^ 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 mucli confusion 
in the iise of the terms. 

- For a detailed study of tlie nucleus in Protista, see Calkins in Arch. ProUstcnk. 
vol. ii. 1903. 



26 PROTOZOA 



When cell-division is alDout 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, C), 
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, E). 
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 lie 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 centrosonie, 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 

^ 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 eftects to 
such physical forces as magnetism, static electricitj', 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, Intcrpretadon Dindmica dc la Division CrIuJar, 1902 ; Rhumbler, in 
Arcfi. Entu-. xvi. 1903, p. 476 ; Hartog, C.R. cxx.xviii. 1904, p. 1525, and "On the 
Dual Force of the Dividing-cell." pt. i. Proc. Hoy. Soc. 1905 B. Ixxvi. j.. 548. 



NUCLEAR DIVISION 



27 



of enaliling us to watch the changes m the distribution of the 
lines under changing conditions or continued strain. 

Tlie chromosomes are now completely split, 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 sliort of the 




Fio. 7. — Completion of mitotic cell-division. G, splitting of equatorial plate [ep) ; H, 
recession of daughter clironiosomes ; I, J, reconstitiition of these into new nuclei, 
fission of the centrioles and of the cytoplasm. //", Central fibres of spindle ; n, 
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 daugliter- 



PROTOZOA 



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 " whicli 
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 tlie 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 
liereditary 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 difiicult 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 
conunonly maintained that the chromatin represents a " germ- 

' See Th. Boveri, Enjchnissc neb. d. Konstitution d. chromatischcn Suhstanz dcs 
Zcllkcrns (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 thev contain. 



MITOSIS OR KARYOKINESIS 



29 



plasm " or " idioplasm " of relnti\ely great persistence, which 
g'ives 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 




Fig. 8. — Fissiou witli modified karyokinesis iu the Filose Rhizopod Eufjhjpha. A, out- 
growth of half of the cytoplasm, passage of siliceous plates for young shell 
oiitwards ; B, completion of shell of second cell, formation of Mi</-«-nuclear spindle ; 
C, D, further stages. (From Wilson, after Schewiakott'.) 

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 
Eiifihjpha (Fig. 8). 

In many Sarcodina and some Sporozoa the nucleus gives off 
small fragments into the cytoplasm, or is resolved into them ; 



^ The fact tliat it is Iiy mitotic division that the uiiditrcrcntiated germ-cells 
lU'oduce the "differentiated" tissue-cells of the body of the highest animals, is 
again irreconcilable with such theories, whose chief advocates have been A. Weis- 
niann and his disciv>les. 



30 • PROTOZOA 



they luive 1 »een termed " chromidia " Ly IJ. Hertwig. New 
nuclei may be formed by their growth and coalescence, tlie 
original nucleus sometimes disappearing more or less completely. 

In certain cases 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 tliis and the uninucleate or true cell. Thus in 
one species of Amoeba {A. hiwudeatcC) 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 " wiLliout reference to their mode of origin. 

The rhytlim 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. Eest is rare, 
and assumed only when the cell is exposed to sucli unfavourable 
external conditions as starvation, drought, etc. ; it 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 growtli, 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 tliis process the number of individuals is rapidly 

' Temporary i)lastoganiy is a jirocess fouiid in sonic, Foraniinifera. where two 
organisms unite by their cytoplasms so that there can be complete blending of 
these, while the nuclei remain distinct : thej- ultimately separate again. In the 
conjugation of the Infusoria, the union of the cytoplasms is a temporary 
plastogamy (see ji. 148 f ). 

- See Figs. 9, 20, -'A. 34, etc., pp. .54, S9, 95, 101. 



I BROOD-FORMATION COLONIES 3 I 

inereased, hence it has received the name of " sporulation." The 
term spores is especially applied 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, " llagellulae " if flagellate), " aplanospores," if 
motionless. "VVe 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 tlie 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 I'rotista must have been the starting- 
points for the Higher Animals and Plants ; probably apocytial 
Protista were the starting-points of the Fungi. In the Higlier 
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 

' One obvious effect of lirood-roriHatiou is to augment nipidl}- the ratio of 
sui>eitiuial area to bulk : alter only three divisions (p. 23, note) the ratio is 
doubled ; if the divisions be nine in succession so as to produce a brood of .'J12, the 
I'atio 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 
con-elate with that increased activity ; so that they disseminate the sjiecies, 
spreading far and wide, and justifying the name of "spore" in its primitive sense 
(from the Greek o-7retpw— I scatter [seed]). 



PROTOZOA 



completed before the cytoplasm divides ; tlius 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 througli 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-suiDijly 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 rei^letion. 
When a cell has entered on such course of " miserly " conduct, it may lose 
all power of drawing on its ovn\ 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 Ijoth.- We may call this resumjition 
" germination." 

Very often in the study of a large and complex oi-ganism 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.jiass 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 imder what would outAvardly seem to be most a})propriate conditions. 
A certain lapse of time is an essential factor for sprouting. It would appeaj- 
that in the Potato the starch can only be digested hj 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 sujjervened ; and that sprouting can only 

^ This condition may be protracted in the segmentation of the egg of certain 
Higher Animals, such as Per i2)atus {Yo\. Y. p. 20). It is clearly only a secondary 
anil 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 develoii. This 
has lieen mistenned "Chemical fertilisation," di.scovered within the last six years 
1)}' Jacques LoeL. and already the subject of an enormous literature. 



I SYNC, AMY GAMETES ZYGOTE 33 

take place when solul^le 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 nuist be very slow in a resting organism ; and 
any external stinudus tliat will tend to protojjlasmic 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 
]iroducing 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 
tlie 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 sejaarates 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 Avith 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 

^ See Hartog in Bcp. Brit. Ass. 1896, p. 933, 1900, p. 786. 
- Commonly called "fertilisation," or "sexual union," inadeipuite aiul inis- 
leailing terms. 

VOL. T D 



34 PROTOZOA 



oases which prevail among the Higher Animals and Plants, the 
larger cell is motionless, and the smaller is active, ciliate, flagellate, 
or amoe])oid : 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 hvo 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 JNIanunals and Sauropsida there seems also to lie a rheotactic 
action of the cilia lining the oviducts, which work downwards, and so induce 
the sperms to swim u^Jwards 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.- 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. 

As a rule, one at least of the j)air-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 jihases of mitosis, or 
even in the "resting state." A filjrillation of the cytoplasm during the 
jirocess, radiating around a centrosome or two centrosomes indicates a strained 
condition."' 

^ For details see Hartog, "Some Problems of Reproduction," Quart. Journ. Mkr. 
Sci. xxxiii. p. 1, xlvii. p. 583; and Ann. Biol. vol. iv. (1895) 1897 ; E. B. "Wilson, 
Yves Delage, and Hcnneguy (references on p. 3, note) ; and for a singularly clear 
and full treatment of the processes in Protozoa, Arnold Lang, Lchrb. d. Vcryl. 
Anat. 2nd ed. Lief. 2, " Protozoa," 1900. 

" This phenomenon, which we have termed "exogamy," is connnon in I'roto- 
I)hyta ; it has been clearly demonstrated by Sehaudinn in Foraininit'era and the 
Lobose Rhizopod Trichosj^lMa-ium (p. 53 f. Fig. 9), and by Pringsheim in tiie 
Volvocine Pandorina (p. 128 f. Fig. 45). It is quite independent of the dilferentia- 
tion of binary sex. 

■■' Other modes of synganiy, such as karyoganiy and plastogamy, we shall discuss 
below, ]ip. 69, 148 ; see also p. 30. 



I REGENERATION ANIMALS AND PLANTS 35 

Regeneration. — Finally, experiments have been made by 
several obse^^■ers as to the effects of removing pa,rts of l*rotozoa, 
to see how far regeneration can take place. The chief results 
are as follows : — 

1. A nucleated portion may regenerate comphtehj, if of 
sufficient size. Consequently, multinucleate forms, such as 
Actinosphaerium (Heliozoa, Fig. 19, p. T-j, 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 Eadiolarian 
"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- 
liood Ijy taking in one another's washing. For part of the food 
material taken in in this way is applied 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 Masted in by-products. Clearly, 
then, the sup])ly 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 lUol. Crnl.ralh. iv. ]>. 710, v. ]>. 137 (1884-6), in 7/(;r. Gcs. Frcihurg, 
i. ii. 1886-7 ; Verworn (reference on ji. 16) ; F. R. Lillie in Journ. Morph. xii. 1896, 
p. 239 ; Nussbauni in^rcvV. laikr. Ana/,, xxvi. 1886, \>. 485 ; Balbiani in IlccucU Zool. 
Suisse, V. 1888, in Zool. Anz. 1891, pp. 312, 323, in Arch. Micro(jr. iv. v. 1892-3. 
For Higher Organisms especially see T. H. ^loigan, JlcycncrcUion, 1901. 



36 PROTOZOA 



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 
sulpliates 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, tliey 
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, etc.) and 
free oxygen ; and from these carbohydrates or fats, together with 
ammonium salts or nitrates, etc., the vegetal protoplasm at large 
can 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 jihenol and thymol, 
and acids as salicylic acid, etc., and their salts and esters. 

■•^ 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 ray.s," is not only 
inoperative, but has a destructive action on the pigments themselves, and even 
on the protoplasm. Chloi-ophyll is present in all eases even when more or less 
modified or masked by the accomiianiment of other ]iigments. 



I ANIMALS AND PLANTS 37 

distinguished as " holophytic," and that from lower substances, 
which, however, contain organically combined carbon, as " sapro- 
ph}tic," 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 
ditticulty. 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 

^ Similar]}', threads unite the cells of the colonial plant -Flagellate Volvox, 
passing through the thick gelatinous cell-wall (pp. 126-127, Fig. 44). 



3 8 PROTOZOA 



in abeyance for tlie 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 j^hysiological consideration, and we 
have now arri^■ed at a morphological distinction, very valid 
among higher organisms. 

Higher Plants consist of cells for the most ^"'""'^ (^(«'h 
isolated in its oion cell-ca^vity, save for the few slender threads of 
communication. 

Higher AiYTMALS consist of cells that are rarely isolated in 
this way, hut are mostly in mutucd contact over the greater j^art 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, li\dng 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. 



1 ANIMALS AND PLANTS 39 

tliougli never wholly absent. lutiacellular 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 wliich have the power 
of manufacturing true food-stuffs from lower chemical sul^stanccs 
tlian proteids, often with tlie 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 tlieir 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 
differentiated fibrils in the cytoplasm of individual cells. Plants 
that can form carboliydrates 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 syncytes are rare — the cells being each invested with its own 
wall, and, at most, only communicating by minute threads with 
its neighliours. No trace of a central nervous system witli 
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 
fil)rils. Their food (except in a few parasitic groups) is always taken 

' Pit,niients soluble in tlic ordinary solvents of fats, sncli as ctliei licnzoi, 
cliloroforin. etr. 



40 PROTOZOA 



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 JMetazoa. All Metazoa fulfil 
the above conditions. 

But when we turn to the Protozoa we find that many of the 
characters evade us. There are some Dinoflagellates (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 lie quite 
off the possible track of the origin of Metazoa from Protozoa. 
Indeed, a strong natural line of demarcation lies between Metazoa 
and Protista. Of the Protozoa, certain groups, like the Foramini- 
fera and Eadiolaria 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- 
intr the livinfj world into the Metazoa, or Higher Animals, which 



I METAZOA, METAPHYTA AND PROTISTA 4 1 

are sliarply 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 Ciliata, 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.). 



CHAPTEE II 

PROTOZOA {COXTIXUED) : SPONTANEOUS GENERATION 

characters of protozoa classification 

The Question of Spontaneous Generation 

From the first discovery of tlie 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 wlio l)elieved tliat 
Lice bred directly from the filth of human skins and clothes ; ^ and 
that Blow-fiies, 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. Piedi (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 intellii^cnt men of fair general 
education, even belonging to a learned profession, tliat tliis is not the case. 

42 



CHAP. II SPONTANEOUS GENERATION 43 

contemporary, in the latter half of the seventeentli century 
adduced strong reasons for ascribing the origin of the organisms 
of putrefaction to invisible air-borne eggs. L. Joblot and H. 
Balcer in the succeeding half-century investigated the matter, and 
sliowed that putrefaction was no necessary antecedent of the 
appearance of tliese 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 
AVrisberg 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 sufliciently long at tlie 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 Needhani. 

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 Ijy the elder I'ouchet. 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 wliile 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 
^\■ith 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 brouglit about the settling of such particles in the elbows 



44 PROTOZOA 



or on the sides of the tulje : 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 Eev. 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.^ 



PEOTOZOA 

Organisms of various metabolism, formed of a single cell or 
a'pocyte, or of a coloiiy of scarcely differentiated cells, lohose organs 
are formed by differentiations of the protoplasm and its secretions 
and accretions ; not convposed. of differentiated multicellular tissues 



^ Dr. H. Charlton Bastiaii has recenth' maintained a contrary thesis {The 
Nature and Origin of Living Matter, 1905), but lias 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 si)ecialised for a definite function ; the term "organ" 



HISTORY 45 



This definition, as we have seen, excludes Metazoa (including 
Mesozoa, Vol. II. p. 92) sharply from Protozoa, hut leaves an un- 
certain boundary on the botanical side ; and, as systematists 
share with nations the desire to extend their sphere of iniluence, 
we shall here follow tlie 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 Pioyal 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 tlie 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, Leger, and Labbe 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, 
Claparede 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 grouit of cells or tissues in a Metazoon or 
Metaphyte. AVe do not consider that tliis distinction warrants tlie introduction of 
new words into the terminology of general Zoology, however convenient these may 
be in an essay on the jiarticular question involved. 

1 This has been especially tlie case with tlie Flagellata, tlic Proteoniy.Ka, and 
the Mycetozoa. 



46 PROTOZOA 



the largest nuniber of species to the roll. Ehrenberg about 1840 
described, indeed, an enormous nuniber 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 JVIetazoa, and largely advanced our con- 
ceptions of protoplasm. His work was continued in Germany by 
Ernst Haeckel, who systematised our knowledge of the Eadiolaria, 
Greeff, Eichard Hertwig, Fritz Schaudinn, and especially Biitschli, 
who contributed to Bronn's Thier-Rcicli a monograph of monu- 
mental conception and scope, and of admirable execvition, on 
which we have freely drawn. Cienkowsky, a Eussian, and James- 
Clark and Leidy, both Americans, have made contributions of 
high quality. 

Lankester's article in the Emydoixvdia Britannica was of 
epoch-making quality in its philosophical breadth of thought. 

Delage and Herouard have given a full account of the Protozoa 
in their TraiU de Zoologie ConcrHe, vol. i. (1896) ; and A. Lang's 
monograph in his Vergleichende Anatomic, 2nd ed. (1901), contains 
an admirable analysis of their general structure, habits, and life- 
cycles, together with fall descriptions of well- selected types. 
Calkins has monographed "The Protozoa" in the Columbia 
University Biological series (1901). These works of Biitschli, 
Delage, Lang, and Calkins contain full bibliographies. Dotlein 
has published a. most valuable systematic review of the Protozoa 
parasitic on animals under the title Die Protozoen ah Parasiten 
%nd Krankheitserreger (1901); and Schaudinn's Archiv filr 
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, Eadiolaria, Foraminifera, etc. ; it 
is clear and glassy in the Lol)ose Eliizopods and the Acrasieae ; 
it is continuous with a firm but delicate superficial pellicle of 
niembraiious character in most Flagellates and Infusoria ; and this 
pellicle may ag;iin 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 (Colcps, Fig. 54, 



II PROTOPLASM — OEOGKAPHICAL DISTRIBUTION 47 

p. 150). Again, it may I'orm 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 fiagella are motile 
thread-like processes of active protoplasm which perforate the 
pellicle ; they may be condjined 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 Ciliates. 

The Geographical Distribution of I'rotozoa 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 
lieated 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, — Llutit, thread-like, or anastomosing. In some cases the protoplasm 
shows a gliding motion as a whole without any distinct pseudopodium, as in Amoeba 
liiiiax (Fig. 1, p. 5), and a pseudopodium may pass into a thin, active flagellum, 
whicli is, however, glutinous and serves for the capture of prey : such often occurs 
in the Lobosa Podostoma and Arcuothrix, Avhich are possibly two names for one 
species or at least one genus ; and in many cases a slender pseudopodium may be 
waved freely. 

- See Schewiakofl", *' Ueb. d. Geograjih. A'erbreitung d. Siisswasserprotozoen," 
in Mim. Acad. SI. Pitersb. ser. 7, xli. 1893, No. 8. His views apply to most 
minute acpuitic organisms— Animal, Vegetable, or Protistic. 



48 PROTOZOA 



bution," just as with the fresh-water Tuibellaria and the Eotifers 
(vol. ii. pp. 4 f., 226 f.). We can distinguish in fresh- water, as in 
marine 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 
" limicolous " (or " sapropelic," as Lauterborn terms them), and to 
be found among the bottom ooze. Many species are " epipliytic " 
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-liairs 
of mosses and tlie 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 Eadiolaria ; 
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 Chythidieae, 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 exliibiting 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 PiIIIZopoda in the old wide sense (including all 



CLASSIFICATION 49 



that move by pseudopodia during the great part of tlieir 
active life), and the FLA(iELLATA in the widest sense, are 
not easy to split up ; lor many of the former have flagellate 
reproductive cells, and many of the latter can emit pseudopodia 
with or witliout the simultaneous retraction of their flagella. 
The Eadiolapja are well defined by tlie presence in the 
body plasm of a central capsule marking it off into a 
central and a periplieral portion, the former containing the 
nucleus, the latter emitting tlie 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 
tliat have flagella as their principle organs of movement or nutri- 
tion during the greater part of their active life. The remaining 
groups (which with the Eadiolaria compose the Sarcodina of 
Blitschli), are the most difficult to treat. The Ehizopoda, as we 
shall limit tliem, are naked or possess a simple shell, never of 
calcium carbonate, have pseudopodia that never radiate abundantly 
nor brancli freely, nor coalesce to form plasmatic 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 Mycetozoa 
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 Heliozoa resemble the Eadiolaria 
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 Pkoteomyxa 
forms a sort of lumber-room for beings which are intermediate 
between the Heliozoa, Ehizopoda, and Flagellata, usually passing 
through an amoeboid stage, and for tlie most part reproducing by 
Ijrood-formation. Zoospores that possess flagella are certainly 
known to occur in some forms of Foraminifera, Ehizopoda, 
Heliozoa, nnd Eadiolaria, though not by any means in all of 
each group.^ 

1 See E. R. Lankester, art. " Protozoa " in Eucycl. Brit. 9tli ed. (1885), reprinted 
with additions in "Zoological Articles." "We cannot accept liis primary division 
into Cortieata and Gynmoniyxa, which would split up the Flagellata and mark off 
the Gregarines from the other Sporozoa. 

VOL. I E 



50 PROTOZOA 



A. Pseudopodia the principal means of locomotion and feeding ; flagella 

absent or transitory . . . . .1. Sarcodina 

(1) Plastogamy only leading to an increase in size, never to the forma- 

tion of " fructifications." 

(«) Pseudopodia never freely coalescing into a network nor fine to 

the base ..... Rhizopoda. 

(*) Ectoplasm clear, free from granules ; pseudopodia, usually 

Ijlunt .... Ehizopoda Lobosa 

(**) Ectoj)lasm finely granular ; iiseudopodia slender, branching, 

but not forming a network, jiassing into the body by 

basal dilatation . . . Rhizopoda Filosa 

(h) Pseudopodia branching freely and coalescing to form networks ; 

ectoplasm granular ; test usually calcareous or sandy 

FORAMINIFERA 

(c) Pseudopodia fine to the very base ; radiating, rarely coalescing, 
(i.) Pseudopodia with a central filament . Heltozoa 

(ii.) Pseudopodia without a central filament. 

(*) Body divided into a central and a periplieral jjart liy a 

" central capsule " . . . Radiolaria 

(**) Body without a central capsule . Proteomyxa 

(2) Cells aggregating or fusing into plasmodia V)efore forming a complex 

"fructification" ..... Mtcetozoa 

B. Cells usually moving by " euglenoid " wriggling or by excretion of a trail 

of vi.scid matter ; reproduction by alternating modes of brood-forma- 
tion, rarely by Spencerian fission . . .II. Sporozoa 

C. Flagella (rarely numerous) the chief or only means of motion and 

feeding . . . . . III. Flagellata 

D. Cilia the chief organs of motion, in the young state at least ; nuclei 

of two kinds ..... IV. Infu.soria 



CHAPTER III 

PROTOZOA {(JOXTIXUED) : SARCODIisA 

I. Sarcodina. 

Protozoa jjcrformi^ir/ most of their life-pi'ocesses hy 23seudo}3odia ; 
nucleus freqiiently giving off fragments {chroniidia) which may 
flay a 'part in nuclear reeonstitution on division ; sometimes with 
hrood-cells, lohich may he at first flagellate ; hut never reproducing 
in the flagellate state} 

1. EnizopoDA 

Sarcodina of simple form, ivhose pseudopodia never coalesce into 
networks (1)/ nor contain cm axial fllameyit (2), which commonly 
midtiply hy hinary fission (3), though a hrood-formation may 
occur ; which may temporarily aggregate, or undergo temporary or 
2)ermanent p^lastogamic union, hut never to form large plasmodia 
or complex fructifications as a 2^Telude to spore-foi^^nation (4) ; test 
iclien present gelatinous, chitinous, sandy, or siliceous, simple and 
l-chamhered (5). 

Classification.^ 

1. Ectoplasm dutinct, cleai- ; iiseudoiMidia lilunt or ta]>eving, Imt not liraiicli- 
ing at the apex ...... Lohosa 

Amoeba, Auctt. ; Pelomyxa, Greeff ; Trichosphaerium, A. Sclmeid. ; 
JHnamoeha, Leidy; Am2)hizonella, GreeS ; Centropyxis, Stein; Arcella, 



' On this ground I have referred Paramocba, GreelT, to tlie Cryptomonadineae. 

- Dill'erences (1) from Foraminifcra ; (2) from HclUr.oa ; (3) from Protcomyxa 
and Sporozoa ; (4) from My.vomyectcs ; (5) from many Foraminifcra. 

" I have not followed the usual classification into Gymnamoebaeand Thecamoehae, 
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 Fiagellata and 
Infusoria, and does not appear to liave any great systematic importance. 
51 



5 2 PROTOZOA 



Elir, ; IHffliigia, Leclercq; Lecqueureusia, Schlumberger ; Hyalosphenia, 
Stein; Quadrula, F. E. Sch.; Hcleojjera, Leidy ; Podosfomn, CI. and L. ; 
Arcuothrix, Hallez. 
II. Ectoplasm undifferentiated, containing moving granules ; jjseudopodia 
branching freely towards the tijis .... Filosa 

Eugli/pha, Duj. ; PaulincUa, Lauterb. ; Cyphoderia, Schhimb. ;. 
CampascHS, Leidv ; Chlamydophrys, Cienk. ; Gromid, Duj. = Hyalojms, 
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. jVIore- 
over, indeed, in a few of this group (Fodostoma, Arcuothrix), as 
in some Heliozoa, the flagellum or flagella may persist or be 
reproduced side by side with the pseudopodia. The subdivision of 
the Ehizopoda 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 Lobosa there is a clear layer of 
ectosarc, which appears to be of a greasy nature at its surface 
film, so that it is not wetted. In the Pilosa, as in most other 
Sarcodina, this film is al3sent, 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 l^ranching and fraying out, as it were, at the tip, 
as in the Filosa ; nay, in the normal movements of Amoeba Umax 
(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 gi^-es 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 Schaiidinu in Fora- 
niinifera) M'as fully recognised and generalised by R. Hertwig in Arrli. Prof/ist. 
i. 1902, p. 1. 



HI SARCODINA RHIZOPODA 5 3 

it is a iVesh-Wciter dweller, living in the bottom ooze of ponds, 
etc., riclily charged with organic debris. 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 ar.y 
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," i.e. an investment distinct 
from the outermost layer of the cell-body. The simplest cases 
are those of AmpliizoncUa, Dinamoelia, and Trichosjjhaerium , 
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 tlie rupture. In 2''nchos]jhacriuvi (Fig. 9) the test 
is perforated by numerous pores of constant position for the 
passage of the pseudopodia, closing when these are retracted ; 
and in tlie " 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, 

^ Stolu in Z. 'tfiss. Zool. Ixviii. 1900, p. 625. Lilian Veley, however, gives reasons 
for regarding them as of proteid composition, /. Linn. Soc. {Zool. ) xxix. 1905, p. 374 f. 
Tliey disappear when the Pdormjxa is starved or supplied with only proteid food. 



54 



TROTOZOA 



foi'ined ill the cytoplasm in tlie neigliboiirhood of tlie nucleus, 
and connected by chitinous cement. Among these Qtcadrula 
(Fig. 10, A) is Lobose, with square plates, Uuglypha (Fig. 8, 




Fig. 9. — Trichos])haerium 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-rtagellate zoospores or (exogametes) ; 8, liberation of gametes ; 9, 10, more highly 
magnified pairing of gametes of diflerent 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 otlier genera 
again, such as Cyplioderia (Filosa), the plates are merely chiti- 

^ This genus contains two sausage-shaperi, blueibh-green plastids, possibly sym- 
biotic Cyanophyceous Algae. 



RHIZOPODA 



55 



nous. Ai^-ain, the shell may be encrusted with sand-grains derived 
directly from without, or from ingested particles, as shown in 
Caitropyxis, Diffiugia (Fig. 10, D), Hehoiiera, and Campascus 
when supplied with powdered glass instead of sand. The 
cement in Difflugia is a sort of organic mortar, infiltrated 
with ferric oxide (more probably ferric hydrate). In Lecqiieu- 
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 Ehizopods (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- 
tains the test of the 
original animal. The 
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. 




Fig. 10. — Test- 1 tearing Rhizopods. A, Qvadrnla 
syvtmelrica ; B, Hyalosphenla lata ; C, Arcella 
vulgaris ; D, Difflvgia pyriformis. (Fioni Lang's 
Comparative Anatomy.) 



56 PROTOZOA 



Reproduction l:)y tission 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 nmltinucleate 
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 TTichosphaerium (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-tlagellate microzoospores (8), which are exogmnous gametes, 
i.e. 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, etc. In Tricliosphaerium 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. luiss. Zool. lix. 1895, pp. 167, 537. 

- C. Scheel has seen Amoeba j)rotcus produce a brood of 500-600 young 
anioebulae, wliich he reared to full size (in Fcstsclir. f. Knpffcr, 1899). 



RHIZOPODA 5 7 



Itirger prey. Temporary encyHtiiR'ut in u " hvpuocyst " is not 
infrequent in both naked and shelled species, and enables them 
to tide over drought and other unfavourable conditions. 

Schaudinn has discovered and worked out true syngamic 
processes; some bisexual, some exogamous, in several other Ithizo- 
pods. In Chlamydophrys stercorea the pairing-cells are equal, 
and are formed by the aggregation of the chromidia into minute 
nuclei around which the greater part of the cytoplasm aggre- 
gates, while the old nucleus (with a little cytoplasm) is lost. 
These brood -cells are 2 -flagellate pairing -cells, which aie 
exogamous : the zygote is a brown cyst ; if this be swallowed by 
a mammal, the original Chlamydo]j]irys appears in its faeces.^ 

Centropyxis aculeata, a species very common in mud or moss, 
allied to Diffliigia, also forms a brood by aggregation aioimd 
nuclei derived from chromidia. The brood-cells are amoeboid, 
and secrete hemispherical shells like those of Arcclla ; some first 
divide into four smaller ones, before secreting the shell. Pairing 
takes place between the large and the small forms ; and the 
zygote encysts. Weeks or months afterwards the cyst opens 
and its contents creep out as a minute Centropyxis. Finally, 
Amoeba coil produces its zygote in a way recalling that of 
Actinosphaerium (pp. 73-V5, Fig. 21): the cell encysts; its 
nucleus divides, and each daughter divides again into two, which 
fuse reciprocally. Thus the cyst contains two zygote nuclei. 
After a time each of these divides twice, so that the mature cyst 
contains eight nuclei. Prol)ably when swallowed by another 
animal they liberate a brood of eight young amoebae. Thus in 
different members of this group we have exogamy, both equal 
and bisexual, and endogamy. 

Most of the Ehizopoda live among filamentous Algae in 
pools, ponds, and in shallow seas, etc. ; some are " sapropelic " or 
mud-dwellers (many species of Amoeba, Pclomyxa, Diffinyia, etc.), 
others frequent the roots of mosses. Amoeba coli is often 
found as a harmless denizen of the large intestine of man. 
Amoeba histolytica, lately distinguished therefrom by Schau- 
dinn, is the cause of tropical dysentery. It multiplies enormously 
in the gut, and is found extending into the tissues, and making 
its way into the abscesses that so frequently supervene in the 
liver and other organs. Chlamydojjhrys stercorea is found in the 

' Arb. Kais. (Icsundhcitsaintc Berlin, xix. 1903. 



58 PROTOZOA 



faeces of several luanimals. The best iiiouograph of this group 
is that of Penard.^ 

2. FORAMINIFEltA" 

SarcocUna vnth no central capsule or distinction of ectosarc ; 
the 'pseuclopodia fine, hranching freely , and fusing ivhere they meet 
to form protoplasmic netivorks, or the outermost in the pelagic 
forms radiating , hut vjithout a central or axial filament : some- 
times dimorphic, reproducing ly fission and hy rhizopod or 
fiagellate ger7ns in thefeio cases thoroughly rnvestigated : all marine 
{with the exceptioji of some of the Allogromidiaceae), and usucdly 
provided with a test of carbonate of lime (" vitreous " calcite, or 
" porcellanous" aragonite?), or of cemented particles of sand 
(" arenaceous ") ; test-tvall continuous, or with the walls perforated 
hy minute p)ores or interstices for the protrusion of pseudopodia. 

The classification of Carpenter (into Vitreous or Perforate, 
Porcellanous or Imperforate, and Arenaceous), according to the 
structure of the shell, had proved too artificial to be used by 
Brady in the great Monograph of the Foraminifera collected by tlie 
"Challenger" Expedition,^ and has been modified by him and others 
since then. We reproduce Lister's account of Brady's classifica- 
tion.^ We must, however, warn the tyro that its cliaracterisations 
are not definitions (a feature of all other recent systems), for rigid 
definitions are impossible : here as in the case, for instance, of 
many Natural Orders of Plants, transitional forms making the 
establishment of absolute boundaries out of the question. In 
the following classification we do not tliink it, therefore, necessary 
to complete the characterisations by noting the extremes of 
variation within the orders : — 

1. Allogromidiaceae : simple forms, often fresh-water and similar to Rhizo- 
poda ; test 0, or chitinous, gelatinous, or formed of cemented jiarticles, Avhetlier 
secreted platelets or ingested granules. Biomyxa, Leidy = Gymnophrys, Cienk. ; 

^ Fmme Bhizopodique du Bassin du Livian, 1902. See also Cash, The British 
Freshwater Rhizopoda and Heliozoa, vol. i., Kay Society, 1905. 

'^ Chapman, The Foraminifera, London, 1902; Lister, "Foraminifera" in Lan- 
kester's Treatise on Zoology, pt. i. fasc. 2, 1903. 

^ Challenger Reports (ZooL), vol. ix. 1884. 

* In Lankester's Treat. Zool. pt. i. fasc. 1. For other classifications see Eimer 
and Fickert in Z. tviss. Zool. Ixv. 1899 ; Rhumbler in Lang's Protozoa, 1901 ; 
and for a fnll synopsis of genera and species, " Systematische Zusanimenstellung 
der recenten Reticulosae " (pt. i. only), in Arch. Prof. iii. 1903-4, ]i. 181. 



Ill FORAMINIFERA 59 

J)iaphorodo7i, Archer; Alloyromia, Rliuiiibl. ( = Gromm, auctt. ^ nee Diij. 
(Fig. 14, 1) ; LieberkUhnia, CI. and Lachni. (Fig. 12) ; Microgromia, R. Hertw. 
(Fig. 11) ; Pamphagus, Bailey. 

2. Astrorliizidaceae : test arenaceous, often large, never truly chambered, 
or if so, asynimetrical. AstrorMza, Sandahl ; Haliphysrma, Bowerb. ; Huc- 
cammina, M. Sars (Fig. 13, 1); Loftusia, Brady. 

3. Lituolidaceae : test arenaceous, often symmetrical or regularly spiral, 
isomorphous with calcareous forms : the chambers when old often "labyrin- 
thine" by the ingrowth of wall-material. Lituola, Lam. ; licophax, Montf. ; 
AmmodiscHs, Reuss ; Trochammina, Parker and Jeffreys. 

4. Miliolidaceae : test porcellanous, imi^erforate, spirally coiled or cyclic, 
often chambered except in Cornusjnra : simj)le in Squamtdina. Gornusinra, 
Max Sch. ; Peneroplis, Montf.; Miliolina, Lam. {mc\. Biloculina {Y\g. 15), 
Triloculina, Quinqueloculma (Figs. 14,4; 15, B), SpirolocuUna (Fig. 13,5) 
of d'Orl).); Ah eolina, d'Orh.; Hauerina, d'Orb. ; Calciiuha, 'Rohoz; Orbitolifes, 
Lam. ; Orbicidina, Lam. ; Alveolina, Park, and Jeffr. ; Nuhccularia, Def. ; 
SquavuUina, Max Sch. (Fig. 14, 3). 

5. Textulariaceae : test calcareous, hyaline, jierforated ; chambers increasing 
in size in two alternating rows, or three, or passing into a spiral. Textularia, 
Def. ; Bulimina, d'Orb. ; Cassidulina, d'Orb. 

6. Cheilostomellaceae : test vitreous, delicate, finely perforated, chambered, 
isomorphic with the spiral forms of the Miliolidaceae. Cheilostomellu, Reuss. 

7. Lagenaceae : Test vitreous, very finely perforate, chambers with a 
distinct pylome projecting (ectoselonial), or turned in (entosolenial), often 
succeeding to form a necklace-like shell. Lagena, "Walker and Boys (Fig. 13, 2) ; 
Nodosaria, Lam. (Fig. 13, 3); Cristellaria, Lam.; Frondicidaria, Def. (Fig. 
13, 4) ; Polymorphina, Lam. ; Ramulina, Wright. 

8. Globigerinidae : test vitreous, perforate ; chamljers few, dilated, and 
arranged in a flat or conical spiral, usually with a crescentic pylome to 
the last. Glohigerina d'Orh (Figs. 13, 6 ; 16, 2) ; Hastigerina, Wyv. Thorns. ; 
Orhidina, d'Orb (Fig. 16, 1). 

9. Rotaliaceae ; test vitreous, perforate, usually a conical spiral (like a 
snail), chambers often subdivided into chamberlets, and with a jiroper wall, 
and intermediate skeleton traversed by canals. Rotalia, Lam. (Fig. 14, 2) ; 
Plan orhidina, d'Orb. (Fig. 13, 9) ; Polytrema, Risso ; BpirUlina, Ehr. (non- 
septate) ; Patellina, Will. ; Discorhina, P. and J. (Fig. 13, 7). 

10. Nummulitaceae : test usually a comj^lex sjjiral, the turns completely 
investing their predecessors : wall finely tubular, often M'ith a proper wall 
and intermediate skeleton. Fusidina, Fisch. ; Pohjstomella, Lam. ; NnmviuHtcs, 
d'Orb. (Fig. 13, 11); Orbitoides, d'Orlx 

The Allogromidiaceae are a well-marked and distinct order, on 
the whole resembling the liliizopoda Filosa, and are often found 
with them in fresh water, while all other Foraminifera are marine. 
The type genus, Allogromia (Fig. 14, 1), has an oval chitinous 
shell. Microgromia socialis (Fig. 11) is often found in aggregates, 
the pseudopodia of neighbours fusing where they meet into a 

^ Tlie type of Dujardiii's genus Groin ia is G. (>rifi>rnns = lIijnlopHS dujardinii, 
M. Sch., wliicli is one of the Filosa. 



6o 



PROTOZOA 



common network. This is due to the fact that one of the two 
daughter-cells at each fission, that does not retain the parent shell, 
remains in connexion with its sister that does : sometimes, how- 
ever, it retracts its pseudopodia, except two which become flagella, 
wherewith it can swim off. The test of Famj^hagus is a mere 
pellicle. In Lieherhuhnia (Fig. 12) it is hardly that; though 
the body does not give off the fine pseudopodia directly, but emits 
a thick process or " stylopodium " ^ comparable to the protoplasm 
protruded through the pylome of its better protected allies ; and 
from this, which often stretches back parallel to the elongated body, 




Fig. 11. — AHcrof/romia socialis. A, entire colony ; B, single zooid ; C, zooid wliicli lias 
undergone binary fission, with one of the daughter-cells creeping out of the shell ; 
D, tiagellula. c.vac. Contractile vacuole ; nu, nucleus ; sh, shell. (From Parker 
and Haswell, after Hertwig and Lesser. ) 



the reticulum of pseudopodia is emitted. Diaphorodon has a 
shell recalling that of Diffliigia (Fig. 10, 1), p. 55), formed of sandy 
fragments, but with interstices between them through which as 
well as through the two pylomes the pseudopodia pass. In all 
of these the shell is formed as in the Ehizopods once for all, and 
does not grow afterwards ; and the fresh-water forms, which 
are the majority, have one or more contractile vacuoles ; in 
Allogromia they are very numerous, scattered on the expanded 
protoplasmic network. 

The remaining marine families may all be treated of generally, 

before noting their special characters. Their marine habitat 

is variable, but in most cases restricted. A few extend up the 

brackish water of estuaries: a large number are found between tide- 

1 This convenient name is due to my friend Dr. A. Kenma of Antwerp. 



FORAMINIFERA 



6i 



marks, or on the so-called littoral shelf exteiuliiiLi,' to deep water ; 
they are for the most part adherent to seaweeds, or lie anion*^ 
sand or on the niiul. Other forms, again, are pelagic, snch as 
Glohigerina (Figs. 1.3, 6, 16, 17) and its allies, and float as part 
of the plankton, having the surface of their shells extended by 
delicate spines, their pseudopodia long and radiating, and the outer 




Fig. 12. — Lieberkvhnia, a fresli-water Rliizopod, fruin the egg-shaped shell of wliicl 
branched pseudopodial tilameiits protrude. (From Yervvorn.) 



part of their cytoplasm richly vacuolated ("alveolate"), and pro- 
bably containing a lic^uid lighter than sea water, as in theKadiolaria. 
Even these, after their death and the decay of the protoplasm, 
must sink to the bottom (losing the fine spines by solution as they 
fall) ; and they accumulate there, to form a light oozy mud, the 
" Globerina-ooze " of geographers, at depths where the carbonic 
acid under pressure is not adequate to dissolve the more solid 
calcareous matter. Grey Chalk is such an ooze, consolidated by 



62 PROTOZOA 



the lapse of time and the pressure of superincumbent layers. 
Some Foraminifera live on the sea bottom even at the greatest 
depths, and of course their shell is not composed of calcareous 
matter. Foraminifera may be obtained for examination by care- 
fully washing sand or mud, collected on the beach at different levels 
between tide-marks, or from dredgings, or by carefully search- 
ing the surface of seaweeds, or by washing their roots, or, again, 
by the surface or deep-sea tow-net. The sand used to weight 
sponges for sale is the ready source of a large number of 
forms, and may be obtained for the asking from the sponge- 
dealers to whom it is a useless waste product. If this sand is 
dried in an oven, and then poured into water, the empty shells, 
tilled, with air, will float to the surface, and may be sorted by 
fine silk or wire gauze. 

From the resemblance of the shells of many of them to the 
iSTautilus they were at first described as minute Cephalopods, or 
Cuttlefish, by d'Orbigny,-^ and their true nature was only elucidated 
in the last century by the labours of Williamson, Carpenter, 
Dujardin, and Max Schultze. At first they possess only one 
nucleus, but in the adult stage may become plurinucleate 
without dividing, and this is especially the case in the " micro- 
sphaeric " states exhibited by many of those with a complex 
shell ; the nucleus is apt to give off fragments (chromidia) which 
lie scattered in the cytoplasm. At first, too, in all cases, the 
shell has but a single chamber, a state that persists through 
life in some. When the number of chambers increases, their 
number has no relation to that of tlie nuclei, which remains 
much smaller till brood-formation sets in. 

Tlie shell-substance, if calcareous, has one of the two types, 
porcellanous or vitreous, that we have already mentioned, but 
Polytrema, a form of very irregular shape, though freely 
perforated, is of a lovely pink colour. In the calcareous shells 
sandy particles may be intercalated, forming a transition to the 
Arenacea. In these the cement has an organic base associated 
with calcareous or ferruginous matter; in some, however, the 
cement is a phosphate of iron. The porcellanous shells are often 
deep brown by transmitted light. 

'^ The name Foraminifera was used to express tlie fact tliat the chambers 
conimuiiicated by pores, not by a tubular siphon as in Nautiloidea and Ammonoidea 
(Vol. III. j.p. 393, 396). 



FORAMINIFERA 



^?> 



Despite the apparent iiiiifornnty of tlie protoplasmic body in 
this group, tlie shell is infinitely varied in form. As Carpenter 




g.Planorbulina 



ll.Nummuiires 



Fig. 13. — Shells of Foraminifera. In 3, 4, ami 5, a shows tlie siirlace view, and h a 
section ; 8a is a diagram of a coiled cell without supplemental skeleton ; 86 of a 
similar form with supplemental skeleton {s.sk) ; and 10 of a form with overlapjniig 
whorls ; in 11« half the shell is .shown in horizontal section ; 6 is a vertical .section ; 
a, aperture of tlie shell ; 1-15, successive chambers. 1 beins,' .always the oldest or 
initial chamber. (From Parker and Haswcll, after other authors.) 



wriies, in reference to the Arenacea, " There is nothing more 
wonderful in nature than the building up of these elaborate and 
symmetrical structures l)y mere jelly-specks, presenting no traces 



64 PROTOZOA 



whatever of tliat definite organisation which we are accustomed 
to regard as necessary to the manifestations of conscious life. . . . 
The tests (shells) they construct when higlily magnified bear 
comparison with the most skilful masonry of man. From 
the same sandy bottom one species picks up the coarsest quartz 
grains, unites tliem together with a ferruginous cement, and thus 
constructs a flask -shaped test, having a short neck and a single 
large orifice ; another picks up the finer grains and puts them 
together with tlie same cement into perfectly splierical tests of 
the most extraordinary finish, perforated with numerous small 
pores disposed at pretty regular intervals. Another species 
selects the miimtest sand grains and the terminal portions of 
sponge-spieules, and works them up together — apparently with 
no cement at all, but by tJie mere laying of the spicules — into 
perfect white spheres like homoeopathic globules, each showing 
a single-fissured orifice. And another, which makes a straight, 
many-chambered test, the conical moutli of each chamber 
projecting into the cavity of the next, while forming the walls 
of its chambers of ordinary sand grains rather loosely held 
togetlier, sliapes the conical mouths of the chambers by firmly 
cementing togetlier the quartz grains which border it." The 
structure of the sliell is indeed variable. The pylome may be 
single or represented by a row of holes (Fenerojylis, Orhitolites), 
or, again, tliere may be several pylomes (Calcituba) ; and, again, 
there are in addition numerous scattered pores for the protrusion 
of pseudopodia elsewhere than from the stylopodium, in the 
whole of the " Yitrea " and in many " Arenacea " ; and, as we 
sliall see, this may exercise a marked influence on the structure 
of the shell. 

In some cases tlie shell is simple, and in Cornuspira and 
Spirillina increases so as to have tlie form of a flat coiled tube. 
In Calcituba the shell branches irregularly in a dichotomous 
way, and the older parts break away as the seaweed on which 
they grow is eaten away, and fall to the bottom, while the 
younger branches go on growing and branching. The fallen 
pieces, if they light on living weed, attach themselves thereto 
and repeat the original growth ; if not, the protoplasm crawls 
out and finds a fresh weed and forms a new tube. In the 
" I'olytlialamia " new chambers are formed by tlie excess of the 
protoplasm emerging and surrounding itself witli a shell. 



FORAMINIFERA 



65 



organically united with the existing chamber or chambers, and 
in a space-relation which follows definite laws characteristic of 




3. SquamuUna 



4. Miliola {Qmnqueloculina) 



Fig. 14. — Various forms of Foraminifera. In 4, Miliola, «, shows the living animal ; b, 
the same killed and stained ; a, aperture of shell ; /, food particles ; nu, nucleus ; 
•s/i, 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 



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, 8&), and the space between the two 
adjacent walls is filled with an intermediate layer traversed ])y 
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 
Glolngerina, Hastigerina, and the like (Fig. 17). In the 
" Imperforata " 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 
Orhitolites the first few chambers of the shell have the character 
of a Milioline, in Orhicidina 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 Orhulina 
(Fig. 16 i) is formed as an investment to a shell indistinguish- 
able from Glohigerina, which is ultimately absorbed. In 
some cases, as Ehumbler has pointed out, the more recent 
and higher development shows itself in the first formed 
chambers, while the later, younger chambers remain at a lowlier 
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 Lagena(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 Entosoleiiia was 
founded. Shells identical in minute sculpture are, however, found 
with either form of neck, and, moreover, the polythalamial shells 
(N'odosaria, Fig. 13 3), formed of a nearly straight succession of 
Lagena-h]<.e chambers, may have these chambers with their com- 



FORAMINIFERA 



6/ 



munications on either type. Ehurabler goes so far as to suggest 
that all so-called Lagena shells are either the first formed 
chamber 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 




Fig. 15. — A, Megilosphenc B, iiiu i 
The luicrosplienc form begins on tii 



{Bi/hvIdui I lliL initial chamber. 

utinaiyYie. (troni \^a.\kiuti' 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 hy Schaudinn, and in great part in 
PolystomeUa, Orhitolites, etc., 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) 



68 PROTOZOA 



conjugation produce the microsplieric young. The microspheric 
forms early become nmltinucleate, and have also numerous 
chromidia detached from the nuclei, whicli they ultimately replace. 
These collect in the outer part of tlie shell and aggregate 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 




Fig. 16. — 1, OrbuJina miiversa. Hiijlily inafriiitierl. 2, Glohigerina hulloides. 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 tlie 4-nucleate cells so formed are resolved 
into as man V 1 -nucleate, 2-flagellate swarmers, which. conjuo;ate 



FORAMINIFERA 



69 



only exogamously} The fusion of tlieir 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 ah 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, Fatellina and Discorhina, plastogamy 
precedes brood formation, the cytoplasms of the 2-5 pairing 
individuals contracting a close union ; and then the nuclei 
proceed to break up icithout fusion, while the cytoplasm 




Fig. 1/. — JShell ol b'l'-bii/cruia hullmiJes, li-oiii tow-net, showing invebtnient of spiues 
(From Wyville Thomson.) 



aggregates 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 
])seudopodiospores form their shells while near one another, they 
may coalesce to form monsters, as often happens in Orhitolites.- 

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. Orhilnlitcs u. and. Foraniiniferen," in Arch. 
Protist. i. 1902, p. 193. 



JO PROTOZOA 



composed largely of Tcxtxdaria 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 princiixdly 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.^ 



3. Heliozoa 

Sarcodina with radiate non-anastoitiosing pseudo^iodia of gran- 
ular protoplasm, each icith a stiff axial rod passing into the body 
plasma ; no central cap)sule, nor clear ectoplasm ; skeleton when 
present siliceous ; nucleus single or multiple ; contractile vacuole 
{or vactcoles) in fresh-water species, superficial and prominent at the 
surface in diastole; reproduction hy fission or hudding in the 
active condition, or ly hrood-forjnation in a cyst, giving rise to 
resting spores ; conjugcUion isogamous in the only ttvo species fully 
studied; habitat fioating or among vjeeds, mostly fresh wcUer. 

1. Naked or with an investment only wlien encysted. 

ArHROTHORACA. — Actinolo'phus F.E. Sch. ; Myxastrum Haeck. ; 
Gipnnos2)hae.m Sassaki ; IHmorpha (Fig. 37,5, p. 112) Gruber ; 
Adinomonas Kent ; Adinofhrys Ehrb. ; Adinos])haeriuvi St. ; 
Camptoiicvia Schaiid ; Nndearia Cienk. 

^ The alleged Archaean genxis Euzoon, founded by Carjienter and Dawson on 
structures found in the Lower Laurentian serpentines (ophicalcites), and referred 
to the close i)roxindty of Nummulites, has been claimed as of purely mineral 
structure by the petrologists ; and recent biologists have admitted this claim. 



HELIOZOA 



/I 



•2. Invested witli a gelatinous layer, sometimes traversed by a firmer elastic 
network. 

Chlamydophora. — Heteroijhiijs Arcli. ; MKstiinqihnjs Frenzel ; 
Acanthociistis, Carter. 

3. Ectoplasm with distinct siliceous spicules. 

Chalarothoraca. — Raphidiophrys Arch. 

4. Skeleton a continuous, fenestrated shell, sometimes stalked. 

Desmothoraca. — Myriophrys Penard ; Clathridina Cienk. ; Orbu- 
linella Entz. 



Tliis class were at first regarded and described as fresh-water 
Eadiolaria, but the differences were too great to escape the 
greatest 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, E. Hertwig, Lesser, 
and latterly to Schaudinn, who has monographed it for the 
"Tierreich" (1896); and Penard has published a more recent 
account. 

Actino'phrys 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 ectosarc, and a denser in- 
ternal layer the endosarc. 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 fig. u.—AcUnophrys sol. a, Axial 
the fine granular plas„>, showing «'-~f IS'^'t; tL.r 

currents of the granules. The axial (From Lang's Comparative Aim- 

filament disappears when the pseudo- '""''^' ''^''' f-renacher. ) 
podia are retracted or bent, and is regenerated afterwards. This 
bending occurs 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 




' Possibly composed of the same proteid, "acantliin," that forms spicules of 
greater permanence in the Acantharia among the Radiolaria (p. 75 f. Figs. 24, 25, A). 



72 



PROTOZOA 



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. A 
gelatinous cyst wall forms about the two which are scarcely more 
than in contact with their rays withdrawn. Then in each the 
nucleus divides into two, one of which passes to the surface, and 
is lost (as a " polar body "), while the other approaches the 




Fig. 19. — Acfi>ios23haerium eichnrnii. A, entire aiiinial with two contractile vacuoles 
(c.vac) ; B, a portion much magnified, showing alveolate cytoplasm, pseudopodia 
with axial rods, non-nucleate cortex (an-t), multiple nuclei {7uc) of endoplasm (med), 
and food- vacuole [chr). (From Parker and Haswell.) 

corresponding nucleus of tlie mate, and unites with it, while at 
the same time the cytoplasms fuse. Within the gelatinous cyst 
the zygote so formed divides to produce two sister resting spores, 
from each of which, after a few days, a young Actinirphrys escapes, 
as may take place indeed after encystment of an ordinary form 
without conjugation. 

The axial rods of the pseudopodia may pass either to the 
circumference of the nucleus or to a central granule, correspond- 
ing, it would appear, to a centrosome or blepharoplast ; or again. 



HELIOZOA 73 



iu the plurinueli'ate niariue genus Camptonmni, eacli rod aluits 
on a separate cap on the outer side of each nucleus. The 
nucleus is single in all l>ut the genera Actiiiosphaerium, 
Myxastrum, Camptonema, and Gymnosphaera. The movements 
of tliis group are very slow, and are not well understood. A 
slow rolling over on the points of the rays has been noted, and 
in Camptonema they move very decidedly to effect locomotion, 
the whole body also moving Amoeba - fashion ; but of the 
distinct movements of the species when floating no explanation 
can be given. The richly vacuolate ectoplasm undoubtedly helps 
to sustain the cell, and the extended rays must subserve the 
same purpose by so widely extending the surface. Dimorpha 
(Fig. 3 7, 5, p. 11 2) has the power of swimming by protruding a pair 
of long flagella from the neighbourhood of the eccentric nucleus ; 
and Myriophrys has an investment of long flagelliform cilia. 
Actinomonas has a stalk and a single flagellum in addition to 
the pseudopodia ; these genera form a transition to the Flagellata. 

Several species habitually contain green bodies, which multiply 
by bipartition, and are probably Zoochlorellae, Chlamydomona- 
didae of tlie same nature as we shall find in certain Ciliata (pp. 
154, 158) in fresh-water Sponges (see p. 175), in Hydra viridis 
(p. 256), and the marine Turbellarian Convohda (Vol. II. p. 43). 

Reproduction by fission is not rare, and in some cases (Acan- 
thocystis) the cell becomes multinuclear, and buds off 1 -nucleate 
cells. In such cases the buds at first lack a centrosome, and a 
new one is formed first in the nucleus, and passes out into the 
cytoplasm. These buds become 2-flagellate before settling down. 
In Clathridina the formation of 2-flagellate zoospores has long 
been known (Fig. 20,3). In. Actinospliaerium (Fig^. 1^, 21), o. 
large species, differing from Actinophrys only in the presence of 
numerous nuclei in its endoplasm, a peculiar process, which we 
have characterised as endogamy, results in tlie formation of resting 
spores. The animal retracts its rays and encysts ; and the 
number of nuclei is much reduced by their mutual fusion, or hy 
the solution of many of them, or by a combination of the two 
processes. The body then breaks up into cells with a single 
nucleus, and each of these surrounds itself with a wall to form a 
cyst of the second order. Each of these divides, and the two 
sister cells then conjugate after the same fashion as in Actino- 
phrys, but the nuclear divisions to form the coupling nucleus are 



74 



PROTOZOA 



two in number, i.e. the nucleus divides into two, one of wliicl 

/ 




2.NucIearia 



3.Clahhrulina 



Fig. 20. — Various forms of Heliozoa. In 3, a is the entire animal and h the flagellula ; 
c.vac, contractile vacuole ; g, gelatinous investment ; nu, nucleus ; psd, pseudopodia ; 
sk, siliceous skeleton ; sp, spicules. (From Parker and Haswell, after other authors.) 

goes to the surface as the lirst polar body, and the sister of this 
again divides to form a second polar body (which also passes to 



[lELIOZOA — RADIOLARIA 



75 



the surface) and a pairing nucleus/ The two cells then fuse 
completely, and surround themselves with a second gelatinous 
cyst wall, separated from the outer one by a layer of siliceous 
spicules. The nucleus appears to divide at least twice before the 
young creep out, to divide immediately into as many Actino- 
jiJtri/s -like cells as there were nuclei; then each of these 
multiplies its nuclei, to become apocytial like the adult form. 
Schaudinn admits 2-4 genera (and 7 doubtful) and 41 species 
12 :J 4 5 



^^ 



NoNo 



ji^N^N^-^w^ 



N, 



Fig. 21. — Diagram illustrating the conjugation of Actinosphaerium. 1, Original cell ; 
2, nucleus divides to form two, N^Ni ; 3, each nucleus again divides to form two, 
Ng and n^, the latter jiassing out with a little cytoplasm as an abortive cell ; 4, 
repetition of the same process as in 3 ; 5, the two nuclei N4 hiive fused in syngamy 
to form the zygote nucleus N.. 

(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 
Orhulinella has only been found in a salt-pond ; Acfdnoj^hrys sol 
is both fresh-water and marine, and Actinoloiihus has 1 species 
fresh-water, the other marine. One of the 14 species of Aeantho- 
ci/sfis is marine ; the remaining genera and species are all 
inhabitants of fresh water." 



4. liADIOLAKIA 

Sarcodina tcith the 'jirotoplasm divided Inj a j^)erforat€d 
chiiinous central cctpside into a central mass surrounding the 
nucleus, and an outer layer ; the pseudopodia radiate, never anasto- 
mosing enough to form a Tnarlced netiuork ; skeleton either siliceous, 
of spicides, or perforated; or of definitely arranged spicules of 
proteid matter {acanthiii), sometimes cdso coalescing into a 
latticed shell ; reproduction hy fission and hi/ zoospores formed 
in the central capside. Habitat marine, susp)ended at the surface 
(planJdon), at varying dep>ths (zonaricd), or near the bottom (abyssal). 

^ Such divisions into functional and abortive sister nuclei arc 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 Z)('/?iorjj/irt Gruber 
(Fig. 37 5, p. 112), Mastigophrys Frenzel, Cilicphrys Cienk., and Adinomonas 
Usually referred to Flagellates. 



76 



PROTOZOA 



The following is Haeckel's classification of the Eadiolaria : — 

I. PoRULOSA (Holotrypasta). — Homaxoiiic, 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 
acantliin, whose branches may coalesce into a latticed shell ; nucleus 
dividing early. 








^ 



Fig. 22.— Collozoum inerme. A, B, C, tlu-ee forms of colony ; D, small colony with central 
capsules (c.cff^s), containing nuclei, and alveoli [vac) in ectoplasm; E, isospores. 
with crystals (c) ; F, anisospores ; nu, nucleus. (From Parker and Haswell.) 

II. OscuLOSA (Monotrypasta). — Monaxonic ; 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. Nassellarta (Monopylaea).— 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. Phaeodaria (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 "). 



HELIOZOA KADIOLARIA 



77 



SpL'MELLARIA. 

Sublegion (1). Colloparia.'^ — Skeleton absent or of detached spicules; 
colonial or simple. 
Order i. Colloidea.- — Skeleton absent. (Families 1, 2.) ThalassicoUa 
Huxl. ; Thalassoj^hysa Haeck. ; Collo:.omn Haeck. ; Collo.sphaera 
J. Miill. ; Actissa Haeck. 
Order ii. Beloidea. — Skeleton spicular. (Families 3, 4.) 
Sublegion (2). Sphaerellaria. — Skeleton continuous, latticed or spongy, 
reticulate. 



cent, caps 




Fig. 12,.—Aciinomma asteracanthion. A, the shell with portions of the two outer 
spheres broken away ; B, section sliowing the relations of the skeleton to the 
animal. cent, caps, Central capsule ; ex. caps.pr, extra-capsular protoplasm : nn, 
nucleus ; sk. 1, outer, .■<k. 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 iv. Prunoidea. — Skeleton a piolate sjihaeroid or cylinder, 
sometimes constricted towards the middle, single or concentric. 
(Families 11-17.) 

Order v. Discoidea. — Shell flattened, of circular plan, simj^le or con- 
centric, rarely spiral. (Families 18-23.) 

Order vi. Larcoidea. — Shell ellipsoidal, with all three axes unequal 
or irregular, sometimes becoming spiral. (Families 24-32.)- 

1 K. Brandt, in Arc.'i. Prot. i. 1902, p. 59, regards the presence of spicules as not 
even of generic moment, and subdivides the Collodaria into two families — Ct)//w^(6 
(solitary), and Sphaerozoea, colonial, i.e. with numerous central capsules. 

- Drover adds an additional order— S]iiiaeroin-lida, distinguished by a basal (or 
.1 basal and an apical i jiylonie. 



78 



PROTOZOA 



B. ACANTHARIA. 

Order vii. Actinelida. — Radiul spines numerous, more than 20, 
usually grouped irregularly. (Families 33-35.) Xiphacantha 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 
the spines. (Families 39-41.) Dorataspis Haeck. (Fig. 25, A). 

Order x. Prunophracta. — Radial spines 20, unequal ; latticed shell, 
ellipsoidal, lenticular, or doubly conical. (Families 42-44.) 




Fio. 2i.—X iphacaiUha (Acantluiria). From tlie surface. The skeleton only, x IflO. 
(From Wyville Thomson.) 



Nassellakia. 

Order xi. Nassoidea. — Skeleton absent. (Family 45.) 

Order xii. Plectoidea. — Skeleton of a single l)ranching spicule, the 

l:)ranches sometimes reticulate, l)ut never forming a latticed shell or 

a sagittal ring. (Families 46-47.) 
Order xiii. Stephoidea. — Skeleton with a sagittal ring continuous 

with the branched spicule, and sometimes other rings or branches. 

(Families 48-51.) Lithocercus Theel (Fig. 26, A). 
Order xiv. Spyroidea. — Skeleton with a latticed shell developed 

around the sagittal ring (cephalis), and constricted in the sagittal plane,. 

with a lower chamber (thorax) sometimes added. (Families 52-55.) 



KADIOLARIA 79 



Order xv. Botryoidea. — As in Spyroidea, but with tlie cephalis 3-4 

lobed ; lower chambers, one or several successively formed. (Families 

56-58.) 
Order xvi. Cvrtoidea. — Shell as in the preceding order.^, but without 

lobing or constrictions. (Families 59-70.) Theoconus Haeck. 

(Fig. 25, B). 
D. Phaeodaria. 

Order xvii. Phaeocystina. — Skeleton or of distinct spicules ;. 

capsule centric. (Families 71-73.) J.ttZac<MiM(7;i Haeck. (Fig. 26, B). 
Order xviii. Phaeosphaeria. — Skeleton a simple or latticed sphere,. 

with no oral opening (pylome) ; capsule central. (Families 74-77.) 
Order xix. Phaeogromia. — Skeleton a simple latticed shell with a 

pylome at one end of the principal axis ; capsule excentric, siib-apical. 

(Families 78-82.) Pharyngella Haeck. ; Tuscarora Murr. ; Haeclel- 

iana Murr. (Fig. 28). 
Order xx. Phaeoconchia. — 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 hollov^ substance of the 
Phaeodaria (p. 84). They rank now as Silicotlagellates (p. 114).. 

The Eadiolarian 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 
proljably 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. 

' Verwnrn has shown that Thalassicolla nucleata can, when tlie 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 rc-fornied at 
their bases, and carries them farther out from the central capsule. See General 
rhysiology (Engl. cd. 1899), p. -MiK 



8o 



PROTOZOA 



The " yellow cells " of a symbiotic Flagellate or Alga, Zooxan- 
thella, are embedded in the jelly of all except Phaeodaria, and 
the whole ectosarc has the average consistency of a firm jelly. 

The pseudopoclia 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- 





FiG. 25.— Skeletons of 7?«r?;Hrt;-m,. A, Domtaspis ; 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 myophrisls, 
whose action seems to be to pull up the jelly and increase the 
volume of the spherical l)ody so as to diminish its density. 

The i)itracaj)sular j^^'otoplasui is free from ZooxantheUa 
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- 



RADIOLARIA 



iiig- into yellow or brown, tlutu^h violet, blue, and green also 
occur. The " phaeodium," ^ however, that gives its name to the 
Phaeodaria, is an aggregate 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. 20, 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 
tlie several perforations of the lattice -work, finally coalescing 
outside completely, so as to show no signs of the joins. In the 
Xassellaria 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, 

^ 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- 
jilasni, and to pass through the astropyle into the ectoplasm, where it accumulates. 
It is proliably 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. Jahrh. Anat. xiv. 1000, p. 203. 

VOL. I Cx 



82 



PROTOZOA 



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 tlie surface of the 



SJcel. 



Fig. 26. — A, Lithocercus cmnularis, 
with sagittal ring (from Parker 
and Haswell). B, Aulactinium 
aclinastrum. C, calyninia ; cent, 
caps., km, central capsule ; 
Ext. caps, pr.. Extracapsular, 
and Int. caps.pr., intracapsular 
protoplasm ; n, nu, nucleus ; 
0/5, operculum ; j'K pliaeodium ; 
psd, pSeudopodium ; Skel., 
skeleton ; z, Zooxauthella. 
( From Lang's Comparative 
Anatomy, after Haeckel. 




i \ X 



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 



■espon( 
of our worhl. 



1 Dreyer lias 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. Zettschr. xxxix. 1904, p. 297. 



RADIOLARIA 8 3 



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 
ISphaerocapsidae 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) 
-keletou is that of detached spicules, simple or complex, or 
passing into a latticed shell, often with one or more larger 
openings (pylomes). Eadiating spines often traverse the whole 
of the cavity, becoming continuous with its latticed wall, and 
bind firmly the successive zones when present (Fig. 23). 

Calcaromma calcarea was described by Wyville Thomson as 
having a shell of apposed calcareous discs, and Myxohrachia, 
by Haeckel, as having collections of the calcareous Coccoliths and 
Coccospheres. In both cases we have to do with a Eadiolarian 
not possessing a skeleton, but retaining the undigested shells 
of its food, in the former case {Actissa) in a continuous layer, 
in the latter {Thalassicolla) 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 "j 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 



the last one opening by a pylonie (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. 




Fiij. ^r.— Hclieiue of various possiljle skeletal forms deposited in tlie meshes of an 
alveolar system, most of which are realised in tlie Radiolaria. (From Verworn, 
after Dreyer.) 



The central capsule (rarely inconspicuous and dilticult, if not 
impossil.)le 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, i.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 tlie projecting tube 
(" proboscis "). 

Reproduction in the Eadiolaria 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 



RADIOL ARIA 



85 



the ivmaining Eadiolaria (Monocyttaria). They may either lack 
a skeleton (Collozoidae, Fig. 22), or have a skeleton of detached 
spicules (Sphaerozoidae), or possess latticed shells (Collosphaeridae) 
(tue for each capsule, and would seem therefore to belong, as only 
differentiated by their colonial habit, to the several groups having 
tliese 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. 




A B C 

Fi«;. 28.— Shells of Challengeridae : A, Tuscarora; B, Pharyngdla ; C, llaeckeliana. 
(Frnni Wyville Thomson.) 

Two modes of reproduction by fiagellate zoospores lia"\'e 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 
" anisospores " 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 

^ Znnl. Jahrh. Anat. xiv. 1900, ]>. 203. 



86 PROTOZOA 



endoplasni : the nucleus first undergoes lirood division, and the 
plasma within the capsule Ijeconies concentrated about its 
offspring, and segregates into the spores : the extracapsular 
plasm disintegrates.^ 

The Yellow Cells {Zooxanthella), so frequently found in the 
Eadiolaria were long thought to be constituents of their body. 
Cieukowsky found that when the host died from being kept in 
unchanged water, the yellow cells survived and nmltiplied freely, 
often escaping from the gelatinised cell-wall as bitiagellate 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 " Fabnella-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 Collosijhaera. Both these forms live in the state known 
as " symbiosis " with their host ; i.e. they are in mutually helpful 
association, the Eadiolarian absorbing salts from the water for 
the nutrition of both, and the Alga or Flagellate taking up the 
COg 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 niitrition of the host. A similar union l)etween a 
Fungus and a coloured vegetal (" holophytic ") organism is 
known as a Lichen. 

The Suctorian Infusorian Amochoj'hri/a 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 Silicoliagellate family Dictyochidae are found temporarily 

' Porta has described reproduction by spores and by budding in Acantharia, 
Iie7id. H. 1st. Lomb. xxxiv. 1901 (ex Journ. Ji. Micr. Soc. 1903, p. 45). In 
Thalasso2)hysa and its allies zoospore reproduction appears to be rejtlaced by a 
process in which the central capsule loses its membrane, elongates, becomes 
niultinuclear, and ultimately breaks up into the nucleate portions, each annexing 
an envelope of ectoplasm to become a new individual (see Arch. Prof., vol. i. 1902). 



RADIOLARIA 8/ 



embedded in the ectoplasm of some of the Phaeocystiiia, and 
have a skeleton of similar nature. Their true nature was sliown 
by Borgert. 

The Amphipod crustacean Hyperia ^ may enter the jelly of 
the colonial forms, and feed there at will on the host." 

Haeckel, in his Monograph of the Eadiolaria of the Challenger 
enumerated 739 genera, comprising 4318 species ; and Dreyer has 
added G 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 
Eadiolaria are found living at all depths in tlie sea, by tlie 
superficial or deep tov/-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 Eadiolarian 
ooze, which is distinguished from other shallower deposits chiefly 
througli 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 
Eadiolaria. The greatest wealth of forms is found in tropical 
seas, tliough in some places in cold regions large numbers of 
individuals of a limited range of species have been found. 

Eadiolaria 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 Polycystineae. 
Tripolis {Kiesehjuhr) of Tertiary ages have been found in many 
parts of the globe, consisting largely or mainly of Eadiolaria, and 
representing a Eadiolarian 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 
Eadiolarian 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, 

^ Brandt, "Die Koloniebildenden Radiolarien,"' in Fauna u. Flora des Golfes v. 
Xeapel, xiii. 1885, gives a full account of the Zooxantliellae and Diatoms, and notes 
tlie parasitism of Hyperia. 

- See Kijppen in Zool. Anz. xvii. 1894, p. 417. For Sticholonche, see K. 
Hertwig in Jena. Zeitsch. xi. 1877, p. 324 ; and Korotneff in Zcitsch. wiss. Zool. 
li. 1891, p. 613. Borgert's paper on Dictyochidae is in the same volume, p. 629. 



88 PROTOZOA 



the Cambrian. The older forms are simple Sphaerellaria and 
Xassellaria. From a synopsis of the history of the order in 
Haeckel's Mo7iograph (pp. clxxxvi.-clxxxviii.) we learn tliat 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 tlie 
labours of Haeckel, Cienkowsky, E. Hertwig, Karl Brandt, and 
A. Borgert. 

5. PPvOTEOMYXA 

Sarcodina vjithout a clear ectoj^htsm, vjkose active forms are 
amoeboid or Jiagellate, or pass fro7n the latter foo^m to the former ; 
midtiplying chiefly, if not exclusively, hy hroodformation in a 
cyst. No complete cell-pai7'ing (syngamy) knoivn, though the 
cytoplasms may unite into jdasmodia ; p)seudopodia of the amoeboid 
forms usually radiate or filose, but without axial filaments. Sapro- 
phytic or parasitic in living animcds or p)lants. 

This group is a sort of lumber-room for forms which it is 
hard to place under Ehizopoda 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, etc. : 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 tliey usually recall Actimphrys 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 liost-cell 
(Fig. 29 5). They may be divided as follows: — 



PROTEOMVXA 



89 



A. ^NIyxoidea. — Flagella 1-3 ; zoospores separating at once. 

1. ZoospoREAE. — Brood -cells escaping as Hagellulae, even if they 

become amoeboid later. CiliGphrys Cieuk. ; Pseudospora Cienk. 
(Fig. 29). 

2. AzoospoREAE. — Cells never flagellate. Protomyxa Haeckel ; Plasmo- 

(liophora \Yoroi\h\; Vampyrella Cienk. ; Serums2)ori(lmm'L. Pfeifl'er. 

B. C'atallacta. — Brood-cells of cyst on liberation adhering at the centre to 

form a spherical colony, multiflagellate ; afterwards separating, and 
becoming amoeboid. Magosphaera Haeckel (marine).^ 

Plasmodiopliora infests the roots of Crucifers, causiug the 
disease known as " Hanburies," or " fingers and toes," in turnips, 
etc. Serumsporidium dwells in the body cavity of small Crustacea. 




-Pseiidospora limlstedtii. 1, 2, Flagellate zoospores : 3, young anioebula, 
with two contractile vacuoles, one being reconstituted by three minute formative 
vacuoles ; 4, 5, an anioebula migrating to a fuugus hypha through the wall of 
which it has sent a long pseudopodium ; 6, anioebula full-grown ; 7, 8, mature 
cells rounded off, protruding a fiagellum, 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 ; Ji, flagellum ; n. 
nucleus, x ai>out ^f^". 

]\Iany of this group were described by Cienkowsky under the 
name of " Monadineae " (in Arch. Mih: Anat. i. 18G5, 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, " Fihthiere oder Schleim- 
pilzc" in Schenk's Handh. d. Bot. vol. iii. pt. ii. (1887). To 
Lankester {Encyd. Brit., reprint 1891) we owe the name here 
adopted. Zopf has successfully pursued their study in recent 

^ Jlost of Haeckel's Monera, described as iion-nucleate, belong liere. Several 
have been proved to be nucleate, and to be rightly placed here ; and all rt(|uire 
renewed study. 



90 PROTOZOA 



papers in his Beitr. Med. 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. Mycetozoa (Myxomycetes, Myxogastres) 

Sarcodina moving and feeding hy 2^seudopodia, with no skeleton, 
aggregating more or less com])letely into comjjlex "fructifications " 
before forming 1 -nucleate resting siJores ; these may in the first 
instance literate fiagellate zoospores, which afterwards become 
amoeboid, or may be amoeboid from, the first ; zoospores ccqmUe of 
forming hyiJnocysts from which the contents escape in the original 
form. 

1. Aggregation taking place without plastogamy, zoospores amoeboid, witli 

a clear ectosarc ..... Acrasieae. 

Gopromyxa Zopf ; Dicfyostelium BrefelJ. 

2. Aggregation remaining lax, with merely thread-like connexions, excejit 

when encystment is to take place ; cytoplasm finely granular throughout ; 
complete fusion of the cytoplasm doubtful . . Filgplasmgdieae. 

Lahyrinthula Cienk. ; Chlamydomyxa Archer ; Leijdenia (?) 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 ...... Myxomycetes. 

Fidigo Hall. ; Chondrioderma Rostaf. ; Didymimn Schrad. (Fig. 30). 

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 oi Amoeha 
Umax (Fig. 1, p. 5). 

II. Filoplasmodieae. — Chlamydomyxa- is a not uncommon 
inhabitant of the cells of bog-mosses and bog-pools, and its 
nutrition may l;)e holophytic, as it contains chromoplasts ; but it 

^ 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 Chlamydomyxa; Hieronymus, abstracted by .lenkinson, in Quart. J. Micr. 
Sci. xiii. 1899; Penard, Arch. Protist. iv. 1904, p. 29G. 



Ill MVCETOZOA — MVXOMYCETES 9 I 

Ciin also feed amoeba-fashion. Lahyrinthula is marine, and in 
its fructification each of the component cells forms four spores. 
Lqidenict has been found in the Huid of ascitic dropsy, associated 
with malignant tumour. 

III. 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 {e.g., the Puff- 
balls), whence they were at first called Myxogastirs. De Bary 
first discovered their true nature in 1859, and ever since they 
have l)een claimed l)y botanist and zoologist alike. 

The spore on germination liberates its contents as a minute 
fiagellate, with a single anterior lash and a contractile vacuole 
(Fig. 30, C). It soon loses the lash, becomes am.oeboid, and 
feeds on bacteria, etc. (Fig. 30, J), 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 
lieeome 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 



determine the rupture of the fruit-wall and the scattering of the 
spores. 

Again, in some cases the plasmodia themselves aggregate in 
tile same wav as the arnoeboids do in the Acmsicac, and combine 




Fig. oO. — Didyiiiiani diffonne. A, two sporangia [sp(j 1 and 2) ou a fragment of leaf (/) ; 
B, section of sporangium, with ruptured outer layer («), aud threads of capillitium 
(cp) ; C, a llagellula with contractile vacuole (twac) aud nucleus (lut) ; D, the same 
after loss of tlagelluni ; 6, an ingested bacillus ; E, au amoehula ; F, conjugation of 
amoebulae to form a small plasmodium ; G, a larger Plasmodium accompanied liy 
numerous amoebulae ; sp, ingested spores. (After Lister.) 



to form a compound fruit termed an " aethalium," ^ with tlie 
regions of the separate plasmodia more or less clearly marked off. 
The species formerly termed Aethalium 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. 



MYCETOZOA 93 



diameter of a foot and more, and a thickness (»!' two inelies. 
Cliondrioderma cliff asum, often utilised as a convenient " laboratory 
type," is common on the decaying haulms of l)eans in tlie late 
autumn. The interest of tliis group is entirely hiologicnl, save 
for the " flowers of tan."' ^ 

' The group was nmnograplieil l\v Scliriiter in Engler ami Piaiitl's I'dnnun- 
fainilkn, I. Teil, Al)t. 1, 1S97. See also A. Lister's Monograpli of the I\rycetozoa, 
1894 ; Massee, JMonog. of the Myxogastres, 1893 ; Sir Edward and Agnes Fry, The 
Jfycdozoa, 1899 ; and Massee MacBride, The North American Slime Moulds, 1899. 



CHAPTER IV 

PROTOZOA {cOXTIXUED): SPOKOZOA^ 

II. Sporozoa. 

Protozoa parasitic in Metazua, usually intracellular for at 
least part of their cycle, rarely possessing pseudopodia, or flagella 
{save in the sperms), never cilia; reproduction hy hrood formation, 
often of cdternating 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 Eay 
Lankester in England commenced the study of species that dwell 
in the blood, destined to be of such moment for tlie well-being of 
man and the animals in his service ; and since then our knowledge 
has increased by the labours of Manson, Eoss and Minchin at 
home, Laveran, Blanchard, Thelohan, Leger, Cuenot, Mesnil, 
Aime Schneider in France, Grassi in Italy, Schaudinn, Siedlecki, 
L. and E. Pfeiffer, Dotlein 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 tlieir hosts. 
Wasielewski, " Sporozoenkunde " (1896); Labbe, "Sporozoa" (in Ticrrcich, 1899). 
Doflein's " Protozoen als Parasiten und Krankheitsevreger " (1901) contains most 
valuable information of the diseases i>roduced 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 



SPOROZOA 



95 



As u type we will take a simple form of the highest group, the 
( Tregarinidaceae, Monocystis, which inhabits the seminal vesicles of 
tlie earthworm. In its youngest state, the " sporozoite," it is a 
naked, sickle-shaped cell, which probably makes its way from the 
L;ut into one of the large radial cells of the seminal funnel, where 




31. — Liiiikesteria ascidiae, sliowiug lite - cycle. a, b, c, Sporozoites in digestive 
epitlieluim cells of host ; d, e, srrowtli stages ; /, free gregariiie ; g, association ; 
h, encystnieut ; i, j, brood - divisions in associated mates; Jc, pairing- cells ; 
I, synganiy ; ?/;, zygote ; n, o, p, nuclear divisions in spores ; cj, cyst wiili adult 
spores, each containing 8 sickle-germs. (After Luhe, modified from Siedlecki.) 



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 
endosarc, 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 

^ For its reactions see Butschli, Jixh. Protist. vii. 1906, p. 197. 



g6 PROTOZOA 



muscles of Metazoa ; besides these it contains proteid granules 
which stain with carmine, and oil-drops. The ectosarc 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 jfibrils disposed in a network 
with transverse meshes, which effect the wriggling movements of 
the cell. The endosarc 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 peculiar changes by 
which its volume is considerably reduced. When this process of 
" nuclear reduction " is completed, each of the mates undergoes 
brood-divisions {j), 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 (I'-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 " epiplasm," and ultimately degene- 
rates, as do a certain number of the lirood-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-q), 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 Lanlcsteria, which is the form we figure on i>. 9;". 
is perforated by a terminal pore, through which the clear plasma of the sarcocj'te 
may protrude as a pseudopodiiim. 

- This account is taken from Cuenot (in Arcli. dc Biol. 1900, p. 49), which con- 
firms Siedlecki's account of the process in the allied genus Lmikcstcria in Bull. 
Acad. Cracoiv , 1899. Wolters's previous description, assimilating the processes 
to those of Actinoiihrys, is by these authors explained as the result of imperfect 
preservation of his material. 



IV SPOROZOA — CLASSIFICATION 97 

We may now pass to the classiticatioii of the group. 

A. Telosporidea. — Cells 1-nucleate until the onset of brood -formation, 
which is simultaneous. 

1. Gregarixidaceae. — Cells early 2:)rovided 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. 

(i.) 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. .... O'phryocystis A. Schn. 

(ii.) AcEPHALiNiDAE. — Cellone-chambered, usually without an epimerite 
for attachment. Monocijstis F. Stein ; Lankesteria Mingazzini. 

'iii.) DiCYSTiDAE. — Cell divided by a plasmic partition ; ejjimerite 
usually present. Grecjarina Dufour ; Stylorhynchus A. Schn. ; 
Fterocephalus A. Sclm. 

2. CocciDiACEAE. — Cells of simple structure, intracellular in Metazoa. 
Pairing between isolated cells usually sexually differentiated asoosphere 
and sperm, the latter often flagellate. Brood-formation of the adult cell 
giving rise to sickle-shaped zoospores (merozoites), or j^rogamic and pro- 
ducing the gametes. Oosperm motile or motionless, finally producing 
a brood of spores, which again give rise to a brood of sickle-sjiores. 
(i.) CocciDUDAE. — Cell permanently intracellular, or very rarely 

coelomic, encysting or not l:)efore division ; zoospores always 
sickle-shaped ; oosperm encysting at once, producing s^iores with 
a dense cell-wall i:)roducing 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. 
Lanheresterdla Laljbe ; {Drepanidium Lank. ;) Karyolysus Lablje ; 
Haemogreyarina Dan ile vvsk i. 

(iii.) 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, jjassing into the coelom, 
producing naked spores which again j^roduce 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 ; Haltfridium Labbc'.^ 

B. Neosforidia. — Cells becoming multinucleate apocytes before any l)rood- 
formation occurs. Brood -formation progressive through the apocyte, not 
simultaneous. 

' See p. 120. 



98 



PROTOZOA 



1. ^Iyxosporidiaceae. — Naked parasites in cold-blooded animals. Spore- 
formation due to an aggregation of cytoplasm around a single nucleus 
to form an arcliespore, which then j^roduces a complex of cells within 
which two daughter-cells form the spores and accessory nematocysts. 
Mijxidium Biitsch. ; Myxoholus Blitsch. ; Henneguya Thelohan ; Nosema 
Nageli {=Glu(jea Th.j. 

2. AcTiNOMYXiDiACEAE.^ — Apocyte resolved into a sporange, containing 
eight secondary sporanges (so-called spores), of ternary symmetry and 
provided with three polar nematocysts. 

3. Sarcosporidiaceae. — Encysted parasites in the muscles of Vertebrates, 
with a doulile membrane ; spores simple. Sarcocystis Lankester. 

Monocystis offers us the simplest type of Gregarinidaceae. In 
most Gregarines (Figs. 3 1,3 2) the sporozoite enters the epithelium- 





Fig. 32. — Gregarina hlaiiarum Sieb. A, two eeplialoiits, embeilded by their epimerite 
[cp), ill cells of the gut-epithelium ; den, deutonierite ; nn, nucleus ; pj\ protonierite ; 
B\ B'-, two free specimens of an allied genus ; the epimerite is falling off in B", 
which is on its way to become a sporont ; C, cyst {cy) of A, with sporoducts (s^rZ) 
discharging the sjjores {sp), surrounded by an external gelatinous investment (</). 
(From Parker and Haswell.) 

cell of the gut of an Arthropod, Worm or Mollusc, and as it enlarges 
protrudes the greater part of its Inilk into the lumen, and may 
become free therein, or pass into the coelom. The attached part 
is often enlarged into a sort of grapple armed with spines, the 
" epimerite " ; this contains only sarcocyte, the other layers being 
absent. The freely projecting body is usually divided by an 
ingrowth of the myocyte into a front segment (" protomerite "), 
and a rear one (" deutonierite "), with the nucleus usually in the 
latter. In this state the cell is termed a " cephalont." Con- 
jugation is frequent, but apparently is not always connected with 

^ See CaulJery and Mcsnil, "Rech. sur Ics Actinomyxidies," Arch. Bot. vi. 1905, 
p. 272 f. 



SPOROZOA 99 



syngaiuy or siiore-foriiiaticui ; soiuetiines IVoiu two to five may 
be aggregated into a cliaiu or " syzygy." The number of cases 
in which a syngamic process between two cells has been observed 
is constantly being increased. In Stylorliynchus (Fig. 33) the 
conjugation at first resembles tliat of Monocystis, but the actual 
pairing-cells are bisexually differentiated into sperms in the one 
parent, and oosplieres in the other ; it is remarkable that here the 
pear-sha[)ed sperms are apparently larger than the oospheres. In 
rteroccphahis the chief difference is that the sperms are minute.^ 
In all cases of spore-formation the epimerite is lost and the 
septum disappears ; in this state the cell is termed a sporont. 
Sometimes tlie epiplasm of tlie sporont forms tubes (" sporoducts "), 
which project tlnough tlie cyst-wall and give exit to the spores, 
as in Grcgarina (Fig. 32, C), a parasite in the beetle Blaps. 

Gregarines infest most groups of Invertebrates except Sponges 
and perhaps Coelenterates, the only exception cited being that of 
Epizoantlius glacialis, a Zoantharian (p. 406). They appear to 
be relatively harmless and are not known to induce epidemics. 

The Coccidiaceae never attain so high a degree of cellular 
ilifferentiation as the Gregarines, which may be due to their 
habitat; for in the growing state they are intracellular parasites. 
Their life-history sIjows a .double cycle, which has been most 
thoroughly worked out in Coccidiidae by Schaudinn and Siedlecki 
in parasites of our common Centipedes. We take that of 
Coccidiitm schuhergi (in Lithohius forficcdus'),hegiYmmg^Nii\\ the 
sporozoite, which is liberated from the spores taken in with the 
food, in the gut of tlie Centipede. This active sickle-sliaped cell 
(Fig. 34, /; enters an epithelial cell of the mid-gut, and grows 
therein till it attains its full size (ft), when it is termed a 
" schizont " ; for it segments (Gk. cr-xil^oi, " I split ") superficially 
into a large number of sickle-shaped zoospores, the " merozoites " 
(c), resembling the sporozoites. The segmentation is superficial, 
so that there may remain a large mass of residual epiplasm. 
The merozoites are set free by the destruction of the epithelium- 
cell in which they were formed, and which becomes disorganised, 
like the residual epiplasm. Each merozoite may repeat the 

^ Leger, Arch. Zool. Exp. ser. 3, x. and ser. 4, v. (1902-3) ; for a full discussion 
of tiie relations of association and conjugation in Gregarines, see Woodcock in 
Quart. Journ. Mkr. Sci. 1. 1906, p. 61 f. 

- A Lithobius is llgured in Vol. \ . p. 45. 



lOO 



PROTOZOA 



behaviour of the sporozoite, so that the disease spreads freely, 
and becomes acute after several reinfections. After a time the 
adult parasites, instead of becoming schizonts and simply forming 
merozoites by division, differentiate into cells that undergo a 
binary sexual differentiation. Some cells, the " oocytes " (d, e), 
escape into the gut, and the nucleus undergoes changes hj 
which some of its sulistance (or an abortive daughter-nucleus) 
is expelled to the exterior (/), such a cell is now an " oogamete " 
or oosphere. Others, again, are spermatogones (h): each when full 
grown on escaping into the gut commences a division (i, j), like 




Fig. 33. — Bisexual pairing oi Stijlorhynchus. a, Spermatozoon ; h-c, fusion of cytoplasm 
of spermatozoon and oosphere ; /, g, fusion of nuclei ; h-j, development of wall to 
zygote ; k, I, formation of four sporoblasts ; I, side view of spore ; m, mature sporo- 
zoites in spore. (After Lc'ger.) 



that of the schizonts. The products of this division or segment- 
cells are the flagellate sperms (s) : they are more numerous and 
more minute than the merozoites produced by the schizonts, and 
are attracted to the oosphere by chemiotaxy (p. 23), and one 
enters it and fuses with it {g). The oosperm, zygote or fertilised 
egg, thus formed invests itself with a dense cyst-wall, as a 
"oospore" (Jc), its contents form one or more (2, 4, 8, etc.) 
spores ; and each spore forms again one, two, or four sickle- 
shaped zoospores (" sporozoites "), destined to be liberated for a 
fresh cycle of parasitic life when the spores are swallowed by 
another host. 

In some cases the oogametes are at first oblong, like ordinary 



SPOROZOA 



nierozoites, and round off in the gut. The microgametocyte, or 
spermatogone, has the same character, but is smaller ; it applies 
itself like a cap to one pole of the oogamete, which has 
rounded off; it then divides into four sperms, whose cytoplasm 




hG. 34. — Life-hi.story of Coccidinm schuhergi. n, Penetration of epithelium-cell of Lost 
by sporozoite ; b-d, stages of multiple cell -formation in naked state (schizogony) ; e.f, 
formation of oogamete ; rj, conjugation ; h-j, formation of sperms (s) ; k, development 
of zygote (fertilised ovum) to form four spores ; I, formation of two zoospores (or 
sickle germs) in each spore. (From Calkins's Protozoa, after Schaudinn.) 

is not sharply separated ; one of these then separates from the 
common mass, enters the oogamete, and so conjugation is effected, 
with an oosperm as its result. This latter mode of conjugation 
is that of Adelea ovata and Coccidinm lacazei : the former is 
])rol)ably the more primitive and the commoner. Tiic s])erjns 



PROTOZOA 



of Ooccidiidae, when free, usually possess two long ilagella, either 
both anterior, or a very long one in front and a short one behind, 
both turned backwards. 

The genus Coccidmm affects many animals, and one species in 
particular, C. cuniculi Eivolta, attacks the liver of young rabbits,^ 
giving rise to the disease " coccidiosis." Coccidium may also 
produce a sort of dysentery in cattle on the Alpine pastures of 
Switzerland ; and cases of human coccidiosis are by no means 
unknown. Coccidium-\\\ie l)odies have been demonstrated in the 
human disease, " moUuscum contagiosum," and the " oriental 
sore " of Asia ; similar bodies have also been recorded in smallpox 
and vaccinia, malignant tumours and even syphilis, but their 
nature is not certainly known ; some of these are now referred to 
Flagellata (see p. 121). 

Closely allied to the Coccidiidae are the Haemosporidae, 
dwellers in the blood of various cold-blooded Vertebrates," and 
entering the corpuscles as sporozoites or merozoites to attain the 
full size, when they divide by schizogony; they are freed like those 
of the next family by the breaking up of the corpuscle. The 
merozoites were described by Gaule (1879) as "vermicles" 
(" Wlirmchen "), and regarded by him as peculiar segregation- 
products of the blood ; though Lankester had described the same 
species in the Frog's blood as early as 1871, with a full recogni- 
tion of its true character. His name, Drcpanidium, has had to 
give way, having been appropriated to another animal, and has 
been aptly replaced by that of Lanhesterella. The sexual process 
of Kari/olysus has been found to take place in a Tick, that of 
Haemogregarina in a Leech, thus presenting a close analogy to 
the next group, which only differs in its less definite form in the 
active state, and in the lack of a cell-wall during brood- formation. 

Laveran was the first to descril^e a member of the Acysto- 

^ The schizont forms of some species, before tlie invariable alternation of 
schizogony and sporogony had been made ont clearly, were regarded as "mono- 
genic" genera, under the names of ^iwicnffi, A. Schn., and Pfciffcrdla, Labbe ; 
while those in which the formation of spores containing sickles had been clearly 
seen were termed "digenic." Labbe's monograph, "Die Sporozoen," in the 
Tierrcich, is unfortunately written from this point of view, which had already 
become doubtful, and is now demonstrated to bo erroneous, cliicfly by tlie laliours 
of Schaudinn and Siedlecki. 

^ A species has been described, however, in the blood of the Indian Gerbille 
{Gerhillus incUcxis), completing the sexual process in the Louse of its host. A 
figure of G. acgyptivs will be found in Vol. X. (1902) p. 475. 



SPOROZOA 103 



sporidae, in 1880, as an organism always to l)e found in the 
blood of patients suffering from malarial fever ; this received the 
rather inappropriate name of Plasmodium, which, by a pedantic 
adherence to the laws of priority, has been used by systematists 
as a generic name. Golgi demonstrated the coincidence of the 
stages of the intermittent fever with those of the life-cycle of the 
parasite in the patient, the maturation of the schizont and 
liberation of the sporozoites coinciding with the fits of fever. 
Manson, who had already shown that the Nematodes of the 
blood that give rise to Filarial haematuria (see Vol. II. p. 149) 
have an alternating life in the gnats or mosquitos of the common 
genus Cuhx} in 1896 suggested to Eonald Eoss that the same 
might apply to this parasite, and thus inspired a most successful 
work. The hypothesis had old prejudices in its favour, for in 
many parts there was a current belief that sleeping under 
mosquito - netting at least helped other precautions against 
malaria. Eoss found early in his investigations that Cvlex was 
a good host for the allied genus Hmmofrotcus or Proteosoma, 
parasitic in birds, but could neither inoculate man with fever 
nor be inoculated from man. He found, however, that the 
malaria germs from man underwent further changes in the 
stomach of a " dappled-wing mosquito," that is, as we have since 
learned, a member of the genus Anopheles. Thenceforward the 
study advanced rapidly, and a number of inquirers, including 
Grassi, Koch, MacCallum (who discovered the true method of 
sexual union in Haltcridium "), and Eoss himself, completed his 
discovery by supplying a complete picture of the life-cycles of the 
malaria-germs. Unfortunately, there has been a most unhappy 
rivalry as to the priority of the share in each fragment of the 
discovery, whose history is summarised by Nuttall, we believe, 
with perfect fairness.^ 

The merozooite is always amoeboid, and in this state enters 
the blood corpuscle ; herein it attains its full size, as a schizont, 
becoming filled with granules of " melanin " or black pigment, 
probably a decomposition product of the red colouring matter 
(haemoglobin). The nucleus of the schizont now divides re- 

^ There is no difference between a mosquito (little fly) and a gnat, both names 
are applied indiscriminately to thin-bodied Diptera of the group Nemocera which 
attack man ; only tlie females bite (see Vol. VI. pp. 466-468). 

- Regarded by Schaudinn as a state of the Flagellate Trypanosoma (p. 119 f.). 

* In Qtiart. Journ. Micr. Sci. xliv. 1901, p. 429. 



I04 



PROTOZOA 



peatedly, and then the schizont segments into a flat brood of 
germs (merozoites), relatively few in the parasite of quartan 
fever {Hacmarnoeha malariae, Fig. 35, E-G), many in that of 



® ® 



@ ® # 




9 fj, 
3S 






g^^EB 



^ . ^, 



1/ tz^^^ 




Fig. 35. — Lil'e-history of Malarial Parasites. A-G, Amoebula of quartau parasite to sporu- 
latiou ; JI, its gametocyte ; I-M, amoebula of tertian parasite to sporulation ; iV. 
its gametocyte ; 0, T, " crescents " or gametocytes of Laverania ; PS, sperm-forma- 
tion ; U-\\\ maturation of oosphere ; A", fertilisation ; Y, zygote. a, Zygote 
enlarging in gut of Mosquito ; b-e, passing into the coelom ; f, 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 {H. vivax, 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 Haemamoela, 



SPOROZOA 105 



which imluces 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, Eoss) these resting-cells are 
crescentic,-with blunt horns, and are usually termed half-moons 
(Fig. 35, 0, 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 Xho, Arwphchs'. the crescents become round, 
and then they, like the already round ones of Haemamoeha, 
differentiate in exactly the same way as the corresponding cells 
of Coccidium schuhergl. 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 " rohjmitus 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-c). 
Here it segments into a number of spheres (" zygotomeres " of 
Koss) corresponding to the Coccidian spores, but which never 
acquire a proper wall (/). These by segmentation produce at 
their surface an immense quantity of elongated sporozoites 
(the " zygotoblasts " or "blasts" of Eoss, 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 (A), 
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 l)een 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- 



I 06 PROTOZOA 



amocha, sending it to England, where it was made to bite Dr. 
Hanson's son, who had never had fever and whose blood on 
repeated examination had proved free from any germs. In the 
nsual time he had a well-defined attack of the fever corresponding 
to that germ, and liis blood on examination revealed • the 
Hacmamoeba 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 tliat by mere precautions against the 
bit.^s of Anopheles, and tliese 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, etc., the pools left by dried-up brooks and torrents, as 
well as larger masses of stagnant w"ater, 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 otlier 
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, tbat as the relatively 
benign intermittent fevers \v,x\e 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 Trypanosoma, that in 
their less active states they have been unhesitatingly placed here 
(seep. 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. 3G) are parasitic in various 

1 It would seem that resting-cells, i.e. the crescents and corresponding spheres, 
of Laverania and Hacmamocha 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 lavourable to new sporulation occur. 



SPOROZOA 



lO 



coIJ-IiIooiUhI animals. They are at least binueleate in the youngest 
tree state, and l)ecome large and niultiuvicleate apocytes, which 
may Imd off outgrowths as well as reproduce by spores. The 
spores of the apocyte are not produced by simultaneous breaking 
up, ])ut 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, like 
those of a Coelen- 
terate (p. 246 f.), at 
the expense of the 
surrounding plasm ; 
while the third nu- 
cleus divides to form 
the two final nuclei 
of the reproductive 
body. The whole 

aggregate of the reproductive body and the two nematocysts 
enveloped in a bivalve shell. In what we may call germination, 
the nematocysts eject a thread that serves for attachment, the 
valves of the shell open, and the binueleate mass crawls out and 
grows afresh. Xosema hombycis Nageli (the spore of which has 
a single nematocyst) is the organism of the " Pebrine " 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 
welter after it had laid its eggs and seeking for pebrine germs. If 
the mother proved to be infected, her eggs were destroyed, as the 
eggs she had laid were certain to be also tainted. Balbiani com- 
pleted the study of the organism from a morphological standpoint. 
Some :\[yxosporidiaceae produce destructive epidemics in fish. 




Fig. 36.— a, Mi/xiiUiim Ueherldhniu ainoeVioid pliast 

Myxoholus mulleri, spore with discharged nematocysts 
(ntc) ; C, spores (psorosperms) of a Myxosporidian. 
nfc, nematocysts. (From Parker and Haswell.) 



IS 



I08 PROTOZOA 



The Dolichosporidia or Sarcosporidiaceae are, in the adult 
state, elongated sacs, often foiuul in tlie substance of the volun- 
tary muscles, and known as " Eainey's " or " Mieseher's Tubes " ; 
they are at first uninucleate, then multinucleate, and then break 
up successively into uninucleate cells, the spores, in each of 
which, V)y diAision, are formed the sickle-shaped zoospores.^ 

^ Leger and Duboscq have found that Sarcocydis 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 {COXTIXUED) : FLAGELLATA 

III. Flagellata. 

FliOTOZOA moving (andfeedimj in holozuic forms) /;?/ long Jiafjella : 
Ijseudopodia lohen developed usucdly transitory : nucleus single or if 
multiple not hiform : reproduction occurri^ig in the active state and 
usucdly hy longitudinal fissio7i, sometimes alternating ivith hrood- 
formation in the cyst or more rarely in the active state : form 
usucdly definite: a firm pellicle or distinct cell-wall often present. 
The Flagellates thus defined correspond to Blitschli'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 tliat 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 
Xematodes and most Crustacea). Even as thus limited tlie 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 li)Ugitudiiial (transverse only in a cyst), or if nuiltipk', 
radial and comjilete : ])Ldlicle aljsent, thin, or if armour-like, with not 
more than two valves. 

I. Food taken in at any part of the ))ody liy pseudo2)odia 

1. Pantosto.mata 
Midticilia Cienk. ; Mastiyamoeba F. E. Sch. (Fig. 37, 4 . 

' The alleged niicrouucleus of certain forms appears to be merely a "blcpharo- 
plast '' (sec p. 19) ; even when of nuclear origin, as in Trypanosomo, it has no 
fuiirtion in reproduction like the microuucleus of Infusoria (sec pp. 115, 120 f. ). 

log 



PROTOZOA 



II. Food taken in at a di-tiiiite point or points, or by absorption, or 
nutrition liolopliytic. 

1. No reticulate siliceous shell. Uianiuter under 51)0 jj. (1/50"). 
* Contractile vacuole simple (one or more). 
((*) Colourless : reserves usually fat : liolozoic, saprophytic or 

parasitic . . . .2. Protomastigaceae 

(/J) Plastids yellow or brown : reserves fat or proteid : nutrition 

variable : body nalced, often amoeljoid in active state (C nudae), 

or with a test, sometimes containing calcareous discs 

(" coccoliths," " rhabdoliths ") of jjeculiar form (C loricatae) 

3. Chrysomonadaceae 

ChromiUiiia Cieuk. ; Chrysainoeha Klebs ; Hydrurus Ag. 

Dinohryon Ehrb. (Fig. 37, 11) ; Syncrypta Ehrb. (Fig. 37, 12) ; 

Zooxanthella Brandt ; Pontosphaera Lohm. ; Coccolithophora 

Lohm. ; Rhahdosphaera Haeck. 
(y) Green, (more rarely yellow or Ijrown) or colourless : reserves 

starch : fission longitudinal . . 4. Crvpto.monadaceae 

Gryptomonas Ehrb. (Fig. 37, 9) ; Faramoeba Creetf. 
(8) Green (rarely colourless) : fission multiple, radial 

5. VOLVOCACEAE 

'^* System of contractile vacuoles complex, witli accessory formative 
vacuoles or reservoir, or both. 

(e) Pellicle delicate or absent : pseudopodia often emitted : 
excretory pore distinct from fiagellar pit : reserves lat 

6. Chlorojionadaceae 
Chloravioeba Lagerheim ; Thauimttomastvx, Lauterljorn. 

(0 Pellicle dense, tough or hard, often wrinkled or striate : con- 
tractile vacuole discharging by the flagellar pit. Nutrition 
variable . . . . .7. Euglexaceae 

Eaglena Ehrb. ; Astasia Duj. (Fig. 37, 3) ; Anisonerna Duj. ; 
EiUreptia Perty (Fig. 42, p. 12-J); Trachelomonas Elirb. (Fig. 
37, 1) ; Gryptocjlena Elirb. 

2. Skeleton an open network of hollow siliceous spicules. Plastids 
yellow. Diameter under 500 /x. . 8. Silicoflagellata 
IHctyocha Ehrb. 

3. Diameter over 500 /x. JMoutli opening into a large reticulate 
endoplasm : flagella 1, or 2, very une([ual. !). Cystoflagellata 
Nodiluca Suriray (Fig. 48) ; Leptodisctis 11. Hertw. 

1j. Fission oblique or transverse : flagella two, dissiniilai', the one coiled 

round tlie base of the other or in a traverse groove ; pellicle often dense, 

of numerous armour-like plates . . 10. Dinoplagellata 

Ceratiuni Schrank ; Gymnodinium Stein; Pendininm Elirb. (Fig. 46); 

Fouchetia Schiitt ; Pyrocystis Murray (Fig. 47); Folykrikos Biitschli. 

The Protomastigaceae and Volvocaceae are so extensive as to require 
further subdivision. 

Protomastigaceae 

I. Oral spots 2. Flagella distant in pairs. . . Distomatidae 

II. Oral spot 1 or 0. 



FLAGELLATA — CLASSIFICATION 



A. Flagcllum 1. 

(«) No anterior ])rucess : ol'ten ]lara.'^itic . . Oikomoxadidak 

Oikomonas K. (Figs. 37, 2, S) ; Trijimnosoma Ch'iiljy (Fig. 39, a-f) ; 
Treponema Vuill. (Fig. 39, y-i). 
(b) Anterior ^jrocet^s unilateral or iiroboscidiforni : cell often tliecate 

BiCOECIDAE 

Bicoeca Clark ; Poteriodaidron St. 
ic) Anterior process a funnel, surrounding the base of the flagelluni : 
cells often tliecate. 
(i.) Funnel free .... Craspedomonadidae 

Codo.mja Clark ; Alonosiga CI. ; J'olyocca Kent ; Protcroftpov gia 
Kent ; Salpingoeai CI. 
(ii.) Funnel not emerging from the general gelatinous investment 

Phalansteridae 
E. Flagella 2, unequal or dissimilar in function, the one sometimes short and 
thick, 
(rt) Both flagella directed forwards . . . Monadikae 

Monas St. ; Anthop)lujsa Bory (Fig. 37, 13j. 
(6) One flagellum, usually the longer, turned backwards. Bodoniuae 

Bodo St. (Fig. 38). 
C. Flagella 2, equal and similar . . Amphimonadidae 

Amphimonas I)uj. ; Diplornita K. (Fig. 37, 10) ; llhipidodendron St. 
(Fig. 37, U). 
L). Flagella 3 . . . . . . Trimastigidae 

Ballitujeria K. (Fig. 37, 6) ; Custia Leclercq. 

E. Flagella 4 or more : mostly parasitic in Metazoa. Polymastigidae 
Trichomonas Donne ; Tetramitus Perty (Fig. 37, 7) ; Hexamitus Duj. ; 
Lamhlia Blanchard. 

F. Flagella numerous, sometimes constituting a complete ciliiform invest- 
ment, and occasionally accompanied by an undulating membrane : 
parasitic in Metazoa. 

(rt) Flagella long : nucleus single ; parasitic in insects Trichonymphidae 
Dinenympha Leidy ; Joenia Grassi ; Fyrsoiujmplia Leidy ; Triclto- 
nijmpha Leidy ; Lopliomonas St. ; Maupasia Schew. 

(h) Flagella short, ciliiform, ujiiformly distributed : nuclei veiy 
numerous, all similar : parasitic in Ami>liil)ia . Opalixidae 

Opalraa Purkinje and Valentin (Fig. AV). 

Volvocaceae 

A. Cells usually isolated, separating after fission or brood -foimation. 
Usually green (sometimes red), more rarely colourless sajjrojjhytes 

Chlamydomonadiuae 
ChlamydomonuH Ehrb. ; Phacotus Perty ; Polytoma Ehrb. ; SplnnreUa 
Sommerf. (Fig. 43) ; Zoochlorella. 

B. Cells multii)lying in the active state by radial divisions in the same 

jilane and usually incurving to form a spherical colony, united in a 
gelatinous investment, sometimes traver.^ed by plasmic threads 

Volvocidae 
Gomum O.F.]\[. ; Eudorina Elirb. ; Pandorina Bojy (Fig. 45) ; Stephano- 
sphaera Cohn ; Volvox L. (Fig. 44). 



PROTOZOA 




e.Oallingeria 



S.Oikomonas 



aCryptomonas io.Di|,lomifa 




.\ W. y 



M? "•'"^^./^ 



%: 



"# 



--^r- 



I 

ll.DInobryQH 12.Sy ncry JJ ttt 13. Anl'hojjhysa 14.Rhi|)iclodenclron 

FiQ. 37.— Various forms of Flagellata. 2, 6-8, 10, 13, 14, Protomastigaceae : 11, 12, 
Chrysomonadaceae ; 9, Cryptoiiionadaceae ; 1, 3, Euglenaceae ; 4, Pantostoniata : note 
branched stalk in 13 ; branched tubular theca in 14 ; distinct thecae in 11 ; stalk 
and theca in 10. In 2, flagellate (a) and amoeboid {h) phases are sliown ; in 5, 
flagellate (a) and Heliozoan {&) phases ^ ; in 8 are shown two stages in the ingestion 
of a food particle (/) ; cAr, plastoids ; f.r«c, contractile vacuole ; /, food particle ; 
f), gullet; U theca'; nv, nucleus ; p, protoplasm ; per, peristome ; r.?', vacuole of 
ingestion. (From Parker and Haswell, mostly from Biitschli's Protozoa.) 

1 Diimrpha is now referred to Heliozoa (p. 70). 



FLAGELLATA I I 3 



The modes of nutrition are threefold : tlie simplest forms 
live in liquids containing decaying organic mutter which tliey 
ahsorl) through their surface (" saprophytic ") : others take in food 
either Amoeba fashion, or into a vacuole formed for the purpose, 
or into a definite moutli (" 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 tliat sliow chromatophores at one time and 
lack tliem at another ; or, again, the same individual {Euglena) 
may pass from holozoic life to saprophytic {Paramoeha, 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 {Polyoecci). This stalk may have a varying consistency. 
In Anthophi/sa (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 tlie 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 tlie l:)ody of the cell forms a cup 
or " tlieca," within which the cell lies quite free or sticking to it 
Ijy 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 Bhijndodendron (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 
'■' cuticle " (in the holophytic species formed of cellulose), or even 
a bivalve or multivalve shell of distinct plates, hinged or over- 
lapping {Cryptorjhna, Phacolus, Dinofiagellates). The wall of the 

' I.e. resembling the thread-like water Algae. 

- Trichocysts (see p. 142) occur in some Chloromonadaceae.; and the Dino- 
flagellatc Pohjkrikos possesses true nematocysts (see p. 131). 

VOL. I I 



114 PROTOZOA 



Coccolithophoridae, a family of Chrysomonadaceae, is strengthened 
by embedded calcareous spicules (" coccoliths," " cyatlioliths," 
" rhabdoliths "), which in the most complex forms (cyatlioliths) 
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 li\ing 
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 fresli 
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 Bodo saltans a single anterior 
anchoring lash, by which they spring up and down against the 
organic debris 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. 

^ For a full monograph of this family see H. Lohmaiin, in Arch. f. Pi-otistcn- 
kunde, voh i. 1902, p. 89. 

2 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 Iho 
Kodonidae (and the zoospores of many Chytridieae, which have most of the 
characters of the Flagellates, though habitually removed to the Fungi). 



FLAGELLATA I I 5 



An uiidulatiug membrane occurs, sometimes passing into tlie 
tiagelluin in certain genera, all parasitic, such as Trypanosoma 
(incl. Herpetomonas), Trichomonas, Hexamitus, and Dineni/mpha. 

In some cases the flagellum (or flagella) is inserted into a 
detinite pit, which in allied forms is the mouth-opening. The 
contractile vacuole is present in tire 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 discliurge into a permanently visible " reservoir." This again 
may discliarge directly to the surface or tlirough the pit or canal 
in which the flagellum takes origin (^Euglena). 

The " chromatophore " may be a single or double plate, ov 
multiple.^ In tlie 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" maybe (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 wlien 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- 
pList " 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 tlie cyst is usually multiple ; " in the coloured 
forms, however, vegetative growth often alternates with 
division, giving rise to plant-like bodies. Polytoma and oLlier 
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. Conjug-ation 
has been observed in many species. In some species of 
Chlamydomonas it takes place after one or both of the two 

^ Tlie colouring matter is chlorophyll or some allied colouring matter. In (ho 
jellow and brown forms the additional pigment is termed loo.sely "diatomin." 
but its identity with that of Diatoms is in no case proved. 

^ Notably in the Craspedomonadidae, where transverse division also occurs. See 
Raoul France, Z>ic Craspcdomonadineen (Buda-Pesth, 1897). 



I I 6 PROTOZOA 



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 w'e 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 light 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 tw^o, to follow up one of tlie 
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) ; - 

^ And also in the "Monads," described by Dallinger and Drysdale, see above. 

'^ In CcTcomonas dujardinii, Folytovia uvella, and I'ctramitios rostratus the 
gametes resemble the ordinary forms and are isogamous. In Monas dallingeri and 
JJodo caudaf/us 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 liave even attemjjted to repeat the English observations 
und.T the same severely critical conditions, and therefore consider the attacks so 
far unjustified. Schaudinn has observed conjugation between Trichomonas indi- 
viduals which have lost their flagella and become amoeboid ; also in Laviblia intes- 
tinalis and in Trypanosoma {Halteridium ?) noctuac (Fig. 39) " Reduction-divisions " 
(see p. 75, note 1) of the nuclei take place before fusion, and the nuclear pheno- 
mena are described as "complicated " {Arb. Kais. Gesundheitsamtc, xx. 1904, p. 387). 
Faramoela cilhardii in its adult state is colourless, amoeboid, multiciliate. It forms 
a brood cyst, from which are liberated flagellate zoospores, with a chromatoiihore, 
■whit'Ii reproduce by longitudinal fission in this state. They may also conjugate. 



FLAGKLLATA 



117 



ti.e zygote encysted ; and within the cj.t the protoplasmie body 







under w 



eut brood-formation, the outcome of which was £ 



a mass of 



I 8 PROTOZOA 



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 believed 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 tempera- 
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.E.S. xxvii. 1878, p. 332. 



FLAGELLATA 1 I 9 



un increased toleration and resistance from one generation or 
cycle to another. 

As we noted above (p. 40), the study of tlie Flagellates has 
been largely in the hands of botanists. After the work of Biitschli 
in Bronn's Thier-Picich , Klebs ^ took up their study; and the prin- 
cipal monographs during the last decade have appeared in Engler 
and Prantl's Pjianzenfaviilien, where Senn "- treats the Flagellates 
generally, AVille ^ the Yolvocaceae, and Schiltt the " Peridiniales " 
or DinoHagellata ; ■* 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 
carefully studied by Dallinger and Drysdale belong to the genera 
Bodo, Cercornonas, Tetramitiis, Monas, and DaUingcrid. Many 
others are parasites in the blood or internal cavities of higher 
animals, some apparently harmless, such as Trichomonas vaginalis, 
parasitic in man, others of singular malignity. Costia necatrix, 
infesting the epithelial scales of fresh-water fish, often devastates 
hatcheries. The genus Trypanosoma, Gruby, contributes a 
number of parasites, giving rise to deadly disease in man and 
beast.'' T. leivisii is common in Eodents, but is relatively harm- 
less, T. evansii is the cause of the Surra disease of Euminants 
in India, and is apparently communicated by the bites of " large 
brown flies " (almost certainly Breeze Flies or Tabanidae, Vol. YI. 
p. 48 1). T. hrucei, transferred to cattle by the Tsetse Fly, Glossina 
ynorsitaiis (see Yol. YI. Fig. 244, p. 513) in Equatorial Africa, is 
the cause of the deadly ISTagana 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, Mai 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. Iv. 1893, p. 353. 2 | t^^^^ ^,^^ -, .,^ ^c,qq 

3 In the Chlorophyccae, 1. Teil, Abt. 2, 1897. ■• 1. Teil, Abt. 1. h, 1896. 

* Besides tlie above, Daiigeard, in various papers in his periodical Le Bofaniste, 
has treated of most of the groups, and Raoul France has monographed tlie P0I3'- 
tomeae in the Jahrb. wiss. But. xxvi. 1894, p. 29.5, and Dill the genus Chlainii 
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 
Feb. 1, 1906, see Woodcock, " Tiie HaenioHagellates," in Quart. Journ. Micr. Sci. 
1. 1906, p. 151. 



I20 



PROTOZOA 



fever recently recognised on the West Coast has been found to bo 
the early stage of the sleeping-sickness, thai; 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 T. gamhiense is transferred l)y an inter- 
mediate host, a kind of Tsetse Fly {GlossinaiMlpalis). ►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 
HaUcrLdium,\\j is really 
a Tryimnosoma ; ^ for 
the accomplishment of 
successful sexual re- 
production it retpnrei; 
transference to the 
gut of a gnat {Culex). 
The germs may infect 
the ovary, and give 
the offspring of the 
insect tlie innate 
power of infecting 
Owls. Thus a new 
T. or. ^, , , .. ^ ^ c • light is shed on the 

Fig. 39. — Morphology ot Trypanosoma, a-f, Stages \n °_ ^ 

development of TnjiMnosoma nociuae from the Origin ot the Cocci- 
active zygote ("ookinete"); h, first division of .];„pppp whnsp "bbmf s " 
nucleus into larger (trophic) and smaller (kineto-) '-ii^^^flt!^ ^^^ ii'J^t; uidbUfc, 
nucleus ; c, d, division of smaller nucleus and its in the insect llOSt re- 
transformations to form " blepharoplast " and myo- -, ■, rr 
nen.es ;/, adult Trypanosoma ; g! h, i, Treponema Semblc Trypanosoma 
zeemannii of Owl ; rj, Trypanosonie form ; h, in their morpholooy. 
Suirochaeta form ; i, rosette aggregate. (After ^1 -, rn- i 

Schaudinn.) The humaii Tick 

fever of the Western 
United States and the epizootic Texas fever are known to be duo 
to blood parasites of the genus Firoplasma (Bahesia), of which 
the free state is that of a Trypanosoma It appears certain that 
Texas fever, tliough 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 
Trypanosonie germs, and will by their bites infect otlier animals. 

' Doubts still subsist as to the interpretation of Sehaudinu's observations. 




FLAGELLATA 121 



It would seem probable that the virulence of the Persian Tick 
(Ari/as jyersica) 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 Firo2Jlasma. 

Trypanosoma is distinguished by the expansion of its flagelhini 
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 Eose 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 Sjnrochaeta ohermeieri. 
Schaudinn has shown that this and other similar blood parasites 
are closely allied to Trypanosoma] and since the original genus 
was founded on organisms of putrefaction which are undoubtedly 
Schizomycetes, Yuillemin has suggested the name Treponema. 
T. ptallidum 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-Clyik. They are 
attached either to a substratum, by a stalk produced by the l)ase 
of the cell, or to otlier members of the same colony ; they are 
distinguished by the protrusion of the cytoplasm around the 
l)ase 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. 

^ Quart. Journ. Micr. Sci. xlvi. 1902. 

- A Zatnbezian Tick infects man with a TrciJonema, producing relapsing- fever ; 
another species is found in the tropical di.sease "frainl>oesia " ("yaws" or "jiarangi"). 

^ Stated by Geza Entz and Raoul France to be due to the spiral twisting of a 
plasmic membrane, and to be like a cone formed by twisting paper, witli tlie free 
edges overlapping. 



PROTOZOA 



The agitation of the flagelhim determines a stream of water 
upwards along the outer walls of the funnel ; and the food- 
par tides 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 tlie two so formed continue to produce a staliv, the result is 




l.Monosiga. 2.Salpingoeca. S.Polyoeca. 4.Hroferospon9ia. 

Fig. 40. — Various forms of Craspedomonadidae. 2, «, Adult cell ; 2, b, loiigitudiual 
fission ; 2, c, the production of flagellulae by brood-formation ; c, collar ; crac, con- 
tractile vacuole ; Jl, tlagellum ; I, theca ; 7iu, nucleus ; s, stalls. (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 tlieir 
flagellum, become amoeboid, and finally undergo brood-formation 
to produce minute zoospores. This is the form which by its 
differentiation recalls the Sponges, and has been regarded as a 



FLAGELLATA I 23 



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 monograplier of the family is Eaoul France, 
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. Y. p. 356), nothing is known. Some of them 
have a complete investment of motile flagella, like enormously 



Fig. 41. — Opalina 
ranarvm. A, liv- 
ing specimen ; B, 
stained specimen 
showing nuclei ; 
C, stages iu nuc- 
lear division ; 
D - r, 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. 
nv, Nucleus. 
(From Parker's 
Biology, after 
Saville Kent and 
Zeller.) 



long cilia, which in Dinenymplia appear to coalesce into four 
longitudinal undulating membranes. Lopkonionas inhabits the 
gut of the Cockroach and ]\Iole-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. V>\\t 
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 Lcidy. For the most recent description of this group see Grassi 
and Siindias in Quart. Journ. Micr. Sci. xx.xix. (figures) and xl. )>. 1 (text), 1S97. 




124 



PROTOZOA 



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 tlie Euglenaceae, Euglena viridis is a very common 




Fig. 42. — Longitudinal Fission of Eutreplia viridis (Euglenaceae), showing cliloroplasts, 
micleus, and Hagella ai'ising 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 Eotifers, such as Hydatina scnta (Vol. II. Fig. 
106, p. 199) and Brachionus. Euglena is about O'l 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 

^ Bezzcnberger has given an analytical table of the eleven known species of the 
genus Opalina in Arch. Protist. iii. 190^, p. 138. 



FLAGELLATA I 2 5 



power tlie rest of the cell is green, owing to the numerous chluro- 
pliyll bodies or . ehloroplasts. 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- 
chronie." 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, 
l)ranching 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 light reaction, Eughna 
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 tlie Chrysomonadaceae the genus Zooxanthella, Brandt, 
has already been described under the Eadiolaria (p. 86), in the 
jelly of which it is symbiotic. It also occurs in similar union in 
the marine Ciliates, VorticeUa sertidariae and ScT/j^hidia scorpaenae, 
and in Millepora (p. 261) and many Anthozoa (pp. 373 f., 396). 

Of the Chlamydomonadidae, Sphaerella {Hacmatococcus, 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, CJdamydomonas, 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, 

^ Such inoveiiieuts, permissible by the perfectly flexible but firm pellicle, are 
tormeil "metabolic" or " euglenoid " in contradistinction to "amoeboid." They 
also occur in many Sporozoa. 



26 



PROTOZOA 



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 tlie 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, 



Fig. 43. — Sphaerdla 
jdnvialis. A, iiiolile 
stage ; B, resting 
stage ; C, D, two 
modes of fission ; E, 
SphaereUa laci(sfri.% 
motile stage, clir, 
Chromatophores ; 
c.vac, contractile 
vacuole ; c.ir, cill- 
wall ; /, tiagelhi ; 
»M«, nucleus; «!«', nu- 
cleolus ; jji/r, pyre- 
noids. (From Par- 
lier'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, Pr oaks par asita, Vol. II. p. 227. 




FLAGELI.ATA 



127 



plate bends up (as in the gastrulation of the double cellular plate 
of the Nematode Cucullanus, Vol. II. p. 136), 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 




Fig. 44. — Voh-ox (ilohator. A, entire colony, enclosing several daugliter-colonies ; B, 
the same during sexual n.aturity ; C, four zooids in optical section ; D'-D^, develop- 
ment of jjarthenogonidium ; E, ripe spennogonium ; F, sperm ; G, ovum ; H, 
oosperm, a, Partlienogonidia ; /, flagellum ; ov, ovum ; ovy, ovaries ; 2^9^ pigment 
spot ; .s/), sperms ; Spij, spermogonia dividing to form sperms. (From Parker's 
Biology, after Colin and Kirchner.) 



(" parthenogonidia ") of a new colony ; they begin segmenting 
before the colony of which they are cells is fi'eed. 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 



PROTOZOA 



the case may be. Tliese 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 life. 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, Faridorina, 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). 

Siephanospliacra 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 Eudorina, 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 occur : S x S, S X M, S X L, M x ]\I, M x L. 
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 



FLAGELLATA 



129 



and small are capable, each with its like, of et^ual, undifl'eren- 
tiated conjugation ; so that we have a dillerentiation (^f sex far 
other than that of ordinary, binary sex. Eudorina, 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 




Fig. 4,">. — Pamlorina moruvi. A, entire colony : B, asexual reproduction, each zooiil 
dividing into a daughter-colony ; C, lilieration 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, alter Goebel.) 

of a colony are spermogonia, producing each a brood of sperms, 
while the rest are the oospheres. The transition to Volrox must 
have arisen through the sterilisation of the majority of cells of 
a colony for the better nutrition of tlie 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 



30 PROTOZOA 



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, in 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 tliis class, attaining a maximum diameter 
of 1 5 /i, (y '^q") and even 375 fj, ( ^V') ^^ Pyrocystis noctiluca. The 
special character of the group is tlie 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 " Cilioflagellata," which had of course to be abandoned 
when Klebs discovered the true structure." There is a distinct 
cellulose membrane, sometimes silicified, to tlie 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 striiigs, separates 
the peripheral cytoplasm from the central, within which is 
the large nucleus. There are in most species one or more chro- 
matopliores, coloured by a yellowish or brownish pigment, wliieh 
is a mixture of lipochromes, distinct from diatomin. In a few 
species the presence of these is not constant, and these species 

^ 111 tlie Adinidae there is no groove ; the two lashes arise close together, and 
the one is coiled round the base of the other. 
- In Unt. Inst. TUhiiujcn, i. 1883, p. 233. 



FLAGELLATA 



131 



show variability as to their nutrition, wiiich is soniotinies 
holozoic. Uiuler these conditions tlie cell can take in food- 
particles as bulky as the eggs of Eotifers 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, witli 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. 
Xematocysts (see p. 246 f.) are 
present in Pohjkrilcos, 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 
cliains, notably in Ceratiimi and Fic 
PolykrilMS, the latter dividing 
transversely and occurring in 
chains of as many as eight. The 
process of division may take place 
when the cell is active, or in a cyst, as in Fyrocystis (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 capable of playing the part of gametes, 
and conjugating in pairs.^ 

The Dinofiagellates are for the most part pelagic in habit, float- 
ing at the surface, and when abundant tinge the water of fresh- 
water lakes or even ponds red or brown. Feridinium (Fig. 46) 
and Ceratiuvi (the latter remarkable for the horn-like backward 
jirolongations of the lower end) are common genera both in the sea 




I'cikUnium divergens. a, 
Flagellum of loiigitiulinal groove ; 
b, tlagelluiu of transverse groove ; 
<•/•.(•, contractile vacuole surrounded 
by fouiuuive vacuoles ; n, nucleus. 
(After Scliiitt.) 



^ Conjugation of adults has been observed by Zederbauer {Bcr. Deutsch. Gcs. 
x.\ii. 1904). A sliort connecting tube is formed by tlie meeting of outgrowths 
from either mate ; their protoplasmic contents meet and fuse herein to form a 
spherical resting-spore, as in tiie Conjugate Algae. 



132 



PROTOZOA 




and fresh-waters. Gyvinodinium pulviseulus is sometimes parasitic 
in Aj)pendindaria (Vol. VII. p. 68). Polykrikos ^ has four trans- 
verse grooves, each with its Hagellum, 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. Peridiniuvi 
is certainly found fossil in 
the firestone of Delitzet, be- 
longing to the Cretaceous. A 
full monograph of the group 
under the name " Peridi- 
niales " w^as published by 
Schiitt.- 

The Cystoflagellates con- 
tain only two genera,^ Kocti- 
luca, common at the surface 
of tranquil seas, to which, 
as its name implies, it gives 
phosphorescence, and Lepto- 
discus, found by K. Hert- 
wig in the Mediterranean. 
Noctiluca is enormous for a 
Flagellate, for with the form of 
a miniature melon it measures 

Pyrocystis fusiformis, Murray, about 1 mm. {-^-r'.') Or morC in 

^ ^^' ^'~ t:^.?"^'^ diameter. In" the depression 

is the "oral cleft," from one 
end of wliich rises, by a broad base, a large coarse iiagellum, 
as long as the body or longer and transversely striated. In 
front of the base of the flagellum are two lip-like promin- 



X 100. Prom the surfn 
Current. (From Wyville Thomson.) 



1 According to Bergh, Polykrikos has as many nuclei as grooves, each accompanied 
by one or more "niicronnclei." Possibly these latter bodies are merely blepliaroplasts, 
in connexion with the transverse flagella. 

2 Engler and Prantl's PJlanzenfamilicn, 1. Teil, Abt. 1, 1896. 

» The luminous genus, Pyroeijstis (Fig. 47), regarded as a Cystoflagellate by 
Wyville Thomson, has a cellulose wall, no mouth, and in the zoospore state has 
the two flagella in loncritudinal and transverse grooves of the Dinoflagellata. 



FLAGELLATA 



133 



eiices, 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, llagellum, usually called the cilium. Behind 
these the oral groove has an oval space, the proper mouth ; 
hehind 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 
])ellicle, except at the oblong- 
mouth, and the lips antl 
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 filling the 
interspaces. The wliole 
arrangement is not unlike 
that found in many plant- 
cells, but the only other 
Protists in which it occurs 
are the Ciliata Trachelius (Fi 
central mass contains the large nucleus. jVocfilnca 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 liy spuru- 
lation or brood-formation.-' 
' This process has tlie character of telolecithal segmentation in a .Metazoan egg. 




— Xnctituca miliaris, a marine Cysto- 
fl:i<:;ellate. (From Verworu.) 



06, p. 153) and Loxodcs. The 



34 PROTOZOA 



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 tlie cytoplasm atrophies, 
and the hillocks formed by the plasmic outgrowths around the 
final daughter -nuclei liecome separate as so many zoospores 
(usually 25 6 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 viev/, a naked Dino- 
flagellate, whence it seems that the Cystoflagellates are to l)e 
regarded as closely allied to that group. Leptodisnts is concavo- 
convex, circular, with the mouth central on the convex face, 
1-flagellate, and attains the enormous size of 1-5 mm. (jVO ^^^ 
diameter. 

The remarkable phosphorescence of Noctiluca 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 light 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 3ficrosco2}e : " — " 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 

^ See Doflem, in Zoo!. Jahrh. Anat. xiv. 1900, p. 1. - London, 1753, 402-403. 



FLAGELLATA I 3 5 



the I'hial 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 likewise 
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 
]\Iotion reacheth : this chiefly happens when the Sea hath been 
greatly 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 Doflein have elucidated the conjugation. 



CHAPTER VI 

TROTOZOA {continued) : INFUSORIA (CILIATA AND SUCTORIA) 

IV. Infusoria. 

Complex Protozoa, never liolophytic save hy symhiosis with ^iJant 
commensals, never amoeboid, with at some 2Jcriod numerous short 
cilia, of definite outline, ivith a double nuclear afjiaratus con- 
sisting of a large meganucleus and a small micromtchus (or 
several),^ the latter alone taking part in conjugation (Jcaryo- 
gamy), and giving rise after conjugation to the neio 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 Ehizopoda. 

' On this account Hickson has termed the group "Heterokaryota" in Lankester's 
Treat. Zool. i. fasc. 1, 1903. 

- See Fiaker, Employment for the Jlicroscopc, 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 



CILIATA 137 



I. CiLIATA 

Infusoria, u-ith a mouth, and cilia by ivhich they move and 
feed; usually with undulating membranes, memhranellae, cirrhi, 
or some of these. Genera about 144 : 27 exclusively marine, 50 
common to both sea and fresh water, 27 parasitic on or in ]\Ieta- 
zoa, the rest fresh water. Species about 500. 
We divide the Ciliata thus : ^ — 

(I.) Moutli habitually closed, opening by retraction of its circular or slit- 
like margin ; cilia uniform . Order 1. Gyjinostomaceae. 
Lacrymaria, Elirb. ; Loxodes, Ehrb. ; Loxophyllum, Duj. ; Lionotus, 
Wrez. ; Trachelius, Schrank ; A7nphileptus, Ehrb. ; Actinoholu.% St. ; 
IHdiniuvi, St. ; Scaphiodon, St. ; Dysteria, Huxl. ; Coleps, Nitzscli. ; 
Dileptus, Duj. ; Ileonema, Stokes ; Mesodmium, St. 
(II.) Mouth permanently open, usually equipped with one or more undu- 
lating membranes, receiving food by ciliary action (Tricho- 
STOJiATA, Biitschli) 
(a) Cilia nearly uniform, usually extending over the whole body, 
without any special adoral wreath of long cilia or membra- 
nellae ; mouth witli one or two undulating membranes at its 
margin or extending into the short pharynx. 

Order 2. Aspirotrichaceae. 
Paramecium, Hill ; Colpnda, 0. F. ]\Iiill. ; Colp)idium, St. ; Leuco- 
phrys, Ehrb.; Cyclidium, CI. and L. ; Lemhadion, Perty ; 
Cinetochilum, Perty; Pleuronema, Duj.; Ancislruni, IMauj). ; 
Glaucoma, Ehrb. ; XJronema, Duj. ; Lemhus, Cohn ; Urocentrum, 
Nitzsch ; Icthyophtheirius, Fouquet. 
(h) Strong cilia or membranellae forming an adoral wreath, and 
bounding a more or less enclosed area, tlie " 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. Heterotrichaceae 
Spirostomuvi, Ehrb. ; Bursarin, O. F. IMull. ; Stentor, 
Okcn; FoUiculma, hanili.; Co7ichophtheirus, 8t.; Balan- 
tidium, CI. and L.; Nyctotherus, Loidy; Metopus, CI. and 
L. ; Caenomorpha, Perty; Piscomorpha, Levander ; 
Blepharisma, Perty. 
(ii.) Body cilia limited in distribution or absent ; peristome 
anterior, nearly circulai', sinistrorse. 

Order 4. Oligotrichaceae. 
Halteria, Duj. ; Marijna, Gruber ; Tintinnus, Schrank ; 
Dictyocystis, Ehrb.; Stromhidium, CI. and L. {=Tor- 
quatella, Lank.l 
(iii.) Peristome extending backwards along tlie ventral face, 
which alone is provided with motile cirrlii, etc. ; dorsal 
cilia fine, motionless. . Order 5. Hypotrichaceae. 

^ Orders 1 and 2 constitute together the Holotrkha of Stein ; Butschli regards 
3 to 6 as sections of Spirotrocha. 



138 PROTOZOA 



Stylonychia, Ehrb. ; Kerona, 0. F. Mlill. ; Oxytricha, 
Ehrb. ; Ewplotes, Elirb. ; Stichotricha, Perty ; Schizo- 
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, CI. ; Tn'chodina, Ehrb. ; Vorticella, L. ; 
Zoothamnium, Bory ; Carchesium, Ehrb. ; Ejnstylis, 
Ehrb.; Opercularia, Lamk.; Vaginicola, Lamk. ; 
Pyxicola, Kent ; Oothurnia, Ehrb. ; Bcyphidia, 
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" = ;^ 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 
diffluence 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, 2^er) ; 
these, on careful examination, prove to be transverse triangular 
plates, which after death may fray into cilia." They are the 

^ Dextrorse in all but Lichno2^hora and Spirochona. 

- Each membranella is a transversely elongated oval in reality, and below it is 
a double row of ])asal granules, corresponding to the individual cilia that consti- 
tute it. Similarly, the undulating nieiubranes have a single row of basal granules. 



CILIATA 



139 



This 



" adoral menil)ranellae." 
and there crosses over 
the edge of the body to 
the ventral aspect, and 
then curves inwards 
towards the median line, 
which it reaches about 
half-way back, where it 
passes into the pharynx 
(7/1). It forms the front 
and left-hand boundary 
of a wedge-shaped de- 
pression, the " peri- 
stomial area," the right- 
hand lioundary 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 " (p<>c) 
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. 

In some allied genera (not in Stj/Ionj/chia), at 
the inner side of each adoral memljranella, is a 



row passes to the left blunt angle. 








PiQ. 49.— Ventral view of Stylonychia mytilus. a.c, 
Alxloniiiial cirrlii ; an, anus discharging the shell 
of a Diatom ; c.c, camlal cirrhi ; c.p, dorsal cirrhi ; 
cr, contractile vacuole ; e, part of its replenishing 
canal ;/.c, frontal cirrhi ; /.r, food vacuoles; n, 
internal undulating niennbrane ; I, lip ; ?", mouth 
or pharynx ; mc, marginal cirrhi ; iV, N, lobes of 
nieganucleus ; n, n, micronuclei ; 0, anterior end ; 
2^er, adoral memliranellae : por, preoral cilia ; j^.om, 
preoral undulating membrane ; .?.//, sense hairs. 
(Modified from Lang.) 



the base and on 
' paroral ' cilium. 



I40 PROTOZOA 



All these motile organs, with the exception of the preoral cilia, 
pass into the pharynx ; but the adoral nienibranellae soon stop 
short for want of room. There are some seventy memljranellae 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 " {mc), which, like tlie 
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 " (/.c). 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.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 {aii) 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 " endosarc," and a firmer " ectoplasm " 
or " ectosarc." The former is rich in granules of various kinds, 
and in food-vacuoles wherein the food is digested. The mode of 
ingestion, etc., 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 (e) 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 {JSf, N), united by a slender thread ; and (2) two minute 
" micronuclei " {n, n), one against either lobe of the meganucleus. 

Stylonijchia multiplies by transverse fission, the details of 
which are considered on pp. 144, 147. 

The protoplasm of Ciliata is the most differentiated that we 



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 eaeli species, ihougli 
it may be subject to temporary flexures and contractions. T'lu- 
pellicle varies in rigidity ; where the cilia are abundant it is pro- 
portionately delicate, and scarcely differs from the ectoplasm proper, 
saye 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-cilia are fine, and often 
reversible in action, which is exceptional in the organic world. 
They may be modified or combined in various w^ays. We have 
seen that in Stylonychia some are motionless sensory hairs. The 
cirrhi and setae sometimes fray out during life, 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 tlie 
" vibratile styles" of Eotifers (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 

^ Tail-like appendages are found in Scaphiodon and in Dysteria and its allies 
(Gymnostomaceae), Urocentrum (Aspirotrichaceae), Discomoiyha and Caenomorpha 
(Heterotrichaceae). In the first two and last two cases they are prolongations of 
the body ; in tlie third an aggregate of cilia. One or more long caudal setiforni 
cilia are present in the genera Lembadion, Pleuroncma, Cyclidium, Lemhus, 
Cinctochilum, 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. Faure-Fremiet terms such a zone 
or annular brush a "scopula" ("Struct, de I'app. fixateur chez les Vorticellides," 
Arch. ProHst. vi. 1905, p. 207). For a discussion of the finer structure of the cili.i 
in Ciliata, and the mechanism of their action, sec Schuberg, Arch. Prvtisl. vi. 
1905, p. 61. 



PROTOZOA 



protoplasm it has a honeycombed or alveolate structure, but in 
this case tlie alveoli are permanent in their arrangement and 
position. Kows of these alveoli run under tlie 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 tlireads running along the 
inner walls of the alveoli of the superficial layer are differen- 
tiated into muscular fibrils or " myonemes," to which structures 





.^ 



Fig. .'iO.— Eutosare of Ciliata. «-/', from Stentor coeruleiis ; g, Holophrya discolor, a. 
Transverse section, showing cilia, pellicle, canals, and myonemes ; b, surface view 
below pellicle, showing myonemes alternating with blue granular streaks ; c, jiiore 
superticial view, showing rows of cilia adjacent to myonemes ; d, myoneme, highly 
magnihed, showing longitudinal and transverse striation ; e, two rows of cilia ; /, g, 
optical sections of ectosarc, showing pellicle, alveolar layer (a), myonemes (m), and 
canals in ectosarc. (Fi'om Calkins, after Metschnikoff, Biitschli, and John.sou.) 



so many owe their marked longitudinal striation on the one 
hand, and their power of sudden contraction on tlie other. The 
appearance of transverse striation may be either due to transverse 
myonemes, 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 ectosarc are often found trichocysts/ analogous 

^ See jMitrojiliaiiow " Sur les Tnciiocystes . . . du Paravioccium," Arch. 
I'rotist. V. 1904, p. 78. 



CILIATA 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 [x long in Paramecium) at right angles to 
the surface, which on irritation, chemical (by tannin, acids, etc.) 
or mechanical, emits or is converted into a thread several times 
the length of the cilia (33 fi), often barbed at the tip. In the 
predaceous Gymnostomaceae, such as DuUnrum, tlie 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 tliey feed. In most of tlie Peritrichaceae they are, 
when present, limited to the rim around the peristome, while in 
the majority of species of Ciliata they have not been described, 
ribrils, possibly nervous,^ have been described in the deepest layer 
of the ectosarc 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), tlie 
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, r) or 
elongated canal. 

The endosarc, in most Ciliates well differentiated from the 
ectosarc, 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. 

^ The " neurophane " fibrils of Neresheimer, Arch. Protist. ii. 1903, p. 305 1'. 

- SometiniL's tlie 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 difl'erent ones have an independent rhythm. 

•* It is from such conclusive cases that the universal cliaracter of a discharge to 
the surface has been inferred in tlie rest of Protista possessing tliis organ. 



144 PROTOZOA 



In a few genera (Bidinium, for instance) the course from mouth 
to anus is a direct straight line, and one may almost speak of a 
digestive tract. In Loxodes and I'racUelius (Fig. 5 6) the endo- 
sarc, as in the Flagellate Noctiluca (Fig. 48, p. 133), has a 
central mass into which tlie food is taken, and whicli sends out 
lobes, which branch as they approach and join tlie ectoplasm. 
The endosarc contains excretory granules, probably calcium phos- 
pliate, droplets of oil or dissolved glycogen, proteid spherules, 
paraglycogen grains, etc. 

The nuclear apparatus lies at the inner boundary of the 
ectoplasm. The " meganuclcus " 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 meganucleus 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- 
tinctly 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 : in this process the cliromatin is resolved 
into threads whifh divide longitudinally, but the nuclear wall 

1 Gruber {Ber. Ges. Freib. 1888) lias sliowu tliat in several marine Ciliata 
tlie meganucleus is represented by an enormous number of minute granules dis- 
seminated through the endosarc, which, on the approach of fission, unite into a 
single meganucleus. As an adjacent micronucleus makes its apjiearance at tliis 
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. 

- In the peculiar Peritrichan Spirochona the division of the meganucleus is a 
much more complex process than usual, and recalls that of tlie undifferentiated 
nuclei of many Rhizopods (see Ronipel in Z. wiss. Zool. Iviii. 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. 



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 wliich the 
ohl meganuclei are completely disorganised and broken up and 
their debris 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 (" Eeusenapparat " 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 
Fleuronema (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. 
Tlie pharynx at its lower end (after a course exceptionally long 
and devious in the Peritrichaceae ; Figs. 51, 60) ends against the 
soft endosarc, where the food-particles accumulate into a rounded 
pellet ; this grows by accretion of fresh material until it passes 
into the endosarc, 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-animalcule {Carcliesium) 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 

^ Save the Opalinopsidae, wliich are usually termed " Opalinidae " ; but -which 
cannot retain the latter name on the removal of the genus Oi)alina to tha 
Flagellates. 

VOL. I L 



146 



PROTOZOA 



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." 



Fig. 51. — Carchesium 
pohjjnnuih. Scheme 
of the path taken by 
the ingested food in 
digestion and expnl- 
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 
nieganucleus (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 
((lots) 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. 
Tlie vacuole passes steadily along the endosarc for a certain 
time after its sudden admission into it, and then enters on a 
phase of quiescence. A little later the contents of the vacuole 
aggregate together in the centre of the vacuole, where they are 
surrounded by a zone of clear liquid ; this takes place in the 
hollow of the nieganucleus, in this species horseshoe -shaped. 
The vacuole then slowly passes on towards the peristome, lying 
deep in the endosarc, and the fluid peripheral zone is absorbed. 

1 Phil. Trans, elxxxv. 1895, i)p. 355 f. 




CILIATA 147 



For some time no change is sliown in the food-material itself: 
tliis is the stage of "storage." Eventually a fresh zone of liquid, 
the true digestive vacuole, forms again round the food-pellet, and 
this contains a peptic juice, of acid reaction. The contents, so 
far as they are capable of being digested, liquefy and disappear. 
Ultimately the solid particles in their vacuole reach the anal 
area of the vestibule, and pass into it, to be swept away by the 
overflow of the food-current. The anus is seated on a transverse 
ridge about a third down the tube, the remaining two -thirds 
being the true pharynx. 

Fission is usually transverse ; but is oblique in tlie conical 
Heterotrichaceae, and longitudinal in the Peritrichaceae. It in- 
volves the peristome, of which one of the two sisters receives the 
greater, the other the lesser part ; each regenerates what is missing. 
When there are two contractile vacuoles, as in Paramecium, 
either sister receives one, and has to form another ; where there 
is a canal or reservoir divided at fission, an extension of this 
serves to give rise to a new vacuole in that sifter which does not 
retain the old one. In some cases the fission is so unequal as 
to have tlie character of budding (^Spirocliona). We have de- 
scribed above (p. 144) the relations of the nuclear apparatus in 
fission. 

Several of the Ciliata divide only when encysted, and then 
the divisions are in close succession, forming a brood of four, 
rarely more. This is well seen in the common Colpoda cucidlus. 
In the majority, however, encystment is resorted to only as a 
means of protection against drought, etc., or for quiet rest after a 
full meal {Lacrymaria). 

Maupas ^ has made a very full study of the life-cycles of 
the Ciliata. He cultivated tliem under the usual conditions 
for microscopic study, i.e. on a slide under a thin glass cover 
supported by bristles to avoid pressure, preserved in a special 
moist chamber ; and examined them at regular intervals. 

The animals collect at that zone where the conditions of 
aeration are most suitable, usually just within the edge of the 
cover, and when well supplied with food are rather sluggish, not 
swimming far, so that they are easily studied and counted. 
"When well supplied with appropriate food they undergo binary 
fission at frequent intervals, dividing as often as five times iu 

1 Arch. Zool. Exp. (2) vi. vii. 1888 1889. 



48 



PROTOZOA 



the twenty-four hours at a temperature of 65-69'' F. {Glaucoma 
scintillans), so that in this period a single individual has resolved 
itself into a posterity of 32; but such a rapid increase is 
exceptional. At a minimum and a maximum temperature 
multiplication is arrested, the optimum lying midway. If the 
food-supply is cut off, encystment occurs in those species capable 
of the process ; but when there is a mixture of members of 
different broods of the same species, subject to the limitations 
that we shall learn, conjugation ensues. Under the conditions 




Fig. 52. — Paramecmm caudatum, stages ia conjugation, gul, GuUut ; vir/.mi., niega- 
micleus ; Mg.nu, reconstructed meganucleus ; mi.nu, niicronucleus ; Mi.nii, recon- 
structed uiicronucleus ; o, mouth. (From Parker and Haswell, after Hertwig.) 

of Maupas' investigations he found a limit to the possibilities of 
continuous fissions, even when interrupted by occasional encyst- 
ment. The individuals of a series ultimately dwindle in size, 
their ciliary apparatus is reduced, and their nuclear apparatus 
degenerates. Thus the ultimate members of a fission -cycle show 
a progressive decay, notably in the nuclear apparatus, wliich 
Maupas has aptly compared to " senility " or " old age " in the 
Metazoan. If by the timely mixture of broods conjugation be 
induced, these senile degenerations do not occur.^ In Stylonychia 

^ Calkins has recently found that the vitality within a cycle is rhythmical, 
vitli alternations of more and of less frequent tissiou?, under the saiiie set of 



CI LI ATA 



149 



niytilus the produce of a being after conjugation died of senility 
after 336 fissions; in Leucophrys after 660. 

Save in the Feritrichaceae (p. 151) conjugation takes place 
between similar mates, either of the general character and size of 
the species, or reduced by fissions, in rapid succession, induced by tlie 
same conditions as those of mating. The two mates approach, lying 
parallel and with their oral faces or their sides {Stentor) together, 



/\ A 

M2 A2 /'-^ Mj 



/\ A 

/*2 _M, M2 /f, 

/\ 



A /\ 

z, z. z, z. 

r lA" r 



z, z, 

A /\ 

z, z, z. z, 

I \ \ \ 



Fin. 5-3. — Diagram of conjugation in Volpulimn colpoda. Horizontal line means degenera- 
tion ; parallel vertical lines, separation of gametes ; broken lines (above), boundary 
between pairing animals ; (below), first fission ; single vertical line, continuity or 
enlargement. M, Meganucleus ; fi, micronucleus ; Z, zygote-nucleus. 

and partially fuse thereby ; tliough no passage of cytoplasm is 
seen it is probable that there is some interchange or mixture.^ 

The meganucleus lengthens, becomes irregularly constricted, 
and breaks up into fragments, which are ultimately extruded or 
partially digested. The micronucleus enlarges (Fig. 5 2, A) and 

conditions ; and that minute doses of beef-tea or various mineral salts will not 
only keep up the higher rate, but even stave off senescence. Minute doses of 
alcohol will keep up the higher rate, but not avert senescence. He considers tliat 
Maupas' generalisations are in most respects too sweeping {Arch. Entw. xv. 1902, 
p. 139). But Dr. James Y. Simpson informs me that the possibility of stimulative 
regeneration has been found to be limited. See also Calkins and Lieb, Arch. Prot. 
i. 1902, p. 355. 

^ As inferred by Hickson from the prolongation of tlie union. 



so 



PROTOZOA 



undergoes three successive divisions, or, strictly speaking, two 
fissions producing four nuclei, of which one only undergoes the 
third. The other three nuclei of the second fission degenerate 
like the meganucleus.^ Of the two micronuclei of this last 
division one remains where it is as a " stationary " pairing 
nucleus, while its sister passes as a " migratory " pairing-nucleus 
into the other mate, and fuses with its stationary pairing-nucleus. 




Fig. 54. — Four individuals of Golems hirius (Gymnostomaceae) swarming about and 
ingesting a Vorticella (?) (From Verworn.) 

Thus in either mate is formed a " zygote-nucleus," or " fusion- 
nucleus." All these processes are simultaneous in the two 
mates ; and the migratory nuclei cross one another on the 
bridge of junction of the two mates (Fig. 52, C). Each mate now 
has its original cytoplasm (subject to the qualification above), 



^ When there are at the outset two or more micronuclei all undergo the first 
two fissions, but only one undergoes the tliinl. 



CILIATA 



151 



but its old nuclear apparatus is replaced by the fusion-nucleus. 
This new nucleus undergoes repeated fissions ; its offspring enlarge 
unequally, the larger being differentiated as mega-, the smaller 
as micro-nuclei. The mates now separate (Fig. 52, F, G), and 
by the first (or subsequent) fission of each, the new mega- and 
micro-nuclei are distributed to the offspring. CoJpidium colpoda 




Imc. t/T 



Fig. 55. — Paramecium caudalum (Aspirotrichaceae). A, The living animal from the 
ventral aspect ; B, the same in optical section, the arrows show the course taken 
by food-particles, huc.gr, Buccal groove ; cort, cortex ; cu, cuticle ; c.vac, con- 
tractile vacuole ;/. rac, food vacuole; gitl, gullet; med, medulla; mth, mo\\i\\ ; 
nu, meganucleus ; jxcrm, micronucleus ; trch, trichocysts discharged. (From 
Parker's Biology.) 



offers the simplest case, on which we have founded our diagram 
showing the nuclear relations. During conjugation the oral 
apparatus often atrophies, and is regenerated ; and in some cases 
the pellicle and ciliary apparatus are also " made over." 

In the Peritrichaceae the mates are unequal ; the larger is 
the normal cell, and is fixed ; the smaller, mobile, is derived from 
an ordinary individual by brood -divisions, which only occur 
under the conditions that induce conjugation (Fig. 60). Here, 
though the two pairs of nuclei are formed, it is only the migratory 



I 5 2 rUOTOZOA 



nuclei that unite, the stationary ones ahorting in both mates. 
During the final processes of conjugation the smaller mate is 
absorbed into the body of the larger, and so plays the part of 
male there. But this process, though one of true binary sex, 
is clearly derived from the peculiar type of equal reciprocal 
conjugation of the other Infusoria. 

The Ciliata are almost all free-swimming animals with the 
exception of most of the Peritrichaceae, and of the genera we now 
cite. Folliculina forms a sessile tube open at either end ; and 
Schizotricha socialis inhabits the open mouths of a branching 
gelatinous tubular stem, obviously secreted by the hinder end 
of the animal, and forking at each fission to receive the produce. 
A similar habit to the latter characterises Maryna socialis ; all 
three species are marine, and were described by Gruber.^ Stentor 
habitually attaches itself by processes recalling pseudopodia, and 
often forms a gelatinous sheath. 

Tlie majority of the Oligotrichaceous Tintinnidae inhabit free 
chitinous tests often beautifully fenestrated, as in Dictyocystis. 

Many genera are parasitic in the alimentary canal of various 
Metazoa, but none appear to be seriously harmful except 
Iclithyophtheirius, which causes an epidemic in fresh-water fish. 
Quite a peculiar fauna inhabit the paunch of Euminants. 
Nyctotherus and Balanticlnun are occasionally found in tlie 
alimentary canal of Man.^ 

Tlie Gymnostomaceae are predaceous, feeding for the most 
part on smaller Ciliates. We have described the peculiar char- 
acter of the mouth and pharynx in this group, and the mail-like 
pellicle of Coleps (Fig. 54). LoxophyUu7n is remarkable for the 
absence of cilia from one of the sides of its flattened body, and 
the tufts of trichocysts studding its dorsal edge at regular 
intervals. Aciinololus has numerous tentacles, exsertile and 
retractile, each bearing a terminal tuft of trichocysts, which 
serve to paralyse such active prey as Halteria. Ileonema has 
one tentacle overhanging the mouth ; and Mcsodinium has four 
short sucker-like projections around it.^ It has only two girdles 

^ Zeitschr. wiss. ZooL xx.xiii. 1880, p. 439. 

^ Bezzenberger has given a key to the species of tliese two genera in Arch. Prof. 
iii. 1903, pp. 149, lf)7. 

^ We note that Lacrymaria is prolonged in front into a long, slender flexilile 
"neck," with the mouth terminal. This swan-like conformation is "mimicked" 
by Dileptus and Lionotus, where the neck, like the prostomium of worms, is a more 



CILIATA 



153 



of cilia, which are stout and reseiiiLle fine-pointed eirrhi. 
In Dysteria the cilia are exclusively ventral, and the naked 
dorsal surface has its pellicle condensed into a bivalve shell ; a 
posterior motile process (" foot ") and a complex pharyngeal 
armature add to the exceptional characters of the genus. 

The Aspirotrichaceae are well known to every student of 
" Elementary Biology " by the " type " Paramecium (Fig. 55), 
so common in infusions, especially when containing a little 
animal matter. P. hursaria often contains in its endosarc the 




Fig. 56. — Trachelius orwiii. A, general view ; B, sectiou through sucker ; C, section 
through contractile vacuole and its pore of discharge, al, Alveolar layer of ecto- 
plasm ; cil, cilia; c.v, contractile vacuole ; m, mouth ; K, nieganucleus ; s, sucker, 
from which pass inwards retractile myonemes. (After Clai-a Hamburger.) 

green symbiotic Flagellate Zoochlorclla. Colpoda cucullus, very 
frequent in vegetable infusions, usually only divides during 
encystment, and forms a brood of four. Phuronema chrysalis 
(Fig. 57) is remarkable for its habit of lying for long periods 
on its side and for its immense undulating membrane, forming 
a lip on the left of its mouth ; Glaucoma has two, right and left. 
The Heterotrichaceae present very remarkable forms. Spiro- 
stomum is nearly cylindrical, and, a very giant, may attain a 

extension of the front of the body above and beyond the mouth ; all three swim with 
jieculiar grace. Trachelius (Fig. 56) has a distinct cup-shaped sucker behind the 
mouth, and is remarkable, like Loxodcs, for the branching disposition of its 
endosarc. 



54 



PROTOZOA 



length of 4 mm. (^"). Stentor can attach itself by its hinder end, 
wliich is then finely tapered and prolonged into a few pseudopodia ; 
its body is trumpet-shaped, with a spiral peristome forming a 
coil round its wide end, and leading on the left side into the 
mouth. Many species when attached secrete a gelatinous sheath 
or tube. >S'. 'polymorphus is often coloured green by Zoochlorella 
(p. 125); S. coeruleus^ and S. igneus owe their names to the 
brilliant pigment, blue or scarlet, deposited in granules in lines 
between the conspicuous longitudinal myonemes. From their 




Fig. 57.— Pleuro7iema chrysalis (Aspirotrichaceae). A, Unstimulated, lying quiet ; 
B, stimulated, in the act of springing by the stroke of its cilia. (From Verworn.) 



large size and elongated meganucleus accompanied by numerous 
micronuclei, these two genera have frequently been utilised for 
experiments on regeneration. In Metopus sigmoides the peri- 
stomial area forms a dome above its wreath of membranellae ; 
and in M. 2Jyriformis this is so great as to form the larger part 
of the cell, which is top -shaped, tapering behind to a point. 
CaeMomorpha (Fig. 58) has the same general form, with a peg- 
like tail, and possesses a girdle of cirrhi." The converse occurs in 

^ The pigment of this species has been examined and described by Lankester 
under tlie name of "blue stentorin" (Quart. Journ. Micr. Sci. xii. 1873). 

^ For a full account of Cacnomorpha, Metopus, and allied forms, see Levander, 
Beitr. z. Kenntn. emigcr Ciliatcn, Dissert. Helsingfors, 1894. 



CILIATA I 5 5 



Bursaria ; the cell is a half ellipse, something like a common twin 
tobacco-pouch when closed : a deep depression thus occupies the 
whole ventral surface, and opens by a wide slit extending along 
the anterior end. The peristomial area occupies the dorsal side 
of the pocket so formed, and the mouth is in the hinder left- 
hand corner. Ble^oharisma sp. is parasitic in the Heliozoon 
BapJiidiojjhri/s mridis (Fig. 20, i, p. 74). 

Among Oligotrichaceae, Haltcria, common among the debris 
at the bottom of pools in woods containing dead leaves, is 
remarkable for an equatorial girdle of very long fine setae, and 



V;: 



t 

[1.771—%: ' 



Fig. 58. — Caenomorpha uniserialls. crh. Zone of cirrhi ; c.t, cilia of tail ; c.v, contractile 
vacuole ; cav, ciliary wreath ; g, granular aggregate ; in, zone of membranellae ; 
N, meganucleus ; m, micronucleus ; oe, pharynx ; t, tail-spine ; t^, accessory 
spiue ; u.m, undulating membrane; v, vacuole; ,■:, precaudal process. (After 
Levander.) 

for its rapid erratic darting movements, alternating with a 
graceful bird-like hover. The Tintinnidae are mostly marine, 
pelagic, with the general look of a stalkless Vorticella ; some 
have a latticed chitinous shell.^ 



Among Peritrichaceae, Vorticella (Fig. 60) and its allies have 
long been known as Bell-animalcules to every student of pond-life. 
The body has indeed the form of an inverted bell, closed at its 
mouth by the "peristome," or oral disc; this is a short, inverted 

^ Torquatella tyjnca, described by Lankester as possessing a continuous undu- 
lating membrane for its peristomial wreath, is identified by Biitschli as a Strom- 
lidium, possessing exceptionally large membranellae. 



156 



PROTOZOA 



truncate cone set obliquely so that its wide base hardly projects 
at one side, but is tilted high on the other ; the edge of the bell 
is turned out into a rim or " collar," separated from the disc by 
a deep gutter. The collar, habitually everted or even turned 
down, contracts over the retracted disc when the animal is 
retracted (E^), which is brought about by any sort of shock, or 
when it swims freely backwards. For the latter purpose a 
posterior ring of cilia (or rather membranellae) is developed 
round the hinder end of the bell (A, cr, W). The cilia of the 
adoral wreath are very strong, united at the base into a con- 





FiG. 59. — Stentor poly- 
morphus. I, Young 
iiidiviflual at- 
triclied. extended ; 
II, adult in fission, 
contracted ; cv in 
I, afterent canal of 
contractile vacu- 
ole ; in II, con- 
ti'actile vacuole ; N, 
nioniliform niega- 
nucleus (micro- 
nuclei omitted) ; 
0, mouth ; the fine 
lines are the myo- 
neme fibrils. (From 
Verworn.) 



tinuous membrane, and indeed themselves partake of the com- 
posite nature of membranellae. The wreath forms more than 
one turn of a right-handed spiral, the innermost turn ending 
abruptly on the disc, the outer leading down into tlie mouth at 
the point where the disc is most tilted and the groove deepest.^ 
The pharynx (2?) is long, and contains an undulating membrane 
{u.m) on its inner side projecting out through the mouth, and 
numerous cilia ; it leads deep into the body (2?). The first part 
is distinguished as the " vestibule " {v), as into it opens the anus, 
and the contractile vacuole {cv.), the latter sometimes opening by 
u reservoir (r). The body contains in the ectoplasm myonema- 

' Outside the principal wreath is another of fine cilia ("paroral"), standing 
out at an an^le. 



CILIATA 



157 



fibrils which, by their contraction, withdraw the disc, and at the 
same time circular fibrils close the peristome over it. In the 
type-genus the pellicle is continued into a long, slender elastic 
stalk (s), of which the longitudinal myoneme fibrils of the ecto- 
plasm converge to the stalk, and are prolonged into it as a 
spirally winding fibre, sometimes transversely striated.^ The 
effect of the contraction of this is to pull the stalk into a helicoid 




Fig, 60. — Vorlkella. A, expanded; B, stalk in contraction; c, eversible collar below 
peristome ; cr, line of posterior ciliary ring ; c.v, contractile vacuole ; m, muscle 
of stalk ; N, meganucleus ; n, micronucleus ; p, pharynx ; r, reservoir of contractile 
vacuole ; s, tubular stalk ; u.m, undulating membrane in vestibule ; r, hinder end 
of vestibule. E^ E'-, two stages in binary fission ; E^ free zooid, with posterior 
wreath ; F', F- division into mega- and niicro-zooids [m) ; G', G-, conjugation ; m, 
microzooid. (Modified from Bdtschli, from Parker and Haswell.) 



spiral (like a coil -spring), with the line of insertion of the 
muscle along the inner side of the coils, which is, of course, the 
shortest path from one end to the other (Fig. 60, B). 

The members of the Vorticellidae are very commonly attached 
to weeds or to various aquatic Metazoa, each species being more 
or less restricted in its haunts. Vorticella, the type, is singly 

^ Covered with a rather lax structureless membrane (sarcolemma), which is 
spirally wrinkled when the muscle contracts. I am unable to verify Geza Entz's 
observations, adopted by Calkins and Delage. 



5 8 PROTOZOA 



attached to a contractile stalk ; fission takes place in the vertical 
plane, and one of the two so formed retains the original stalk, 
while the other swims off (Fig. 60, E^-E^), often to settle close by, 
so that the individuals are found in large social aggregates, side 
by side, fringing water- weeds with a halo visible to the naked eye, 
which disappears on agitation by the sudden contraction of all 
the stalks. Carchesium and Zoothamnium differ from Vorticella 
in the fact that the one daughter-cell remains attached by a 
stalk coming off a little below the body of the other, so as to 
give rise to large branching colonies. 

In Carchesium (Fig. 51) the muscular threads of each 
cell are separate, while in Zoothanuiuim they are continuous 
throughout the colony. Epistylis has a solid, rigid stalk, and 
may give rise to branching colonies, which often infest the 
body of the Water-Fleas (Copepoda) of the genus Cydoj-ts. 
Opercularia is characterised by the depth of the gutter, the 
height of the collar, and the tapering downward of the elongated 
disc. Vaginicola, Pyxicola, Cothurnia, Scy2)hidia, all inhabit 
tubes, some of extreme elegance. Oi^hrydium is a colonial 
form, found in ponds and ditches, resembling Opei^cularia, but 
inhabiting tubes of jelly ^ that coalesce by their outer walls into a 
large floating sphere ; it usually contains the green symbiotic 
Flagellate Zoochlorella. Trichodina is free, short, and cylindrical, 
with both wreaths permanently exposed, and is provided with a 
circlet of hooks within the aboral wreath. It is often parasitic, 
or perhaps rather epizoic, on the surface of Hydra (see p. 254), 
gliding over its body ^ with a graceful waltzing movement ; it 
occurs also in the bladder and genito-urinary passages of Newts, 
and even in their body-cavity and kidneys. 



II. SUCTORIA = TeNTACULIFEKA 

Infusoria xoith cilia only in the yoimg stated vnthout mouth 
or anus, hut ahsorhing food (usually living Ciliates) hy one or more 
tentacles, perforated at the a'pex ; mostly attached, frequently 
epizoic, rarely parasitic in the interior of other Protozoa. 

^ Of the composition of cellulose (Halliburton, in Quart. Journ. Micr. Sci. 
XXV. 1885, p. 445). 

- As does tlie Hyitotrichan Kcrona 2}olyporu7n. 
^ Permanently ciliate in ITyjyocoma and Suctorclla. 



VI SUCTORIA = TENTACULIFERA I 59 

Acineta, Ehrb. (Fig. 61, 2) ; Amoehophrya, Koppen ; Choanofhrya, 
Hartog (Fig. 62); Dendrocometes, St. (Fig. 61, 4); Bendrosoma, 
Ehrb. (Fig. 61, 9) ; Endosphaera, Engelin. ; Ephelota, Str. Wright 
(Fig. 61, f), 8) ; Hypocoma, Gruber ; Ophryodendron, CI. and L. 
(Fig. 61, 7); Podophrya, Ehrb. (Fig. 61, 1); Bhyncheta, Zenker 
(Fig. 61, 3); Sphaerophrya, CI. and L. (Fig. 61, 6), Sudorella, 
Frenzel ; Tokophrya^ Biitschli. 

This group, despite a superficial resemblance to the Heliozoa, 
show a close affinity to the Ciliata ; the nuclear apparatus is 
usually double though a micronucleus is not always seen ; the 
young are always ciliated, and the mode of conjugation is 
identical in all cases hitherto studied. Most of the genera are 
attached by a chitinous stalk (Fig. 61), continued in Acineta 
into a cup or " theca " surrounding the cell. The pellicle is firm, 
often minutely shagreened or " milled " in optical section by fine 
radial processes, whether superficial rods or the expression of 
the meeting edges of radial alveoli is as yet uncertain. The 
pellicle closely invests the ectosarc, is continued down into 
a tubular sheath, from the base of which the tentacle rises, and 
upwards to invest the tentacle, and is even prolonged into its 
cavity in Clioanopkrya, the only genus where the tentacles are 
large enough for satisfactory demonstration. These organs may 
be one or more, and vary greatly in character. They may be (1) 
pointed for prehension, puncture, and suction {Ei^helota, Fig. 
61, 5); (2) nearly cylindrical, with a slightly "flared" truncate 
apex {Podophrya, Fig. 61, i«) ; (3) filiform with a terminal knob ; 
(4) "capitate" {Acineta, Y\g. 61, 2); (5) bluntly truncate and 
capable of opening into a wide funnel for the suction of food ^ 
{Choanoijhrya, Fig. 62; Rhyncheta, Fig. 61,3). Their move- 
ments, too, are varied, including retraction and protrusion, 
and a degree of flexion which reaches a maximum in Bhyn- 
cheta (Fig. 61, 3), whose tentacle is as freely motile as an 
elephant's trunk might be supposed to be were it as slender in 
proportion to its length. They are continued into the body, 
and in Choanojfhrya may extend right across it. In Podoplirya 
trold the pellicle rises into a conical tube about the base of the 
tentacle, which is retracted through it completely with the prey 
in deglutition. In Dendrocometes, Dendrosoma, and Ophryo- 
dendron (Fig. 61, 4, 9, 7), the tentacles arise from outgrowths of 

^ In this case the debris of the live prey torn up by the Cyclops on vhich 
they live. 



PROTOZOA 




7.0|»hpyodenclron 



S.Ephelo^o 



9. Dendrosomo 



Fig. 61.— Various forms of Suctoria. 1, a and 5, two species of Podophrya ; f, a. 
tentacle niucli enlarged; 2, o, Acineta johji ; 2, b, A. tuherosa, with four ciliated 
buds ; in 6 the animal has captured several small Ciliata ; 8, a, a specimen multiply- 
ing by budding ; 8, 6, a free ciliated bud ; 9, a, the entire colony ; 9, b, a portion of 
the stem ; 9, c, a liberated bud. a, Organism captured as food ; b.c, brood-cavity ; 
bd, bud; c.vac, contractile vacuole; I, test; mg.nu, megaimcleus ; mi.nu, micro- 
nucleus ; im, nucleus ; t, tentacle. (From Parker and Haswell, after Biitschli and 
Saville Kent. ) 



SUCTORIA l6l 



the cell-body. The mechanism of suction is doubtful ; but 
from tlie way particles from a little distance How into the open 
funnels of Choanophrya, it may be the result of an increase of 
osmotic pressure. The external pellicle of the tentacles is 
marked by a spiral constriction/ which may be prolonged over 
the part included in the sheath. The endosarc is rich in oil- 
drops, often coloured, and in proteicl granules which sometimes 
absorb stains so readily as to have been named " tinctin bodies." 
It usually contains at least one contractile vacuole. 

In Dendrocometes (and perhaps others) the whole cell may 
become ciliated, detach itself and swim off; this it does when 
its host (Gammarns) moults its cuticle. 

In fission or budding we have to distinguish many modes. 
(1) In the simplest, after the nuclear apparatus has divided, the 
cell divides transversely; the distal half acquires cilia and swims 
off to attach itself elsewhere, wdiile the proximal remains 
attached. The tentacles have previously disappeared and have 
to be formed afresh in both. (2) More commonly fission passes 
into budding on the distal face ; a sort of groove deepens around 
a central prominence which becomes the ciliated larva (Fig. 62, 
f ?/t) ; the tentacles of the " parent " are retained. This process 
passes into (3) "internal budding," where a minute pit leads 
into a bottle-shaped cavity.'' (4) Again, the budding may be 
multiple, the meganucleus protruding a branch for each bud, 
while tlie micronucleus, by successive divisions, affords the supply 
requisite. Sphaerojjhrya (Fig. 61, 6) and Endosphaera multiply 
freely by fission within their Ciliate hosts, and were indeed 
described by Stein as stages in their life-cycle. Conjugation of 
the same type as in most Ciliates has been fully worked out in 
Dendrocometes alone, by Hickson,^ who has found the meganuclei 
(though destined to disorganisation) conjugate for a short time 
by the bridge of communication before the reciprocal conjugation 
of the micronuclei. 

We have referred to the endoparasitism of two genera. 
Amoehophrya lives in several Acanthometrids, and in the aberrant 
Eadiolarian Sticliolonche (see p. 86). The attached species are 

^ The spiral ridge figured by Hertwig (Fig. 61, i, c) is probably an incorrect re- 
presentation of this structure, exceedingly minute in all genera but Choanophrya. 

- In Choano2)hi-ya I have failed to find any pore, and believe the bud-formation 
to be strictly endogenous. 

" See Quart. Journ. Micr. Sc. xlv. 1902, p. "25. 
VOL. I M 



i6: 



PROTOZOA 



some of them indifferent to their base ; others are only found on 
Algae, or again only epizoic on special Metazoan hosts, or even 
on special parts of these. Thus Ilhynchcta is only found on the 
couplers of the thoracic limbs of Cyclops, and Choanophrya on 
the ventral surface of its head and the adjoining appendages. 




Fig. 62. — Chomwphn/a infundibulifera. A, adult ; B-D, tentacles in action in various 
stages ; E, tentacle at rest ; F, young, just settled down. «, «, a. Tentacles in various 
stages of activity ; c, central cavity ; c. v, contractile vacuole ; em, ciliated embryo 
showing contractile vacuole and nucleus ; /, spiral ridge ; m, muscular wall of 
funnel ; n, nucleus ; tr, opening of funnel. (A-D, F, modified after Zenker ; E, 
original. ) 

AVe owe our knowledge of this group to the classical works 
o{' Ehrenberg, Claparede and Lachmann, Stein, E. Hertwig, and 
lUitschli. Plate has shed much light on Dcndrocometes, and 
Hickson has studied its conjugation. Ischikawa ^ has utilised 
modern histological methods for the cytological study of Ephelota 
hiitschliana. Eene Sand has written a useful, but unequal, and 
not always trustworthy monograph of the Order,^ containing an 
elaborate bibliography. 

' In Journ. Coll. Sc. Japan, x. 1S96. 

- J^tude monographique sur Ic groupc des Tcntaculiftres, Ann. Soc. Behjc Micr. 
xxiv.-xxvi. 1901. 



PORIFERA (SPONGES) 



ICtERNA B. J. SOLLAS, B.Sc. (Lond.) 

Lecturer on Zoology at Newuliani College, Cambridge. 



163 



CHAPTER VII 

POEIFERA (sponges) ^ 

INTRODUCTION HISTORY DESCRIPTION OF HALICHONDRIA 

PA NICE A AS AN EXAMPLE OF BRITISH MARINE SPONGES 

AND OF EPHYDATIA FLUVIATILIS FROM FRESH WATER 

DEFINITION POSITION IN THE ANIMAL KINGDOM. 

Sponges occupy, perhaps, a more isolated position than any other 
animal phylum. They are not only the lowest group of multi- 
cellular animals, but they are destitute of multicellular relatives. 
They are all aquatic and — with the exclusion of a few genera 
found in fresh water — marine, inhabiting all depths from between 
tide marks to the great abysses of the ocean. They depend for 
their existence on a current of water which is caused to circulate 
through their bodies by the activity of certain flagellated cells. 
This current contains their food, it is their means of respiration, 
and it carries away effete matters. Consequently sponges cannot 
endure deprivation of oxygenated water except for short periods, 
iind only the hardiest inhabit regions where the supply is 
intermittent, as between tide marks. This also renders useless 
attempts to keep specimens in tanks, unless tlie water is 
frequently renewed. 

The outward appearance of sponges has an exceptionally wide 
range, so that it is difficvdt to give a novice any very definite 
picture of what he is to expect when searching for these animals. 
This diversity is in part due to the absence of organs of suflicient 
size to determine the shape of the whole or limit its variation, 

' To Professor AV. J. Sollas, Sc.D., F.R.S., who undertook to write the cliapters 
on Porifera when the worii was first planned, the Author and the Editors are 
indebted for his kind assistance in reading and criticising this article. 

165 



1 66 PORIFERA 



that is to say, tlie separate organs are of an order of size inferior 
to that of the entire body. The animals are fixed or lie loose 
on the sea bottom ; there are in no case organs of locomotion, 
and again no sense-organs, no segregated organs of sex, and as a 
rule no distinction into axis and lateral members. It is by 
these negative characters that the collector may easily recognise 
a sponge. 

History. — Sponges are, then, in many of their characters 
unique ; and they present a variety of problems for solution, both 
of special and general interest, they are widely distributed in 
time and space, and they include a host of forms. It therefore 
causes no little surprise to learn that they have suffered from a 
long neglect, even their animal nature having been but recently 
estaljlished. Though known to naturalists from the time of 
Aristotle, sponges have been left for modern workers as a 
heritage of virgin soil : it has yielded to them a rich harvest, 
and is as yet far from exhausted. 

The familiar bath sponge was naturally the earliest known 
member of the phylum. It is dignified by mention in the Iliad 
and in the Odyssey, and Homer, in his choice of the adjective 
" full of holes," iroXvTp-qro'i, shows at least as much observation 
as many a naturalist of the sixteenth and seventeenth centuries. 
Aristotle based his ideas of sponges entirely upon the characters 
of the bath sponge and its near allies, for these were the only 
kinds he knew. Witli his usual perspicuity he reached the 
conclusion that sponges are animals, tliough sliowing points of 
likeness to plants. 

The accounts of sponges after Aristotle present little of 
scientific interest until the last century. Doubtless this is in 
part due to the absence of organs which would admit of dis- 
section, and the consequent necessity of finer methods of study. 
Like other attached forms, sponges were plant or animal as it 
pleased the imagination of the writer, and sometimes they were 
" plant animals " or Zoophyta : those who thought them animal 
were frequently divided among themselves as to whether they 
were " polypous " or " apolypous." An opinion which it is 
somewhat diificult to classify was that of Dr. Nehemiah Grew,^ 
wlio says : " No Sjwnge hath any Lignous Fibers, but is wholly 
composed of those which make the Pith and all the pithy parts 

' Ilarities belonging to the Royal Society i^reservcd at Gresham College, 1686. 



HISTORY 167 



of a Plant, ... So thut a S})ongc, instead of beinj^ a Zoopliyton, 
is but the cue-half of a Plant." 

Sponges figure in herbals beside seaweeds and mushrooms, 
and Gerarde says : ^ " There is fovnid growing upon rockes near 
unto the sea a certaine matter wrought together of the foanie 
or froth of the sea which we call Spunges . . . whereof to speak 
at any length would little benefit the reader . , . seeing the 
use thereof is so well known," About the middle of the eighteenth 
century, authors, especially Peyssonnel, suggested that sponges 
were but the houses of worms, which built them much as a bee or 
wasp builds nests and cells. This was confuted by Ellis in 1765," 
when he pointed out that the sponge could not be a dead structure, 
as it gave proof of life by " sucking and throwing out water." 
To Ellis, then, is due the credit of first describing, though im- 
perfectly, a current set up by sponges. He mentions that Count 
Marsigli ^ had already made somewhat similar observations. 

It was not till 1825 that attention was again turned to the 
current, when Eobert Grant approached the group in a truly 
scientific manner, and was ably supported by Lieberkiihn. It 
would be impossible to do justice to Grant in the brief summary 
to which we must limit ourselves. The most important of his 
contributions was the discovery that water enters the sponge by 
small apertures scattered over the surface, and leaves it at certain 
larger holes, always pursuing a fixed course. He made a few rough 
experiments to estimate the approximate strength of the current, 
and, though he failed to detect its cause, he supposed that it was 
probably due to ciliary action. Grant's suggestion was afterwards 
substantiated by Dujardin (1838), Carter (1847), Dobie (1852), 
and Lieberkiilm (185 7). These five succeeded in establishing 
the claims of sponges to a place in the animal kingdom, claims 
which were still further confirmed when James-Clark * detected 
the presence of tlie protoplasmic collar of the flagellated cells 
(see pp. 171, 176). Data were now wanted on which to base 
an opinion as to the position of sponges within the animal 
kingdom. In 1878 Schulze ^ furnished valuable embryological 
facts, in a description agreeing with an earlier one of Metschni- 
koff's, of the amphiblastvda larva (p. 226) and its metamorphosis. 

^ Gerardc's IFerhal, enlarged and revised hif Thomas Jo/inson, 1636, p. 1587. 

- PhiL Trans. Iv. p. 280. =' Ilistoirc Pliys. dc la iVrr, 17'25. 

■» Mem. Boston Sac. i. 1867, p. 305. ■' Zritschr. tviss. Zool. .xxxi. 1S78, p. 262. 



1 68 rORIFERA 



Then Blitschli ^ (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 
H. panicea will be found in Bowerbank's useful Monograph.^ 

' Ann. Mag. Nat. Hist. (5) xiii. 1884, p. 381. 

2 Quart. Jotirn. Micr. Sci. xxiv. 1884, p. 612. 

^ The name was coined by Dr. Fleming from x'''^'^ " silex " and x^^'^po^ "car- 
tilage," and as these roots could only give Chalic-choiidria it is not surprising that 
those who have not referred to Dr. Fleming's statements give the derivation as 
aXs ' ' sea " and x<5''5pos. 

■• Monograph of British Sponges, vol. iii. pi. xxxix.-xl. For revision of nomen- 
clature in this Monograph, see Hanitsch, Tr. Liverp. Biol. Soc. viii. 1894, p. 173. 



STRUCTURE OF HALICHONDRIA I 69 



The colour of the species is as inconstant as its form, ranging 
from green to light brown and orange. MacMiinn concludes 
from spectroscopic work that H. 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. Histohaematin 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 H. 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 A V'*^!* 

structure is then visible on this 
surface, and among British sponges 
this is 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- FiG.es.-Portion of the surface of 

//.jja/ucea, from dried specimen. 
comb has a row of them along its a, natural size ; B, magnified. 

upper edge. Much more numerous l^^.^ ^^'^^ '^"^^^ P'^*^^^"' ^'"^ 
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 ciirmine 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, 
lor as soon as it is plunged into water its current bursts vigor- 
ously forth, and is rendered visible l:)y the ]);irticles of detritus 
that have accumulated in the interior during the period of 
1 Jouru. Plujslol. ix. 1888, p. 1. 




rORIFERA 



exposure and consequent suspended activity. "The oscula tlien 
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 



— A£|;;___^^.Y?^^- ^":^^ ^ 




Fig. 64. — H. jjanicea : 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 cliamber-bearing regions are tlie 
" 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 compo.sed 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 tlie excur- 



CELLS AND SPICULES 



171 



rent and incurrent canals. The flagellated chambers are lined 
by " choanocytes " (cf. Fig, 70, p. 170); these are cells provided 
at their inner end with a tlagelluni 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 tlie first place, it 
contains cells which have a 
common origin with the pina- 
coeytes, and wdiich together with 
them make up the " dermal 
layer " ; these are the " collency tes " 
and " scleroblasts " ; secondly, it 
contains " archaeocytes," cells of 
independent origin. 

Collencytes are cells witli 
clear protoplasm and thread-like 
pseudopodial processes ; they are 
distinguished as stellate or bipolar, 
according as these processes are 
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 tlie 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 — i.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 




\i>. — Diagrammatic section of a 
siliceous Sponge, a.p, Apopyle ; d.o, 
dermal ostia ; ex.c, excurrent, or ex- 
halant canal ; in.c, inenrrent canal ; 
V, osculum. (Modified from Wilson.) 



172 



PORIFERA 



pointed at l)oth 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.^ 




Fki. 66. — Cut end of a length of a siliceous spicule from Ilt/a/o/unna sieholdii, with the 
lamellar structure revealed by solution. x 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. jxcnicea 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 GeUins varius.^ 
The free -swimming larvae escape by the 
ing osculum ; they are minute oval bodies moving 
rapidly by means of a covering of cilia. 
The greater part of the body is a dazzling 
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. Macj. Nat. Hist. (4) xx. 1877, l>. 285 ; Biitschli, Zcitschr. f. wiss. 
Zool. xix. 1901, p. 236. 

- Minchin, "Sponges" in Treatise on Zoology, edited by E. Ray Lankester, p. 
87. See also Biddei-, Proc. Roy. Soc. li. 1892, p. 474. 

3 Zu-jI. Jalirb. Anat. vii. 1894. 




(i. ()7. — Kree- 
larva of Gellius varius, 
in optical section, a, 
Outer epithelium ; jtn', 
pigment ; .r, hinder 
pole. (After Maas. ) 



DEVELOPMENT 1 73 




meiit takes place in a screw line ; when this ceases the larva 
rests on its hinder pole, and tlie cilia cause it to turn round 
on its axis. 

Sections sliow that tlie larva is built up of two layers : — 

1. " The inner mass," consisting of various kiiuls 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, wliich possesses a nucleolus ; 
these are the archaeo- 
cytes; (2) differentiated 
cells, of which tlie nucleus 
contains a chromatin net : 
these give rise to pinaco- 
cytes, collencytes, and 
scleroblasts. Some of them -^ 

form a flat epithelium ^"^' ^^' — Longitudinal section through the hinder 

1 1 • 1 ' P°^^ °^ ^^^^ ^''"'^''''' °f ^- varius. a, Flagellated 

which covers the hinder cells ; ma^, undifferentiated cell ; mu\ differen- 

P-.le. Some of the sclero- t''^**^*^ '/"j ^'(v i''^"'"'"* ' •"' '"^''^^'^ °^ ^""'''^'" 

^ _ pole. (Alter Maas.) 

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 tlie most important process of the meta- 
morphosis ; it is followed by a pause in the outward ch.uiges, 
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 ; tlie flagellated cells, which have lain in con- 
fusion, become grouped in small clusters. These become flagellated 
chambers, communications are established between the various 
])ortions of the canal system, and its external apertures arise. 
There is at first only one osculum. The larvae may be obtained 
l»y 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 kecj) the temperatun^ constant. Tbey will undergo meta- 



174 PORIFERA 




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. i^cinicea may 
i/Zli y' 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. 

Fig. 69.— Larva of Gdliua varius shortly after But it is advisable tO 

fixation. The pigmented pole, originally ., , . „ , . 

posterior, is turned towards the reader. R, aVOld Spcakmg ot a multl- 

Marginal membrane witli pseudopodia ; x, oSCulatc Sponge aS a ColonV 

hinder pole. (After Rlaas.) . 5! . , , "^ 

01 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 lise 
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) fiuviatilis, 
a cosmopolitan species. The search for specimens is most likely 

^ Materials for the Study of Variation, 1894, p. 30. 

2 Arch, dc 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 ^/^iYl'Z?.4 77^ 175 

to be successful 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 l)eneath 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 tlesh-tint to green, according to the 
exposure to light. 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 Hesh- 
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 Ephydatia Jiuviatilis is very similar to that 
of Haliclwndria 2^((nicea, 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 whicli arise 
from the floor of the subdermal cavity are as irregular as in 
H. 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, wliich may have a quite smooth surface or may 

' Quart. Journ. Micr. Hci. xxii. 1882, p. 229. 

- But see Gamble and Keeble, Quart. Journ. Micr. Sci. xlvii. 1904, p. 363, wlio 
sliow that various gi'een 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 Zoochlordlu, on p. 126. 



1/6 PORIFERA 



be covered in various degrees with minute conical spines (Fig. 72, 
a, h). 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 lie side by side, while in the 
connecting fibres fewer or freqviently 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- 




FiG. 70. — Ephijdatia flmnatilis. Section of flagellateil cliamber, showing the choanocytes 
passing through the apopyle. (Alter Vosniaer 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 meml^ers of most aquatic in- 
vertebrates.^ 

1 Sollas, Tr. Dublin Sue. (2) iii. 1884, p. 87. 



GEMMULES OF EPHYDATIA 



177 



Ephydatia Jiuviatilis uormally produces not only free-swim- 
ming larvae of sexual origin, but also internal gemmules arising 
asexually. Tliese 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 sliown that on tlie death and disintegration of 
the mother sponge some of the gemmules remain attached to the 
old skeleton, some sink and some float. Tliose which remain 




Fig. 71. — Portion of the skeletal franie- 
work of E. fluviatilis. a. Main 
fibres ; h, counectiug fibres. (After 
^Veltner.) 








Fig. 72. — Spicules of JiJ. Jiuviatilis. a.h.c^ 
Oxeas, spined and smooth ; d.e, aniphi- 
discs, side and end views. (After 
Potts.) 



attaclied are well known to reclothe the dead fibres with living 
tissue. They inlierit, as it were, the advantages of po.sitiou 
which contributed to tlie survival of the parent, as one of th& 
selected fittest. The gemmules which sink are doubtless rolled 
short distances along tlie bottom, while those which float 
have the opportunity of widely distributing tlie species witli 
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 remarkal)le for their powers of 

' Arch. Xalurij. li.\. 1890, p. "240. 
VOL, I X 



PORIFERA 



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 confirmed 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" C." 

Of important bearing on tlie question of the utility of the 
gemmules are certain instances in which E. 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 
Fig. 73.— Geinimiie of E. activity in winter, the flagellated chambers 
'£c"''(After Potfso''" ^^^^ ^^ ^^^^nt (Lieberklihn), 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 tlie 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 tliat 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. 

' Weltner, Blatt. Aquar. Fr. vii. 189G, p. 277, and " Spongillidenstudien," 
Arch. Naturrj. ii. 1893, p. 271. 




VII GE^^mULES OF EPffVD A T/.4 l^g 

The mature geinmules consist of a more or less splierical 
mass of cells, which we sliall refer to as yolk cells, and of a 
complex coat. Tlie 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 cliitinous 
layer surrounded by an air - chamber layer, wliich is finely 
vesicular, showing a structure recalling plant tissue, and con- 
taining amphidiscs arranged along radii passing through tlie 
centre of the gemmule. One of the discs of each amphidisc 
lies in the inner chitinous coat, while the other lies in a similar 
membrane which envelopes the air-chamber layer and is termed 
the outer chitinous coat. 

Marsliull has suggested that one function of the amphidiscs is 
to weight the gemmules and thus protect tliem 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 tlie amphidiscs. 

A study of the development of 
EphydcUict gemmules vividly illus- 
trates various characters of the inner fig. 74.— Part of a longitudinal 
processes of sponges. Specially note- «f ^.i°'^ «*' "" gemmi^ie of E^hy- 

'■ , . . f. n datia sp. passing through the 

worthy are the migrations of cells pore («)• (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 gennnule 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 

' Evans, Quart. Journ. Micr. Scl. xliv. 1900, p. 72. 




8o PORIFERA 



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 amphidiscs 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 E. 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 l)y 
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. — AVe may now deflne sponges as multicellular, 

1 Ann. Mag. Nat. Hist. (2), x. 18S2, j). 365. 

■- /'. Ac. Philad. 1887, pp. 158-278. 

^ Evans, Quart. Juurn. Micr. Sci. xlii. 1899, p. 363. 



SYSTEMATIC POSITION 



two -layered animals; with pores perforating the body-walls and 
admitting a current of water, which is set up by the collared 
cells of tlie " gastral " layer. 

Position in the Animal Kingdom. — Sponges are tlie only 
iiuilticellular animals which possess clioanocytes, and their mode 
of feeding is unique. Since tliey are two -layered it lias 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 
cases from the endoderm. Tliese weiglity differences between 
sponges and tliat group of Metazoa to wliich they would, if of 
Metazoan nature at all, be most likely to sliow reseml:)lance, 
suggest that we sliould seek a separate origin for sponges and 
Metazoa. AVe naturally turn to tlie 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, 12S). 

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 tlie 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 
the Choanoflagellate genus rroterosj)onrjia (Fig. 75), described by 



82 



PORIFERA 



CHAP. V 



Saviile Kent, and since rediscovered both in England and 
abroad.^ This is a colony of unicellular individuals emljedded 
in a common jelly. The individuals at the surface are 
choanoflao-ellate, while in the interior the cells are rounded 




Fig. 75. — Proferospongia haeckeli. a, Amoeboid cell : h. a cell dividing : r, cell 
with small collar ; z, jelly. x 800. (After S. 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. 

^ France, Organismus der Craspedomonadcn, Budapest, 1S97, p. 217. 



CHAPTER VIII 

rOEIFEEA (cOXTIXUED) : FORMS OF SPICULES CALCAREA 

HOMOCpELA HETEROCOELA HEXACTINELLIDA DEMOSPON- 

GIAE TETRACTfNELLIDA MONAXONIDA CERATOSA KEY 

TO BRITISH GENERA OF SPONGES 

Sponges fall naturally into two branches differing in the size of 
their choanocytes : in the ]\'Iegamastictora these cells are rela- 
tively large, varying from 5/x to O/a in diameter ; in MiCROMAS- 
TICTORA they are about 3/a 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 occurred 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). 
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, h, I). 

Uniradiate monaxon spicules are termed " styli." 

II. Teiraxons. — Spicules in which growth proceeds from an 

^ Sollas, Encyclopedia Britannica, art. "Sponges," 1887. 

2 Sollas, Ann. Mar,. Xat. Hist. (5) iii. 1879, p. 23 ; Challenger Fujiort, vol. xxv. 
pt. Ixiii. 1888, p. Iii. 

183 



84 



PORIFERA MEGAMASTICTORA 



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.* 

III. Triaxons. — Spicules in 
which growth is directed from 
an origin in both directions 
along tliree rectangular axes. 
One or more actines or one or 
two axes may be suppressed. 

IV. Polyaxons. — Spicules in 
which radiate growth from 
a centre proceeds in several 
directions. 

Y. Spheres. — Spicules in 
which growth is concentric 
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 Ijelong 
to a single class, Calcarea, which stands alone in the branch 
Meo-amastictora. 




Fig. 76.— Types of megascleres. a, Rhalxliis 
(monaxon cliactine) ; h, stylus (moiiaxoii 
monactine) ; c, triod (tetrax'ou triactine) ; 
d, calthrop (tetraxoii tetractine) ; e, 
triaxon hexactine ; f, euaster. 



BRANCH I. MEGAMASTICTOEA 



CLASS CALCAEEA 

Calcarea are marine shallow- water forms attached for tlie most 
XJart 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 



viii CALCAREA — HOMOCOELA I 85 

term " triradiate system " (Minchiii). 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 ecjual : 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 posssess 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 witli other fundamental 
differences in structure and development." 

xVs in Halielwndria, 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 

' Miuchiii, Laiikestfii-'s Treatise on ZaoJoi/y, pt. ii. 1900. 
- .Mincliin, loc. cif. p. 110. 



i86 



PORTFERA 



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 whicli is 



:nown oni 



Calcarea. 




}. 77. — The two types of Asconid 
collar cells. A, of Clathrina, 
nucleus basal ; B, of Leuco- 
solenia, nucleus not basal, 
liagellum arising from the basal 
nuclear membrane. (A. after 
Blinchin ; B, after Bidder.) 



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 
the sponge to such an extent as quite 
to obliterate temporarily the gastral 
cavity." 

The choanocytes show certain con- 
stant differences in structure in the 
families Clathriuidae and Leucoso- 
leniidae respectively. In the former, 
the nucleus of the choanocyte is 
in the latter, it is apical, and 
the flagellum can lie traced down to 
it (Fig. 77). 
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 
Leucosoleniidae an " amphiblastula." 

The fact that it is possible to classify the Calcarea 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 

' Bidder, Quart. Journ. Micr. Sci. xxxii. 1891, p. 631, and Minchin, Quart. 
Journ. Mia: Sci. xxxiii. 1892, jx 266. 

^ Minchin, Lankester's Treatise on Zoolorjy, p. 30. 



CALCAREA — HETEROCOELA 



187 



still seem to assert their independence, the flagella not lashing 
in concert/ hut 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 





Fig. 78. — Transverse section of the body- wall 
of Sycon carteri, showing articulate tiibar 
skeleton, gastric ostia {a.})), tufts of oxeas at 
the distal ends of the chambers {fl.ch), and 
pores {p). (After Dendy.) 



Fig. 1'^.— Sycon coronation. At a 
a portion of the wall is removed, 
exposing the paragaster and the 
gastric ostia of the chambers 
opening into it. 



close set, leaving more or less quadrangular tubular spaces, the 

^ Vosmaer and Pekelharing, Vc7-/i. Ak. Amsterdam, (2) vi. 3, 1898, p. 1. 



i88 



PORIFERA 



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 tlie radial tubes and forms 

collectively the " tubar skeleton." 
It is characteristic of Sycettidae 
that the tubar skeleton is of the 
type known as " articulate " — i.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 tlie tube. 

The walls of the paragaster 
are known as the"gastral cortex"; 
tliey contain quadriradiate spi- 
cules, of which the triradiate 
systems lie tangentially in the 
gastral cortex, while the apical 
ray projects into the paragaster, 
and is no doubt defensive. The 
distal ends of the chambers 
bristle with tufts of oxeate 
spicules, and the separate cliam- 
bers are distinguishable in sur- 
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). Vig. 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. Mkr. Set. .\z.\-v. 1894, p. 230. 




Fig. 80. — Si/con sftosum. Yoniig Sponge. 
X 200. d, Dermal cell ; <j, gastral 
cell ; 0, osculuin ; ^j, pore cell ; sp-^, 
monaxon ; sp.^, triradiate spicule. 

(After Maas.) 



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. Minvite observation has shown ^ that this 
latter event is brought about by immigration of pinacocytes from 
the exterior. These cells creep through the jelly of the dermal 




Fig. 81. — .S'. seiosum. Young Sponcce witli )iu wlioil of radial tubes, o, Osculum ; /), 
pore ; sj)^, monaxon , s/^j, qunliu uliitt spiLuU (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, Zcitschr. iviss. Zool. Ixvii. 1899-1900, p. 215. 



190 



PORIFERA 



meet ; and there results a slieet 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 witli a complex wall. The cortex may be enormously 
developed, so as to form more than half the tliickness of the 




Fig. 82. — Sycon raphanus. A, Lougiludinal 
section of young decalcified Sponge at a 
stage somewhat later than that shown in 
Fig. 81. B, Transverse section of the 
same through a whorl of tubes, d, Dermal 
membrane ; g, gastral membrane ; II, 
paragaster ; sp*, tetraradiate spicule ; T, 
radial tube. (After Maas.) 



(7.0 cl I 




Fig. 83. — Transverse section of the 
body-wall of Ute, passing longi- 
tudinally through two chambers. 
a.p, Apopyle ; d.o, dermal ostium ; 
Jl.ch, flagellated chamber or radial 
tube ; i.c, inb.alant canal ; jj, pro- 
sopyle. (After Deudy.) 



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 8yco% — 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 
Sijcon to undergo that same process of growth by which the 



CALCAREA HETEROCOELA 



191 



Sycon itself was derived from the Ascou, we sliall then have a 
sponge with a canal system of the type seen in Lcucandra 
among British forms, but more diagrammatically shown in the 
foreign genus Lmixilla (Fig. 




Transverse section through the 
body -wall of Gmntiopsis. d.o, Dermal 
ostium ; Jl.ch, flagellated chamber ; i.c, 
long incurrent canal traversing the thick 
cortex to reacli the chamber layer ; ji, 
apopyle. (After Dendy.) 



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 

enibryological research. 

In Lcucandra 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 y\g. 84 

size and rounded form of its 

chambers. This change of 

form marks an advance in 

efficiency ; for now the Hagella 

converge to a centre, so that 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 
j||p / fO"" Y^ %\ ' , ^^ types of canal system 

'■"^■*'' fcii^K ; ■•'\ — that of Homocoela, 

of Sycon, and of 
Lcucandra and Leu- 
cilla. These are con- 
veniently termed the 

Fig. 85.— Transverse section through the body -wall of first, SCCOud, and 
Leucilla. <;.o, Dermal ostium ; f.c.c, exhalant canal ; ^i ■ i f-i^-^pc rPQnPP 
A c/i, chamber; if, inhalant canal. (After Dendy.) tllUU L} pes rcbpec- 

tively, and may be 
Ijriefly described as related to one another somewhat in the 
same way as a scape, umbel, and compound umbel among 




192 PORIFERA 



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, Utc and 
Leucandra stand side by side. This treatment implies a belief 
that tlie tliird 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 conspicuous 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 sulvf imilies : — 

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 triradiate spicules 
in tlie fibres undergo a modification into the " tuning-fork " type 
(Fig. 86, C), to enable them to be compacted into smooth fibres. 

^ "Die Kalkschwiimme," 1871. - Dendy, loc. cit. p. 159. 

2 Quart. Journ. Micr. Sci. .\xxvi. 1894, i>. 127. 



CALCAREA PHARETRONTDAE 



193 



" Tuning-forks," though not exclusively conlined to Pharetrouids, 
are yet very characteristic of them. 




Fig. 86. — Portions of the skeleton of Petrostroma schulzti. A, Frameworlc -witli en- 
skeathing 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 hy 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 ; Flectro- 
ninia halli ^ and Bactronella were 
found in Eocene beds of Victoria ; 
Forosphaera,^ long known from the 
Chalk of England and of the Con- 
tinent, has recently been shown by 
Hinde^ to be nearly allied to Flectro- 
ninia ; finally, Flectinia * 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 
discovered. The fused spicules are 
equiangular quadriradiates ; they are 
united in Fetrostroma by lateral 
fusion of the rays, in Flectroninia (Fig. 87) and Forosphaera by 

' Doederlein, Zuol. Jahrh. Abth. Anat. x. 189(5, p. 15, pi. ii. and iii. 
- Hinde, Quart. Journ. Geol. Soc. Ivi. 1900, p. 50. 

'^ Hinde, Tr. R. Micr. Soc. 1904, p. 3. * PoCta, Bull. Acad. Bohtme, 1903. 

VOL. I 




Fio. 87. — A spicule from the skeleton 
framework of Plectroninia, show- 
ing the terminally expanded rays. 
(After Hinde.) 



194 



PORIFERA 



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. 




Astrosdera v.ul- 
leijnna, Lister. A, the 
Sponge. X about 3. ^j. 
The ostia on its distal 
surface. B, a portion 
of the skeleton show- 
ing four polyhedra 
with radiating crystal- 
line fibres. C, an 
ostium ; the surround- 
ing tissue contains 
young stages of poly- 
liedra. (After Lister.) 



Astrosdera wil/ri/ana ^ 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 
Astrosdera as aragonite, and the elements are solid polyhedra, 
> J. J. Lister in Willcy's Zoolojical Jksulls, pt. iv. 1900, p. 459. 



VIII CALCAREA ASTROSCLERIDAE I 95 

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. 
Tlie chambers are exceptionally minute, especially for a calcareous 
sponge, comparing with those of other .sponges as follows : — 

Astrosdem chambers, 10/xX S/j, to ISfxX 11/u,. 
Smallest chambers in Silicea, 15//, x 18/t to 'I-i/xx '31 fx. 
Smallest chambers in Calcarea, 60/i x 40/i,. 

In its outward form Astrosdera resembles certain Pharetronids. 
The minute dimensions of the ciliated chambers relegate Astro- 
sdera 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 difticult to conceive 
that its relations may be rather with the non-calcareous than 
the calcareous sponges. 



BEANCH II. MICEOMASTICTOEA 

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 ]\Iicromastictora, in a natural group, opposed to 
the Megasmastictora as of equal value. 

The subdivision of the Micromastictora is a matter of some 
difhculty. The Hexactinellida alone are a well circumscribed 
group. After their separation there remains, besides the askeletal 
genera, an assemblage of forms, the Demospongiae, whicli 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 crnx of the systematist. It is perhaps 
safest, while recoe;nisinn: that manv 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. MYXOSPOXGIAE 

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 Aplysilla, 
are flagellated. 

Halisarca, also British, is easily distinguished from Oscarella 
hj the presence of a mucus-like secretion which oozes from it, 
and by the absence of the bright coloration characteristic of 
Oscarella. It naturally suggests itself that the coloration in 
the one case and the secretion in the other are protective, and 
in this respect perform one of the functions of the skeleton of 
other sponges. The chambers are long, tuljular, and branched. 
There is no hypophare. 

1 Mem. Soc. Zool. France, 1896, p. 119. 
- Arch. Zool. Exp. (3) iii. 1895, p. 561, pi. xxiii. 



HEXACTINELLIDA 19/ 



CLASS II. HEXACTINELLIDA ' 

Silicispongiae, defined hy tlieir spicules, of 'which the rays lie 
idong three rectangular axes. The canal system is simple, with 
thimhle-shaped chambers. Tlic Jwdy-icall is divided into endosome, 
cctosome, and choanosome. 

Some authors would elevate the Hexaetinellida to the position 
uf a third main sub-group of Porifera, thus separating them from 
other siliceous sponges. In considering this view it is important 
to realise at the outset that they are deep-water forms. They 
bear evident traces of the influence of their habitat, and like 
others of the colonists of the deep sea, are impressed with 
marked archaic features. Yet tliey are still bound to other 
Micromastictora, first by the small size of tlieir choanocytes, and 
secondly by the presence of siliceous spicules. This second 
character is really a double link, for it involves not merely the 
presence of silica in the skeleton, but also the presence in each 
spicule of a well-marked axial filament. Now this axial filament 
is a structure which is gaining in importance, for purposes of 
classification, in proportion as its absence in Calcarea is becom- 
ing more probable. The Hexaetinellida are the only sponges, 
other than the bath sponge, which are at all generally known. 
They have won recognition by their beauty, as the bath sponge 
by its utility, and, like it, one of their number — the Venus's 
Flower-Basket — forms an important article of commerce, the chief 
fishery being in the Philippine Islands. This wonderful beauty 
belongs to the skeleton, and is greatly concealed when the soft 
parts are present. 

We have said that the Hexactinellids are deep-sea forms ; 
they are either directly fixed to the bottom or more often 
moored in the ooze by long tufts of rooting spicules. In the 
"glass-rope sponge," the rooting tuft of long spicules, looking 
like a bundle of spun glass, is valued by the Japanese, who 
export it to us. In Mo7iorhaphis the rooting tuft is replaced by 
a single giant spicule," three metres in length, and described as 
" of the thickness of a little finger " ! Probably it is as a result 
of tlieir fixed life in the calm waters of the deep sea^ that 

^ F. E. Schulze, Challenycr Monograi^h, xxi. 

2 Chun, " Alls den Tiefen des Weltmeeres," 1900, p. 481. 

' Shipley, "Fauna of the Antarctic Regions." See also p. 216. 



igS 



PORIFERA 



sd. h: 



Hexactinellids contrast witli most other sponges by tlieir 
symmetry. It should not, however, be forgotten that many of 
the Calcarea which inhabit shallow water exhibit almost as 
perfect a symmetry. 

The structure of the body-wall in Hexactinellida is so constant 
as to make it possible to give a general description applicable to 

all members of tlie 
group. It is of con- 
siderable thickness, 
but a large part is 
occupied by empty 
spaces, for the actual 
tissue is present in 
minimum quantity. 
In the wall the cham- 
ber-layer is suspended 
liy trabeculae of soft 
tissue, between a der- 
mal membrane on the 
outside and a similar 
gastral membrane on 
the inner side (Fig. 
89). Thus the water 
entering the cluimbers 
through their numer- 
ous pores has first 
passed tlirough the 
ostia in tlie dermal 
membrane and tra- 
versed the subdermal 
trabecular space ; on 
leaving the chambers 
it flows through tlie 
subgastral trabecular 
space and the ostia in the gastral membrane, to enter the para- 
gaster and leave the body at the osculum. The trabeculae 
and the dermal and gastral membranes together constitute tlie 
dermal layer. This conclusion is based on comparison with 
adults of the otlier groups, for in the absence of embryo- 
logical knowledge no direct evidence is available. According to 




Fig, 



Longitudinal section of a young specimen of 
Lanuginella pupa O.S., with commencing formation 
of the oscular area, x 35. d.m, Dermal membrane ; 
g.vi, gastral membrane ; ^jr/, paragaster ; stl.tr, sub- 
dermal trabeculae ; Sg.tr, subgastral trabeculae. 
(After F. E. Schulze.) 



HEXACTINEI.LIDA 



199 



the Japanese investigator, Is;io Ijima/ the dermal and gastral 
membranes are but expansions of the trabeculae, and the 
trabeculae themselves are entirely cellular, containing none of 
the gelatinous basis met with in the dermal layer of all other 
sponges. There is no surface layer of pinacocytes, the cells 
forming the trabeculae being all of one type, namely, irregularly 
branching cells, connected with one 
another by their branches to form 
a syncytium. In the trabeculae 
are found scleroblasts and archaeo- 
cytes. 

The chambers have a charac- 
teristic shape : they are variously 
described as " thimble -shaped," 
" tubular," or " Syconate," and 
they open by wide mouths into 
the subgastral trabecular space. 
Their walls have been named the 
memhrana reticularis from the fact 
that, when preserved with only 
ordinary precautions, they are seen 
as a regular network of proto- 
plasmic strands, with square meshes 
and nuclei at the nodes. This 
appearance recently found an ex- 
planation when Schulze, for the first time, succeeded in preserv- 
ing the collared cells of Hexactinellids.'' Schulze was then 
able to show that the choanocytes are not in contact with 
one another at their bases, where the nuclei are situated, but 
communicate with one another by stout protoplasmic strands. 
The form of the choanocyte can be seen in Fig. 91. 

To Schulze's description of the chamber, Ijima has added the 
important contributions that every mesh in the reticulum func- 
tions as a chamber pore or prosopyle ; and that porocytes, such 
as are found in Calcarea, are wanting. This structure of the 
chamber -walls, the absence of gelatinous basis in the dermal 
layer, and the slight degree of histological differentiation in 




. 90. — Portion of the body-wall of 
Walteria sp., showing the thimble- 
shaped flagellated chambers, aljove 
which is seen the dermal mem- 
brane. (After F. E. Schulze.) 



' J. Coll. Japcm, XV. 1901, pp. 128, 147, 190. 

- Fauna Ardica (Roeraer and Schaudinn), i. 1900, p. 8-1 ; and Sitzh. Akad. 
Berlin. 1899, p. 98. 



200 



PORIFERA 



the same layer, added to the more obvious character of thimble- 
shaped chambers, are the chief archaic features of Hexactinellid 
morphology. 

The skeleton which supports the soft parts is, like them, 
simple and constant in its main features. It is secreted by 

scleroblasts, which lie in the 
trabeculae, and is made up of 
only one kind of spicule and its 
modifications. This is the hexac- 
tine, a spicule which possesses six 
rays disposed along three rect- 
angular axes. Each ray contains 
an axial thread, which meets its 
fellow at the centre of the spicule, 
where they together form the 
axial cross. Modifications of the 
hexactine arise either by reduc- 
tion or branching, by spinulation 
or expansion of one or more of 
the rays. The forms of spicule 
arising by reduction are termed pentactines, tetractines, and so 
on, according to the number of the remaining rays. Those rays 
which are suppressed leave the proximal portion of their axial 
thread as a remnant marking their former position (Fig. 94). 
Octactine spicules seem to form an exception to the above state- 
ments, but Schulze has shown that they too are but modifications 
of the hexactine arising by (1) branching of the rays of a 




P'iG. 91. — Portion of a section of the 
menibraua reticularis or chamber- 
wall of Schaudinnia arctica. x 1500. 
(After F. E. Schulze.) 




Fig 




92. — A, discohexaster, 
la which tlie four cladi 
a, a', b, b', c of each ray 
start directly from a cen- 
tral nodule. B, disco- 
octaster, resulting from 
the redistribution of the 
twenty -four cladi of A 
into eight groujis of 
three. (After Schulze, 
from Delage. ) 



hexactine, followed by (2) recombination o'i the secondary rays 
(Fig. 92). 

The various spicules are named, irrespective of their form, 
according to their position and corresponding function. The 



HEXACTJXELLIDA 



arrangement of the spicules is best realised by means of a 
diagram (Fig. 93). 

The deviations from tliis ground-plan of Hexactinellid struc- 



Prostalia 



( Principal 
Parenchymalia J Comital 




marginalia 



Intermedia 






A 

Dermaiia <* Autoderm Nl 
I Hypoderm---i 




Dictyonalia 



Canalaria 



Prostali, 






Fig. 9.3. — Scheme to show the arrangement of spicules in the Hexactinellid skeleton. 
CancJuria, mic-roscleres in the walls of the exciirrent canals ; iJermalia Auto- 
(ferm[aliu], microscleres in the dermal memlirane ; D. H)ipoderm[aHu\ nioie deeply 
situated (lernialia ; Dictyonalia, parenchymalia which become fused to form the 
skeletal framework of Dictyonina ; Gastralia Autogastr{alia\ microscleres in the 
gastral membrane ; Gastralia Htjpognsti\alia'], more deeply situated gastralia : 
Pareiichi/inalia I'rinci^ndla, main supporting spicules between the chambers ; P. 
CoinitaJkt., slender diactine or triactine spicules accompanying the hast ; /■". Intermedia. 
microscleres lietween the P. principalia ; Prostalia, projecting spicules ; P. basalia, 
rooting spicules, from the base ; P. marginalia, defensive spicules, round the oscular 
rim ; P. plcuralia, defensive spicules, from the sides. (From Delage and Herouard, 
after F. E. Schulze.) 



ture are few and simple. They are due to folding of the chamber- 
layer, or to variations in the shape of the chambers, and to increasing 
fusion of the spicules to form rigid skeletons. A simple condition 
of the chamber-layer, like that of the young sponge of Fig. 89, 



202 PORIFERA 



occurs also in some adult Hexactinellids, e.g. in Walteria of the 
Pacific Ocean (Fig. 90). Thus is represented in this order the 
second type of canal system described among Calcarea. More 
frequently, however, instead of forming a smooth sheet, the 
chamber-layer grows out into a number of tubular diverticula, 
the cavities of which are excurrent canals ; these determine a 
corresponding number of incurrent canals which lie between 
them. In this way there arises a canal system resembling 
the third type of Calcarea. By still further pouching so as 
to give secondary diverticula, opening into the first, a com- 
plicated canal system is formed, as, for example, in Ewplectella 
suherea. 

To return to the skeleton, the most complete fusion is attained 
by the deposit of a continuous sheath of silica round the apposed 
parallel rays of neighbouring spicules. This may be termed tlie 
dictyonine type of union, for it occurs in all those forms originally 
included under the term Dictyonina, in which the cement is 

deposited ^j«?'i passu with tiie 
formation of the spicules. 
In other cases connecting 
bridges of silica unite the 
spicules, or there may be a 
connecting reticulum of 

Fin. 94.— Amphidisc, at « are traces of the siliceOUS threads, Or, again, 

four missmg rays. ^^^.^ crossing obliquely may 

be soldered together at the point of contact. These more 
irregular methods occur in species where the spicules are free at 
their first formation. Spicules originally free may later be 
united in a true Dictyonine fashion. The terms Lyssacina and 
Dictyonina are useful to denote respectively : the former all 
those Hexactinellida in which the spicules are free at their first 
formation, and the latter those in which the deposit of the 
cementing layer goes hand in hand with the formation of the 
spicules. But the terms do not indicate separateness of origin 
of the groups denoted by them, for there is evidence that 
Dictyonine types have been derived repeatedly from Lyssacine 
types, and that in fact every Dictyonine was once a Lyssacine. 

The real or natural cleft in the class lies between those genera 
possessing amphidiscs (Figs. 94, 97) among their microscleres, and 
all the remainder of the Hexactinellida which bear hexasters (Fig. 




HEXACTINELLIDA 



xn- 



96). The former set of 
discopliora, the latter 
the Hexasterophora. 

Sub-Class 1. Am- 
phidiscophora. — Ayyi- 
phidiscs are present, 
hexasters absent. A 
tvft of rooting spicules 
or hasalia is always 
present. The ciliafti^ 
chambers deviate mar' 
or less from the typical -^S 
thiinble shap)e, and the 
membrana reticidaris 
is continuous from 
chamber to chamber 
(Figs. 94, 95, 97). 



genera ci institute tlie sub-class Aniplii- 



-^M/ 








FiL.. yt).— Hexasters. 
B, Horicome ; 



A, GrapliioliL'xastcr 
C, onychaster. 



genera, wliich niav he distin; 



Fig. 95. — Portion ol Ijody-wall of llyolonema, 
section, showing tlie irregular chambers. 

Sub -Class 2. Hexastero- 
phora. — Hexasters are present, 
ainphidiscs absent. The cham- 
bers have the typiccdregidarform . 
and are sharply marked off from 
one another (Figs. 90, 96). 

All the Amphidiscophora 
have Lyssacine skeletons ; in 
the Hexasterophora both types 
of skeleton occur. The sub- 
division of tlie Hexasterophora 
is determined by the presence 
or absence of uncinate spicules. 
An " uncinatum " is a diactine 
spicule, pointed at both ends 
and bearing barbs all directed 
towards one end. This method 
of classification gives us a 
wholly Dictyonine order, 
Uncinataria, and an order 
consisting partly of Dictyo- 
nine, partly of Lyssacine 
uished as the AxUNCTNATARIA. 



204 



PORIFERA 




Fig. 97. — ITyaloaema thnmscni. A. 
Whole specimen with rooting tuft 
and Epizoanthus crust ; B, pinulus, 
a spicule characteristic of but not 
peculiar to tlie Amphiiliscophora, 
occurring in tlie dermal and gastral 
membranes ; C, amphidisc with 
axial cross ; D, distal end of root- 
ing spicule with grapnel. (After 
F. E. Schulze.) 

inserted in a sponge " ; next 



Ova liave rarely beeii found, and 
sexually produced larvae never ; but 
Ijiina has found archaeocyte clusters 
in abundance, and his evidence is 
in favour of tlie view that they 
give rise asexually to larvae, described 
by him in tliis class for the first 
time (see p. 231). 

Tioth sub-classes are represented 
in British waters : the Amphidisco- 
pliora by Hyalonema tlwmsoni and 
Pheronema carpenteri ; the Hexas- 
terophora by Ewpledella suberea and 
Asconema setvhalense, and of course 
possibly by others. 

Hyalonema thomsoni, one of tlie 
glass -rope sponges, was dredged by 
the Porcupine off the Shetland 
Islands in water of about 550 
fathoms. The spindle-shaped body 
of the sponge is shown in Fig. 97. 
Its long rooting tuft is continued 
right up its axis, to end in a conical 
projection, which is surrounded by 
four apertures leading into corre- 
sponding compartments of the 
paragaster. 

The crust of Anthozoa of the 
genus Epizoanthus (p. 406) on the 
rooting tuft is a constant feature in 
this as in other species oi Hyalonema. 
It contributed to make the sponge 
a puzzle, which long defied inter- 
pretation. The earliest diagnosis 
the genus received was the " Glass 
Plant." Then the root tuft was 
thought to be part of the Epizo- 
anthus, which was termed a "most 
aberrant Alcyonarian with its base 
we liear of the sponge as parasitic 



HEXACTINELLIDA 



>os 



on the Sea Anemone. Finally, the root tuft was shown to be 
proper to the 
sponge, which was, 
however, figured 
upside down, till 
some Japanese col- 
lectors described 
the natural posi- 
tion, or that in 
which they were 
accustomed to 
find it. 

Pheroneynacar- 
penteri was found 
by the Lightning 
off the north of 
Scotland in 5 3 
fathoms. The 
goblet - shaped, 
thick walled body 
and broad, ill- 
defined root tuft 
are shown in Fig. 
98, but no figure 
can do justice to 
the lustre of its 
luxuriant pros- 
talia and delicate 
dermal network 
with stellate knots 
at regular inter- 
vals. The basal i a 
are two - pronged 
and anchor-like. 

Both the Hexas- 
terophoran genera 
were dredged off 
the north of Scot- 
land, and both conform to the Lyssacine type without uncinates. 
EuplectcUa suberea is a straight, erect tube, anchored Ijy a tuft 




-Pheronemn carpenter!. 
Wyv'ille Thomson.) 



2o6 



PORIFERA 




Euphotella mipci lalis. 
(Alter Ijii.ia.) 



of basalia. The upper end of the tube is closed by a sieve 
plate, the perforations in which are oscula, while the beams 
contain flagellated chambers, so that the sieve is simply a modified 
portion of the wall. It is a peculiarity of 
this as of one or two other allied genera 
that the lateral walls are perforated by 
oscula. They are termed parietal gaps, 
and are regularly arranged along spiral 
lines encircling the body. 
(i Ijima, who has dredged Euplectellids 

99 —Sieve phte ot from the watcrs near Tokyo, finds that 
in young specimens oscula are confined to 
the sieve plate ; parietal gaps are secon- 
dary formations. The groundwork of the skeleton is a lattice 
similar to that shown in Fig. 100. The chamber-layer is much 
folded. Various foreign species of Eiiphctella afford interesting 
examples of association with a Decapod Crustacean, Spongicola 
venusta, of which a pair lives in the paragaster of each specimen. 
The Crustacean is light pink, the female distinguished by a 
green ovary, which can be seen through the 
transparent tissues. It is not altogether 
clear what the prisoner gains, nor what fee, 
if any, the host exacts. 

Ijima relates that the skeleton oi Euplec- 
tclla is in great demand in Japan for 
marriage ceremonies. He also informs us 
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 Fio. lOO.— Skeletal lattice 
apparently constant association is that of IfteTti^'S""^'''"^''' 
the Hydroid stocks which inhabit Waltcria. 

F. E. Schulze describes Stephanoscyiohus viirabilis (see p. 318) in 
a specimen of Walteria fiemm'mgi ; 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. 




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 Fig. 101.— Part of tlie specimei] of /"ro- 

,-, -1 . 1 , n ■ T^ • tospomiia fcnestrala in the Sedf^wick 

bilurian and above all m Devonian Museum. Cambridge. Nat. size, 
strata, and have been " assigned (-^^'er Soiias.) 
in turn to pine cones, Foramini- 

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 sm-face of 
^~^^^ /'' "^-^' the fossil presents a series of lozenges 
Fig. 102.— a portion of the forming a regular mosaic. Each lozenge 
outer surface of a Recepta- jg the expanded end of one of the rays 

cuhtul, Acanthncoma bar- . . \ . in 

randei, in which the ex- ot a spicule ; it coiiceals four rays m one 
panded outer rays of the i tangential to the wall of the cup- 

spicules are partially de- ^ ' o r 

stroyed, revealing the four shaped fossil, while the sixtli ray pro- 
jects vertically to the wall into the cavity 
of the cup. In the genus Becei'ftaculites 
itself there is an inner layer of plates abutting against the inner 

' Sollas, Quart. Journ. Gcol. Sue. 1880, p. 362. 
- Quart. Journ. Gcol. Soc. xl. 18S-i, p. 795. 







tangential ravs V>eneath. 
3. (After Hinde.) 



208 



PORIFERA 



ends of the sixth rays, and at present prolDleniatic. 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- 
ber of fossil Dictyonine species 
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 
Fia. 103.— A node of the skeleton of Hexactinellids, but, as first pointed 
Ventriculites from the Cambridge ^j^^ bv Carter, it is presented by 

Greeusaud. (After Sollas. ) •' r. , , , 

one or two forms, of which Aulo- 
cystis grayi Bwk is best known. The majority of the fossil 
Hexactinellida belong to the Dictyonine section, a fact attrilnit- 
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 tliese 8 -rayed spicules 
from hexactines by some similar method ; while the typical 




"Monograph British Fossil Sponges," Pa^acoji^ Soc. xl. and xli. 1887 and 



DEMOSPONGIAE 20g 



spicule of the Heteractinellida is a euaster. Hence we may refer 
the Octactinellid fossils to tlie 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 phylum. 

Correspondingly it is the most successful group, the majority 
of existing sponges coming within its boundaries. A few geneia 
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 ha^■e taken up the evolution 
of the canal system at the stage where it was left in Zeucanclra 
aspcra — a stage which the ancestral Demosponges must have 
reached quite independently of tlie Calcarea. These commoner 
members are thus already gifted w4th the advantages pertaining 
to a spherical form of ciliated chamber, and so, too, is the Ehagon 
(Fig. 105), an innnature 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 : tliey 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, tlius 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 Ijody 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 V 



2IO 



PORIFERA 



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 Ehagon, 
then, the canal system is of tlie 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 




Fig. 104. — Diagram of (A) eiirypylous and (B) apliodal canal systems, a. Apnpyle ; «', 
apliodus ; JH, excurrent canal ; 7, incurrent canal ; 2'> pi'osopyle ; ^Z, short jiro- 
sodus. (After Sollas.) 

changes involved go hand in hand with increasing bullc of the 
dermal layer. A glance at the accompanying figures will show at 
once the connexion between the phenomena. The increase in tlie 
dermal layer (1) greatly reduces the extent of the lumen of tlie 
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 l)y way of narrow tubes, one 
proper to each chamber and termed " prosodus," the canal system 
is of the " diplodal " type. 

Cortex. — All the stages in tlie formation of a cortex are to 
be seen among the adult members of the group. Certain species 
(e.g. Plaldna monoloplia, F.E.S.) are destitute even of an ectosome, 



DEMOSPONGIAE 2 I I 



otliers have a simple dermal membrane (Halichondria 2Mnicea, 
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, e.g. in Geodia, or to a less extent in 
Tethya, or tliere 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 tlie 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 tlie other hand, the same end — coherence — has been secured 
by two new metliods, 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 
Litliistid 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 fortlicoming. For convenience, we 
accept three subdivisions and define them thus : — 

I. Tetractinellida. — Demospongiae possessing tetraxou or triaene 
spicules or Litliistid desnias. 
II. MoNAXONiDA. — Demospongiae possessing monaxon but not tetraxon 
si^icules. 
III. Ceratosa. — Demospongiae in which the main skeleton is formed of 
fibres of spongin. The fibres may have a core of sand-grains or of 
foreign si)icules, 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 



PORIFERA 



Vosmaer. Again, some Monaxonida approximate to Tetractiuel- 
lida, and we might, with Vosmaer, unite tliem under the title 
Spicnlispongiae. 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 riglit up to the coast line, and in deep water 
up to and beyond the 1000 fathom line. Occasionally they lie 
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 Tetilla, or a massive tangle, as in Cinachyra harhata ; 
in these cases the sponge is merely anchored, so that it rests 
at the level of the surface of the ooze ; in other cases, e.g. 
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. Choristiua. — Tetractinellida with qua(h-ii'adiate sjacules, which are 
never articulated together into a rigid network. 
II. LiTHiSTiDA. — Tetractinellida with branching scleres (desnias), 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. 

Plaldna 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 

distinct ectosome ; the chandlers are eurypylous. The skeleton 

^ Sollas, Challcnijcr Mo)ioijrap]i, .xxv. 1888. 



TETRACTINELLIDA 



213 



consists of microcalthrops and their derivatives. The hypopliare 
is well developed. Plakina thus shows a certain amount of 
resemblance to Oscarella (p. 196), witli which it shares the very 
remarkable possession of flagellated pinacocytes. 

One of the species of Tetilla, T. pecUfera, continues the series. 
The folds of its choanosome are 
more complicated tlian in P. 
monolopha, and their outer ends 
are bridged together by a thin 
layer of ectosome (cf species 
of Sijcon 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 Foecillastra com- 
pressa from the north of Scot- 
land and Orkney and Shetland 
is at about the same stage of 
development, 1)eing witliout Fig, 
cortex and having eurypylous 
chambers, but it is not so good 
an example, as the folds of its choanosome are confused. 

From T. fcdifera we pass to the other species of Tetilla and 
all the higher genera of Choristida ; these possess a cortex not 
of homologous origin in tlie various cases, but probably to 




10."i. — Diagrniiimatic vertical sections 
of A, Rhao-on ; B, Plakina : C, Tellllu 
pedifera. 




fb 



IT 



B 

Fig. 106. — A, CranieUa type ; B, Stellettid type, ch, Chone ; co, collenchyma ; d.o, 
dermal ostia ; fb, fibrous tissue ; i.e. iutercortical cavity ; sd, subderinal cavity ; 
sji, sphincter. (After Sollas.) 

be classified under one of two heads, typified by SteUcUa and 
CranieUa respectively (Fig. 106). 



214 



PORIFERA 



In the Stellettids the cortex arises by the centrifugal growth 
of a dermal membrane such as that of Tetilla 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 
througliout or collencliymatous in 
its outer portion and fibrous in tlie 
deeper layers. In the Stellettid 
type the centrifugal growth of tlie 
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 a 
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 
any knowledge of the development 
one would certainly have supposed 
that the subdermal cavity, pore-sieve 
and sphinctrate passages of Craniella 
represented a number of chones, of 
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 distriljutiuu, appearing in some genera of 




;. 107. — Disyringa dissimilis. 
Diagrammatic longitudiual section 
of the Sponge. x ^. a, b, c, 
Transverse sections at the levels 
indicated to show subdivision of 
the lumina of the excurrent and 
incurrent tubes ; e.t, excurrent 
tube ; ij, incurrent tube ; o, os- 
culum. (After SoUas.) 



TETKACTINELLIDA 2 I 5 



each family but not in others. The genus Pachymatisma, of which 
we have the species P. johnstonia and P. vormani 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. 

Bisyringa dissimilis is remarkable for the perfection of its 
symmetry, and for the absence of that midtiplication 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 — Spongocardiuni gilchristi ^ — from Cape Colony, in which 
the dermal ostia are concentrated in one sieve -like patch 
at the opposite pole to the single osculum. Bisyringa 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) (Eig. 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 probalily descendants of Monaxonida. 

Owing to the consistency of the skeleton Lithistida are 
frequently found as fossils. The commonest known example is 
Siplwnia? As in the case of so many other fossil sponges the 
skeleton is often replaced by carbonate of lime, a fact whicli 

^ Marine Investigations in South Africa, i. 1902, p. 224. 

- Cf. Sollas, Encydo2ucdia Britannica, 1887, art. "Sponges," and Sclirammen, 
Mitth. Mus. Hildesheim, 14, 1901. 

^ Sollas, Quart. Journ. Gcol. Soc. xxxiii. 1877, p. 790. 



2l6 PORTFERA 



misled some of the earlier investigators but was established by 
the researches of Sollas and Zittel. 



Sub-Class 11. 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 Axinella 
spp. occur in shallow water and in various depths down to 2385 
fathoms, Axinella erecta ranges from 90 to 1600 fathoms, 
Bhjlocordyla 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 Trichostemma 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, wliich 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, w^hether of descent or parentage, with 
the Tetractinellida, and a second set typically non-corticate : these 
latter are the Halichondrina, the former are the Spintharophora. 

' Ridley and Dendy, Challenger Monograph, lix. 1887. 
- Ibid.\u 262 ; cf. also p. 197. 



MON AXON IDA 2 1/ 



Order I. Halichondrina. 

We have already seen typical examples of tlie Halicliondrina 
in Hidichondria |;«7itcea and Ej^hydatia fiuviatilis. AVitliin the 
Halicliondrina tlie 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 
Ficnicra or Gel I his), 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, i.e. 
fulfilling the functions of support, while the spicules merely beset 
its surface as defensive organs, rendering the sponge unfit for 
food. Filires 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 SpongUIa, 
that the spongin fibres are continuous with a delicate cuticle at 
the surface of the sponge. In Ecniera 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 lircadth, 
ultimately leaving the fibre free." 

Order II. Spintharophora. 

These corticate forms are further cliaraetcrised by the arrange- 
ment of their megascleres, which is usually, like that of most 

1 Quart. J. Micr. Sci. xli. 1901, p. 477. 
^ Loisel, J. dc I'Anat. ct Phtjs. xxxiv. 1898, p. 1. 



2 I 8 PORIFERA 



Tetractinellida, radial, or approximating to radial. The niicro- 
scleres are, when present, some form of aster. The cortex 
resembles that of Tetractinellida, and v. Lendenfeld has described 
chones in Tethya lyncurium} 

The existence of the above points of resemblance between 
Spintharophora and Tetractinellida suggests a relationship between 
the two groups as its cause. In judging tliis 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 Tetilla. 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 Frotcleia " 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, Clionidae 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. Ixix. 1896, p. 22. 

2 Challenger Report, lix. 1887, p. 214. 

3 Topsent, Zoologie Descri2)tivc, i. ; also Cotte, C. R. Soc. Biol. Paris, 1902, 
pp. 638-639. 

•* Topsent, Arch. Zool. Exp. (3) viii. 1900, p. 36. 



MONAXONIDA 219 



been calculated^ that sponge skeletons may give rise with 
considerable rapidity to beds of flint nodules ; in fact, it 
appears tliat a period so short as fifty years is sufficient for 
the formation of a bed of flints out of the skeletons of sponges 
alone. 

Suherites 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 Fagurus, and gradually envelops it, 
becoming very massive, and completely concealing the shell, 
without however closing its mouth. The aperture of tliis 
always remains open to the exterior, however great the growth 
of the sponge, a tubular passage being left in front of it, which 




Fig. 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 
great 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. 

FiciLlina Jicus 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 metaraps, one of 
which, from its fig-like shape, gives it its name. 

' Sollas, Challenger Monograi^h, xxv. pt. Ixiii. ISSS, p. Ixxxix. 

^ Topsent, Arch. Zool. Exp. (3) viii. 1900, p. 226. For an account of certain 
very remarkable structures termed diaphragms in Cliona mucronata and C. cnsifera, 
see Sollas, Ami. Mag. Nat. Hist. (5) i. 1878, p. 54. 



220 PORIFERA 



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 theii* associates in their own sul)- 
class. 

The genera Aulcna and FJioriosj^o^ifjia, 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. 

Fhoriosponr/ia, as far as its main skeleton is concerned, is a 
typical Ceratose sponge, with fibres of the areniferous type, ln;t 
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 consideraljle 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. lantliella 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 

^ R. von Lendenfeld, Monograph of Horny Sjwnges, 1889, p. 831. 



CERATOSA KEY TO BRITISH GENERA 



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, Eus^jongia 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 Hip2Jospongia 
also form a source of somewhat inferior bath sponges. 

Among Dendroceratina, Dartvinella 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. 

rSkeleton calcareous . . . . . .2 

I Skeleton siliceous . . . . . .6 

"I Skeleton horny, or -witliout free spicules . . .53 

(^Skeleton absent . . . . .55" 

I'Gastral layer continuous . . . . .3 

\ Gastral layer discontinuous, confined to chambers . . 4 

/'Equiangular triradiate systems present . . . Clathrina 

\Triradiate systems all alate .... Leucosolenia 

r Chambers tubular, radially arranged . . . .5 

1^ Chambers spherical, irregularly scattered . . Leucandra 

^ f Tufts of oxeate spicules at the ends of the chambers . Sycon 

(Oxeate spicules lying longitudinally in the cortex . Ute 

TAU the spicules hexradiate or spicules easily derived from hexradiate 

G I ^yv^ ' 

j Some of the spicules calthrops or triaenes . . .10 

[Megascleres uniaxial . . . . . .15 

., /"Amphidiscs present . . . . ' . .8 

\Amphidiscs absent . . . . .9 

(Rooting spicules a well-defined wisp ; four apertures lead into the 
gastric cavity .... Hyalonema (homsoni 
Rooting tuft diffuse ; sponge oval ; osculum single 
Phcronema carpenteri 

[Sponge tubular, dermal and gastral piuuli alj.sent Eiipledella subei-ca 
9. - Sponge a widely open cuj) ; dermal and gastral pinuli present 

[ Asconema setahalense 

i Tetractine spicule, a calthrop or triaene with short rhabdome ; 

10. - microsclere a spined microxea . . Dercitus hucklandi 

[Triaenes with fully developed rhabdome . . .11 



222 



PORIFERA 




109. — Microscleres of Demospongiae. a, b, Sigmaspires viewed in different directions ; 
c,d, bipocilli viewed in different directions ; c,toxaspire ;./',/', spiraster ; //, sauidaster ; 
h, anipliiaster ; i, sigma ; j, diancistra ; k, isocliela ; I, m, anisochelae viewed in 
different directions ; n, cladotyle ; o, toxa ; fj, forceps ; q, oxyaster ; r, spheraster ; 
s, oxyaster with 6 actines ; t, anotlier with 4 actines ; it, another with rays reduced 
to two (centrotylote microxea) ; v, tylote microrhabdus ; u\ tricliodragmata ; 
X, oxeate microrhabdus or microxea. 



11. 



fMicroscleres sigmata .... Craniella cranium 
(Sigmata absent, asters present . . . . .12 

[Microscleres include sjiirasters . 
\ Microscleres include sterrasters . 
[ Microscleres include euasters : sinrasters and 

[Two kinds of euaster present .... SteUetta 

4 Microscleres include a euaster and a sanidaster or amphiaster 
y Stryphnus 'ponderosus 

(Microscleres include microrlialxli . Pachymatisma johnstoma 



Poecillastra compressa 

. 14 

terrasters absent . 13 



(Microscleres include many-rayed euastei's 

( Some of the microscleres asters . 
^^ Microscleres absent, or not asters 

[Skeleton radiate ; asters of more than one kind 
I Sponge encrusting ; asters of one kind only 
[skeleton fibrous 

[Megascleres all diactinal ; chelae present 
- ]\Iegascleres all diactinal ; chelae absent 
[Some or all of the megascleres monactinal 



Cy (Ionium miller i 

. 16 
. 17 

Tdhya 
. Hifmedesmia 
. Axinella spj). 

. Desmacidon 
. 18 
. 19 



KEY TO BRITISH GENERA 



223 



18. 



19. 



24. 
25. 

26. 

27. 

28. 

29. 

30. 

31. 
32. 



. 56 
. 22 

Acarnus 

3 fonniiig tlie 

Plocaviia 

. 20 

Hamacantha 

Forcepia 

Hymeraphia 

Icqjhon 
Pocillon 

. 28 
. 30 



/'Habitat fresh Avater .... 
( Habitat marine .... 

Megascleres include cladotyles . 

Megascleres include dumb-bell or gausage-shaped spicule: 
main reticulum .... 

]\Iicroscleres include bipocilli 

Microscleres include diancistra . 

]Megascleres include forceps 

Skeleton formed of isolated monactines vertically placed 

None of the above peculiarities jjresent 

('Skeleton fibre not echinated 
(Skeleton fibre echinated 

(Skeleton with echinating spicules 
(Skeleton without echinating spicules 

f Spongin abundant .... 

(Spongin scanty .... 

(Fibre not echinated .... 
(Fibre echinated .... 

fFibre with a single axial series of spicules 

\ Fibres with numerous spicules arranged polyserially 

[Microscleres absent . . . , 

- IMicroscleres sigmata anclV 
[Microscleres sigmata or / ' ' 

(Skeleton confused .... 

(Skeleton reticulate .... 

TEind and fistulous appendages present ; microscleres sigmata Oceanapia 
-No rind; skeleton reticulate; microscleres sigmata and) n it 

(No rind ; skeleton reticulate ; microscleres sigmata or J * 

/"Skeleton confused or formed of bundles of spicules with echinating 

spined styles . . . .29 

^ Skeleton fibrous or reticulate, or formed of short columns . 45 

Skeleton formed of a dense central axis, and columns radiating from it 

I to the surface . . . . . .52 

[Spicules of the ectosome styles .... Pytheas 

■I Spicules of the ectosome oxeas or absent . . Clathrissa 

(Main skeleton confused. Special ectosomal skeleton absent Spanioplon 

TMegascleres of the choanosome not difl'ering from those of the 



. 23 

. 25 

. 24 

Liplodemia 

Chalina 
Pachychalina 

. 26 

. 27 

Halichondria 
Eeniera 



J ectosomi 

1 Megascleres of 



the clioanosome dilferiny from those 



( some 

fClielae absent . 
I Chelae present 

fTrichodragmata present 
(Trichodragmata alj.sent 



of th 



31 

ecto- 
. 32 

. 33 

. 44 

Tedania, 
. 42 



224 



PORIFERA 



Fig. 110. — Megascleres. a-l 
and q-s, Modifications of 
nionaxon type. «, Stroii- 
gyle : b, tylote ; c, oxea ; 
d, tylotoxea ; e, tylostyle ; 
/, style ; g, spined tylo- 
style ; h, sagittal triod (a 
triaxoii form derived from 
nionaxon) ; j, oxytylote ; k, 
auatriaene ; I, protriaene ; 
m, sterraster (polyaxon) ; 
n. radial section through 
the outer part of m, show- 
ing two actines soldered 
together by intervening 
silica ; o, desma of an 
Anomocladine Lithistid 
(polyaxon) ; q, crepidial 
strongyle, basis of rhab- 
docrepid Lithistid desma ; 
?•, young form of rhab- 

docrepid desma, showing crepidial strongyle coated with successive layers of silica ; s, 

rhabdocrepid desma. 




33. 

34. 

35. 
36. 
37. 
38. 
39. 
40. 

41. 

42. 
43. 



rSkeleton reticulate or fibrous . . . . .34 

I Skeleton radiate or diffuse . . . . .37 

1 Skeleton with radiating fibres forming a reticulum with others crossing 
[ them at riglit angles .... Quasilhna 

/"No microscleres . . . . . .35 

- Microscleres sigmata andV .^, -ii ^ ^ • i i ^ 

' =" ' toxa with or without trichodragmata 

Desmacella 



Microscleres signiata or j 



(Sponge fan- or funnel-shaped . 

(^Sponge not fan- or funnel-shaped 

C Megascleres slender and twisted 

\Megascleres somewhat stout, not twistt'd 

(Sigmata present, skeleton diffuse 

(Sigmata absent .... 

rSkeleton more or le.ss radiate 

^Skeleton diffuse ; sponge boring 

f Sponge discoid with marginal fringe 

(^Si)onge massive or stipitate without marginal fringe 

(Sponge body prolonged into mammiform projection; 

\Sponge body without mammiform projections . 

[No microscleres. Megascleres tylostyles witli or without styles 
J Suberites 

[Microscleres centrotylote. Megascleres styles or tylostyles Ficulina 
rChoanosomal megascleres smooth . . . .43 

\Choanosomal megascleres spined . . . Dendoryx 

(Microscleres chelae and sigmata of about the same size .Lissodendoryx 
\ Chelae, if present, smaller than the signiata . . Yvesia 



. 36 

Hymcniacidon 

FhakelUa 

Tragosia 

Bicmma 

. 38 

. 39 

Clio n a 

. Halicnemia 

. 40 

I'ohjmasfia 

" . 41 



KEV TO BRITISH GENERA 



225 



OplUitaspongia 

Axinella 

. 48 

. 49 

Myxilla 



I'Isochelae ...... Esperiopsis 

\ Anisoclielae ...... Esperella 

fFiln-es or colunuis pluniosL' . . . .46 

I Fil ires or columns ectyoniiK' . . . .47 

/'Microscleres toxa .... 

\Microscleres alij^eiit .... 

/"Skeleton reticulate .... 

\ Skeleton not reticulate 

fiMicroscleres j^ resent. Spicules of the fibre core spined 

(Microscleres absent. Sjiicules of the fibre core smooth . Lissomyxilla 

j" >rain skeleton formed of plume-like columns . . . .50 

^ Main skeleton formed of horny fil)i'e.s (ectyonine). Special dermal 
[ skeleton wanting ..... Claihria 

JDermal skeleton contains styles only . . . Microciona 

[Dermal skeleton contains diactine spicules with or without styli 51 
/']\Iain skeleton columns with a core of smooth oxeas Plumohalichondria 
(Main skeleton columns with a core of spined styles . Stylostichon 
rCentral axis contains nuich spongin. Echinating spined styli 
I present ...... Raspailia 

I Central axis with little or no spongin. Spined styles aKsent. Pillars 

[ radiating from the axis support dermal skeleton . Ciocahjpta 

[Ground substance between chambers clear; chambers pear-.shaped or 

oval ; eurypylous ..... Sponcjelia 

54 



44. 
45. 
46. 
47. 

48. 

49. 

50. 
51. 

52. 

53. 

54. 
55. 
56. 



(Ground substance granular. Chambers spherical with aphodi 

/'Fibres not pithed ; sponge fan-shaped . . . Leiosella 

\ Fibres pithed ; sponge massive .... Aphjsina 

j" Chambers long, tubular, branched . . . Halisarca 

(Chambers not much longer than. broad ; not branched . Oscarella 

JAmphidiscs present ..... Ephydatia 

(Amphidisco absent ..... Spoiifjilla 



VOL. I 



CHAPTER IX 

rORIFERA {continued) : KEPEODUCTION, SEXUAL AND ASEXUAL 

PHYSIOLOGY DLSTPJBUTION 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). 



\ 



X 






w 






c.s. 

Flc. 111. — A, ainphihlastuhi larva nf ^ijcon raphanns ; B, later .sta:je, showing invagina- 
tion oi'tlie flagellated cells, c.s, Segmentation cavity ; fc, ectoderm ; en, endodenn. 
(After F. E. Schulze, from Balfonr.) 

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 tlie 
amphihlastula, and the other the parenchy inula. 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 



DEVELOPMENT 2 2/ 



these types are Imt 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. HI) 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 
cavity which is largely filled up with amoebocytes. The 
flagellated cells are invaginated into the dome of rounded cells 
during metamorphosis, in fact, become the choanocjtes 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 llanca. (Fig. 112). When 
hatched it consists of a wall surround- 
ing a large central cavity and liuilt up 
of flagellated cells interrupted at the 
hinder pole by two cells {p.</.c) — the 
mother -cells of archaeocytes. Before 
the metamorphosis, certain of the flagel- 
lated cells leave the wall and sink into 2^!/^ 
the central cavity, and undergoing Fig. 1 12.— .Median longitudinal 

, • I ^ 1 T 1 • section of pareuclivniula 

certani changes establish an inner mass i^,,.^ ^j. chArhm hhmca. 
of future dermal cells. By subsequent iJ-ii-'-; Posterior granular 

, . ,t . . „ n , 1 cells — arcliaeocvte niotlier- 

metaiuorphosis the remaining flagellated (.gUj. (Alter Mindiin.) 

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. Uanca, 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. Uanca, 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 Lfucosohnia. It is liatehed as a 
' Cf. ilinchiu in E. Piay Lankester's Treatise, p. 77. 




228 PORIFERA 



completely tiagellated lurva : its archaeocytes are internal (as in 
Sycon) ; future dermal cells, recognisable as such, are absent. 
They arise, as in C. hlanca, by transformation of flagellated cells : 
but (1) this process is confined to the posterior pole, and (2) the 
internal cavity is small and filled up with arcliaeocytes. Con- 
sequently the cells whicli have lost their flagella and become 
converted into dermal cells cannot sink in as in C. hlanca : they 
accumulate at the hinder pole, and thus arises a larva half 
flagellated, half not ; in fact, an amphililastula. Or, l^riefly, 
in Leucosolenia the larva at hatching is a parenchymula, and 
when ready to fix is an amphiblastula ; and, again, the differ- 
ence between tlie 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 developmental 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 tlie adult.^ The metamorphosis is comparable 
to that of C. hlanca. 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) " Imdding," (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 liy 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 hoiry oleics ~ 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, 
where the bud is constricted from the parent. Such a reversal 
1 Maas, Zool. Centralhl. v. 1898, p. 581. - Arch. Zool. Exp. viii. 1879, p. f.9. 



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 





Fig. \\Z. —Loiihocalyx j^hilipjxjisis. The specimen bears several buds attached to it by 
long tufts of spicules. (After F. E. Schulze.) 



H 




Fig. 114. — Leucosolenia botryoides. A, a piece of the Spouge laden with buds, a-f; i, 
the spicules of the buds directed away from their free ends ; k, the spicules of the 
parent directed towards the osculuni, j. B, a bud which has been set free and has 
become fixed by the e.'ctremity 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 HoU," 1894, p. 43. 



PORIFERA 




regeneratiou of Coelenteratii and other forms, concluded that a 
kind of " polarity " existed in tlie tissues of certain animals. 

In Oscardla lohvlaris^ the buds are transparent floating 
bladders, derived from little prominences on the surface of the 
sponge. Scattered in the walls of tlie bladders are flagellated 
chambers, which ojien into tlie central cavity. The vesicular 
nature of the buds is doubtless an adaptation, lessening their 
specific gravity and so enaliling them to float to a distance from 
the parent. 

GemncmlaXion.— Spongilla has already afforded us a typical 
example of tliis process, Gemmules very similar to those of 

Siiongilla are known in a 
few marine sponges, especi- 
ally in Suheritcs 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 tlie 
spongin coat, sometimes 
absent ; possibly its absence 
may be correlated with 
the piling of one layer of 
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 Tethyar 
Mere microscopic examination of a Tethya 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 




Fig. 115. — Gemmules of Ficulina. A, vertical 
section of gemmules in situ ; B, vertical sec- 
tion of upper portion of one gemmule. m, 
Micropyle. 



1 F. E. Seluike, Zoul. Jnz. ii. 1879, p. 636. 
Maas, Zcitschr. xciss. Zool. Ixx. 1901, p. 263. 



IX 



GEMMULATION 



31 




and are tinally freed, like the buds of the nexactinellid Loplio- 

valyx{Vi^. lis). 

The comparison of the process of development on the one hand 

by g-emmules, and on the other by larval development, is of some 

interest/ In l)oth 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 iind 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 

seldom observed. 
^ In Hexactinellida the place of 
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 egg-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 
f " asexual larvae " was 
first made by Wilson in the Monaxonid 
Es2')erella ; in this case the asexual 

larva is, as far as can be detected, identical with that developed 
A similar phenomenon, the production 

Maas, loc. cit. p. 284. - J. CoU. Japan, -w. 1901, y. 180. 



Fig. 116. — Develoi^ment of the tri- 
radiate and quadriradiate spicules 
of Clathrina. (1) Three sclero- 
blasts ; (2) each has divided : the 
spicule is seen in their midst ; {'i) 
addition of the fourth ray by a 
porocyte. j), Dermal apertuve of 
pore ; v, fourth ray. (After 
Miuchin.) 




^t 




Fig. 117. — Three stages in the 

development of the triradiate dlSCOVei'V 
spicules of Sycnn setosum 
1200. (After Maa.s.) 



232 



PORIFERA 



of apparently identical larvae by both sexual and asexual 
methods, has been observed in the Coelenterate Gonionema 
murbachii} 

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. 
The triradiate spicules of the Sycet- 

Fiu. lis. — Develojimeiit ol monaxoii . . . 

spicules. A, from Spongiiia tidac, on the other hand, originate 
/«c«s<m, showmg the .single j^ a sinfde cell,^ but the quadri- 




scleroblast. (After Evans.) B, a 



qm 



very large monaxon, from Leuco- radiate spiculcs are formed from 

sdema, on which many sclero- ^| ^ ^j addition of a fourth 

blasts are at work. (Alter Maas.) J 

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 tlie 



' Perkins, Johns Hopkins Univ. Circ. xxi. 1902, \>. S7. 

- For details of this interesting process see Mincliin, Qiuirt. J. Micr. Sci. xl 
1898, p. 469. 

" Maas, Zeifschr. wiss. Zool. Ixvii. 1900, p. 225. 



DEVELOPMENT OF SPICULES 



division of tlie original scleroblast, otliers are drawn from the 
surrounding tissue. In TctJiya, for example, and in Lcueosoleriuc ^ 
the scleroblasts round the large monaxon spicules are so numerous 
as to have an almost epithelioid arrangement. 

Tlie large oxeas of Tetilla, Stellctta, and Geodia, however, are 
formed each within a sinude scleroblast." 



o a<> 






^{vJff'AA.A^ 



Fig. 119. — Development of spheraster. A, of Tethya, from union of two quadriradiate 
spicules. (After Maas.) B («-e), of C7to«c?ri7te, from a spherical globule. (After Keller.) 

Triaenes have been shown ^ to originate as monaxons with 
one swollen termination, froifi 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 microscleret 
might be great. Maas believes that he has shown that the 
spherasters of Tethya are 
formed by the union of 
minute tetractine cal- 
tlirops (Fig. 119,A). If 
this view should be con- 
firmed, it would afford a 
very strong argument 
for the Tetractinellid 
afhnitios of Tethya. 

Keller,* on the otlier 
luiud, tinds that the spherasters of the Tetractinellid Chondrilla 






Fig. 120. — Stages in the development of tlie micro- 
scleres oi Placospongia. (After Keller.) 



' Maas, SB. Ah. Milnchcn, xxx. 1900, p. 553, and Zeitschr. loiss. Zool. Ixx. 
1901, p. 265 ; see also Sollas, Ann. Mag. Kat. Hist. (5) ix. 1880, p. 401. 
- Sollas, Challcnrjcr Monogrcqih, xxv. 1888, p. xlv. 
= Sollas, ibid. pp. 13 and 34, pi. v. ^ Zeitschr. iviss. Zool. Hi. 1891, p. 294. 



234 



PORIFERA 




originate as spheres (Fig. 119, B) ; and spheres have been observAl 
in the gemmule of a Tethya ; 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, howe^'er, as will 
be seen from Fig. 120, shows 
that they are not polyaxon but 
spiny monaxon spicules. Placo- 
spongia is consequently trans- 
ferred to the Monaxonida Spin- 
tharaphora. 

Sterrasters originate within 
an oval cell as a number of 
hairlike fibres^ (trichites), which 
are united at their inner ends. 
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. Protosponr/in, p. 207). 



Fig. 121. — Three stages in the development 
of an anisochela. al, Ala ; al', lower 
ala ;/, falx ; ,/'', lower falx ; r, rostrum ; 
r', lower rostrum. (After Vosmaer anil 
Pekelharing.) 



Physiology 

Production of the Current. — It is not at first sight obvious 
that the lashing of flagella in chambers arranged as above 

1 I. Sollas, P. Zool. Sue. London, ii. 1902, p. 2ir.. 

•- Sollas, Aim. Mag. Nat. Hist. (5) ix. 1880, p. -102. 

^ Bowerbank, and also Vosmaer and Pekelharing, Vcrh. Ale. Amsterdam (2) vi. 



3, li 



* J. Coll. Jaimn, xv. 1901, p. 19.3. 



PHYSIOLOGY 235 



described, between an inhalant and an exlialant system of canals, 
Avill 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 chamlier 
do not vibrate in concert, but that each keeps its own time. 
This, however, is of less consequence than might seem to be tlie 
case. Two conditions are essential to produce the ol)served 
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 nmst 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 lie round the periphery. Such a distribution of 
pressures would be set up if each flagellum caused a How 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 present 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 

^ Vosmaer and Pekelliaring, J'c7-h. Ak. Amsterdam, 1898. 

~ See Bidder, P. Camb. Soc. vi. 1888, p. 183 : Sollas, ChaUenger Monngraph, 
XXV. 1883, pp. xviii.-xxi. : and Vosmaer and Pekelliaring, he. c.it. 



236 PORIFERA 



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 
oscidar rim is only a special case of a de^'ice 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 is 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 ecjual 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 chain1)er 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 237 

aphodal and diplodal eliainbers are as efficient as many of the 
eury pylons type. 

It is manifest tliat the enrrcnt is tlie l)earer of the supply 
of food; but it re(|uires more care to discover (1) what is tlie 
nature of the food ; (2) Ijy wliieh of tlie cells bathed by the 
current the food is captured and by which digested. The 
answer to tlie latter question lias 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 imr excellence ; but the 
pinacocytes perform a small share of the function of ingestion, 
and in the higher sponges where the dermal tissut^ has aecpiired 
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, l)ut that possibly decaying 
substances in solution may eke out their diet. Loisel, in 1898,"^ 

1 Carter and Lieberkiilin in 1S56, Hacckel in 1S72, MetschnikolT in 1879, and 
many later workers. 
- Die Kalksehv-iiinme, 1872, i. \k '-'u'l. " J. Anat. PInjsiol. 1898, pji. 1, 6, 234. 



38 PORIFERA 



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. Wlien 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 SiJongiUa 
supplied with filtered spring-water, to which w^as added the 
filtered juice obtained from another crushed sponge. This 
Spongilla lived and budded, and was in good health at tlie 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 eacli 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 tlie spicules luu'e 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 Ijy developing 
Spongillids from water in which the percentage of silica present 
must have been exceedingly small. The young sponges climbed 

1 Mtm. Ac. St. Felersb. (7) xxvi. 1878, p. 10. 
- Sollas, Challenger Rex>ort, xxv. yi. Ixiii. p. Ixxxviii. 



I 



THYSIOLOGY DISTRIBUTION 



239 



up the strands of spicules as they formed 
them, leaving tlie lower parts behind and 
adding to the upper ends. 

Of the pliysiology of tlie pigments of 
sponges not nmch is yet known : a useful 
sunnuary of facts will be found in Yon 
Fiirth's text-book.^ 

Spongin. — Von Ftirth ^ 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 iodine. 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 I'o 
to 1*G 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. Each 
group has, however, its characteristic bathy- 
metrical range : the facts are best displayed Fig. 122.— The ordinals mea 




X 



by means of curves, as in Fig. 122, which 
is based wholly on the results obtained by 
tlie "Challenger" Expedition. The in- 
formation as to littoral species is con- 
sequently inadequate, and we have not the 
data requisite for their discu.ssion. 

Sponges generally (a) and Monaxonida 
in particular (/>) 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 

^ Vci-'jl. P/'djsiuloijie d. nicdcrcn Tltierc, 1903, p. Ai\ 



(i.) the iiuniLer of 
species, a-f, and (ii.) the 
number of stations, «'-/', 
at which successful hauls 
were made. The abscissae 
measure the depth : thus 
at I. the dejtth is from 
to 50 fathoms ; at H. 
from 51 to 200 ; at 111. 
from 201 to 1000 ; at IV. 
from 1001 upwards. «, «', 
are the curves for Sponges 
generally ; ft, ft', for Mon- 
axonida ; f, c, forHexacti- 
nellida ; d, d', for Tetrac- 
tinellida ; e, e, for Cal- 
carea; /,/', for Ceratosa. 



240 PORIFERA 



richer, for the station curve (a) rises abruptly from I. to II., 
while the species curve (a) in the same region is almost 
horizontal. 

The Hexactinellid curve (c) culminates on III., showing that 
the group is characteristically deep water. That for Tetracti- 
nellida (d) reaches its greatest height on II., i.e. between 51 
and 200 fathoms. Even here, in their characteristic depths, 
the Tetractinellida fall below the Hexactinellida, and ftir 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 wliicli 
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 sliould 
be true also of the Hexactinellida and of the deep-water species 
of Tetractinellida and of Monaxonida. 

While the family groups are cosmopolitan, 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 



DISTRIBUTION IN SPACE AND TIME 



;4i 



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 palaeoutology 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 :^ — 

"■" CAIN020IC 



MEGAMASTICTORA 

Calcarea Homocoela 



orantiioae 
Phabetbones 

OlALVTINAE 

Lithoninae 
MICROMASTICTORA 

Hexactinellioa 

Receptaculitidae 

Hetehactinellioa 

Octactimellida 

TETfiACTlNELLfDA 
CMOBrSTIDA 
LlTHISTIDA 

MONAXONIDA 
CtRATOSA 



> 7 '". 5 



Fig. 123. — Table to indicate disti-ibution 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 

^ Fur fui-thcr details see Zittel, Lclirhuch dcr Pahteontulo(jic, and Felix Bernard, 
Elements de Palaeontolcgie, 1894. 

VOL. I R 



242 PORIFERA 



ounce of spicules at least one ton of sea water must pass tlirough 
the body of the sponge. Obviously from such a weak solution 
the deposition of silica will not occur by ordinary physical 
agencies ; it recjuires the unexplained action of living organisms. 
This may account for tlie fact that deposits of flint and cliert 
are always associated with organic remains, such as Sponges and 
Eadiolaria. 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 lime by 
the silica takes place, so that in the case of chalk the shells of 
Foraminifera, such as Glohigerma and Tcxtidaria and those of 
Coccoliths, are converted itito 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 on a 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 wliicli 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 tlie 
spicular silie;i. 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 Foniiatioii of Flints," in The Age of tlte 
Earth, 1905, p. 131. 



COELENTERATA AND CTENOPHORA 



S. J. HICK SON, M.A., F.RS. 

Formerly Fellow and now Honorary Fellow of Downing College, 
Beyer Professor of Zoology in the Victoria University of Manchester. 



243 



CHAPTER X 



COELENTERATA 



INTRODUCTION CLASSIFICATION HYDROZOA ELEUTHEROBLASTEA 

MILLEPORINA GYMNOBLASTEA CALYPTOBLASTEA GRAP- 

TOLITOIDEA STYLASTERINA 

The great division of the animal kingdom called Coelen- 
TEKATA was Constituted in 1847 by E, Leuckart for those 
animals which are commonly known as polyps and jelly-fishes. 
Cuvier had previously included these forms in his division 
Eadiata 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 (/cotXo9 = hollow, 
evT€pov^ the alimentary canal) was therefore iiitroduced, and it 
may be taken to signify tlie important anatomical feature that 
the ])0(ly-cavity (or coelom) and the cavity of the alimentary 
canal (or enteron) of these animals are not sejiarate 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 tliis respect they have a 
superficial resemblance to many of tlie 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 



2^6 COELENTERATA 



The radial syminetiy has been acquired in the two divisions 
along different lines of descent, and has no further significance 
than the ada^^tation of different animals to somewhat similar 
conditions of life. It is not only in the animals formerly 
classed by Cuvier as Eadiata, 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 zouid, was 
originally introduced on a fancied resemblance of a Hydra to a 
small Cuttle-fish {Fr. Poulpe, Lat. Polypus). 

The body of the Coelenterate, then, consists of a body- 
wall enclosing a single cavity (" coelenteron "). The body- wall 
consists of an inner and an outer layer of cells, originally called 
by AUman 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 is 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 1:iy 
cell-lined canals ; Init 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 grov/th 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 jelly- 
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" (Pig- 124). 



NEMATOCYSTS 



247 



This is an organ produced within the body of a cell called 
the " cnidoblast," and it consists of a vesicular widl or capsule, 
surroiuiding 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 sufticiently 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 Ahyonium and in many other 
Alcyonaria they are very small (in Aley- 
onium the nematocyst is 0'0075 mm. in 
length previous to discharge), and when 
discharged exhibit a simple oval capsule 
with a plain thread attached to it. In 
Hydra (Fig. 124) there are at least two 
kinds of nematocysts, and in the larger 
kind (0"02 mm. in length previous to dis- 
charge) the base of the thread is beset 
with a series of recurved hooks, which 
during the act of discharge probably assist 
in making a wound in the organism 
attacked for the injection of tlie irritant 
fluid, and possibly hold the structure in 
position while the thread is being dis- 
charged. In the large kind of nematocyst 
of Millepora and of Cerianthus there is a 
band of spirally arranged but very minute 
thorns in the middle of the thread, but 
none at the base. In some of the Siphono- 

phora the undischarged nematocysts reacli their maximum size, 
nearly 0'05 nnn. in length. 

"Wlien a nematocvst has once been discharged it is usually 




Fig. 124. — Nematocyst 
[Ncm) of Hydra grisea, 
enclosed within the cnido- 
blast. Ci\'C, Cnidocil ; 
/', thread of nematocyst ; 
^ff, myophan threads in 
cnidoblast ; X, nucleus 
of cnidoblast. (After 
Schneider.) 



248 COELENTERATA 



rejected from the body, and its place in the tissue is taken by a 
new nematocyst formed by a new cnidoblast ; 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 ("cnidopod"), 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 cnidoblast 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, Scyphozoa, 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 (e.g. 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, l)ut are introduced 

1 JVilhifs Zool. Results, pt. ii. 1899, p. 127. 
- Murbach, Archiv f. Xatunj. l.x. Bd. i. 1894, p. 217. 



CLASSIFICATION 249 



into the body with its food.^ The nematocysts that occur in 
the Infusorian Epistylis umlellaria 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. Hydrozoa. — "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 
(AIcyo7iium), the Sea-pens, and the Precious Coral of commerce. 

CLASS I. HYDEOZOA 

In this Class of Coelenterata two types of body-form may be 
found. In such a genus as Ohclia 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. Grosvcnor, Proc. lioij. Soc. Ixxii. 1903, p. 462. 



250 COELENTERATA HYDROZOA cHAr. 

endoclerm (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-like 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 Ohelia is called the "medusome." 

It is difficult to determine whether, in the evolution of the 
Hydrozoa, the hydrosome preceded the medusome or vice verm. 
By some authors the medusome is regarded as- a specially modified 
sexual individual of the hydrosome colony. By others tlie 
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, wherefas 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 0, the life-histories of 
the Hydrozoa may be represented by the following formula' : — 

{Hydra) 

{Scrtularid) 
(Ohelia) 
(Tyiriojye) 
{Gcryonici) 

hydrosome is usually very simple. It 



1. 




- H - 


2. 




- H - III - 


3. 




- H - ^I - 


4. 




0-h-n-O 


5. 




- M - 


The structure 


of 


the hydrosome 



HYDROSOME AND MEDUSOME 



251 



one or two 



consists of a branched tube opening by mouths at the ends of 
the liranches 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 moutli is usually a 
small round aperture situated on the summit of tlie hypostome, 
and at the base of the hypostome there may 
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), 
which become free from the parent, or 
it may be a colony of zooids in organic 
connexion with one another formed by 
the continuous gemmation of the original 
zooid derived from the fertilised ovum 
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-swinnning existence. The body is expanded to form a disc, 
" umbrella," or Ijell, 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 




Fig. 125.- — Diagram of a ver- 
tical section through a 
hydrosome. Vod, Coeleu- 
teron ; Ect. ectoderm ; End, 
endoderm. Between the 
ectoderm and the endoderm 
there is a thin mesogloea 
not represented in the 
diagram . M, mouth ; T, 
tentacle. 




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-iimbrellar cavity." 

In the medusome of nearly all Hydrozoa tliere 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 coeleuteric cavity, which is usually called the gastric 
cavity, and from this a number of 
canals pass radially tlirough the meso- 
gloea to join a circular canal or ring- 
canal at the margin of tlie umbrella. 

A special and important feature of 
the medusome is the presence of sense- 
organs called the " ocelli " and " stato- 
FiG. 126.-Diagram of a vertical cysts," situated at the margin of the 
section through a medusome. umbrella or at the base of the 

cod, Coeleuteron ; M, mouth ; , , ■■ 

Man, manubrium ; R, radial tentacles. 

canal; r, ring or circular canal; The OCcUi may USUally be reCOg- 

T, tentacle ; v, velum. . ^ '^ ^ , / ° 

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 tliickening of tlie 
cuticle to form a lens. The exact function of tlie ocelli may not 
be fully understood, but there can be little doubt that they are 
light -perceiving organs. 

The function of the sense-organs known as statocysts, how- 
ever, has not yet been so satisfactorily determined. They were 
formerly thouglit to be auditory organs, and were called 
" otocysts," but it appears now tliat 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, tliat is, the function of the per- 
ception of the position of the body in space, and tliey are 
consequently called statocysts. In the Leptomedusae each 
statocyst consists of a small vesicle in the mesogloea at tlie 
margin of tlie 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 ELEUTHEROBLASTEA HYDRA 253 

projecting into tlie vesicle ; in other Traehomedusae, 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 ojf the 
umbrella, and resembles a short l>ut loaded tentacle. Eecent 
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 like 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 H vidyaris and H. oligactis^ 
and eight in H. xii^idis, 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 

1 H. Jung, Morph. Jahrh. viii. ISSl, p. 339. 



2 54 COELENTERATA HYDROZOA chap. 

before they themselves produce buds, but in H. 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 is probable tliat 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 Ijeen 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 classical 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. Rhcinland, xlix. 1893, pp. Vi, M, 40, 41. 

- For an account of the development and of the chitinous nienilirane see A. 
Bruier, Zdtsclir. f. toiss. Zool. lii. 1891, p. 9. 

2 Trembley, 3Ie mo ires pour scrvir a VHistoire d'un genre de Polypes d\'au douce, 
1744. 



X ELEUTIIEROBLASTEA 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- 

FlG. 127. — A series of drawings 
of Ihjih-a, showing tlie atti- 
tudes it assumes during one 
of tlie more rapid movements 
from place to place. 1, The 
Htjdra bending over to one 
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, reassuniing thu 
ei-ect posture. (After Trem- 
l.ley.) 

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 
o\'er 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 l^pward. The body now bends 
over again until tlie foot attaches itself close to the attached 
tentacles. These loosen in their turn, and so the Hydra is again 




356 COELENTER ATA H VDROZOA 



ill its normal 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 H 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.^ 

H. viridis. — Colour, grass -green. Average number of 
tentacles, eight. Tentacles shorter than the body. Embryonic 
chitinous membrane spherical and almost smooth. 

H. vidgaris, Pallas {H 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. 

H. oligactis, Pallas {H. fiiscci, 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 Frotohydra (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. 

Protoh.ydra^ was found in the oyster-beds off Osteiid, and 
resembles Microhydra in the absence of tentacles. It multiplies 
by transverse fission, but neither gemmation nor sexual repro- 
duction has been observed. 

Halercmita is a minute hydriform zooid which is also marine. 
^ G. Wagner, Quart. Journ. Micr. Sci. xlviii. 1905, p. 589. - See p. 12C. 

^ Hydra 2)allida, Beardsley, has been found to be very destructive to the fry of 
the Black-spotted Trout in Colorado, U.S. Fish. Mep. Bull. 1902, p. 158. 

■* For figures of Frotohydra see Chun, Bronn's Thier-Reich, " Coelenterata," 
1894, Bd. ii. pi. ii. 



MILLEPORINA 257 



It was found by Schaudinn ^ in the marine aquarium at Berlin in 
water from Eovigno, on the Adriatic. It reproduces by gemma- 
tion, but sexual organs have not been found. 

Another very remarkable genus usually associated with the 
Eleutheroblastea is PolyiJodium. 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 riUhenus) in the river Volga.^ 
This stolon gives rise to a number of small IfT/dra-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, Eotifers, and other minute 
organisms. The stages between these hydriform individuals and 
the parasitic stolon have not been discovered. 



Order II. Milleporina. 

Milhpoi'a was formerly united with the Stylasterina to form 
the order Hydrocoralliua ; but the increase of our knowledge of 
these Hydroid corals tends rather to emphasise than to minimise 
the distinction of Millepora 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 anatondcal and histological peculiarities it is distinct. As 
there is only one genus, Mille2)ora, 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*1 5 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. 
■^ M. Ussov, Morph. Jahrh. xii. 1887, p. 137- 
VOL. I S 



258 COELENTERATA HYDROZOA chap. 

vertical tube divided into sections by horizontal calcareous plates 
(Fig. 129, Tah). These plates are the "tabulae," and constitute 
the character upon which Millepora 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- 




FiG. 128. — A portion of a dried colony oi Millepora, showing the larger pores (gastro- 
pores) surroiin<led 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 Millepora belongs to the Hydrozoa was 
made by Agassiz ^ in 1859, but Moseley^ was the first to give 

^ This organism is usually described as a fungus (Achlya), but it is probably a 
green Alga. See J. E. Duerden, Btill. Aincr. 3Ius. Nat. Hist. xvi. 1902, p. 323. 
'^ Bihl. Univ. de Geneve, Arch, des Sciences, v. 1859, p. 80. 
=* Phil. Trans, cxlvii. 1876, p. 117. 



MILLEPORINA 259 



an ade([uate account of the general anatomy. The colony 
consists of two kinds of zooids — the short, thick gastrozooids (Fig. 
129, 0) provided with a mouth and digestive endoderm, and 
the longer and more slender mouthless dactylozooids (B) — 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 Millepora 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, t), 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- 
•cysts 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, 
0'02x0'025 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 Millepora 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," 
' S. J. Hicksou, U'llley's Zool. Jicsults, pt. ii. 1899, p. 127. 



26o 



COELENTERATA HYDROZOA 



having a greater diameter tliau that of the gastrozooid tubes, can 




^>^..J^^^ 



be recognised even in the dried skeleton. It is not known how 
frequently the sexual seasons occur, but from the rarity in the 



MILLEPORINA 26 1 



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 MiUepora 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. 

MiUepora 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 Eed 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. 

MiUepora, 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. Tliere 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 liy 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 MiUepora 
in depth, but it may be an important one. 

The generic name MiUepora has been applied to a great many 
fossils from different strata, but a critical examination of their 
structure ftiils to show any sufficient reason for including many 
of them in the trenus or even in the order. Fossils that are 



262 COELENTERATA HYDROZOA chap. 

undoubtedly 3fillepora 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 Axopora from the Eocene of France, but this genus 
differs from MiUepora 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 Axopora 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 pronovmced 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 diHer- 
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 (Coiymorpha), into which 
long filamentous processes project for the support of the zooid. 
The remarkable species Hyj)ohjtus p)eregrinv.s ^ from Wood's Holl, 
1 Quart. Journ. Micr. Sci. xlii. 1899, p. 341. 



GYMNOBLASTEA ANTHOMEDUSAE 263 



however, has no aboral processes, and appears to be only 
teniporarily attached to foreign objects by the secretion of the 
perisarc. Among the solitary Gymnoblastea several species 
reach a gigantic size. Corymorpha is 50—75 mm. in length, but 
Monocaub's 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 Tuljidaria 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. 130). 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 Ijranches of the colony and a considerable portion of the 
body-wall of each zooid in the Gymnoblastea are usually protected 
by a thin, unjointed " perisarc " of chitin secreted by the ecto- 
derm ; but this skeletal structure does not expand distally to 



COELENTERATA HYDROZOA 



ft in a a cup-like 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 
Monohrachium) or two (in Lar sahellarum), but usually the 
number is variable in each individual colony. In many cases, 
such as CordyloiJhora, 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 
{Tuhularia, Cory- 
morpha, Monocmdus), a 
distal series round the 
margin of the mouth 
which may be arranged 
in a single circlet or 
scattered irregularly on 
the hyposome, and a 
proximal series arranged 
in a single circlet some 
little distance from the 
Branchio- 
ceriantlius im2yerator 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 monomorphie, but 
there are cases in which different forms of zooid occur in the 
same colony. In Hyclr actinia, 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 




Fig. 130. — Diagrammatic sketch to show the method jj^outh. In 
of branching of Bougainvillia. gon, Gonophores ; 
Ilr, hyilrorhiza ; t.z, terminal zooid. 



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 
" blastostyles," 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 
without 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, i.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, Hyhocodov), or 
from the margin of the umbrella {Eleutheria). 

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 



side of the umbrella (Fig. 132, A). The mouth leads iuto 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 l)orne 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 
manubrial sexual organs. The 
tentacles are rudimentary in Amal- 
thea ; in Corymorplia there is only 
one tentacle ; in Perigonimus there 
are two ; and in Bougainvillia they 
are numerous; but the usual number 
is four or six. The radial canals 
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 sabellarum 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 




Fig. IZl.^MeiXwiSiof C'UiJ<i)iema, from 
the Bahamas, showing peculiar ten- 
tacular processes on the tentacles, 
the ocelli at the base of the ten- 
tacles, the swellings on the manu- 
brium that mark the position of 
the gonads, and the radial and ring- 
canals of the umbrella. (After 
Perkins.) 

are usually simple and four 



GYMNOBLASTEA ANTHOMEDUSAE 



267 



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 
dasliing 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 




A B 

Fk;. 132.— Two stages in tlie ilevelopinent of tlie Medusa of Lar sabellarnm {Willsia 
stellata). A, first stage with six canals without branches ; B, third stage with six 
canals each with two hiteral 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 medusiforin 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 

^ " Gynuioblastic Hydroids," Iluy Society, 1871, p. 359. 



268 COELENTERATA HVDROZOA 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, Dieoryne on the shells of various Molluscs, 
Tulularia has been found on a Cephalopod, and EctoplcAira (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 Sahella, of Campaniclava cleodorae 
on the living shells of the pelagic Mollusc' Cleodora cuspidata, 
and of a Gorgonia on the tubes of TtLlmlaria ixirasitica, 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 A2^hrodite that lives 
at the great depth of 2900 fathoms. *S'. sjwngicola and S. 
ahyssicola are found associated with certain deep-sea Horny 
Sponges. *S'. minoi is spread over the skin of the little rock 
perch Minous 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, Ijut of very uncertain position in tlie 
system, appears to be somewhat modified in its structure by 
its parasitic habits on the fish Seriola zonata. Corydcndrhim 

' Hincks. British Hxjdroid Zoophytes, 1868, p. 74. 
- Ann. Maci. Nat. Hist. (6) x. 1892, p. 207. 
3 Fewkes, Bull. Mas. Com2). Zool. xiii. 1887, p. 224. 



X GYMNOBLASTEA ANTHOMEDUSAE 269 

'parasitlcum is said to be a parasite living at the expense of 
Uudendriimi raconosinn. Mncstra is a little Medusa which 
attaches itself by its nianuljriuni to the Mollusc Phyllirlioe, and 
may possibly feed upon the skin or secretions of its host. 

Nearly all the species of the order are found in shallow sea 
w^ater. Stylactis vermicola and the "Challenger" specimen of Mono- 
caidus imjjerator occur at a depth of 2900 fathoms, and some 
species of the genera Eiulendrium 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 CordylopUora 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 pruvisional. 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 Boiigainvillia belonging to this family the gonophores are 
liberated in the form of free-swimming Medusae formerly known 
by the generic name HijJiJocrene. 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 lips of 
the manubrium. Bougainvillia 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 

' Hartlaub, JViss. Mceresimt. deutsch. Mccrc in Kiel N.F.I. 1S94, p. 1. 



.270 COELENTERATA HYDROZOA chap. 

Dicoryne, which forms spreading colonies on GasLeropod shells 
.and has free gonophores provided with two simple tentacles, 
while the other organs of the medusome are remarkably degenerate. 
In Garveia and Uttdendrium 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 tliat are usually 
placed in this family, of which the medusome stage only is 
known, are Lizzia (a very common British Medusa) and Rathkea. 
In Margelopds 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 perisarc 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. Hydractinia 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 Tluunnostyius, 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- 
iella, 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). 

' Carter, An7i. Mag. Nat. Hist. (4) xix. 1877, p. 44 ; (5) i. 1878, p. 298. 



GYMNOBLASTEA— ANTHOMEDUSAE 



271 



Fam. Tubulariidae. — This important and cosmopolitan family 
is represented in tlie British seas by several common species. 
The zooids of the hydrosojne of Tubularia have two circlets of 
numerous filiform tentacles. Tlie 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 hei'dit. The stem and main branches are substantial, 




Y\G.\ZZ.—CtiatdUirHsca About 11 it si/c VUlt Baldwin Spencer.-) 

and consist of a network of branching anastomosing tul)es 
supported by a thick and fenestrated chitinous perisarc. Tlie 

' Tlie aberrant genus Hypohjtus (p. 262) may belong to this family. 
- Spencer, Trans. Roy. Soc. Vkt. 1892, p. 8. 



2 72 COELENTERATA — HVDROZOA 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 
tlie coast of East Africa as far as Zanzibar, and have also been 
described from .la})aii. 

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 Glohiccjys. 

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. Syyicoryne is a 
common and widely distributed genus with numerous unbranched 
capitate tentacles irregularly distributed over a consideral^le 
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'. j^f'olifera and S. sijjhojwphora) 
the Medusae are reproduced asexually by gemmation from the 
long manubrium. A common British Anthomedusa of this family 
is Dipure/ia, 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-swinnning 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. 

Clavri contains a common British species with a creeping 
hydrorhiza frequently attached to shells, and with adelocodonic 
gonophores. Cordylo'pho'ra is the genus which has migrated into 
fresh water in certain European localities (see p. 269). It forms 
well-developed brandling 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 



OVMNOBLASTEA ANTHOMEDUSAE 273 



the family Tiaridae. Of these Tiara, a very Itrightly coloured 
jelly-tish somethiies attaining a height of 40 mm., is found on 
the British coasts, and AmpJiinema is found in considerable 
numliers at Plymouth in September. Tvrritopsis is a Medusa 
with a hydrosome stage like Dendroclava. "For Stomatoca, see 
p. 415. 

Fam. Corymorphidae. — This family contains the interesting 
British species Corymoiyha 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 Stecnstrujna, and are note- 
worthy in having only one long moniliform tentacle, opposite to 
one of the radial canals. 

The gigantic Ifonocaulus impcrator of Allman was ol)taiued 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 300 fathoms 
off the Pacific coast of North America as Branchiocerianthus 
urccolus 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, how'ever, appear 
to differ from Corymorpha in having adelocodonic gonophores. 

Fam. Hydrolaridae. — This family contains the remarkable 
genus Lir, which was discovered by Gosse attached to the margin 
of the tubes of the marine Polychaete worm Sahella. 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 l)een known for a long time by the name Willsia, luit 
their life-history has only recently been worked out by Browne."' 

' JoKrn. Coll. Sci. Tokyo, .\iii. 1900, p. 235 (witli a beautiful coloured 
illustration). 

- Proc. ZooJ. Soc. 1897, p. 818. 
VOL. I T 



74 



COELENTERATA HYDROZOA 



Fam. Monobrachiidae. — Monohrachium, found in the White 
Sea by ]\Iereschko\vsky, forms a creeping stolon on the shells of 
TcIIiiii(. The zooids of the hydrosome have only one tentacle. 

Fam. Myriothelidae. — This family contains the single genus 
Myriothda. The zooid of the hydrosome stage is solitary and is 
provided, as in the Coryuidae, 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 M. 2J^^'''yg'ici, 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 " liy Allman. In some of 
the Arctic species Frl. Bonnevie ^ has shown that they are absent. 
Each zooid of ^^. jiltrmiia is hermaphrodite. 

Fam. Pelagohydridae. — This family was constituted by 
Bendy " for the reception of Pclagohydra mirahilis, 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 
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 
scattered over the surface 
of the float. Medusae 
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,^ Pelafiohydra is not the only 
genus iu which the hydrosome floats. Three species of the genus 
Margelo2Jsis have been found that have pelagic habits, and two 

1 Zeitschr. f. wiss. Zool. Ixiii. 1898, p. 489. 
- Quart. Journ. Micr. Sci. xlvi. 1902, p. 1. =* Zool. Zcntralhl. x. 1903, p. 27. 




Ten.Tl. 



Fig. \Zi.— Pclagohydra mirabilis. Fl, The float ; 
J/, position of the nioutli ; Ten.Fl, filamentous 
tentacles of the float. (After Dendy.) 



CALVPTOBLASTEA LEPTOMEDUSAE 



75 



of them have been shown to produce luuuL'rous five-swimmiiig 
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 Felagohydra. 

The af&nities of Pclagohydra 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. Mar- 
(jelopsis 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 ef&cient pro- 
tection for the zooids when retracted. 
Xo solitary Calyptoblastea have been 
discovered. In the simpler forms the 
colony consists of a creeping hydro- 
rhiza, from which the zooids arise 
singly {Clytia johnstoni), but these 
zooids may give rise to a lateral bud 
which growls 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 
of the colony. In the branching- 
colonies the axis is frequently com- 
posed of a single tube of perisarc, 
wdiich may be lined internally by 
the ectoderm and endoderm tissues 
formed by the succession of zooids 
to the branches by gemmation. Such 
monosiphonic. 




Fig. 135. — Part of a liydrocladiuiu 
of a dried specimen of Plumu- 
luria profunda. Gt, Gono- 
tlieca ; He, the stem of the 
hy<lroclailium with joints (j) ; 
Ht. a single hydrotheca ; N, 
neniatophores. Greatly en- 
larged. (After Xnttiug.) 

that have given rise 
a stem is said to be 



COELENTERATA HYDROZOA 



III some of tlie more complicated colonies, however, tlie stem 
is composed of several tubes, wliich 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 " ftiscicled." Tlie 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 zoords are only borne by tlie terminal 
monosiphonic branches, which receive the special name " liydro- 
cladia." The gonopliores of the Calyptoblastea are usually borne 
Ijy rudimentary zooids, devoid of mouth and tentacles (the 
" blastostyles "), protected by a specially dilated cup of perisarc 
known as the " gonotheca " or " gonangium." The shape and size 
of the gonothecae vary a good deal in tlie 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 F. 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 

^ For a discussion of the origin of the polysiphonic stem in Calyptoblastea see 
^N'utting, "American Hydroids," Smithsonian InstitiUion Sj^ccial Bulletin, pt. i. 
1900, !>. 4. - Loc. cit. p. 33. 



CALVl'TODLASTKA LEl'TOMEDUSAE 277 



protect an indefinite person, an individual that may become either 
a sarcostyle ^ or a hydranth.' 

The other forms of phylactoearps are modified branches as in 
Lytocmyus, and those which are morphologically appendages to 
branches as in Cladocarpus, Ac/laojjhenojJsis, and Streptocauhis. 

The structures known as " nematophores " in the Calyptoblastea 
are the thecae 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 OpModes, Lafo'&ina, Oplorhiza, Perisiplionia, 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 
{Plumidaria, etc.), or of peculiar adhesive cells {Aglaophenia and 
some species of Plumidaria). 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 coenosarc. 

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 IMedusae 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. 

^ The term "sarcostyle" is usually apjilied to the dactylozooiil of the Calypto- 
blastea. 



2/8 COELENTEKATA HVDROZOA chap. 

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. Aeq^norea is a fairly common genus, with a 
ilattened umbrella and a very rudimentary manul")rium, 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 Thaumantias alone is 
known, and this is very similar to an Ohelia. 

Fam. Cannotidae. — The hydrosome is quite unknown. The 
Medusae are ocellate, but the radial canals, instead of being 
undivided, as in the Thaumantiidae, 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 liranches, and have therefore a remarkalile 
pinnate appearance. 

Fam. Sertulariidae. — In this family the hydrothecae are 
sessile, and arranged Ijilaterally 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 hj the trawls of fishermen and cast up on 
the sand or beach wdth other zoophytes. The popular name for 
one of the commonest species (>S'. abietinci) 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 Hydralhnanin falcata. It has slender spirally- 
twisted stems and branches, and the hydrothecae are arranged 
unilaterally. 

The genus Grammar ia, sometimes placed in a separate family, 
is distinguished from Serhdaria hj several characters. The stem 
and branches are composed of a numl)er of tubes which are con- 
siderably compressed. The genus is confined to the southern seas. 



X CALYPTOBLASTEA l,EPTOMEDUSAE 2/9 

Fam. Plumulariidae. — The liydrothecae are sessile, aud 
arranged in a single row on the stem and branches. Neniato- 
phores are always present. Gonojihores adelocodonic. This 
family is the largest and most widely distributed of all the 
families of tlie Hydrozoa. Nutting calculates that it contains 
more tlian one-fourth of all tlie Hydroids of the world. Over 
.■:^)00 species liave been descrilied, and more tlian lialf of these 
are found in tlie West Indian and Australian regions. Eepre- 
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 deptlis of over 1000 
fathoms. 

The presence of nematophores may be taken as tlie most 
cliaracteristic 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 Statoplea. 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 Flumularia 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 A. 
antennina and A. ramosa on the British coast, is distinguished 
by the terminal branches being arranged in verticils. 

The two most important genera of the Statoplea are Aglao- 
phenia and Cladocarpus. The former is represented by a few 
species in European waters, the latter is only found in American 
waters. 

Fam. Hydroceratinidae. — The colony consists of a mass of 
entwined hydrorhiza, with a skeleton in the form of anastomosing 
chitinous tubes. Hydrothecae scattered, tubular, and sessile. 
Xematophores present. Gonophores probably adelocodonic. 

This family was constituted for a remarkable hydroid, Clathro- 
zoon ivilsoni, described by AV. B. Spencer from Victoria.^ The 
zooids are sessile, and spring from more than one of the numerous 
anastomosing tubes of the steni and branches. The whole of the 
surface is studded with an enormous number of small and very 
simple dactylozooids, protected by tubular nematophores. Only 

1 Trans. Fcoy. Soc. Victoria, 1S90, p. 121. 



2 8o COELENTERATA HYDROZOA chap. 

a few specimens have hitherto been obtained, the largest being 
10 inches in height by 4 inches in width. In general appearance 
it has some resemblance to a dark coloured fan-shaped Gorgonia. 

Fam, Campanulariidae. — The hydrothecae in this family are 
pedunculate, and the gonophores adelocodonic. 

In the cosmopolitan genus Camjmiudaria the stem is mono- 
siphonic, and the hydrothecae bell-shaped. Several species of this 
genus are very common in the rock pools of our coast between tide 
marks. Halecium is characterised by the rudimentary character 
of its hydrothecae, which are incapable of receiving the zooids even 
in their maximum condition of retraction. The genus Lafoea is 
remarkable for the development of a large number of tightly packed 
gonothecae on the hydrorhiza, each of which contains a blasto- 
style, bearing a single gonophore and, in the female, a single 
ovum. This group of gonothecae was regarded as a distinct 
genus of Hydroids, and was named Cop'pinia} Lafoea dicmosa 
with gonothecae of the type described as Coppinia arcta occurs 
on the British coast. 

Perisiphonia is an interesting genus from deep w^ater off the 
Azores, Australia, and New Zealand, with a stem composed of 
many distinct tubes. 

The genus Zy gop)hy I ax, ivom 500 fathoms off the Cape A^erde, 
is of considerable interest in having a nematopliore on each side 
of the hydrotheca. According to Quelch it should be placed in 
a distinct family. 

Ophiocles has long and very active defensive zooids, protected 
by nematopliores. It is found in the Laminarian zone on the 
English coast. 

Fam. Eucopidae. — The hydrosome stage of this family is 
very similar to that of the Campanulariidae, but the gonophores 
are free-swimming Medusae of the Leptomedusan type. 

One of the best -known genera is Ohelia, of which several 
species are among the commonest Hydroids of the British 
coast. 

Clytia johnstoni is also a very common Hydroid, growing on 
red algae or leaves of the weed Zostera. It consists of a number 
of upright, simple, or slightly branched stems springing from a 
creeping hydrorhiza. When liberated the Medusae are globular 
in form, with four radial canals and four marginal tentacles, but 
' See C. C. Nutting, Proc. U.S. National Museum, xxi. 1899, y. 747. 



GRArTOLITOIDEA 28 1 



this Medusa, like many others of the order, undergoes considerable 
changes in form before it reaches the sexually mature stage. 

Phialidium temporarium is one of the commonest Medusae of 
our coast, and sometimes occurs in shoals. It seems probable that 
it is the Medusa of Clytia johnstoni} By some authors the jelly- 
tish known as Epcntliesis is also believed to be the Medusa of a 
Clytia. 

Fam. Dendrograptidae. — This family includes a number of 
fossils which iKive cL-rtaiu distinct affinities with the Calypto- 
blastea. In Dictyonema, common in the Ordovician rocks of 
Xorway, but also found in the Palaeozoic rocks of North America 
and elsewhere, tlie fossil forms fan -shaped colonies of delicate 
filaments, united by many transverse commissures, and in well- 
preserved specimens the terminal branches bear well-marked 
uniserial hydrothecae. In some species thecae of a different 
character, which have been interpreted to be gonothecae and 
nematophores respectively, are found. 

Other genera are Dendrograptvs, Thamnograptus, and several 
others from Silurian strata. 



Order V. Graptolitoidea. 

A large number of fossils, usually called Graptolites, occurring 
in Palaeozoic strata, are generally regarded as the skeletal remains 
of an ancient group of Hydrozoa. 

In the simpler forms the fossil consists of a delicate straight 
rod bearing on one side a series of small cups. It is suggested 
that the cups contained hydroid zooids, and should therefore be 
regarded as the equivalent of the hydrothecae, and that the axis 
represents the axis of the colony or of a branch of the Calypto- 
blastea. In some of the forms with two rows of cups on the 
axis {Diplograptus), however, it has been shown that the cups are 
absent from a considerable portion of one end of the axis, and 
that the axes of several radially arranged individuals are fused 
together and united to a central circular plate. Moreover, there 
is found in many specimens a series of vesicles, a little larger in 
size than the cups, attached to the plate and arranged in a circle 
at the base of the axes. These vesicles are called the gonothecae. 

The discovery of the central plate and of the so-called gono- 

' E. T. Browne, BenjniF: Museums Atcrlog, 1903, iv. p. IS. 



282 COELEXTERATA HYDROZOA chap. 

thecae suggests that tlie usual coniparison of a Graptolite with a 
Sertularian Hydroid is erroneous, and that the colony or indi- 
vidual, when alive, was a more or less radially symmetrical 
floating form, like a Medusa, of which only the distal appendages 
(possibly tentacles) are commonly preserved as fossils. 

The evidence that the Graptolites were Hydrozoa is in reality 
very sliglit, but the proof of their relationship to any other 
phylum of the animal kingdom does not exist. -^ It is therefore 
convenient to consider tliem in tliis place, and to regard them, 
provisionally, as related to the Calyptoblastea. 

The order is divided into three families. 

Fam. 1. Monoprionidae. — Cups arranged uniserially on one 
side of the axis. 

The principal genera are Monograptvs, witli the axis straight, 
curved, or helicoid, from many horizons in the Silurian strata ; 
Rastrites, with a spirally coiled axis, Silurian ; Didymograptus, 
Ordovician ; and Coenograpt^ts, Ordovician. 

Fam. 2. Diprionidae. — Cups arranged in two or four vertical 
rows on the axis. 

Dijylogrcqjtus, Ordovician and Silurian ; Climacograptus, Ordo- 
vician and Silurian ; and Phyllograptus, in which the axis and 
cups are n.rranged in such a manner that they resemble an ovate 
leaf. 

Fam. 3. Retiolitidae. — Cups arranged biserially on a reticu- 
late axis. 

Retiolites, Ordovician and Silurian ; Stomatograptus, Retio- 
graptus, and Glossograptus, Ordovician. 

Fossil Corals possibly allied to Hydrozoa. 

Among the many fossil corals that are usually classified with 
the Hydrozoa the genus Forosphaera is of interest as it is often 
supposed to be related to MiUejyora. It consists of globular 
masses about 10-20 mm. in diameter occurring in the Upper 
Cretaceous strata. In tlie centre there is usually a foreign body 
around which the coral was formed by concentric encrusting 
growth. Eunning radially from pores on the surface to the 
centre, there are numerous tubules wliich have a certain general 
resemblance to the pore-tubes of Millcpora. The monomorphic 

^ Cf. Schepotieff, Xeurs Jahrh. f. Mineral oijU, 1905. ii. pp. 79-98. 



X FOSSIL CORALS STROMATOPORIDAE 283 

character of these tubes, their very minute si;^e, the absence of 
ampullae, and the general texture of the corallum, are characters 
which separate this fossil ybyj distinctly from any recent 
Hydroid corals. Porosphaera, therefore, was probably not a 
Hydrozoon, and certainly not related to the recent Millepora. 

Closely related to Porosjjhacra apparently are other globular, 
ellipsoidal, or fusiform corals from various strata, such as LofUisia 
from the Eocene of Persia, Parheria from the Cambridge Green- 
sand, and Heterastridium from the Alpine Trias. In the last 
named there is apparently a dimorphism of the radial tubes. 

Allied to these genera, again, but occurring in the form of 
thick, concentric, calcareous lamellae, are the genera Ullij^sactinia 
and Sphaeractinia from the Upper Jurassic. 

Another important series of fossil corals is that of the family 
Stromatoporidae. These fossils are found in great Iteds of 
immense extent in many of the Palaeozoic rocks, and must have 
played an important part in the geological processes of that 
period. They consist of a series of calcareous lamellae, separated 
by considerable intervals, encrusting foreign bodies of various 
kinds. Sometimes they are fiat and plate -like, sometimes 
glolnilar or nodular in form. The lamellae are in some cases 
perforated by tabulate, vertical, or radial pores, but in many 
others these pores are absent. The zoological position of the 
Stromatoporidae is very uncertain, but there is not at present 
any very conclusive evidence that they are Hydrozoa. 

Stromatopora is common in Devonian and also occurs in 
Silurian strata. Cannop)ora from the Devonian has well-marked 
tabulate pores, and is often found associated commensally with 
another coral {Aulopora or Syringoporci). 



Order VI. Stylasterina. 

The genera included in this order resumWe Millepora in pro- 
ducing a massive calcareous skeleton, and in showing a consistent 
dimorphism of the zooids, but in many respects they exhibit 
great divergence from the characters of the Milleporina. 

The colony is arborescent in growth, the branches arising 
frequently only in one plane, forming a flabellum. The cal- 
careous skeleton is perforated to a considerable depth by the 
gastrozooids, dactvlozooids, and nutritive canals, and the gastro- 



284 COELENTERATA HVDROZOA chap. 

pores and dactylopores are not provided with tabulae except in 
the genera Pliohothtms and Sporachqwra. The character which 
gives the order its name is a conical, sometimes torch-like pro- 
jection at the base of the gastropore, called the " style," which 
carries a fold of the ectoderm and endoderm layers of the body- 
wall, and may serve to increase the absorptive surface of tlie 
digestive cavity. In some genera a style is also present in the 
dactylopore, in which case it serves as an additional surface for 
the attachment of the retractor muscles. The pores are scattered 
on all aspects of the coral in the genera SjJoradojwra, Errina, and 
Pliolothrus ; in Sijinipora and Steganopora the scattered dactylo- 
pores are situated at the extremities of tubular spines which 
project from the general surface of the coral, the gastropores 
being situated irregularly between the spines. In Phalangopora 
the pores are arranged in regular longitudinal lines, and in 
Distichojjora they are mainly in rows on the edges of the 
flattened branches, a single row of gastropores being flanked by 
a single row of dactylopores on each side. In the remaining 
genera the pores are arranged in definite cycles, which are fre- 
quently separated from one another by considerable intervals, and 
have, particularly in the dried skeleton, a certain resemblance to 
the calices of some of the Zoantharian corals. 

In Cri/j^tohelia the cycles are covered by a lid-like projection 
from the neighbouring coenenchym (Fig. 136,^1,/ 2). The gastro- 
zooids are short, and are usually provided with a variable number of 
small capitate tentacles. The dactylozooids are filiform and devoid 
of tentacles, the endoderm of their axes being solid and scalariform. 

The gonophores of the Stylasterina are situated in large oval 
or spherical cavities called the ampullae, and their presence can 
generally be detected by the dome-shaped projections they form 
on the surface of the coral. The female gonophore consists of a 
saucer-shaped pad of folded endoderm called the " trophodisc," 
which serves the purpose of nourishing the single large yolk- 
laden egg it bears ; and a thin enveloping membrane composed of 
at least two layers of cells. The egg is fertilised while it is 
still within the ampulla, and does not escape to the exterior 
until it has reached the stage of a solid ciliated larva. All the 
Stylasterina are therefore viviparous. The male gonophore has 
a very much smaller trophodisc, which is sometimes (^Alloijora) 
prolonged into a columnar process or spadix, penetrating the 



ST\"LASTERINA 285 



greater part of tlie gonad. Tlie spermatozoa escape tlirougli a 
peculiar spout-like duct which perforates the superficial wall of 
the ampulla. In some genera {Disticliopora) there are several 
male gonophores in each ampulla. 

The gonophores of the Stylasterina have been regarded as 
much altered medusiform gonophores, and this view may possibly 
prove to be correct. At present, however, the evidence of their 
derivation from Medusae is not conclusive, and it is possible 
tliat they may have liad a totally independent origin. 

Distich opora and some species of Stylaster are found in shallow 
water in the tropics, but most of the genera are confined to 




Fig. 136.— a j^ortion of a l)raiich of CijjptoheUa raviosa, showing the lids Z 1 aud Z 2 
covering the cyclosystems, the swellings produced by the ampullae in the lids am.2}^, 
ff?np^, and the dactylozooids, (fee. x 22. (After Hicksou and England. ) 

deep or very deep water, and have a wide geographical distribution. 
No species have been found hitherto within the British area. 

A few specimens of a species of Stylaster have been found in 
Tertiary deposits and in some raised beaches of more recent 
origin, but the order is not represented in the older strata. 

Fam. Stylasteridae. — All the genera at present known are 
included in this family. 

Sporadoiiora is the only genus that presents a super- 
ficial general resemblance to Millepora. It forms massive, 
])ranching white coralla, with the pores scattered irregularly on 
the surface, and, like many varieties of Millepora, not arranged 
in cyclosystems. It may, however, be distinguished at once by 
the presence of a long, brush-like style in each of the gastropores. 
Tlie ampullae are large, but are usually so deep-seated in the 
coenenchym that their presence cannot be detected from the 
surface. It was found off the Rio de la Plata in 600 fathoms 
of water by the " Challenger." 



2 86 COELENTERATA HYDROZOA chap. 

In Errina the pores are sometimes irregularly scattered, but 
in E. glahra they are arranged in rows on the sides of the 
branches, while in E. ramosa the gastropores occur at the angles 
of the branches only. The dactylopores are situated on nariform 
projections of the corallum. The ampullae are prominent. There 
are several gonophores in each ampulla of the male, but only one 
in each ampulla of the female. This genus is very widely distri- 
buted in water from 100 to 500 fathoms in depth. 

Phcdangopora differs from Errina in the absence of a style in 
the gastropore ; Mauritius. — Pliohothrus has also no style in the 
gastropore, and is found in 100-600 ftithoms of water off the 
American Atlantic shores. 

Distichoiiora is an important genus, which is found in nearly 
all the shallow seas of the tropical and semi-tropical parts of the 
world, and may even flourish in rock pools between tide marks. 
It is nearly always brightly coloured — purple, violet, pale brown, 
or rose red. The colony usually forms a small flabellum, with 
anastomosing branches, and the pores are arranged in three rows, 
a middle row of gastropores and two lateral rows of dactylopores 
on the sides of the branches. There is a long style in each 
gastropore. The ampullae are numerous and prominent, 
situated on the anterior and posterior faces of the branches. 
Each ampulla contains a single gonophore in the female colony 
and two or three gonophores in the male colony. 

Spinipora is a rare genus from off the Eio de la Plata in 
600 fathoms. The branches are covered with blunt spines. 
These spines have a short gutter-like groove at the apex, which 
leads into a dactylopore. The gastropores are provided with a 
style and are situated between the spines. 

Steganopora^ from the Djilolo Passage, in about 600 fathoms, 
is very similar to Sjnnijwi'a as regards external features, but 
differs from it in the absence of styles in the gastropores, and in 
the wide communications between the gastropores and dactylopores. 

Stylaster is the largest and most widely distributed genus 
of the family, and exhibits a consideral^le range of structure in 
the many species it contains. It is found in all the warmer seas 
of the world, living between tide marks at a few fathoms, 
and extending to depths of 600 fathoms. Many specimens, but 
especially those from very shallow water, are of a lieautiful rose 
1 S. J. Hicksou anrl H. England. Siho<ia Expcd. viii. 1904, p. 26. 



STYLASTERINA 287 



or pink colour. The corallum is arborescent and usually flaLelli- 
form. The pores are distributed in regular cyclosystems, some- 
times on one face of the corallum only, sometimes on the sides 
of the branches, and sometimes evenly distributed. There are 
styles in both gastropores and dactylopores. 

^Ulopora is difticult to separate from Stylastcr, but the species 
are usually more robust in habit, and the ampullae are not so 
prominent as they are on the more delicate branches of Stylastcr. 
It occurs at depths of 100 fathoms in the Norwegian fjords. 
A very large red species {A. nvhilis) occurs in False Bay, Cape 
of Good Hope, in 30 fathoms of water. In this locality the 
coral occurs in great submarine beds or forests, and the trawl that 
is passed over them is torn to pieces by the hard, thick branches, 
some of which are an inch or more in diameter. 

Astylns is a genus found in the southern Philippine sea in 
500 fathoms of w^ater. It is distinguished from Stylaster by the 
absence of a style in the gastropore. 

Cryptohelia is an interesting genus found both in the Atlantic 
and Pacific Oceans at depths of from 270 to about 600 fathoms. 
The cyclosystems are covered by a projecting lid or operculum 
(Fig. 136, 11,1 2). There are no styles in either the gastropores 
or the dactylopores. The ampullae are prominent, and are some- 
times situated in the lids. There are several gonophores in each 
ampulla of the female colony, and a great many in the ampulla 
of the male colony. 



CHAPTER XI 

HYDEOZOA {continued) : TRACHOMEDUSAE NARCOMEDUSAE 

SIPHONOPHOKA 

Order VII. Trachomedusae. 

The orders Trachomedusae and Narcoinedusae are probably closely 
related to one another and to some of the families of Medusae at 
present included in the order Calyptoblastea, and it seems 
probable that when the life-histories of a few more genera are 
made known the three orders will be united into one. Very 
little is known of the hydrosonie stage of the Trachomedusae, but 
Brooks ^ has shown that in Liriope, and Murbach ^ that in 
Gonionema, the fertilised ovum gives rise to a Hijdra-like form, 
and in the latter this exhibits a process of reproduction by 
gemmation before it gives rise to Medusae: Any general state- 
ment, therefore, to the effect that the development of the 
Trachomedusae is direct would be incorrect. The fact that the 
hydrosomes already known are epizoic or free-swinmiing does not 
afford a character of importance for distinction from the Lepto- 
medusae, for it is quite possible that in this order of Medusae 
the hydrosomes of many genera may be similar in form and 
habits to those of Lirioije and Gonionema. 

The free border of the umbrella of the Trachomedusae is 
entire ; that is to say, it is not lobed or fringed as it is in the 
Xarcomedusae. The sense-organs are statocysts, each consist- 
ing of a vesicle formed by a more or less complete fold of 
the surrounding wall of the margin of the umbrella, containing 
a reduced clapper-like tentacle loaded at its extremity with a 

' " Life-History of the Hydromedusae/' Mnn. Boston Sac. iii. 1885, p. 3.^9. 
2 Jouni. Morph. xi. 189.^), \). 493. 



CHAP. XI 



TRACHOMEDUSAE 



r/oii 



statolith. Tliis statocyst is innervated by the outer nerve ring. 
Tliere appears to be a very marked difference between these 
marginal sense-organs in some of the best -known examples of 
Tracliomediisae and the corresponding organs of the Leptomedusae. 
The absence of a stalk supporting the statolith and the innerva- 
tion of the otocyst by the inner instead of by the outer nerve 
ring in the Leptomedusae 
form cliaracters that may 
l)e of supplementary value, 
but cannot be regarded as 
absolutely distinguisliing 
the two orders. The stat- 
orhab of tlie Tracliomediisae 
is probably the more primi- 
tive of the two types, and 
represents a marginal ten- 
tacle of the umbrella re- 
duced in size, loaded with 
a statolith and enclosed by 
the mesogloea. Interme- 
diate stages between this 
type and an ordinary ten- 
tacle liave already been 
discovered and descrilied. 
In the type that is usually 
found in the Leptomedusae 
tlie modified tentacle is 
still further reduced, and 
all that can be recognised 
of it is the statolith 
attached to the wall of the 
stat(jcyst, but intermediate 

stages between the two types are seen in the family Olindiidae, 
in which the stalk supporting the statolitli passes gradually into 
the tissue surrounding the statolith uii the one hand and the 
vesicle wall on the other. The radial canals are four or eight in 
numljer or more numerous. They communicate at the margin 
of the umbrella with a ring canal from wliicli a iiuml)er of short 
blind tubes run in tlu^ uiiibrella-wall towards the centre of the 
Medusa (Fig. l.>7, f^'j- These " centripetal canals " are subject to 
VOL. I U 




137. — Liriope rosacea, one of the Geryo- 
iiiidae, I'rom tlie west side of North and 
Central America. Size, 15-20 mm. Colour, 
rose, cp, Centripetal canal ; gon, gonad ; M, 
mouth at tlie end of a long manubrium ; ot, 
statocyst ; ;■, tentacle ; (o, tongue. (After 
Maas.) 



290 COELENTERATA — HYDROZOA chap. 

considerable variation, but are viseful characters in distinguish- 
ing the Trachomedusae from the Leptomedusae. The tentacles 
are situated on the margin of the umbrella, and are four or eight 
in number or, in some cases, more numerous. The gonads are 
situated as in Leptomedusae on the sub-umbrella aspect of the 
radial canals. 

In Gonionema murhachii the fertilised eggs give rise to a free- 
swimming ciliated larva of an oval shape with one pole longer 
^^^jjj^j^ and narrower than the other. The 

''^'^^^^^^^^^^^^ mouth appears subsequently at the 

'^^u^^t''^, --( C^^^^^ narrower pole. The larva settles 

V^-*^^^^*^ down upon the broader pole, the 
- -^^ ' mouth appears at the free extremity, 

t and in a few days two, and later 

: [; two more, tentacles are formed (Fig. 

': 138), 

At this stage the larva may be 

\ said to be I£ydra-\ike in character, 

and as shown in Fig, 138 it feeds 

_ -^--^--^LiLL^iJi--' ^^^^ j.^^g ^^^ independent existence, 

Fii;, 138.— Hydra-hke stage in the ^ • , -, if n i • , • i 

development of Gonionema mur- From itS body-wall buds ariSe whlch 

bachii. One of the tentacles is separate from the parent and give 

carrying a worm (II) to the ^ r o 

mouth. The tentacles are shown rise to similar Hydra -like indi- 
very much contracted but they vij^^ajg, ^j^ asexual generation thus 

are capable of extending to a _ _ o _ 

length of 2 mm. Height of zooid givcs lise to ncw individuals by 

about 1mm, (After Perkins.) ggj^^^ation aS in the hydroSOmC of 

the Calyptoblastea. The origin of the Medusae from this Hydra- 
like stage has not been satisfactorily determined, but it seems 
probable that by a process of metamorphosis tlie hydriform 
persons are directly changed into the Medusae.^ 

In the development of Liriope the free -swimming larva 
develops into a hydriform person with four tentacles and an 
enormously elongated hypostome or manubrium ; and, according 
to Brooks, it undergoes a metamorphosis which directly converts 
it into a Medusa. 

There can be very little doubt that in a large number of 
Trachomedusae the development is direct, the fertilised ovum 
giving rise to a medusome without the intervention of a hydro- 
some stage. In some cases, however (Grryonid, etc.), the tentacles 

1 II. F. Perkins, rroc. Jcnd. Xat. Set. riiil. Xov. 1902, ji. 773. 



TRACHOMEDUSAE 29 1 



appear in development before there is any trace of a sub-umbrella 
cavity, and this has been interpreted to be a transitory but 
definite Hydroid stage. It may be supposed that the elimination 
of the hydrosome stage in these Coelenterates may be associated 
with tlieir adaptation to a life in the ocean far from the coast. 

During the growth of the Medusa from the younger to the 
adult stages several changes probably occur of a not unimportant 
character, and it may prove that several genera now placed in 
the same or even different families are stages in the development 
of the same species. In the development of Liriantha afi^n- 
diculata} for example, four interradial tentacles appear in the 
first stage which disappear and are replaced by four nidial 
tentacles in the second stage. 

As witli many other groups of free-swimming marine animal;; 
the Trachomedusae have a very wide geographical distribution, 
and some genera may prove to l;»e almost cosmopolitan, but the 
majority of the species appear to be characteristic of the warmer 
regions of the high seas. Sometimes they are found at the 
surface, but more usually they swim at a depth of a few fathoms 
to a hundred or more from the surface. The Pectyllidae appear 
to be confined to the bottom of the sea at great depths. 

The principal ftimilies of the Trachomedusae are : — 

Fam. Olindiidae. — This family appears to be structurally 
and in development most closely related to the Leptomedu.sae, 
and is indeed regarded by Goto^ as closely related to the Eucopidae 
in that order. They have two sets of tentacles, velar and ex- 
umbrellar ; the statocysts are numerous, two on each side of the 
exumbrellar tentacles. Eadial canals four or six. Manubrium 
well developed and quadrate, with distinct lips. There is an 
adhesive disc on each exumbrellar tentacle. 

Genera: 0/indias, Olindioidcs, Gonionema (Fig. l')9), and 
H(di calyx. 

As in other families of ]\Iedusae the distribution of tlie genera 
is very wide. Olindias midleri occurs in the Mediterranean, 
Olindioides forviosa off the coast of Japan, Gonionema murhacliii 
is found in abundance in the eel pond at Wood's HoU, United 
States of America, and Halicalyx off Florida. 

Two genera may lie referred to in this place, although their 

1 E. T. 15rowiie, Proc. Zuol. Sue. 1S9G, ].. 495. 
" Mark Annivcrstry Volume, New York, 1908, p. 1. 



292 



COELENTERATA HYDROZOA 



systematic position in relation to each other and to other 
Medusae has not been satisfactorily determined. 

Limnocodium soiverhyi is a small Medusa that was first 
discovered in the Victoria regia tanks in the Botanic Gardens, 
Regent's Park, London, in the year 1880. It has lately made 
its appearance in the Victoria regia tank in the Pare de la Bete 
d'Or at Lyons.i As it was, at the time of its discovery, the only 
fresh-water jelly-fisli known, it excited considerable interest, and 




Fid. 139. — Gonionema mnrhachii. Adult Medusa, shown inverted, and clinging to 
tlie bottom. Nat. size. (Alter Perkins. ) 

this interest was not diminished when the peculiarities of its 
structure were described by Lankester and others. It has a 
rather flattened umbrella, with entire margin and numerous 
marginal tentacles, the manubrium is long, quadrate, and has 
four distinct lips. There are four radial canals, and the male 
gonads (all the specimens discovered were of the male sex) are 
sac-like bodies on the sub-umbrellar aspect of the middle points of 
the four radial canals. In these characters the genus shows general 
affinities with the Olindiidae. The difficult question of the origin 
of the statoliths from the primary germ layers of the embryo and 
son:ie other points in the minute anatomy of the Medusa have 
1 C. Vancy et A. Coiite, Zool. Anx. xxiv. 1901, p. 533. 



XI FRESH-WATER IMEDUSAE 20 3 

suggested the view that Limnocodium is not properly placed in any 
of the other orders. Goto/ however, in a recent paper, confirms 
the view of the affinities of Limnocodium with the Olindiidae. 

The life-history of Limnocodium is not known, but a curious 
Hydroid form attached to Pontederia roots was found in the 
same tank as the Medusae, and this in all probability represents 
the hydrosome stage of its development. The Medusae are 
formed apparently by a process of transverse fission of the 
Hydroid stock " similar in some respects to that observed in the 
production of certain Acraspedote Medusae. This is quite unlike 
the asexual mode of formation of JVIedusae in any other Craspedote 
form. The structure of this hydrosome is, moreover, very 
different to that of any other Hydroid, and consequently the 
relations of the genus with the Trachomedusae cannot be re- 
garded as very close. 

Limnocodium has only been found in the somewhat artificial 
conditions of the tanks in botanical gardens, and its native locality 
is not known, but its association with the Victoria regia water-lily 
seems to indicate that its home is in tropical South America. 

Limnocnida tanganyicae is another remarkable fresh-water 
Medusa, about seven-eights of an inch in diameter, found in the 

lakes Tanganyika and Victoria 

Nyanza of Central Africa."'' It 

differs from Limnocodium in 

having a short collar-like manu-- 

brium with a large round mouth 

1/1 /\ if U (( If J// \\ two-thirds the diameter of the 

/ I j j/ I \ '\ 1 I \ umbrella, and in several other 

' II / II I 1 / V ;i^ot unimportant particulars. It 

^ , ^ , . . , produces in May and June a 

l-ic. liO. — Limnocntda tanriamjicae. , /- ni- i ^ -, ^ 

x2. (After Giintlier. ) large number ot Medusa-buds by 

gemmation on the manubrium, 
and in August and Septemljer the sexual organs are formed in 
the same situation. 

The fixed hydrosome stage, if such a stage occurs in tlie life- 
history, has not been discovered ; l)ut ]\Ir. Moore ^ believes that 

' vS. Goto, I.e. - G. H. Fowler, Qunrt. Journ. Mia: Sci. xxx. 1800, p. r)07. 

^ Limnocnida has recently been discovered by Budgett in the river Niger. See 
Browne, Ann. Nat. Hist. xvii. 1906, p. 304. 
* "The Tanganyika Problem," 190:3, p. 298. 




294 COELENTERATA HYDROZOA chap. 

the development is direct from ciliated plaiiulae to tlie Medusae. 
The occurrence of Limnocnida in Lake Tanganyika is supposed by 
the same authority to afford a strong support to the view that 
this lake represents the remnants of a sea which in Jurassic 
times spread over part of the African continent. This theory 
has, however, been adversely criticised from several sides.^ 

The character of the manubrium and the position of tlie 
sexual cells suggest that Limnocnida has affinities with tlie 
Narcomedusae or Anthomedusae, but the marginal sense-organs 
and the number and position of the tentacles, sliowing consider- 
able similarity with those of Limnocodium, justify tlie more con- 
venient plan of placing the two genera in the same family. 

Fam. Petasidae. — The genus Fetasus is a small Medusa with 
four radial canals, four gonads, four tentacles, and four free 
marginal statorliabs. A few otlier genera associated with Fetasus 
show simple characters as regards the canals and the marginal 
organs, but as very little is known of any of the genera the 
family may be regarded as provisional only. Fetasus is found 
in the Mediterranean and off the Canaries. 

Fam. Trachynemidae. — In this family there are eight radial 
canals, and the statorhabs are sunk into a marginal vesicle. 
Trachynema, characterised hj its xerj long manubrium, is a 
not uncommon Medusa of the Mediterranean and the eastern 
Atlantic Ocean. Many of the species are small, but T. funerarium 
has sometimes a disc two inches in diameter. Homoconema and 
Fentachogon have numerous very short tentacles. 

Fam. Pectyllidae. — This family contains a few deep-sea 
species with characters similar to those of the preceding family, 
but the tentacles are provided with terminal suckers. Fectyllis 
is found in the Atlantic Ocean at depths of over 1000 fathoms. 

Fam. Aglauridae. — Tlie radial canals are eight in number 
and the statorhabs are usually free. In the manubrium there is a 
rod-like projection of the inesogloea from the aboral wall of the 
gastric cavity, covered by a thin epithelium of endoderm, which 
occupies a considerable portion of the lumen of the manubrium. 
This organ may be called tl^.e tongue. Aglaura has an octagonal 
umbrella, and a manubrium which does not project beyond the 
velum. It occurs in tlie Atlantic Ocean and Mediterranean Sea. 

• Cf. Boulenger, Presidential Address to Section D of the British Association 
(Cape Town, 1905)- 



XI TRACHOMEDUSAE NARCOMEDUSAE 295 

Fam. Geryoniidae. — In tliis family tlieie are four or six 
radial canals, tlic statorhabs are sunk iu the niesogioea, and a 
tongue is present in the manubrium. Liriopc (Fig. 137) is 
sometimes as much as tliree inches in diameter. It has a very 
long manubrium, and tlie tongue sometimes projects beyond the 
mouth. There are four very long radial tentacles. It is found 
iu tlie Atlantic Ocean, tlie Mediterranean Sea, and tlie Pacific and 
Indian Oceans. Geryonia has a wider geographical distribution 
than Liriope, and is sometimes four inches in diameter. It differs 
from Lirio2)e in having six, or a multiple of six, radial canals. 
Carmarina of the Mediterranean and other seas becomes larger 
even tlian Geryonia, from which it differs in tlie arrangement of 
tlie centripetal canals. 

Liriantha appendiculata sometimes occurs on the south coast 
of England during September, October, or at other times. 

Order VIII. Narcomedusae. 

The Narcomedusae differ from the Trachomedusae in having 
the margin of the undDrella divided into a number of lobes, and 
in bearing the gonads on the sub-umbrellar wall of the gastral 
cavity instead of upon the radial canals. The tentacles are 
situated at some little distance from the margin of the umbrella 
at points on the aboral surface corresponding with the angles 
between the umbrella lobes. Between the base of the tentacle 
and the marginal angle there is a tract of modified epithelium 
called the " peronium." The manubrium is usually short, and the 
mouth leads into an expanded gastral chamber which is provided 
with lobular diverticula reaching as far as the bases of the 
tentacles. The marginal sense-organs are in the form of un- 
protected statorhabs. Very little is known concerning the life- 
history of any of the Narcomedusae. In Cunoctantha octonaria 
the peculiar ciliated larva with two tentacles ;ind a very long 
proboscis soon develops two more tentacles and creeps into the 
bell of the Anthomedusan Turritopsis, where, attached by its 
tentacles, it lives a parasitic life. Before being converted into a 
IMedusa it gives rise by gemmation to a number of similar 
individuals, all of which become, in time. Medusae. The parasitic 
stage is often regarded as the representative of the hydrosome 
stage reduced and adapted to the oceanic habit of the adult. 



296 COELENTERATA HYDROZOA chap. 

In Ciinina prohoscidea, and in some other species, a ^eiy 
remarkable method of reproduction has been described hj 
Metschnikoff, called by him " sporogony." In these cases young 
sexual cells (male or female) wander from the gonad of the 
parent into the mesogloea of the umbrella, where they develop 
parthenogenetically into ciliated morulae. These escape by the 
radial canals into the gastric cavity, and tliere form a stolon 
from which young Medusae are formed by gemmation. In C. 
proboscidea these young Medusae are like the genus Solmaris, but 
in C. Thododactyla they have the form of the parent. In some 
cases the ciliated larvae leave the parent altogether and become 
attached to a Geryonia or some other ^Medusa, where they form 
the stolon. 

This very interesting method of reproduction cannot be re- 
garded as a primitive one, and throws no light on the origin of 
the order. It might be regarded as a further stage in the 
degeneration of the hydrosome stage in its adaptation to a, 
parasitic existence. 

The Narcomedusae have a wide geographical distribution. 
Species of Aeginopsis occur in the White Sea and Bering Strait, 
but the genera are more characteristic of warmer waters. Some 
species occur in moderately deep water, and Cunarcha was found 
in 1675 fathoms off the Canaries, but they are more usually 
found at or near the surface of the sea. 

Fam. Cunanthidae. — Narcomedusae with large gastral diver- 
ticula corresponding in position with the bases of the tentacles. 
Cunina and Cunoctantha, occurring in the Mediterranean and 
in the Atlantic and Pacific Oceans, belong to this family. In 
Cunina the tentacles may be eight in number, or some multiple 
of four between eight and twenty-four. In Cunoctantha the 
number of tentacles appears to be constantly eight. 

Fam. Peganthidae.— There appear to be no gastral pouches 
in this family. The species of Pegantha are found at depths of 
about 80 fathoms in the Indian and Pacific Oceans. 

Fam. Aeginidae. — The large gastral pouches of this family 
alternate with the bases of the tentacles. Aegina occurs in the 
Atlantic and Pacific Oceans. Aeginopsis. 

Fam. Solmaridae. — In this family the gastral pouches are 
variable, suiiu'timcs corresponding with, sometimes alternating 
with, the bases of the tentacles. The circular canal is represented 



SIPHONOPHORA 297 



iu some genera by solid cords of endotlerm. Solinaris sometimes 
appears in the English Channel, but it is probably a wanderer 
from the warmer regions of the Atlantic Ocean. It is found in 
al:)undance during November on the west coast of Ireland. 



Order IX. Siphonophora. 

In this order the naturalist finds collected together a number 
of very beautiful, delicate transparent organisms to which the 
general term " jelly-fish " may be applied, although their organisa- 
tion is far more complicated and dilficult to describe than that 
of any of the ]\Iedusae. In several of the Hydrozoa the 
phenomenon of dimorphism has already been noticed. In these 
cases one set of individuals in a colony performs functions 
of stinging and catching food and another the functions of 
devouring and digesting it. In jnany of the Siphonophora 
there appears to be a colony of individuals in which the division 
of labour is carried to a much further extent than it is in the 
dimorphic Hydrozoa referred to above. Not only are there 
specialised gastrozooids and dactylozooids, but also gonozooids, 
zooids for propelling the colony through the water (" necto- 
calyces "), protective zooids (" hydrophyllia "), and in some cases 
a specialised zooid for hydrostatic functions ; the wdiole forming 
a swimming or floating polymorphic colony. But this conception 
of the construction of the Siphonophora is not the only one 
that has met with support. By some zoologists the Siphono- 
phoran body is regarded not as a colony of individuals, but as a 
single individual in which the various organs have become 
multiplied and dislocated. 

The multiplication or repetition of organs that are usually 
single in each individual is not unknown in other Hydrozoa. 
In the Medusa of the Gymnoblast Syncoryne, usually known as 
Sarsia, for example, there is sometimes a remarkable proliferation 
of the manubrium, and specimens have been found with three or 
four long manubria attached by a tubular stalk to the centre of 
the umbrella. ]\Ioreover, this complex of manubria may become 
detached from the umbrella and live for a considerable time an 
independent existence.^ 

If we regard the manul)rium of a ]\Iedusa as an orran of the 
1 C. Hartlaul), Verlumdl. Dcutsch. Zool. Gcs. 1S06, i>. 3. 



298 COELENTERATA HYDROZOA chap. 

animal's body, it iniglit be tliought obvious that the plienomeiion 
observed in the Medusae of Syncoryne is a case of a simple 
repetition of the parts of an individual ; Ijut tlie power tliat 
the group of manubria possesses of leading an independent 
existence renders its interpretation as a group of organs a 
matter of some i)iconvenience. If we can conceive tlie idea 
tliat an organ may become detached and lead an independent 
existence, there is no reason why we should not regard the 
Medusa itself of Syncoryne as an organ, and we should be 
driven to the paradoxical conclusion that, as regards several 
genera and families of Hydrozoa, we know nothing at present 
of the individuals, but only of their free-swimming organs, and 
tliat in others the individual has degenerated, although one of 
its organs remains. 

There is, however, no convincing argument to support either 
the conception that the Siphonoplioran body is a colony of 
individuals, or that it is an individual with disjointed organs. 
These two conceptions are sometimes called the " Poly-person " 
and " Poly-organ " theories respectively. The difficulty is caused 
by the impossibility of giving any satisfactory definition in the 
case of the Hydrozoa of the biological terms " organ " and 
" individual." In the higher animals, where the correlation of 
parts is far more complex and essential than it is in Coelenterata, 
a defined limit to the scope of these terms can be laid down, 
but in the lower animals the conception of what is termed an 
organ merges into that which is called an individual, and no 
definite Ijoundary line between the two exists in Nature. The 
difticulty is therefore a permanent one, and, in using the expression 
" colony " for the Siphonophoran body, it must be understood 
that it is used for convenience' sake rather than because it 
represents the only correct conception of the organisation of 
these remarkable Coelenterates. 

Kegarding the Siphonophora as polymorphic colonies, then, 
the following forms of zooids may be found. 

Nectocalyces.' — The nectocalyces are in tlie form of the 
umbrella of a medusa attached to the stolon of tlie colony by 
the aboral pole. They are provided with a velum and, usually, 
four radial canals and a circular canal. There is no manubrium, 
and the marginal tentacles and sense-organs are rudimentary or 
absent. There may be one or more nectocalyces in each colony. 



SIPHONOPIIORA 



299 



and tlioir function is, by rhytlnnic contractions, to pn)})cl the 
colony through tlie water (Fig. 142, N). 

Gastrozooids. — These are tubular or saccular zooids ])rovi(lcd 
with a nioutli and attached by their aboral extremity to tlie 
stolon (Fig. 142, (.1). In some cases the aboral region of the 
zooid is differentiated as a stomach. It is dilated and bears the 
digestive cells, the oral extremity or hypostome being narrower 
and more transparent. In some cases the mouth is a simple 
round aperture at the extremity of the hypostome, but in otliers 
it is dilated to form a trumpet-like lip. 

Dadylozooids. — In Velella and Porjnta the daetylozooids are 
similar in general cliaracters to the tentacles of many Medusae. 
They are arranged as a 



frill round the margin 
of the colony, and 
each consists of a 
simple tube of ecto- 
derm and endoderm 
terminating in a 
knobbed extremity 
richly provided with 
nematocysts. 

In many other 
Si[)honophora, how- 
ever, the daetylozooids 
are very long and 
elaborate filaments, 
which extend for a 
great distance from tlu; 
colony into the sea. 
They reach their most 
elaborate condition in 
the Calycophorac. 

The dactylozooid 
in these forms has a 
hollow axis, and the 
lumen is continuous 
with the cavity of the 
neigh])ouring gastrozooid, 




Fig. 1-11. — A small Crustacean {Rhinocolanvs) caught 
l)y a terminal filament (f.t) of a liattery of Ste2ihu)M- 
p/ii/cs. b. The pio.xinial end of the battery with the 
most powerful nematocysts ; e, elastic l>anil : ^'. 
stalk supporting the hattery on the daotylo/.oniil. 
(After Chun.) 

Arranged at regular intervals on the 
axis is a series of tentacles (" tentilla "), and each of these supports 



300 COELENTERATA HVDROZOA cHAr. 

a kidney-shaped swelling, the " cnidosac," or battery, which is some- 
times protected by a hood. Each battery contains an enormous 
number of nematocysts. In Steph,ano2)liycs, for example, there are 
about 1700 nematocysts of four different kinds in each battery. At 
the extremity of the battery there is a delicate terminal filament. 
The action of the battery in Stephanophyes is, according to Chun,^ 
a very complicated one. The terminal filament lassos the prey 
and discharges its somewhat feeble nematocysts at it (Fig. 141). 
If this kills it, the dactylozooid contracts and passes the prey 
to a gastrozooid. If the animal continues its struggles, it is 
drawn up to the distal end of the battery and receives the 
discharge of a large number of nematocysts ; and if this also 
fails to put an end to its life, a membrane covering the largest 
and most powerful nematocysts at the proximal end of the 
whole battery is ruptured, and a final broadside of stinging 
threads is shot at it. 

The larger nematocysts of these batteries in the Siphonophora 
are among the largest found in Coelenterata, being from 0"5 to 
0"1 mm. in length, and they are frequently capable of inflicting 
painful stings on the human skin. The species of Physalia, 
commonly called " Portuguese Men-of-War," have perhaps the 
worst reputation in this respect, the pain being not only intense 
but lasting a long time. 

Hydrophyllia. — In many Siphonophora a number of short, 
mouthless, non-sexual zooids occur, which appear to have no 
other function than that of shielding or protecting other and 
more vital parts of the colony. They consist of an axis of firm 
mesogloea, covered by a layer of flattened ectoderm, and they 
may be finger-shaped or triangular in form. In Acjalma and 
Praya an endoderm canal perforates the mesogloea and terminates 
in a little mouth at the free extremity. In Athoria and 
Bhodop)hysa the hydrophyllium terminates in a little nectocalyx. 

Pneumatophore. — In all the Siphonophora, with the exception 
of the Calycophorae, there is found on one side or at one 
extremity of the colony a vesicle or bladder containing a gas,^ 
which serves as a float to support the colony in the water. 

1 Ahh. Scnckcnh. Gcs. xvi. 1891, p. 44. 

- This gas is frequently called air. The gas contained in the pneumatophore of 
Physalia was analysed by Schloessing and Richard. C.R. c\xii. 1896, p. 615, and 
found to consist of C0„ 1'7 parts, l.')'!, nitrogen and argon, 83-2. 



SIPHONOPHORA 30I 



This Ijladder or pneumatopliore is probably in all cases a much 
luodified nectocalyx. It shows great variations in size and 
structure in tlie group. It is sometimes relatively very large, as 
in Physalia and Vddla, sometimes very small, as in Fhysophora. 
It is provided with an apical pore in some genera {Rhizophysa), 
or a basal pore in others (Auronectidae), but it is generally closed. 
In the many cliambered pneumatophore of the Chondrophoridae 
there are several pores. 

In many forms two distinct parts of the pneumatophore can 
be recognised — a distal region lined by chitin,^ probably repre- 
senting the sub-umbrellar cavity of the nectocalyx, and a small 
funnel-shaped region lined by an epithelium, the homology of 
which is a matter of dispute. It is believed that the gas 
is secreted by this epithelium. In the Auronectidae the region 
with secretory epithelium is relatively large and of a more 
complicated histological character. It is remarkable also that in 
this family the pore communicates, not with the chitin-lined 
region, but directly with the epithelium-lined region. 

There is no pneumatophore in the Calycophorae, but in 
this sub-order a diverticulum of an endoderm canal secretes a 
globule of oil which may serve the same hydrostatic function. 

The stolon is the common stem which supports the 
different zooids of the colony. In the Calycophorae the stolon 
is a long, delicate, and extremely contractile thread attached at 
one end to a nectocalyx, and bearing the zooids in discontinuous 
groups. These groups of zooids arranged at intervals on the 
stolon are called the "cormidia." The stolon is a tube with 
very thick walls. Its lumen is lined by a ciliated endoderm 
with circular muscular processes, and the surface is covered with 
an ectoderm, also provided with circular muscular processes. 
Between these two layers there is a relatively thick mesogloea 
showing on the outer side deep and compound folds and grooves 
supporting an elaborate system of longitudinal nmscular fibres. 
In many Physonectidae the stolon is long and filamentous, but 
not so contractile as it is in Calycophorae, but in others it is 
much reduced in length and relatively stouter. Tlie nnluction 

1 The chemical composition of the substance liere called "chitin" lias not been 
accurateh^ determined. An analysis of two specimens of Vclella liladders gave 9 "71 
and 10 '35 per cent of nitrogen, which is higher than that of chitin and nearer to 
that of mucin. 



302 COELENTERATA HYDROZOA chap. 

in length of the stolon is accompanied by a complication of 
structure, the simple tubular condition being replaced by a 
spongy complex of tubes covered by a common sheatli of 
ectoderm. In the Auronectidae the stolon is represented l)y a 
conical or hemispherical spongy mass bearing the zooids, and in 
the Ehizophysaliidae and Chondrophoridae it becomes a disc or 
ribbon -shaped pad spreading over the under side of the 
pneumatophore. 

Gonozooids. — The gonozooids are simple tubular processes 
attached to the stolon which bear the Medusae or the degenerate 
medusiform gonophores. In the Chondrophoridae the gonozooids 
possess a mouth, but in most Siphonophora they have neither 
mouth nor tentacles. In some cases, such as A^ithophysa, the 
colonies are bisexual — the male and female gonophores being 
borne by separate gonozooids — but in others (e.g. Physalia) the 
colonies appear to be unisexual. 

As a general rule the gonophores of Siphonophora do not 
escape from the parent colony as free-swimming Medusae, but an 
exception occurs in Velella, which produces a number of small 
free-swimming Medusae formerly described by Gegenbaur under 
the generic name Chrysomitra. This Medusa has a velum, a 
single tentacle, eight to sixteen radial canals, and it bears the 
gonads on the short manubrium. The Medusa of Velella has, 
in fact, the essential characters of the Anthomedusae. 

Our knowledge of the life-history of the Siphonophora is very 
incomplete, but there are indications, from scattered observa- 
tions, that in some genera, at least, it may be very complicated. 

The fertilised ovum of Velella gives rise to a planula which 
sinks to the bottom of the sea, and changes into a remarkable 
larva known as the Conaria larva. This larva was discovered 
by Woltereck ^ at depths of 600-1000 metres in great numbers. 
It is very delicate and transparent, but the endoderm is red (the 
colour so cbaracteristic of animals inhabiting deep water), and it 
may be regarded as essentially a deep-sea larva. The larva 
rises to the surface and changes into the form known as the 
Ratarula larva, which has a simple one - chaml,)ered pneu- 
matophore containing a gas, and a rudiment of the sail. 
In contrast to the Co7iaria, the llatarula is blue in colour. 
With the development of tlie zooids on the under side of this 

1 Zool. Jahrh. SiqrpL 1904, ]i. 347. 



SIPIIONOPHORA 



303 



larva (i.e. the side opposite to the pneumatophore), a definite 
oetoradial symmetry is shown, there being for some time eight 
dactylozooids and eight definite folds in the wall of the 
pnenmatophore. This oetoradial symmetry, however, is soon 
lost as the nmnber of folds in the pneumatophore and the 
number of tentacles increase. 

It is probable that in the Siphonophora, as in many other 
Coelenterata, the production of sexual cells by an individual is 
no sign that its life -history is com- 
pleted. There may possibly be two or 
more phases of life in which sexual 
maturity is reached. 

An example of a complicated life- 
history is found in the Calycophoran 
species Muggiaca Icochii. The embryo 
gives rise to a form with a single 
nectocalyx which is like a Mono'phyes, 
and this by the budding of a second A^ 
nectocalyx produces a form that has a 
remarkable resemblance to a Dii^liijcs, 
but the primary nectocalyx degenerates 
and is cast off, while the secondary one 
assumes the characters of the single 
Muggiaea nectocalyx. The stolon of 
the Muggiaca produces a series of 
cormidia, and as the sexual cells of the 

cormidia develop, a special nectocalyx fig.142.— Free-s\vimiuiugAV5«e« 
is formed at the base of each one 
of them, and the group of zooids is 
detached as an independent colony, 
formerly known as Eudoxia eschschol- 
tzii. In a similar manner the cormidia 
of Doramasia picta give rise to the 
sexual free - swimming monogastric 
forms, known by the name Ersaea picta (Fig. 142). In these 
cases it seems possible that the production of ripe sexual cells is 
confined to the Eudoxia and Ersaea stages respectively, but it is 
probable that in other species the cormidia do not break off from 
the stolon, or may escape only from the older colonies. 

The Siphonophora are essentially free - swimming pelagic 




group of Doramasia picta. 
B, B, batteries of nernatocysts 
borne by the tentilla ; D, 
dactylozooid ; G, gastrozooid ; 
//, hydroi>hyllium ; X, necto- 
calyx ; 0. oleocyst ; /, i, ter- 
iniual filament of a battery ; 
^, <, tentilla. The gonozooid 
is hidden by the gastrozooid. 
X 10. (After Chun,) 



304 COELENTERATA HVDROZOA chap. 

organisms. Some of them (Auronectidae) appear to have become 
adapted to a deep-sea habit, others are usually found in 
intermediate waters, but the majority occur with the pelagic 
plankton at or very near the surface of the open sea. Altliough 
the order may be said to be cosmopolitan in its distribution, the 
Siphonophora are only found in great numbers and variety in 
the sub-tropical and tropical zones. In the temperate and arctic 
zones they are relatively rare, but Galeolaria biloha and Fhi/so- 
phora lorealis appear to be true northern forms. The only 
British species are Magrjiaca atJantica and Cupulita sarsii. 
Velella spirans occasionally drifts from the Atlantic on to our 
western shores, and sometimes great numbers of the pneumatu- 
phores of this species may be found cast up on the beach. Diphyes 
sp., Physalia sp., and Fhysojyhora horealis are also occasionally 
brought to the British shores by the Gulf Stream. 

The Calycophorae are usually perfectly colourless and trans- 
parent, witli the exception of the oil-globule in the oleocyst, 
wliich is yellow or orange in colour. Many of the other Siphono- 
phora, however, are of a transparent, deep indigo blue colour, 
similar to that of many other components of the plankton. 

Most of the Siphonophora, although, strictly speaking, surface 
animals, are habitually submerged ; the large pneumatophores of 
Velella and Physalia, however, project above the surface, and 
these animals are therefore frequently drifted by the prevailing 
wind into large shoals, or blown ashore. At Mentone, on tlie 
Mediterranean, Velella is sometimes drifted into tlie luirl)0ur in 
countless numbers. Agassiz mentions the lines of deep blue 
Velellas drifted ashore on the coast of Florida; and a small 
species of blue Fhysalia may often be seen in long lines on the 
shore of some of the islands of the Malay Archipelago. 

The food of most of the Siphonophora consists of small 
Crustacea and other minute organisms, but some of the larger 
forms are capable of catching and devouring fish. It is stated liy 
Bigelow ^ that a big Fhysalia will capture and devour a full- 
grown Mackerel. The manner in which it feeds is described as 
follows : — " It floats on the sea, quietly waiting for some helpless 
individual to bump its head against one of the tentacles. The fish, 
on striking, is stung by the nettle-cells, and fastened probal)ly by 
them to the tentacle. Trying to run away the fish pulls on the 
^ Johns Uo})kins Univ. Circ. x. 1S91, p. 91. 



XI SIPIIONOl'HORA CALYCOPIIORAE 305 

tentacle. The tension on its peduncle thus produced acts as a 
stimulus on apparently some centre there which causes it to 
contract. The fish in this way is drawn up so that it touches 
the sticky mouths of the squirming siphons [i.e. gastrozooids]. 
As soon as the mouths, covered as they are with a gluey sub- 
stance and provided with nettle-cells, touch the fish they stick 
fast, a few at first, and gradually more. The mouths open, and 
their lips are spread out over the fish until they touch, so that 
by the time he is dead the fish is enclosed in a tight bag com- 
posed of the lips of a dozen or more siphon mouths. Here the 
fish is digested. As it begins to disintegrate partially digested 
fragments are taken into the stomachs of the attached siphons 
(gastrozooids). When they have become gorged they detach 
themselves from the remains of the fish, the process of digestion 
is completed in the stomachs, and tiio nutrient fluid is dis- 
tributed. ..." 

In consequence of the very unsatisfactory state of our know- 
ledge of the life-history of the Siphonophora the classification of 
the order is a matter of unusual difficulty. 

Sub-Order I. Calycophorae. 

The character which distinguishes this sub-order is the absence 
of a pneumatophore. 

The colony usually consists of a long, slender, contractile stolon, 
provided at one end with one, two, or several nectocalyces. Upon 
the stolon are arranged several groups (" cormidia ") of poly- 
morphic zooids. 

The nectocalyces have a well -developed velum, four radial 
canals, and a muscular umbrella- wall. A special peculiarity of 
the nectocalyx of this sub-order is a diverticulum (oleocyst) fi'om 
one of the radial canals, containing a coloured globule of oil. 
The function of this oil-globule is prol^ably similar to that of 
the pneumatophore, and assists the muscular efforts of the necto- 
calyces in keeping the colony afloat. One of the nectocalyces of 
each colony exhibits on one side a deep ectodermic fold, which is 
frequently converted into a pit. At the Ijottom of this pit is 
attached the end of the stolon, the whole of which with its 
numerous cormidia can be withdrawn into the shelter of the 
pit when danger threatens. The cormidia consist of at least four 

VOL. I X 



306 COELENTERATA — HYDROZOA chap. 

kinds of zooids : a gastrozooid with a trumpet-shaped mouth armed 
with nematocysts, a long dactylozooid provided with a series of 
tentilla, and a rudimentary gonozooid bearing numbers of male 
or female medusiform gonophores. These three kinds of zooids 
are partially covered and protected by a bent shield -shaped 
phyllozooid or hydrophyllium. 

Each of the cormidia is unisexual, but the colony as a whole 
is usually hermaphrodite, the male and female cormidia regularly 
alternating, or the male cormidia being arranged on the necto- 
calycine half and the female cormidia on the opposite half of the 
stolon. 

The families of tlie Calycophorae are : — 

Fam. 1. Monophyidae.— In this family there is a single 
conical or mitre -shaped nectocalyx. The cormidia become de- 
tached as free-swimming Uiidoxia or Ersaea forms. 

Sub -Fam. 1. Sphaeronectixae. — The primary nectocalyx 
persists throughout life — Mojwjjhyes and Sphaeronectes. 

Sub -Fam. 2. Cymbonectinae. — The primary nectocalyx is 
thrown off, and is replaced by a secondary and permanent necto- 
calyx — Cynilonectcs, Muggiaea, and Doramasia. 

Fam. 2. Diphyidae, — The primary mitre-shaped nectocalyx 
is thrown off and replaced by two secondary rounded, prismatic, 
or pyramidal, heteromorphic nectocalyces. 

This family contains several sub-families, which are arranged in 
two groups : the Diphyidae Oppositae, in which the two secondary 
bells are opposite one another, and do not exhibit pronounced 
ridges ; and the Diphyidae Superpositae, in which one of the 
two secondary nectocalyces is situated in front of the other, and 
each nectocalyx is provided externally with very definite and 
often wing -like ridges. In all the Diphyidae Oppositae the 
cormidia remain attached, whereas in most of the Dipliyidae 
Superpositae they become free-swimming, as in the Monophyidae. 

The sub-families of the Diphyidae Oppositae are : — 

Sub-Fam. 1. Amphica1!Y0N1NAE. — One of the two secondary 
nectocalyces becomes flattened above to form a shield, and at the 
same time its sub-umbrellar cavity is atrophied, and its radial 
canals reduced. Mitroj^hgcs, Atlantic Ocean. 

Sub-Fam. 2. Prayinae. — The colony exliibits a pair of large, 
obtuse nectocalyces, with a relatively small sub-umbreUar cavity. 
Praya, Mediterranean and Atlantic. 



XI SIPHONOPHORA CALYCOPHORAE PHYSOPHORAE 307 

Sub-Fam. 3. Des:\iophyinae. — The colony bears a large number 
of reserve or tertiary nectocalyces arranged in two rows. Des~ 
■itiophycs, Indian Ocean. 

Sub-Fam. 4. Stephanophyinae. — There are four nectocalyces 
arranged in a horizontal plane. Each one of the cormidia bears 
a nectocalyx, which is periodically replaced. This sub-family is 
constituted for Stephanophyes superha from the Canary Islands. 
It attains a length of 25 cm., and is probably the largest and 
most beautiful of all the Calycophoridae.^ 

The group Diphyidae Superpositae contains the following : — 

Svib-Fam. 1. Galeolapinae. — (laleularia. 

Sub-Fam. 2. Diphyopsinae. — Dipltyes. 

Sub-Fam. 3. Abylinae. — Ahyla. 

These sub-families differ from one another in the character 
and shape of the nectocalyces and in other characters. They 
have a world-wide distribution, Biphyes and Galcolaria extending 
north into the Arctic Seas. Bi-phyes is British. 

Fam. 3. Polyphyidae. — The nectocalyces are numerous, and 
superposed in two rows. The cormidia remain attached. 

The family contains the genera Polyphyes and Hijyj'ojJodius, 
both probably cosmopolitan in warm waters. 

Sub-Order II. Physophorae. 

In this sub -order the primary nectocalyx gives rise to a 
definite pneumatophore. There are four families. 

Fam. 1. Physonectidae. — In this, the largest family of the 
sub-order, there is a monothalamic pneumatophore supporting a 
stolon, which in some forms is of great length, but in others is 
reduced to a stump or pad, on which there are usually found 
several nectocalyces, hydrophyllia, gastrozooids, gonozooids, and 
tentilla. 

The principal sub-families are : — 

AgalminaE. — With a long stolon, bearing at the upper end 
(i.e. the end next to the pneumatophore) two rows of nectocalyces. 
The other zooids are arranged in cormidia on the stolon, each 
covered by a hydrophyllium. Dactylozooids with tentilla. 
Agcdma and Ciqndita, Mediterranean Sea. 

Apolemixae. — Similar to the above, but without tentilla. 

^ C. Chun, Ahli. Scack. Xat. Ges. Frankfurt, xvi. 1S91. 



308 COELENTERATA HYDROZOA chap. 

Apolemia — this genus attains a length of two or three metres. 
Mediterranean Sea. Dicymlm, Indian Ocean. 

Physophorinae. — The pneumatophore larger in proportion 
than it is in the preceding families. The stolon is sliort, and 
bears rows of nectocalyces at the upper end. The gastro- 
zooids, dactylozooids, and gonozooids are arranged in verticils 
on the lower expanded part of the stolon. Hydrophyllia 
absent. Phijsophora, cosmopolitan in the areas of warm sea 
water. 

Fam. 2. Auronectidae. — The pneumatophore is large. The 
stolon is reduced to a spongy mass of tissue on the under side of 
the pneumatophore, and this bears numerous cormidia arranged 
in a helicoid spiral. Projecting from the base of the pneumato- 
phore there is a peculiar organ called the " aurophore," provided 
with an apical pore. This organ has been described as a specially 
modified nectocalyx, l)ut it is probably a specialised develop- 
ment of the epithelium-lined portion of the pneumatophore of 
other Physophorae. The Auronectidae . are found only at con- 
siderable depths, 300 to 1-400 fathoms, and are probably specially 
adapted to that habitat. Rliodalia, Stejohalia, Atlantic Ocean. 

Fam. 3. Rhizophysaliidae. — The pneumatophore is large, or 
very large, in this family. The zooids are arranged in horizontal 
rows on the under side of the pneumatophore {Physalia), or in a 
helicoid spiral on a short stolon (Fj^ilmlia). There are no necto- 
calyces nor hydrophyllia. 

The genus Physalia is the notorious " Portuguese Man-of-War." 
The pneumatophore is a large bladder -like vesicle, sometimes 
attaining a length of 12 cm. One species described by Haeckel 
under the generic name Caravella has a pneumatophore 30 cm. 
and more in length, and dactylozooids attaining a length of 20 
metres. It is a curious fact that only the male colonies of 
Physalia are known, and it is suggested that the female may 
have quite a different form.^ Upihulia has a much smaller bladder 
than Physalia. Both genera have a cosmopolitan distribution 
at the surface of the warm seas. 

Fam. 4. Chondrophoridae. — This family stands quite by 
itself in the sub-order Physophorae, and is placed in a separate 
division of the sub-order by Chun, who gives it the name Tracheo- 
PHYSA. The essential distinguishing characters of the family are 

^ Brooks and Coiiklin, Johns Hopkins Univ. Circ. x. 1S91, No. 88. 



XI SIPIIONOPHORA PHYSOPHORAE 309 

the large poly thalamic pneumutophore udcI the single large central 
gastrozooid. 

The colony is disc-shaped, and has a superficial resenihlance 
to a ]VIedusa. On the upper side is the flattened pneiimatophore, 
covered by a fold of tissue continuous with that at the edge of 
the disc. In Vddla a vertical triangular sail or crest rises from 
the upper side, but this is absent in Forpita. 

The mouth of the gastrozooid opens into a large digestive 
ca\'ity, and between this and the under surface of the pneumato- 
phore there is a glandular spongy tissue called the liver. The 
liver extends over the whole of the under side of the pneumato- 
phore, and sends processes round the edge of the disc into the 
tissues of its upper surface. Intimately associated with the 
liver, and penetrating its interstices, is an organ which appears 
to be entirely composed of nematocysts, derived from the ectoderm, 
and called the central organ. At the margin of the disc there 
is a fringe of simple digitiform dactylozooids, and between the 
dactylozooids and the centrally placed gastrozooid are numerous 
gonozooids. Each of the gonozooids is provided with a distinct 
mouth, and bears the gonophores, which escape before the ripen- 
ing of the gonads as the free-swimming Medusae called Chryso- 
mitra. The pneumatophore consists of a number of annular 
chambers arranged in a concentric manner round the central 
original chamber formed from a modified zooid. These annular 
chambers are in communication with one another, and have each 
two pores (pneumatopyles) opening above to the exterior. The 
most remarkable feature, however, of the system is a series of 
fine branching tubes (" tracheae "), which pass from the annular 
chambers of the pneumatophore downwards into the hepatic 
mass and ramify there. 

There are two well-known genera : Velella with a sail, and 
Forpita without a sail. They are both found at the surface of 
the warmer regions of the great oceans and in the Mediterranean. 
Velella sometimes drifts on to British coasts from the Atlantic. 

The genus Discalia has a much more simple octoradial 
structure. It was found at depths of 2G00 and 2750 fathoms 
in the Pacific Ocean. 



CHAPTER XII 

COELENTEEATA (COXTIXUED) : SCYPHOZOA = SCYPHO:\rEDUSAE 

CLASS II. SCYPHOZOA = SCYPHOMEDUSAE 

The Scyphozoa are jelly-fishes, usually found floating at or near 
the surface of the sea. A few forms (Stauromedusae) are attached 
to rocks and weeds by a stalked prolongation of the aboral region 
of the umbrella. With this exception, however, they are all, in 
the adult stage, of the Medusa type of structure, having a bell- 
shaped or discoid umbrella, from the under surface of which 
depends a manubrium bearing the mouth or (in Ehizostomata) 
the numerous mouths. 

Although many of the species do not exceed an inch or a few 
inches in diameter, others attain a very great size, and it is among 
the Scyphozoa that we find the largest individual zooids of the 
Coelenterata. Some Discophora have a disc three or four feet in 
diameter, and one specimen obtained by the Antarctic Expedition 
of 1898-1900 weighed 90 Ibs.^ The common jelly-fish, ^?(rc/ia, 
of our coasts belongs to a species tliat appears to be very variable 
in general characters as well as in size. Specimens obtained by 
the " Siboga " in the Malay Archipelago ranged from 6 to 64 cm. 
in diameter. The colour is very variable, shades of green, blue, 
brown, and purple being conspicuous in many species ; but a pale 
milky-blue tint is perhaps the most prevalent, the tissues being 
generally less transparent than they are in the Medusae of the 
Hydrozoa. The colour of the Cubomedusae is usually yellow or 
brown, but Charyhdea xaymacana is colourless and transparent. 
The deep-sea species, particularly the Periphyllidae, have usually 
an opaque brown or dark red colour. The surface -swimming 

^ C. E. Borchgrevink, "First on the Antarctic Continent," 1901, p. 227. 
310 



CHAP. XII SCVPHOZOA — SCYPHOMEDUSAE 311 

forms, such as the common Aurelia, Pelagia, Cyanaea, are usually 
of a uniform pale milky-blue or green colour. Generally the 
colour is uniformly distributed, but sometimes the surface of the 
umbrella is freckled with irregular brown or yellow patches, as in 
Dactylometra and many others. There is frequently a special colour 
in the statorhabs which renders them conspicuous in the living 
jelly-fish, and the lips, or parts of the lips, of the manubrium 
have usually a different colour or tone to that of the umbrella. 

There is no reason to believe that the general colour of any 
of these jelly-fishes has either a protective or a warning signifi- 
cance. Nearly all the larger species, whether blue, green, or 
brown in colour, can be easily seen from a considerable distance, 
and the colours are not sufficiently bright or alarming to support 
the belief that they can serve the purpose of warning either fish 
or birds of the presence of a dangerous stinging animal. It is 
possi1)le, however, that the brighter spots of colour that are often 
noticed on the tips of the tentacles and on the lips may act as 
a lure or bait in attracting smallfish and Crustacea. 

Some of the Scyphozoa are phosphorescent, but it is a singular 
fact that there are very few recorded observations concerning the 
phosphorescence or the absence of it in most of the species. The 
pale blue light of Pelagia noctiluca or P. 2^hospho7^a can be re- 
cognised from the deck of a ship in the open ocean, and they 
are often the most brilliant and conspicuous of the phosphorescent 
organisms. 

The food of the Scyphozoa varies a good deal. Charyhdea 
and Periphylla, and probalily many others with large mouths, 
will captvire and ingest relatively large fish and Crustacea ; but 
Chrysaora isosceles'^ apparently makes no attempt to capture 
either Copepoda or small fish, but preys voraciously upon Antho- 
medusae, Leptomedusae, Siphonophora, Ctenophora, and pelagic 
worms. Very little is known about the food of the Khizostomata, 
but the small size of the mouths of these forms suggests that their 
food must also be of minute size. The frequent association of 
small fish with the larger jelly-fish is a matter of some interest 
that requires further investigation. In the North Sea young 
whiting are the constant guests of Cyanaea capillata.' Over a 

1 M. J. Delap, Irish Naturalist, x. 1901, p. 27. 

- E. W. L. Holt, Ee2wrt on the Sea and Inland Fisheries of Ireland for 1902, 
pt. ii. 1903, p. xvi. 



3 I 2 COELENTERATA SCVPHOZOA chap. 

hundred yoiuig horse-mackerel (Caranx tracJncrus) may be found 
sheltering under the umbrella of Ilhizostoma pulmo. As tlie animal 
floats through the water the little fishes hover round the margin, 
but on the slightest alarm dart into the sub-umbrella cavity, 
and ultimately seek shelter in the sub-genital pits> 

Two species of fish accompany the American Medusa Dactylo- 
metra lactea, one a Clupeoid, the other the young of the 
Butter-fish {Stromatcus triacanthus). According to Agassiz and 
Mayer ^ this is not an ordinary case of mutualism, as the fish 
will tear off and devour fragments of the tentacles and fringe of 
the Medusa, whilst the Medusa will in its turn occasionally 
capture and devour one of the fish. 

A great many of the Scyphozoa, particularly the larger kinds, 
have the reputation of being able to sting the human skin, and 
in consequence the name Acalephae ^ was formerly used to 
designate the order. Of the British species Aurelia aurita is 
almost harmless, and so is tlie rarer Bhizostoma pulmo ; but the 
nematocysts on the tentacles of Cyanaea, Chrysaura, and Pelagia 
can inflict stings on the more delicate parts of the skin which 
are very painful for several hours, although the pain has been 
undoubtedly greatly exaggerated in many popular works. 

The soft structure of the Medusae does not favour their pre- 
servation in the rocks, but the impressions left by several genera, 
all belonging apparently to the Ehizostomata, have been found 
in Cambrian, Liassic, and Cretaceous deposits. 

There is reason to believe that many Scyphozoa exhibit a con- 
siderable range of variation in the symmetry of the most important 
organs of the body. Very little information is, however, at 
hand concerning the variation of any species except AvreJia 
aurita, which has been the subject of several investigations. 
Browne * has found that in a local race of this species about 
20 per cent exhibit variations from the normal in tlie number of 
the statorhabs, and about 2 per cent in the number of gastric 
pouches. 

The Scyphozoa are not usually regarded as of any commercial 
or other value, but in China and Japan two species of Ehizosto- 
mata {Rhopilema esculenta and H. verrucosa) are used as food, 

' F. W. Gamble. See E. T. Browne, Proc. I!u)j. Irish Acad. 1900, p. 735. 

- JJiiIl. 3Ius. Gump. Zool. xxxii. 1, 1S9S. 

■• dKa\rj<pT] = -a, nettle. ■* Biouietrika, i. 1901, p. 90. 



GENERAL CHARACTERS 



The jelly-fish is preserved with a mixture of iiluin aud salt or 
between the steamed leaves of a kind of oak. To prepare the 
preserved food for the table it is soaked in water, cut into small 
pieces, and flavoured. It is also stated that these Medusae are 
used by fishermen as bait for file-fish and sea-bream.-^ 

In general structure tlie Scyphozoa occupy an intermediate 
position between the Hydrozoa and the Anthozoa. The very 
striking resemblance of the body-form to the Medusa of the 
Hydrozoa, and the discovery of a fixed hydriform stage in the 
life-history of some species, led the older zoologists to the con- 
clusion that tliey should be included in the class Hydrozoa. 
Eecently the finer details of development have been invoked to 
support tlie view tliat they are Antliozoa specially adapted for a 
free-swimming existence, but the evidence for this does not 
appear to us to be conclusive. 

They differ from the Hydrozoa and resemble tlie Antliozoa in 
the character that the sexual cells are matured in the endoderm, 
and escape to the exterior by way of the coelenteric cavity, 
and not directly to the exterior by the rupture of the ectoderm 
as in all Hydrozoa. They differ, on the other hand, from the 
Anthozoa in the absence of a stomodaeum and of mesenteries. 

The view that the Scyphozoa are Anthozoa is based on the 
belief that the manubrium of the former is lined by ectoderm, 
and is homologous with the stomodaeum of the latter ; and that 
the folds of mesogloea betw^een the gastric pouches are homologous 
with the septa.- 

The Scyphozoa, notwithstanding their general resemblance to 
the Medusae of Hydrozoa, can be readily distinguished from them 
l)y several important characters. The absence of a velum in all 
of them (except the Cubomedusae) is an important and con- 
spicuous cliaracter which gave to the class the name of Acraspeda. 
The velum of the Cubomedusae can, however, be distinguished 
from that of the Craspedote Medusae (i.e. the Medusae of the 
Hydrozoa) by the fact that it contains endodermal canals. 

Sense-organs are present in all Scyphozoa except some of the 
Stauromedusae, and they are in the form of statorhabs (tentaculo- 
cysts), bearing statoliths at the extremity, and in many species, 

' K. Kisliinouye. Zool. Jahrh. Sijst. xii. 1899, p. 206. 

- For the discussion of tliis relationship the reader is referred to Goette, Zcitschr. 
tciss. Zool. Ixiii. 1897, p. 360, and Carlgren, Zool. Anz. xxii. 1899, p. 31. 



314 COELENTERATA SCVPHOZOA chap. 

at the Ijase or between the base and the extremity, one or more 
eyes. These organs differ from the statorhabs of the Hydrozoa 
in having, usually, a cavity in the axial endoderm ; but as they 
are undoubtedly specially modified marginal tentacles, they are 
strictly homologous in the two classes. In nearly all the 
Scyphozoa these organs are protected by a hood or fold formed 
from the free margin of the umbrella, and this character, 
although not of great morphological importance, serves to distin- 
guish the common species from the Craspedote Medusae. It was 
owing to this character that Forbes gave the name Steganoph- 
THALMATA, or " covered-eyed Medusae," to the class. 

Another character of some importance is the presence in the 
coelenteric cavity of all Scyphozoa of clusters or rows of delicate 
filaments called the " phacellae." These filaments are covered with 
a glandular epithelium, and are usually provided with numerous 
nematocysts. They have a considerable resemblance to the 
acontia of certain Anthozoa, and are probably mainly digestive 
in function. These three characters, in addition to the very 
important character of the position and method of discharge of 
the sexual cells already referred to, justify the separation of the 
Scyphozoa from the Medusae of the Hydrozoa as a distinct 
class of Coelenterata. 

The umbrella of the Scyphozoa varies a good deal in shape. 
It is usually flattened and disc -like (Discophora), but it may 
be almost globular {Atorella), conical (some species of Perij)hylla), 
or cubical (Cubomedusae). It is divided into an aboral and a 
marginal region by a circular groove in the Coronata. The 
margin may be almost entire, marked only by notches where the 
statorhabs occur, or deeply lobed as in the Coronata and many 
Discophora. Marginal tentacles are present in all but the 
Ehizostomata, and may Ije few in number, four in Cliaryhcha, 
eight in Ulviaris (Fig. 143), or very numerous in Aurelia and 
many others. The tentacles may be short {Aurelia), or very 
long as in Chrysaora isosceles, in which they extend for a length 
of twenty yards from the disc. 

The manubrium of the Scyphozoa is usually quadrangular in 
section, and in those forms in which the shape is modified in the 
adult Medusa the quadrangular shape can be recognised in the 
earlier stages of development. The four angles of the manubrium 
are of importance in descriptive anatomy, as the planes drawn 



MANUBRIUM 



15 



throui;h the angles to tlie centre of tlie manubrium are calleil 
" perradial," while those bisecting the perradial planes and passing 
therefore through the middle line of the flat sides of the manu- 
brium are called " interradial." 

The free extremity of the manubrium in many Scyphozoa is 
provided with four triangular perradial lips, which may be 
simple or may liecome bifurcated or branched, and have fre- 
quently very elal^orate 

crenate edges beset *y -f 

witli batteries of nem- 
atocysts. In Pelagia 
and Chrysaora and 
other genera these lips 
hang down from the 
manubrium as long, 
ribbon - like, folded 
bands, and according 
to the size of the 
specimen may be a 
foot or more in length, 
or twice the diameter 
of the disc. 

In the Ehizosto- 
mata a peculiar modi- 
fication of structure 
takes place in the 
fusion of the free 
edges of the lips to 
form a suture perforated by a row of small apertures, so 
tliat the lips have the appearance of long cylindrical rods or 
tubes attached to the manubrium, and then frequently called 
the " oral arms." The oral arms may be further provided with 
tentacles of varying size and importance. In many Ehizo- 
stomata branched or knobbed processes project from the outer 
side of the upper part of the oral arms. These are called the 
" epaulettes." 

The lumen of the manulnium leads into a large cavity in the 
disc, which is usually called tlie gastric cavity, and this is ex- 
tended into four or more interradial or perradial gastric pouches. 
The number of those pouches is usually four, but in this, as in 




Fig. 143. — Ulmaris jirototyims. g. Gonad ; /, interradial 
canal ; M, the fringed lip of the manubrium ; 1\ per- 
radial canal ; .S^, marginal sense-organ ; t, tentacle. 
X 1. (After Haeckel.) 



3l6 COELENTERATA SCYPHOZOA chap. 

other features of their radial symmetry, the jelly-fish frequently 
exhibit duplication or irregular variation of the radii.^ 

The gastric pouches may extend to the margin of the disc, 
where they are united to form a large ring sinus, or they may be 
in communication at the periphery by only a very narrow x^assage 
(Cubomedusae). In the Discophora the gastric pouches, however, 
do not extend more than half-way to the margin, and they may 
be connected with the marginal ring-canal by a series of branched 
interradial canals. Between the gastric pouches in these forms 
branched perradial canals pass from tlie gastric cavity to the 
marginal ring canal, and the system of canals is completed by 
unbranched " adradial " canals passing between the perradials and 
interradials from the sides of the gastric pouches to the ring- 
canal (Fig. 143). 

In the Discophora there are four shallow interradial pits 
or pouches lined by ectoderm on the under side of the umbrella- 
wall. As these pits correspond with the position of the gonads 
in the gastric pouches they are frequently called the " sub-genital 
pits." In the Stauromedusae and Cubomedusae they are con- 
tinued through the interradial gastric septa to the aboral side of 
.the disc, and they are generally known in these cases by the name 
" interradial funnels." The functions and homologies of these 
ectodermic pits and funnels are still uncertain. 

The Scyphozoa are usually dioecious, but Chrysaora and 
Lincrgcs are sometimes hermaphrodite. The female Medusae 
can usually be distinguished from the male by the darker or 
brighter colour of the gonads, whicli are band -shaped, horse- 
shoe-shaped, or circular organs, situated on the endoderm of 
the interradial gastric pouches. They are, when nearly ripe, 
conspicuous and brightly coloured organs, and in nearly all 
species can be clearly seen through the transparent or semi- 
transparent tissues of the disc. The reproductive cells are dis- 
charged into the gastric cavity and escape by the mouth. The 
eggs are probably fertilised in the water, and may be retained 
in special pouches on the lips of the manubrium until the 
segmentation is completed.^ Asexual reproduction does not 
occur in the free -swimming or adult stage of any Scyphozoa. 
In some cases (probably exceptional) the development is direct. 
In Pelagia, for example, it is known that the fertilised egg gives 

i See note ^ p. 312. ^ g. A. Minchiii. Proc. Zool. Sue. 1S89, p. 583. 



DEVELOPMENT 3 I 7 



rise to a free-swiimniiig ]\Iedusa similar in all essential features 
to the parent. 

In many species, however, the planula larva sinks to the 
bottom of the sea, develops tentacles, and becomes attached by 
its aboral extremity to a rock or weed, forming a sedentary 
asexual stage of development with a superficial resemblance to 
a Hydra. This stage is the " Scyphistoma," and notwithstanding 
its simple external features it is already in all essential 
anatomical characters a Scyphozoon. 

The Scyphistoma may remain as such for some time, during 
which it reproduces by budding, and in some localities it may 
be found in great numbers on seaweeds and stones.^ 

In the course of time, however, the Scyphistoma exhibits a 
ring-like constriction of the body just below the crown of tentacles, 
and as this deepens the general features of a Scyphomedusa are 
developed in the free part above the constriction. In time this 
free part escapes as a small free-swimming jelly-fish, called an 
''■ Ephyra," while the attached part remains to repeat the process. 
In many species the first constriction is 
followed by a second immediately below it, ' I^C^ 

then a third, a fourth, and so on, until ,^' 

the Scyphistoma is transformed into a long , 

series of narrow discs, each one acquiring, Sifr \ : ..j\^ 
as it grows, the Ephyra characters. Such -; 

a stage has been compared in form to a pile '"^^t- 

of saucers, and is known as the " Strobila." ^|^ 

The Ephyra differs from the adult in ifflr 

many respects. The disc is thin and flat, fig. 144. —The perisarc 
the manubrium short, the margin of the ^'ngkoi^ faM^i^{y\ 
umbrella deeply grooved, while the state- ramifying in the skeleton 
rhabs are mom>ted on bifid lobes whioh t^^^,^Ti!:, 

project outwards from the margin. The in a maceratea specimen. 

strobilisation of the Scyphistoma is a pro- 
cess of reproduction by transverse fission, and in some cases this 
is supplemented by gemmation, the Scyphistoma giving rise to 
a number of buds which become detached from the parent and 
subse(|uently undergo the process of strobilisation. 

The Scyphistoma of Navsitlioe presents us with the most 

1 For good illustrations of tliis see Sir J. Dalycll, " Rare and Remarkable 
Animals of Scotland," vol. i. 1847, pU. 13, 14, 18, 19, 20. 



31' 



COELENTERATA SCYPHOZOA 



remarkable example of this mode of reproduction (Fig. 144), as it 
forms an elaborate branching colony in the substance of certain 
species of sponges. The ectoderm secretes a chitinous perisarc, 
similar to that of the hydrosome stage of many of the Hydrozoa, 
and consequently Stephanoscyphus (Spongicola), as this Scyphi- 
stoma was called, was formerly placed among the Gymnoblastea. 
It is remarkable that, although the Scyphozoan characters of 
Spongicola were proved by Schulze ^ in 1877, a similar Scyphi- 
stoma stage has not been discovered in any other genus. 



Order I. Cubomedusae. 

Scyphozoa provided with four perradial statorhabs, each of 
which bears a statolith and one or several eyes. There are four 
interradial tentacles or groups of tentacles. The stomach is a 

large cavity bearing four 
tufts of phacellae (Fig. 145, 
Plh), situated interradially. 
There are four flattened 
perradial gastric pouches 
in the wall of the umbrella 
which communicate with 
the stomach by the gastric 
ostia {Go). These pouches 
are separated from one 
another by four interradial 
septa ; and the long leaf- 
like gonads are attached 
by one edge to each side 
of the septa. In many 
respects the Cubomedusae 

Fig. 145.— Vertical section in the interradial plane appear tO be of simple 

of Tripedalia cystophora. Go, Gastric ostia ; structure, but the remark- 
Man, manubrium; Pli, group of phacellae; ,, ,.^, . . „ , 

T, tentacles in four groups of three ; tenU ^016 clltterentiation Ot tllC 

perradial sense-organs; ]; velum. (After eVCS and the OCCUrreUCB of 
Conant. ) '' 

a velum (p. 313) suggest 




that the order is a highly specialised offshoot from a primitive stock, 
Fam. 1. Charybdeidae. — Cubomedusae with four interradial 
tentacles. 



1 Archil-. Jlikr. Anat. xiii. 187: 



CUBOMEDUSAE 319 



Charyldea appears to liave a very wide geographical 
distribution. Some of the species are usually found in deep 
water and come to the surface only occasionally, Lut otliers 
(('. j:aymacana) are only found at the surface of shallow 
water near tlie shore. Tlie genus can be easily recognised by 
tlie four-sided prismatic shape of the bell and the oral flattened 
expansion of the base of the tentacles. The bell varies from 
2-6 cm. in length (or height) in C. marsujnalis, but a giant 
form, C. grandis,^ has recently been discovered off Paumotu 
Island which is as much as 23 cm. in heiglit. Tlie colour is 
usually yellow or brown, Ijut C. (jrandis is white and C. xaymacana 
perfectly transparent, 

" Charyldea is a strong and active swimmer, and presents a 
very beautiful appearance in its movements through tlie water ; 
the quick, vigorous pulsations contrasting sharply witji the 
sluggish contractions seen in most Scyphomedusae." It appears 
to be a voracious feeder. " Some of the specimens taken con- 
tained in the stomach small fish, so disproportionately large in 
comparison with the stomach that they lay coiled up, head over- 
lapping tail." - 

Very little is known of the development, but it is possible 
that Tamoya punctata, which lacks gonads, phacellae, and canals 
in the velum, may be a young form of a species of Charyhdca. 

Fam. 2. Chirodropidae. — Cubomedusae with four interradial 
groups of tentacles. 

This family is represented by the genera Chirodropus from 
the Atlantic and Chii'opsalmus from the Indian Ocean and the 
coast of North Carolina. 

Fam. 3. Tripedaliidae. — Cubomedusae with four interradial 
groups of three tentacles. 

The single genus and species Tripedalia cystopliora has only 
been found in shallow water off the coast of Jamaica. Specimens 
of this species were kept for some time by Conant in an 
aquarium, and produced a number of free -swimming planulae 
which settled on the glass, and quickly developed into small 
hydras with a mouth and foiu- tentacles. The further develop- 
ment of this sedentary stage is unfortunately not known. 

^ Agassiz and Jlayer, Mem. Mas. Comp. Zool. xxvi. 3, 1902, p. 153. 
' F. S. Conant, Mem. Johns Hopkins Univ. iv. 1, 1898. 



3 20 COELENTERATA SCYPHOZOA 



Order II. Stauromedusae. 

This order contains several genera pro^'ided with an alioral 
stalk which usually terminates in a sucker, bj means of which 
the animal is temporarily fixed to some foreign oljject. There 
can be little doubt that this sedentary habit is recently acquired, 
and the wide range of the characteristic features of the order 
may be accounted for as a series of adaptations to the change 
from a free- swimming to a sedentary habit. 

It is difficult to give in a few words the characters of the 
order, but the Stauromedusae differ from other Scypliozoa in the 
absence or profound modification in structure and function of the 
statorhabs. They are absent in Lucernaria and the Depastridae, 
and very varialjle in number in Halidystus. 

The statorhab of Halidystus terminates in a spherical knob, 
which is succeeded by a large annular pad or collar bearing a 
number of glandular cells which secrete a sticky fluid. At the 
base of the organ there is a rudimentary ocellus. The number 
is very variable, and sometimes they are abnormal in character, 
being " crowned with tentacles." There can be little doubt that 
the principal function of these organs is not sensory but adhesive, 
and hence they have received the names " colletocystophores " and 
" marginal anchors," but they are undoubtetUy homologous with 
the statorhabs of other Scyphozoa. 

The tentacles are short and numerous, and are frequently 
mounted in groups on the summit of digitate outgrowths from 
the margin of the umbrella. They are capitate, except in 
Tessera, the terminal swelling containing a battery of nemato- 
cysts. 

Very little is known concerning the life-history and develop- 
ment of the Stauromedusae. 

Fam. 1. Lucernariidae. — ]VIarginal lobes digitate, bearing the 
capitate tentacles in groups. Halidystus auricula is a common 
form on the shores of the Channel Islands, at Plymouth, and 
other localities on the British coast. It may be recognised by 
the prominent statorhabs situated in the bays between the 
digitate lobes of the margin of the umbrella. Each of the 
marginal lobes bears from 15 to 20 capitate tentacles. It is 
from 2 to o cm. in length. The genus occurs in shallow water 



xii STAUROMEDUSAE CORONATA 32 I 

off the coasts of Europe and North America, extending south into 
the Antarctic region. 

Ldcernaria differs from Haliclystus in the absence of stato- 
rhabs. It lias the same habit as Haliclystus, and is often found 
associated with it. L. campanulata is British. 

HalicyatJius is similar in external features to Haliclystus, but 
differs from it in certain important characters of the coelenteric 
cavities. It is found off the coasts of Norway, Greenland, and 
the Atlantic side of North America. 

In Capria, from the Mediterranean, the tentacles are replaced 
by a denticulated membrane bearing nematocysts. 

The rare genus Tessera, from the Antarctic Ocean, differs from 
all the other Stauromedusae in having no stalk and in having 
only a few relatively long non-capitate tentacles. If Tessera is 
really an adult form it should be placed in a separate family, 
but, notwitlistanding the presence of gonads, it may prove to be 
but a free-swimming stage in the history of a normally stalked 
genus. 

Fam. 2. Depastridae. — The margin of the umbrella is pro- 
vided with eight shallow lobes bearing one or more rows of 
tentacles. Statorhabs absent. 

Dejmstrum cyathijorme occurs in shallow water at Plymouth, 
Port Erin, and in other localities on the coasts of Britain and 
Norway. The tentacles are arranged in several rows on the 
margin of the umbrella. In Deimstrella from the Canaries there 
is only one row of marginal tentacles. 

Fam. 3. Stenoscyphidae/ — Stauromedusae with simple un- 
divided umbrella margin. The eight principal tentacles are 
converted into adhesive anchors. Secondary tentacles arranged 
in eight adradial groups. Stenoscyphus inahai, 25 cm., Japan. 

Order III. Coronata." 

The external surface of the umbrella is divided into tw^o 
regions, an aboral region and a marginal region, by a well- 
marked circular groove (the coronal groove). The alioral region 
is usually smooth and undivided, but it is an elongated dome, 

^ Kishinouye, Journ. Coll. Sri. Tokijo, xvii. 7, 1902. 

^ A discussion of tlie classification of this order occurs in Vanlioiren, " Acrasped. 
Med. d. deutschen Tiefsee Expedition," iii. 1902, p. 49. 

VOL. I Y 



322 COELENTERATA SCYPHOZOA chap. 

thimble- or cone-shaped, in marked contrast to the flattened 
umbrella of the Discophora. The margin is divided into a 
number of triangular or rounded lobes, and these are continued 
as far as the coronal groove as distinct areas delimited by sliallow 
grooves on the surface of the umbrella. The tentacles arise from 
the grooves between the marginal areas, and are provided with 
expanded bases called the pedalia. The manubrium may be 
short or moderately long, but it is never provided with long 
lips. 

Fam. 1. Periphyllidae.^ — Coronata with four or six stato- 
rhabs. 

In Pericolpa (Kerguelen) there are only four tentacles and four 
statorhabs. In Ferii^hylla, a remarkable deep-sea genus from 
700 to 2000 fathoms in all seas, but occasionally found at the 
surface, there are twelve tentacles and four statorhabs. The 
specimens from deep water have a characteristic dark red-brown 
or violet-brown colour. They are usually small Medusae, but 
the umbrella of P. regina is over 21 cm. in diameter. AtoreUa 
has six tentacles and six statorhabs. 

Fam. 2. Ephyropsidae. — Coronata with eight or more than 
eight statorhabs. 

Ncmsithoe punctata is a small, transparent jelly-fish, not 
exceeding 10 mm. in diameter, of world-wide distribution. Its 
Scyphistoma stage is described on p. 317. N. ruhra, a species of 
a reddish colour found at a considerable depth in the South 
Atlantic and Indian Oceans, is probably an abysmal form. 
Palcphyra differs from Nausithoe in having elongated instead 
of rounded gonads. Linantha and Linuche differ from the others 
in having subdivided marginal lobes. 

Fam. 3. AtoUidae. — Atolla is a deep-sea jelly-fish of very 
wide geographical distribution. It is characterised by the 
multiplication of the marginal appendages, but the number 
is very irregular. There may be double or quadruple the usual 
number of marginal lobes, or an indefinite number. There may 
be sixteen to thirty -two statorhabs, and the number of 
tentacles is quite irregular. Some of the species attain a 
considerable size, the diameter of the umbrella of A. gigantea 
being 150 mm., of A. valdiriae sometimes 130 mm., and of 
A. hairdi 110 mm. 

^ The Peiiiihyllidae constitute Haeckel's order Peromedusae. 



DISCOPHORA 323 



Order IV. Discophora. 

This order contains not only by far the greater number of 
the species of Scyphozoa, but those of the largest size, and all 
those that are familiar to the seaside visitor and the mariner 
under the general term jelly-fish. 

They may be distinguished from the other Scyphozoa by 
several well-marked characters. The umbrella is flattened and 
disc-shaped or slightly domed, but not divided by a coronary 
groove. The perradial angles of the mouth are prolonged into 
long lips, which may remain free (Semaeostomata) or fuse to 
form an elaborate proboscis (Ehizostomata). 



Sub-Order I. Semaeostomata. 

In this sub-order the mouth is a large aperture leading into 
the cavity of the manubrium, and is guarded by four long grooved 
and often tuberculated lips. The margin of the umbrella is 
provided with long tentacles. 

Fam. 1. Pelagiidae, — Semaeostomata with wide gastric 
pouches, which are not united by a marginal ring sinus. Pelagia, 
which forms the type of this family, has eight long marginal 
tentacles. It develops directly from the egg, the fixed Scyphi- 
stoma stage being eliminated.^ It is probably in consecpience 
of this peculiarity of its development and independence of a 
shore for fixation that Pelagia has become a common and wide- 
spread inhabitant of the high seas. In the Atlantic and Indian 
Oceans P. lylwsjjhora. occurs in swarms or in long narrow lines 
many miles in length. It is remarkable for its power of emitting 
phosphorescent light. In the Atlantic it extends from 50° N. 
to 40° S., but is rare or absent from the colder regions. P.peria 
is found occasionally on the west coast of Ireland. Chrysaora 
differs from Pelagia in the larger number of tentacles. There 
are, in all, 24 tentacles and 8 statorhabs, separated by 32 
lobes of the margin of the umbrella. C. isosceles is occasionally 
found off the British coast. It passes through a typical 
Scyphistoma stage in development. Dactylomctra, a very 

' A stage in development before the formation of the sub-umbrellar cavity, but 
subsequent to the formation of the first tentacles, is regarded as homologous with 
the Scyphistoma stage of other Scyphozoa. 



324 COELENTERATA — SCVPHOZOA chap. 

commou jelly-fish of the American Atlantic shores, differs from 
Chrysaora in having sixteen additional hut small tentacles 
arranged in pairs at the sides of the statorhabs. 

Fam. 2. Cyanaeidae. — Semaeostomata with eiglit radial and 
eiglit adradial pouclies, which give off ramifying canals to the 
margin of the umbrella ; but these canals are not united by a 
ring-canal. The tentacles are arranged in bundles on the margin 
of the deeply lobed umbrella. 

The yellow Cyanaea capillata and the blue C. lamarcki are 
commonly found on the British coasts. 

Fam. 3. Ulmaridae. — The gastric pouches are relatively 
small, and communicate with a marginal ring-canal by branching 
perradial and interradial canals and unbranched adradial canals. 

In Ulmaris prototypus (Fig. 143, p. 315) there are only eight 
long adradial tentacles, and the lips of the manubrium are rela- 
tively short. It is found in the South Atlantic. 

Aurelia is a well-known and cosmopolitan genus, which may 
be recognised by the eight shallow lobes of the umbrella-margin 
beset with a fringe of numerous small tentacles. 



Sub-Order II. Rhizostomata. 

In this sub-order the lips are very much exaggerated in size, 
and are fused together by their margin in such a manner that the 
moutli of the animal is reduced to a number of small apertures 
situated along the lines of suture. Tentacles are absent on the 
margin of the umljrella. This sub-order contains some of the 
largest known jelly-fishes, and exliibits a considerable range of 
structure. Tlie families are arranged by Maas^ in three groups. 

Group I. Akcadomyaria. — Musculature of the disc arranged 
in feather-like arcades. Oral arms pinnate. 

Fam. Oassiopeidae. — There are no epaulettes on tlie arms. 
Labial tentacles present. Cassio'peix. is common in the Indo-Pacific 
seas, and extends into the Eed Sea. It includes a great many 
species varying in size from 4 to about 12 cm. in diameter. 

Group II. Radiomyama. — Musculature arranged in radial 
tracts. Oral arms bifid. 

Fam. Cepheidae. — The genera included in this family differ 

1 "Siborja" Exped. Mon. xi. 1903. 



DISCOPHORA 325 



from the Cassiopeidae in the characters of the group. Ccjjhea is 
found in the Indo-Pacific Oceans and Eed Sea. Cotylorhiza is 
common in the Mediterranean Sea and extends into the Atlantic 
Ocean. 

Group III. CvcLOMYArJA. — The group contains the majority 
of the Ehizostomata. Musculature arranged in circular bands 
round the disc. Oral arms primarily trifid, but becoming in 
some cases very comy)licated. The principal families are : — 

Fam. Rhizostomatidae. — With well-marked epaulettes, and 
sixteen radial canals passing to the margin of the umbrella. 

Rhizostoma pulmo ( = Pilcma octojyus), a widely distributed 
species, is often found floating at the surface off the western 
coasts of Scotland and Ireland, and sometimes drifts up the 
English Channel into the German Ocean in the autumn. The 
umbrella is about tw^o feet in diameter, and the combined length 
of the umbrella and arms is four feet. The colour varies consider- 
ably, but that of a specimen obtained off Valencia in 1895 was 
described as follows : " The colour of the umbrella was pale green, 
with a deep reddish margin. Arms bright blue." ^ 

The family includes Siomolojjhus, of the Pacific and Atlantic 
coasts of America, in which the oral arms are united at the base, 
and Rhoijilema, the edible Medusa of Japan and China. 

Fam. Lychnorhizidae. — Here there are only eight radial 
canals reaching as far as the margin of the umbrella, and eight 
terminating in the ring-canal. There are no epaulettes, and the 
oral tentacles are often very long. The family includes Lychno- 
rhiza from the coast of Brazil, Cramhione from the ]\Ialay 
Archipelago, and Cramhessa from the Atlantic shores of France 
and Spain and from Brazil and Australia. The last-named 
genus has been found in brackish water at the mouth of the 
Loire. 

In the families Leptobrachiidae and Catostylidae there are 
eight radial canals reailiing the margin of tlie \imbrella, and 
between them a network of canals with many openings into the 
ring-canal. In a few of the Leptobrachiidae the intermediate 
canal-network has only eight openings into the ring-canal, as in 
the Lychnorhizidae. 

1 Proc. Hoy. Irish Acad. 3rd ser. v. 1900, p. 7-35. 



CHAPTER XIII 

COELENTEKATA {CONTINUED) : ANTHOZOA = ACTINOZOA GENEEAL 

CHARACTERS ALCYONARIA 

CLASS III. ANTHOZOA = ACTINOZOA 

Among the familiar objects included in this class are the Sea- 
anemones, the Stony Corals (Madrepores), the Flexible Corals, the 
Precious Coral, and the Sea-pens. "With the exception of a few- 
species of Sea-anemone, Anthozoa are not commonly found on 
British sea-shores ; but in those parts of the tropical world wdiere 
coral reefs occur, the shore at low tide is carpeted with various 
forms of this class, and the sands and beaches are almost entirely 
composed of their broken-down skeletons. 

The majority of the Anthozoa are colonial in habit, a large 
number of individuals, or zooids as they are called, being organi- 
cally connected together by a network of nutritive canals, and 
forming a communal gelatinous or stony matrix for their pro- 
tection and support. Whilst the individuals are usually small 
or minute, the colonial masses they form are frequently large. 
Single colonies of the stony corals form blocks of stone whicli 
are sometimes live feet in diameter, and reach a height of two 
or three feet from the ground. From the tree or slirub-like form 
assumed by many of the colonies they were formerly included in 
a class Zoophyta or animal-plants. 

But whether the individual polyps are large or small, whether 
they form colonies in the adult condition or remain independent, 
they exhibit certain characters in common which distinguish 
them not only from the other Coelenterata, but from all other 
animals. When an individual zooid is examined in the living 
and fully expanded condition, it is seen to possess a cylindrical 

326 



ANTHOZOA = ACTINOZOA 



1^7 



body, attached at one end (the aboral end) to the common colonial 
matrix or to some foreign object. At the opposite or free ex- 
tremity it is provided with a mouth surrounded by a crown of 
tentacles. In these respects, however, they resemble in a general 
way some of the Hydrozoa. It is only when the internal 
anatomy is examined that we find the characters which are 
absolutely diagnostic of the group. 

In the Hydrozoa the mouth leads directly into the coelenteric 
cavity ; in the Anthozoa, however, the mouth leads into a short 
tube or throat, called the " stomodaeum," which opens into the 
coelenteric cavity. Moreover, this tube is connected with the 
body -wall, and is supported by 
a series of fleshy vertical 
bands called the mesenteries 
(Fig. 146). The mesenteries 
not only support the stomo- 
daeum, but extend some dis- 
tance below it. Where the 
mesenteries are free from the 
stomodaeum their edges are 
thickened to form the im- 
portant digestive organs 
known as the mesenteric 
filaments (w/). It is in the 
possession of a stomodaeum, 
mesenteries, and mesenteric 
filaments that the Anthozoa 
differ from all the other Coelen- 
terata. There is one character that the Anthozoa share with 
the Scyphozoa, and that is, that the gonads or sexual cells (G) 
are derived from the endoderm. They are discharged first into 
the coelenteric cavity, and then by way of the mouth to the 
exterior. In the Anthozoa the gonads are situated on the 
mesenteries. 

Nearly all the Anthozoa are sedentary in habit. They begin 
life as ciliated free-swimming larvae, and then, in a few hours 
or days, they become attached to some rock or shell at the 
bottom and immediately (if colonial) start the process of budding, 
which gives rise to the colonies of the adult stage. Many of 
the Sea-anemones, however, move considerable distances by gliding 




Fig. 146. — Diagram of a vertical section 
through an Anthozoan zooiil. B, Body- 
wall ; G, gonads ; M, mesentery ; mf, 
mesenteric filament ; St, stomodaeum ; 
T, tentacle. 



3 28 COELENTERATA ANTHOZOA chap. 

over the rocks or seaweeds, others habitually burrow in the 
sand {Edtcardsia, Cerianthus), and one family (the Minyadidae) 
are supported by a gas bladder, and float at the surface 
of the sea. The Sea-pens, too, although usually partly buried 
in the sand or mud, are capable of shifting their position 
by alternate distension and contraction of the stalk.-^ The 
Anthozoa are exclusively marine. With the exception of a few 
Sea-anemones that are found in brackish or almost fresh water in 
river estuaries, they only occur in salt sea water. The presence 
of a considerable admixture of fresh water, such as we find at 
the mouths of rivers, seems to interfere very materially with the 
development and growth of all the reef-forming Corals, as will 
be noticed again in the chapter on coral reefs. A few genera 
descend into the greatest depths of the ocean, but the home of 
the Anthozoa is pre-eminently the shallow seas, and they are 
usually found in great abundance in depths of 0-40 fathoms 
from the shores of the Arctic and Antarctic lands to the 
equatorial belt. 

The only Anthozoa of any commercial importance are the 
Precious Corals belonging to the Alcyonarian family Coralliidae. 
The hard pink axis of these corals has been used extensively 
from remote times in the manufacture of jewellery and orna- 
ments. Until quite recently the only considerable and 
systematic fishery for the Precious Corals was carried on in the 
Mediterranean Sea, and this practically supplied the markets 
of the world. In more recent times, however, an im])ortant 
industry in corals has been developed in Japan. In 1901 the 
value of the coral obtained on the coasts of Japan was over 
£50,000, the greater part of which was exported to Italy, a 
smaller part to China, and a fraction only retained for home 
consumption. The history of the coral fishery in Japan is of 
considerable interest. Coral was occasionally taken off the coast 
of Tsukinada in early times. But in the time of the Daimyos 
the collection and sale of coral was prohibited, for fear, it is said, 
that the Daimyo of Tosa might be compelled to present such 
precious treasure to the Shogun. After tlie Meiji reform, how- 
ever (1868), the industry revived, new grounds were discovered, 
improved methods employed, and a large export trade developed. 

There is evidence, however, in the art of Japan, of another 

1 Cf. Darwin, Voyage of the Ecn(jle, chap. v. 



ALCYONARIA 329 



coral fishery in ancient times, of which the history is lost. Coral 
was imported into Japan at least two hundred years ago, and 
used largely in the manufacture of those exc^uisite pieces of 
handicraft for which that country is so justly famous. On many 
of the carved " Netsukes " and other ornaments, however, the 
coral branches are represented as the booty of dark-skinned, 
curly -headed fishermen, " kurombo," and never of Japanese 
fishermen. The coral used in this art -work can hardly he 
distinguished from Mediterranean coral, and there are some 
grounds for believing that Japan imported coral from the far 
West in very early times. But this does not account for the 
" kurombo." The only coast-dwelling people of the type that is 
so clearly carved on these ornaments within the area of the 
Pacific Ocean at the present time are the Melanesians and 
Papuans, and the suggestion occurs that a coral fishery existed 
at one time in the Southern Pacific, wliich has since been lost.^ 

The class Anthozoa is divided into two sub -classes: — I. 

AlC YON ARIA ; II. ZOANTHAEIA. 

In the Alcyonaria the fully developed zooids have always 
eight tentacles and eight mesenteries. In the Zoantharia the 
number of tentacles and the number of mesenteries in the fully 
developed zooids may be six, twelve, twenty-four, or an indefinite 
number, but individuals with eight mesenteries and only eight 
tentacles are not known to occur. 

Sub-Class I. Alcyonaria. 

This sub-class includes a large number of genera living in 
shallow sea-water and a few genera that extend down into deep 
water. With a few doubtful exceptions (Protoalcyonacea) they 
all form colonies composed of a large number of zooids. These 
zooids may be connected together by basal plates or a network 
of basal strands (stolons), or by stolons with additional connect- 
ing bars {Clavnlaria viridis, Syringoj)ora) or by plates {Ihibi^iorci). 
In the majority of the genera the individual zooids are for the 
greater part of their length, from the base upwards, united 
together to form a continuous spongy, colonial mass, which 
determines the shape of the colony as a whole. 

In this last - named group of genera there may be dis- 

^ Hickson, A'. Akad. Wet. Amsterdam, 1905. 



330 COELENTERATA ANTHOZOA chap. 

tinguished the free distal portions of the zooids bearing the 
mouths and tentacles (the "anthocodiae ") from the common colonial 
mass perforated by the coelenteric cavities of the individual 
zooids. The coelenteric cavities are separated by a considerable 
amount of a substance called the " mesogloea," usually gelatinous 
in consistency but chemically more closely related to mucin than 
to gelatin, which is traversed by endodermal canals, rods of 
endoderm cells and a number of free amoeboid cells. In this 
substance, moreover, there are found in nearly all cases numerous 
spicules of carbonate of lime formed by the "scleroblasts " (spicule- 
forming cells) which have wandered from the superficial ectoderm 
of the common colonial mass. This common colonial mesogloea 
with its spicules, endoderm cells, and superficial covering of 
ectoderm is called the " coenenchym." The form assumed by the 
colonies is very varied. In some species of Clavidaria they 
form encrusting plates following the irregularity of the rock or 
stones on which they grow, in Alcyonium they construct lobed 
masses of irregular form, in Sarcoj)liytwni they are usually shaped 
like a mushroom, in Jitncella they are long whip-like rods, in 
most of the Gorgonacea they are branched in all directions like 
shrubs or in one plane to form fan- shaped growths, and in many 
of the Pennatulacea they assume that graceful feather form which 
gives the order its name. 

The consistency and texture of the colonies also varies con- 
siderably. In some cases where the spicules are few or very 
small, the substance of the colony is soft to the touch, and 
frequently slimy at the surface, in other cases the great number 
of the spicules makes the colony hard but brittle, whilst in a 
few genera {Sderophytum, Jleliopora) the colony is so hard that 
it can only be broken by the hand with difficulty. In some 
genera {Spongodes and the Muriceidae) projecting spicules cause 
the surface to be rough or thorny, and in the Primnoidae the 
zooids and the surface of the general coenenchym are protected 
by a series of overlapping scales or plates. 

In all the Alcyonaria the nematocysts are very minute, and 
although they can undoubtedly paralyse minute organisms they 
are unable to penetrate the human skin. None of the Alcyonaria 
have been described as stinging -corals except the Pennatulid 
Vinjularia rumphii. 

Zooids. — The fully formed zooids of the Alcyonaria exhibit 



xiii ALCYONARIA ZOOIDS 33 I 

a remarkable uniformity of structure. They have eiglit inter- 
mesenteric tentacles containing a cavity continuous with the 
coelenteron. Each of these tentacles bears at least two rows of 
simple pinnules, and they ar6 therefore said to be " pinnate " 
tentacles. In some species of Xenia the tentacles may have 
three or four rows of pinnules, which give them a much more 
feathery appearance than is usually the case. In the great 
majority of species a single row of from eight to fourteen pinnules 
is found disposed laterally on each side of the tentacle. The 
mouth is usually small and slit-like with a slight rounded gape 
at tlie ventral extremity. The stomodaeum is usually very 
short, but in Xcnia and in the autozooids of some Pennatulids 
it is relatively much longer. It is not known how far the 
stomodaeum is of importance in the digestion of the food. In 
Xcnia ^ it has probably some importance, as shown by its unusual 
length and the numerous large goblet cells (mucus cells) which it 
exhibits, associated with the fact that the mesenteric filaments are 
relatively very small. In Alcyonium and other Alcyonaria gland 
cells also occur in the stomodaeum, and it is probable that they 
secrete a fluid capable of digesting to some extent tlie food as it 
passes through. The most important part of the digestion, 
however, is performed by the six " ventral " mesenteric filaments. 
Attention has already been drawn to the fact (p. 330) that 
two regions of the zooids of the colonial Alcyonaria can be 
recognised. At the oral end there is a region, which in the 
fully expanded condition consists of a crown of eight tentacles 
surrounding the mouth, and a body-w^all free from its immediate 
neighbours. This region is called the " anthocodia." The 
antliocodia is continuous with a region which forms a part of 
tlie common colonial mass. Some genera seem to have very 
little power of contracting the tentacles or of witlidrawing the 
anthocodiae. The zooids of Stereosoma, of Xenia, of UmleUida, 
and of a few other genera may be described as non-retractile. In 
many cases, however, the tentacles can be considerably con- 
tracted, bent over the mouth, and withdrawn into the shelter of 
the subjacent body-wall. In such a condition the surface of 
the colony exhibits a number of tubular, conical, or convex pro- 
tuberances, called " verrucae," and the colony is said to be 
partially retractile. In many genera, however, the whole of the 

» J. H. Ash worth, Proc. Roy. Soc. Lxiii. 1898, \\ 443. 



332 



COFXENTERATA ANTHOZOA 



anthocodiae can be withdrawn below the general surface of the 
coenenchym, so that the position of the zooids in the colony is 
indicated only by star-like holes, or simple key-hole slits in the 
superficial coenenchym. Such colonies are said to be completely 
retractile (Fig. 147). 

It is often very difficult to determine whether a particular 
species is or is not completely retractile, unless observations can 
be made upon the living colony ; and there are many instances 
of confusion in the work of systematists due to a species being 
described as partially retractile in one instance, and completely 
retractile in another. The complete retraction of the anthocodiae 




Fig. 147. — Diagram of a vertical section of a portion of a lobe oi Alcyonium to show the 
mode of retraction of the anthocodiae. 1, Anthocodia of a zooid fully e.xpanded ; 
2, in the first stage of retraction ; 3, in the second stage ; 4, in the third stage, 
leaving a shallow prominence or " verruca " on the surface ; 5, final stage, the 
verruca flattened down and the coenenchym closed, can. Canal system ; d.m.f, 
dorsal mesenteric filament of a zooiil ; si, siphonoglyph. 



may be effected very slowly, and after continuous irritation only. 
If the colony is killed too quickly, the anthocodiae remain in a 
state of partial retraction. An example of this may be found 
in the common British Alcyoniuyii digitatum. Specimens of this 
species whicli are put into a bucket of sea water and allowed to 
roll about with the movements of a small boat in a rough sea, 
undergo complete retraction ; but if the same specimens be 
allowed to expand in the aquarium, and then plunged into spirit, 
or allowed to dry in the sun, they will die in a condition of 
partial retraction. 

The phenomenon of dimorphism occurs in some Alcyonaria. 
A certain number of the zooids of a colony are arrested in their 
development, and are known as the " siphonozooids." They may 
be distinguished from the fully formed zooids, which, in these 



XIII ALCVONARIA MESENTERIC FILAMENTS 333 

cases, are called the " autozooids," by the absence of tentacles, by 
tlie absence of the six ventral and lateral mesenteric filaments, and 
l)y the incomplete development of the muscles on the mesenteries, 
and of the mesenteries themselves. They are, moreover, frequently 
distinguished by the greater development and extent of the 
ciliated groove or siplionoglyph on the ventral side of the 
stomodaeum. 

It is often difficult to distinguish between true siplionozooids 
and young autozooids, and consequently dimorphism has been 
attributed to some genera in which it almost certainly does not 
occur. Simple dimorphism undoubtedly occurs in the genera 
Heteroxenia, SarcojJhytum, Anthomastus, Lohophytum, Acroijhytum, 
and Paragorgia. It has also been said to occur in Corallium 
(Moseley and Kishinouye), Melitodes (Ridley), and some species 
of Dasygorgiidae. 

The Pennatulacea are trimorphic. The main shaft of these 
colonies is the much modified first formed or axial zooid, adapted 
for the support of all the other zooids. It usually exhibits 
no moutli, no tentacles, and only four of the original eight 
mesenteries. It has no mesenteric filaments and no stomo- 
daeum, and bears no sexual cells. The other zooids of the colony 
are similar in structure to the autozooids and siplionozooids of 
the dimorphic Alcyonaria. 

There are eight mesenteric filaments in all Alcyonarian 
zooids. They have the appearance of thickenings of the free 
edges of the mesenteries. Two of them, called the " dorsal " 
mesenteric filaments, are straight when the anthocodia is ex- 
panded, and extend from the edge of the stomodaeum for a long 
distance down into tlie coelenteron of the zooid ; the other six, 
called the " ventral " mesenteric filaments (i.e. the ventral and 
ventro-lateral and dorso-lateral), are usually short and are almost 
invariably slightly convoluted. The dorsal filaments are built 
up of columnar cells provided with long cilia, and have usually 
no gland cells, the otliers may show a few cilia but are principally 
composed of non-ciliated gland cells. AVhen the bolus of food 
has passed through the stomodaeum it is seized by these ventral 
filaments and rapidly disintegrated by the secretion of its cells. 
The function of the dorsal mesenteric filaments is mainly 
respiratory. During life their cilia produce a current which 
flows towards the stomodaeum. On the ventral side of the 



334 COELENTERATA ANTHOZOA chap. 

stomodaeum itself there is a groove called the " siphonoglyph " com- 
posed of a specialised epithelium bearing long powerful cilia. But 
the current produced by the siphonoglyph flows from the mouth 
downwards into the coelenteric cavity and is thus in the opposite 
direction to that produced by the dorsal mesenteric filaments. It 
is very probable that these two currents on the opposite sides of the 
zooids maintain the circulation of water in the deep-seated parts 
of the colony which is necessary for the respiration of the tissues. 
On each of the eight mesenteries there is a longitudinal ridge 
due to the presence of a band of retractor muscles. The position 
of these muscles on the ventral surfaces of the mesenteries only 
is one of the characteristic features of the sub-class (Fig. 148, 




Fig. 148. — Diagrammatic transverse sections of an Alcyonarian. A, through the stomo- 
daeum ; B, below the level of the stomodaeum. 1)D, Dorsal directive ; dlmf, dorso- 
lateral mesenteric filament ; dmf, dorsal mesenteric filament ; gon, gonad ; Si, 
siphonoglyph ; V.D, ventral mesentery ; V.L, veatro-lateral mesentery. The upper 
half of the section in B is taken at a higher level than the lower half. 

and p. .329). They vary considerably in thickness and extent 
according to the power of retractility possessed by the zooids, 
but they never vary in their position on the mesenteries. 

The skeleton of Alcyonaria may consist of spicules of 
calcium carbonate, of a horny substance frequently impregnated 
with calcium carbonate and associated with spicules of the same 
substance, or in Heliopora alone, among recent forms, of a con- 
tinuous crystalline corallum of calcium carbonate. 

The spicules constitute one of the most characteristic features 
of the Alcyonaria. They are not found in Cornularia, Stereosoma, 
in a recently discovered genus of Gorgoniidae {Malacogorgia), in 
certain Pennatulacea and in Heliopora ; and it is probable that 
they may be absent in some local varieties of certain species of 
Clavularia. 

The spicules of Alcyonaria consist of an organic matrix 



XIII " ALCVONARIA SPICULES 335 

supporting a quantity of crystalline calcium carbonate. In 
some cases {Xenux) the amount of inorganic salt is so small tliat 
the spicule retains its shape after prolonged immersion in an 
acid ; but generally speaking the relative amount of calcium 
carbonate is so great that it is only by the careful decalcification 
of the spicules in weak acetic acid that the delicate fibrous 
organic matrix can be demonstrated. 

The spicules vary in size from minute granules to long 
spindles 9 mm. in length (Spongodes, sp.). They exliibit so 
many varieties of shape that an attempt must be made to place 
them in groups. The most prevalent type perhaps is that 
called the spindle. This is a rod-shaped spicule with more or 
less pointed extremities. They are usually ornamented with short 
simple or compound wart-like tubercles (Fig. 149, 5). Spicules 
belonging to this type are found in all the principal sub- 
divisions of the group except the Pennatulacea. 

In the Pennatulacea a very characteristic form of spicule is a 
long rod or needle marked with two or three slightly twisted 
ridges, frequently a little knobbed or swollen at the extremities. 
In the same group, in Xenia and Heteroxenia among the 
Alcyonacea, and in the family Chrysogorgiidae the spicules are 
in the form of minute discs or spheres^ and in some genera the 
discs may be united in couples (twins) or in threes (triplets) 
by short connecting bars (Fig. 149, 10). More irregular calcare- 
ous corpuscles of minute size are found in some genera of 
Pennatulacea. 

Other characteristic spicules are the warted clubs of JitnceUa, 
the torch-like spicules of Eunicella (Fig. 149, 3), the clubs with 
irregular leaf-like expansions at one extremity (" Blattkeulen ") 
of Eunicea, and the flat but very irregular scales of the Prim- 
noidae. There are also many genera exhibiting spicules of 
quite irregular form (Fig. 149, s). 

In the greater number of cases the spicules lie loosely in the 
mesogloea and readily separate when the soft tissues of the 
colony decay or are dissolved in a solution of potash. In a few 
noteworthy examples the spicules become in their growth tightly 
wedged together to form a compact skeleton, which cannot sub- 
sequently be disintegrated into its constituent elements. In the 
Precious corals (Coralliidae) the spicules of the axial region fuse 
together to form a solid mass of lime almost as hard and com- 



336 



COELENTERATA ANTHOZOA 



pact as the substance of a pearl. In Paragorgia and some other 
closely related genera the spicules of the axis of the colony also 
become tightly wedged together, but the core thus formed is far 
more porous and brittle than it is in the Coralliidae. In 








8 



Fig. 149. — Spicules of Alcyonaria, 1, Club of Juncella ; 2, warted cross of PlexaureUa ; 
o, torch of Eunkella ; 4, needle of Renilla ; 5, warted spindle of Gorgonella ; 6, 
spicule of Pennatula ; 7, foliate club of Kunicea ; 8, irregular spicule oi' Faramuricea : 
9, scale of I'rimnoa ; 10, spicules of Trichngorgia. (5 and 10 original, the re- 
mainder after Kolliker. ) 



Tiihipora (the organ-pipe coral) and in Telesto rubra the spicules 
of the body-walls of the zooids fuse to form perforated calcareous 
tubes. In some species of Sclerophytmn the large spicules of the 
coenenchym become so closely packed that tliey form dense 
stony masses, almost as hard as a Perforate Madreporarian coral. 
The horny substance, allied chemically to keratin, plays an 



XIII ALCYONARIA SKELETON — COLOUR 337 

important part iu the building up of skeletal structures in 
many Alcyonaria. In Clavidaria viridis and in Stereosoma a 
change in the chemical character of the mesogloea of the body- 
walls of the polyps leads to the formation of a horny tube, 
which in the former case is built up of interlacing fibres, and in 
the latter is formed as a homogeneous sheath. In many of the 
Alcyonacea which have a compact axial skeleton the spicules 
are cemented togetlier by a horny matrix. 

In the Gorgonellidae and some others the hard axis is 
formed of a horny substance impregnated with a crystalline 
form of calcium carbonate ; but in the Gorgoniidae, many of the 
Pennatulacea and some other genera very little or no carbonate 
of lime is found in the horny axis. 

The skeleton of the genus Helio'pora differs from that of all 
the other Alcyonaria in its development, structure, and form. 
In the words of Dr. G. C. Bourne,^ " the calcareous skeleton of 
Hdioi^ora is not formed from spicules developed within cells 
but is a crystalline structure' formed by crystallisation of car- 
bonate of lime, probably in the form of aragonite, in an organic 
matrix produced by the disintegration of cells which I have 
described as calicoblasts." It is furtlier characterised by its 
blue colour. A peculiar form of the axial skeleton (Fig. 155), 
consisting of alternate nodes mainly composed of keratin, and 
internodes mainly composed of calcium carbonate, is seen in the 
families Isidae and Melitodidae. In the Melitodidae the nodes 
contain a considerable number of loose spicules, and the inter- 
nodes are mainly composed of spicules in close contact but 
firmly cemented together by a sparse horny matrix. In the 
Isidae the scanty calcareous substance of the nodes, and the 
bulk of the substance of the internodes, is formed of amorphous 
crystalline limestone. 

The Alcyonaria exhibit a great variety of colour. Very little 
is known at present of the chemistry of the various pigments 
found in the group, but they may conveniently be arranged in 
two sections, the soluble pigments and the insoluble pigments. 
To the former section belong various green and brown pigments 
found in the anthocodiae and superficial coenenchym of many 
genera. These are related to chlorophyll, and may be very largely 
the product, not of the Alcyonarians themselv^es, but of the 

' Quart. Journ. Micr. Set. xli. 1899, p. 52L 
VOL. I Z 



338 COELENTERATA ANTHOZOA chap. 

symbiotic "Algae" (cf. p. 2G1) they carry. A diffuse salmon- 
pink colour soluble in spirit occurs in the living Primnoa lepadi- 
fera of the Norwegian fjords, and a similar but paler pink colour 
occurs in some varieties of the common Alcyoniuni digitahim. 
Gilchrist ^ states that when he was preserving specimens of 
Alcyonium jmrpureum from Cape waters a considerable quantity 
of a soluble purple pigment escaped. 

But the predominant colour of Alcyonarians is usually due 
to the insoluble pigments of the calcareous spicules. These 
may be of varying shades of purple, red, orange, and yellow. 
The colours may be constant for a species or genus, or they may 
vary in different specimens of one species, or even in different 
parts of a single colony. Thus the skeletons of Tuhijyora musica 
from all parts of the world have a red colour, the species of the 
genus Anthomastus have always red spicules. On the other 
hand, we find in Melitodes dichotoma red and yellow varieties in 
the same locality, and in M. chamaeleon some of the branches 
of a colony are red and others yellow. In Ghironephthya 
variabilis the colour of the spicules in any one specimen varies 
considerably, but in a collection of several specimens from a single 
locality a kaleidoscopic play of colours may be seen, no two 
specimens being exactly *the same in the arrangement of their 
colour pattern. The influences that determine the colour of the 
spicules is at present quite unknown, and in view of the great 
variability that occurs in this respect, colour must be regarded as 
a most uncertain guide for the determination of species. The 
blue colour of the genus Heliopora is due to a peculiar pigment 
which shows characteristic bands in the spectrum.''^ 

Phosphorescence. — A great many Alcyonaria are known to 
be phosphorescent. Moseley says that " All the Alcyonarians 
dredged by the ' Challenger ' in deep water were found to be 
brilliantly phosphorescent when brought to the surface." The 
phosphorescence of the common British Pennatula j)hos2)horea 
has attracted more attention than that of any other species, 
and has been well described by Panceri, Forbes, and others. 
Porbes ^ says, " The pen is phosphorescent only when irritated by 
touch ; the phosphorescence appears at the place touched, and 

^ Quoted by Hickson, Marine Investigations, S. Africa, iii. 1904, p. 215. 

- G. C. Bourne, Phil. Trans. Eoy. Soc. cLxxxvi. 1895, B. p. 464. 

^ Quoted by Marshall, Ohan PcnnatuUda, 1882, p. 49. 



ALC YONARIA FOOD 339 



proceeds thence in an undulating wave to the extremity of the 
rachis, but never in the opposite direction ; it is only the parts 
at and above the point of stimulation that show phosphorescence, 
the liglit is emitted for a longer time from the point of stimula- 
tion than from the other luminous parts ; detached portions may 
show phosphorescence. When plunged in fresh water, the Pen- 
natula scatters sparks about in all directions — a most beautiful 
sight." 

Panceri was of opinion that the mesenteric filaments were 
the organs of phosphorescence, but the whole question of the 
cause and localisation of the light in these colonies requires 
further investigation. 

Food. — Very little is known about the food of Alcyonaria, 
but it is very probable that it consists entirely of minute larvae 
and other living organisms. When the coeleuteric cavities of 
preserved Alcyonaria are examined, food is very rarely found in 
them, although fragments of Crustacean appendages have occa- 
sionally been seen in the neighbourhood of the mesenteric 
filaments. Experimenting upon Alcyonium digitatmn, Miss 
Pratt ^ has found that the zooids seize and swallow various small 
organisms of a surface -net gathering, and that they will also 
swallow finely minced fragments of the muscle of fish, but that 
they reject many kinds of fish ova. In many tropical and some 
extra - tropical species the superficial canal systems and the 
inter-meseuterial spaces of the zooids contain a large number of 
Zooxanthellae, and their presence seems to be associated in some 
cases with a decided degeneration of the digestive organs. It 
has been suggested that these symbiotic " Algae " prepare food 
materials after the manner of plants, and that these are absorbed 
by the hosts, but it appears improbable that in any case this 
source of food supply is sufficient. It must probably be supple- 
mented in some degree by food obtained by the mouth, and 
digested in the coelenteric cavity. 

The question whether the Alcyonaria can form an important 
part of the dietary of fish or other carnivorous animals may be 
economically important. Fragments of the PennatuUd Virgularia 
have been found in the stomachs of cod and other fish, but with 
this exception there is no evidence that any genus is systematically 
or even occasionally preyed upon by any animal. With a very 

1 Quart. Journ. Micr. Sci. xlix. lOOfi, p. 327. 



340 COELENTERATA — ANTHOZOA chap. 

few exceptions Alcyonaria show no signs of having been torn, 
bitten, or wounded by carnivorous animals. It is improbable 
that the presence of nematocysts in the tentacles can account for 
this immunity, as it is known that some predaceous animals do 
feed upon Coelenterates provided with much larger nematocysts 
than any Alcyonarian possesses. All Alcyonaria, however, have 
a characteristic disagreeable odour, and it is possible, as in many 
other cases, that this is accompanied by an unpleasant taste. 
But if the Alcyonaria themselves are immune, it is possible that 
their large yolk -laden eggs may form a not unimportant source 
of food supply. In places where large colonies flourish, an 
immense number of eggs or embryos must be discharged into the 
water during the spawning season, and of these only a minute 
fraction can survive long enough to found a new colony. 

Reproduction. — The formation of colonies by gemmation has 
frequently been mentioned above. The young buds of a colony 
arise from the endoderm canals in the body-wall of the zooids, in 
the general coenenchym, or in the stolon. They never arise 
from evagination of the coelenteric cavities of the zooids. There 
is no evidence that fission of a colony to form secondary colonies 
ever occurs. Gemmation leads to the increase in the number 
of zooids forming a colony, but not to an increase in the number 
of colonies. 

Fission of the zooids is of extremely rare occurrence ; a single 
case, however, has been recorded by Studer in the genus Gersemia. 
Sexual reproduction usually occurs once in a year ; it is doubtful 
whether it ever occurs continuously. The colonies appear to be 
nearly always dioecious, only one case of hermaphroditism having 
yet been recorded.^ The ova and sperm sacs are usually formed and 
matured on the six ventral mesenteries, rarely on the dorsal pair 
of mesenteries (Fig. 148, B) as well. The spawning season varies 
with the locality. Alcyonium digitatum spawns at Plymouth at 
the end of December, and somewhat later at Port Erin. The 
Pennatulid Renilla and the Gorgonid Leptogorgia spawn in the 
summer months on the coast of North America. In the ]\Iediter- 
ranean Alcyonium palmatum spawns in September and October 
(Lo Bianco), Gorgonia cavolinii in May and June. 

^ Corallium nobile appears to be the exception to this rule, as it is stated that 
colonies and even individual zooids are occasionally hermaphrodite. Lacaze 
Duthiers, "Hist. Nat. du Corail," 1864, p. 127. 



ALCYONARIA DEVELOPMENT CLASSIFICATION 



341 



-Ec 



It is not known for certain when the fertilisation of the ova 
is effected, but in Alcyonium digitatmn, and in the majority of 
the Alcyonarians, it probably takes place after the discharge of 
the ova from the zooids. A few forms are, however, certainly 
viviparous, the larvae of Gorgonia capensis being retained within 
the coelenteric cavity of the parent zooid until they have grown to 
a considerable size. The other viviparous Alcyonarians are Coral- 
Hum nohile (de Lacaze Duthiers), the " Clavulaires petricoles," 
and Sympodium coralloides (Marion 
and Kowalevsky), and three species 
of Ne2^hthya found at depths of 
269 to 761 fathoms (Koren and 
Danielssen). The general features 
of the development are very similar 
in all Alcyonarians that have been 
investigated. The egg contains a 
considerable amount of yolk, and 
undergoes a modified form of seg- 
mentation. The free-swimming larva 
is called a " sterrula." It consists 
of an outer layer of clear ciliated 
ectoderm cells, surrounding a solid fig. 
endodermic plasmodium containing 
the yolk. As the yolk is consumed 
a cavity appears in the endoderm, and the larva is then called 
a "planula" (Fig. 150). The mouth is subsequently formed 
by an invagination of the ectoderm at the anterior pole. 
The development of the mesenteries has not yet been fully 
described. 

Classification. — The sub-class Alcyonaria may conveniently 
be classified as follows : — 




150. — Ciliated "planula" larv; 
of Alcyonium digitutum. Ec 
Ectoderm ; End, endoderm. 



Grade A. Protalcyonacea. 
Grade B. Synalcyonacea. 

Order 1. Stolonifera. 

Order 2. Coenothecalia. 

Order 3. Alcyonacea. 

Order 4. Gorgonacea. 

Order 5. Pennatulacea. 



342 COELENTERATA ANTHOZOA 



Grade A. Protoalcyonacea. 

This Grade includes those genera which, like many sea- 
anemones, do not reproduce by continuous gemmation to form 
colonies. 

Several genera have been described, and tliey have been 
placed together in one family called the Haimeidae. 

Haimea fitnehris, M. Edwards, was found off the coast of 
Algeria ; H. hyalina, Koren and Danielssen, in Norway ; Hartea 
elegans, Wright, from the Irish coast ; Monoxenia darwinii, 
Haeckel, from the Eed Sea, and a large new species found by 
the " Siboga" Expedition in deep water off Ceram. All these 
species, however, are very rare, and there is no satisfactory 
evidence at present that they remain solitary throughout life. 



Grade B. Synalcyonacea. 

The sub-division of the Synalcyonacea into orders presents 
many difficulties, and several different classifications have been 
proposed. Only two orders of the five that are here recognised 
are clearly defined, namely, the Coenothecalia, containing the 
single living genus Heliopora, and the Pennatulacea or Sea-pens ; 
the others are connected by so many genera of intermediate 
characters that the determination of their limits is a matter of 
no little difficulty. 

Order I. Stolonifera. 

These are colonial Alcyonaria springing from a membranous 
or ribbon-like stolon fixed to a stone or some other foreign 
object. The body-walls of the individual zooids may be free or 
connected by a series of horizontal bars or platforms (auto- 
thecalous) ; never continuously fused as they are in other orders 
(coenothecalous). 

In the simplest form of this order, Sarcodictyon catcnatum 
Forbes, the ribbon-like strands of the stolon meander over the 
surface of stones, forming a red or yellow network, from the 
upper surface of which the clear transparent anthocodiae of the 
zooids protrude. When retracted the anthocodiae are drawn 
down below the surface of the general coenenchym, and their 
position is indicated by small cushion-like pads on the stolon. 



ALCVONARIA STOLONIFERA 



343 




Sarcodictyon is found in depths of 10 to 22 fathoms in tlie Irish 
Sea, off the west coast of Scotland, the Shetlands, and off the 
Eddystone Lighthouse, South Devon. 

Another very important genus is Tuhipora, in which tlie 
tubular body-wall of each zooid is very much longer in proportion 
to its diameter than it is in Sarcodictyon, and the anthocodia is 
retracted not into the stolon, but 
into the basal part of the body- 
wall. The zooids are connected 
together by horizontal platforms 
on which new" zooids are formed by 
gemmation. Both horizontal plat- 
forms and the body-walls of the 
zooids are provided with a skeleton 
of fused spicules of a red colour. 

This genus is the well-known 
Organ-pipe coral, and is found some- 
times in immense quantities on the 
coral reefs of both the old and new 
world. 

It may be seen in pools on the 
edge of the reefs at low tides in 
colonies frequently a foot or more 
in diameter. The tentacles are 
often of a bright emerald green colour, and as the anthocodiae 
stand expanded in the clear water they contribute a brilliant 
patch of colour to tlie many beauties of their surround- 
ings. When the coral is disturbed, or the water shallows 
and the anthocodiae are retracted, the dull red colour of the 
skeleton gradually takes the place of the bright green of the 
tentacles. 

It is probable that this order of Alcyonaria was better repre- 
sented on the reefs of some of the earlier periods of the world's 
history than it is at present. The fossil Syringopora, which is 
found abundantly in the carboniferous limestone and other 
strata, was probably an Alcyonarian belonging to this order. It 
resembles TvMpora in its mode of growth, but in place of the 
horizontal platforms connecting the zooids there are rods or bars 
from wdiich new zooids spring (Fig. 152). Similar connecting 
bars are found in the recent Clavidaria {Hiclsonia, Delage) 



Fig. 151. — Tuhipnni m»sua, a joinig 
colony gi owing on a dead Madre- 
pore branch (M). H}), The con- 
necting horizontal platforms ; jw, p, 
the skeletal tubes of the zooids ; 
St, the basal stolon. 



344 



COELENTERATA ANTHOZOA 



viridis of the East Indian reefs (Fig. 153). Other fossil forms 
belonging to the order are Favosites, a very abundant coral of 
the Upper Silurian rocks, and possibly Columnaria. 




Xi^Oy^JKiS^ 



Fig. 152. — Syringopora, a fossil, 
showing autothecalous tubes [th), 
funnel-shaped tabulae {tah), and 
tubular cross-bars (t). 



Fig, 153. — Glavularia {Hicksonia) viridis, with 
creeping stolon and transverse connecting 
tubes. 



The principal families of the Stolonifera are : — 

Fam. 1. CoRNULARiiDAE. — Without spicules; Cormdaria, Lamarck, 

Mediterranean ; Stereosovia, Hickson, Celebes. 
Fam. 2. Clavulariidae. — Clavidaria, Quoy and Gaimard ; Sarco- 

dictyon, Forbes, British ; Sympodium, Elirb ; Syrincjo'pora, 

Cioklfuss, fossih 
Fam. 3. Tubiporidae. — Tuhipora, Linnaeus, tropical shallow water. 
Fam. 4. Favositidae. — Favosites, Lamarck ; Syrinfjolites, Hinde ; 

Stenopora, King. 



Order II. Coenothecalia. 

This order contains the single genus and species Heliopora 
coerulea among recent corals, but was probably represented by a 
large number of genera and species in earlier periods. 



XIII ALCVONARIA — COENOTHECALIA 345 

It is found at the present day in many localities in the warm 
shallow waters of the tropical Pacific and Indian Oceans. It 
usually flourishes on the inside of the reef, and may form masses 
of stone five or six feet in diameter. The coral may easily be 
recognised, as it is the only one that exhibits a blue colour. 
This colour usually penetrates the whole skeleton, but in some 
forms is absent from the superficial layers. 

The skeleton consists of a number of parallel tubes with 
imperforate walls, which are fused together in honey -comb 
fashion. On making a vertical section through a branch of the 
coral it is found that the tubes are divided into a series of 
chambers by transverse partitions or " tabulae." The soft living 
tissues of the coral, the zooids and coenosarc, are confined to the 
terminal chambers, all the lower parts being simply dead cal- 
careous skeleton supporting the living superficial layer. Among 
the parallel tubes there may be found a number of larger 
chambers that seem to have been formed by the destruction ot 
the adjacent walls of groups of about nineteen tubes. These 
chambers are provided with a variable number of pseudo- septa, 
and have a remarkable resemblance to the thecae of some 
Zoantharian corals. That Heliopora is not a Zoantharian coral 
was first definitely proved by Moseley, who showed that each of 
these larger chambers contains an Alcyonarian zooid with eight 
pinnate tentacles and eight mesenteries. The zooids arise 
from a sheet of coenosarc that covers the whole of the living 
branches of the coral mass, and this sheet of coenosarc bears a 
plexus of canals communicating on the one hand with the zooids, 
and on the other with a series of blind sacs, each of which 
occupies the cavity of one of the skeletal tubes as far down as 
the first tabula. The zooids of Helioiwra are very rarely 
expanded during the day-time, and it has been found very 
difficult to get them to expand in an aquarium. The coral, 
however, is frequently infested with a tubicolous worm allied to 
the genus Leucodora, which freely expands and projects from the 
surface. So constant and so numerous are these worms in some 
localities that it has actually been suggested that Heliopora should 
be regarded as a Polychaete worm and not as an Alcyonarian. 
According to Mr. Stanley Gardiner, however, these worms do not 
occur in association with the Heliopora found on the reefs of the 
]\Ialdive Archipelago. 



346 COELENTERATA ANTHOZOA chap. 

There is very strong reason to believe that certain fossil 
corals were closely related to Heliopora ; that Heliopora is in 
fact the solitary survivor of a group of Alcyonarian corals that 
in past times was well represented on the reefs, both in numbers 
and in species. The evidence is not so convincing that other 
fossil corals are closely related to Heliopora, and their true 
zoological position may remain a matter for surmise. The order 
may be classified as follows : — 

Fam. 1. Heliolitidae.^ — Coenothecalia with regular, well- 
developed septa, generally twelve in number, in each calicle. 

Heliolites, Dana, Silurian and Devonian. Cosmiolithus, Lind- 
strom, Upper Silurian. Proheliolites, Klaer, Lower Silurian. 
Plasmopora, Edwards and Haime, Upper Silurian. Proiwra, 
E. and H., Upper Silurian. Gamptolithus, Lindstrom, Upper 
Silurian. Diplo'epora, Quenst, Upper Silurian. Pycnolithus, 
Lindstrom, Upper Silurian. 

Fam. 2. Helioporidae." — Coenothecalia with small irregularly 
arranged coenosarcal coeca, and a variable number of septa or 
septal ridges. Helio2wra, de Blainville, recent. Eocene and Upper 
Cretaceous. Polytremacis, d'Orbigny, Eocene and Upper Cretaceous. 
Octotremacis, Gregory, Miocene. 

The family Coccoseridae is regarded by Lindstrom as a 
sub-family of the Heliolitidae, and the families Thecidae and 
Chaetetidae are probably closely related to the Helioporidae. 

Order III. Alcyonacea. 

This order contains a large number of genera of great variety 
of form. The only characters which unite the different genera 
are that the body-walls of some groups of zooids, or of all the 
zooids, are fused together to form a common coenenchym pene- 
trated by the coenosarcal canals, and that the spicules do not 
fuse to form a solid calcareous, or horny and calcareous, axial 
skeletal support. 

The affinities with the order Stolonifera are clearly seen in 
the genera Xenia and Telesto. Some species of Xenia form 
flattened or domed colonies attached to stones or corals, with 
non- retractile anthocodiae and body -walls united for only a 

1 G. Lindstrom, Handl. k. Svensl: Vet. Akad. xxxii. 1S99. 
- J. W. Gregory, Proc. Roy. Soc. Ixvi. 1899, p. 291. 



ALCVONARIA — ALCYONACEA 



347 



sliort distance at tlie base. Young J\^e7iia colonies are in fact 
Stolonifera in all essential characters. In Telesto prolifera ^e 
find a network of stolons encrusting coral branches and other 
objects after the manner of the stolons of many species of Clavu- 
laria, although the zooids do not arise from these stolons singly, 
but in groups, with their body- walls fused together for a certain 
distance. In Telesto rubra the 
spicules of the body- walls are fused 
together to form a series of per- 
forated tubes very similar in some 
respects to the tubes of Tuhijwra. 

A remarkable genus is Coclo- 
gorgia. Here we find a branching 
colony arising from a basal stolon, 
and the axis of the main stem and 
of each branch consists of a single 
very much elongated zooid bearing 
on its thickened walls the branches ^^ ^ ^ ^ 
of the next series and other zooids. !^'^x% '^ i^ 
It is true that in this genus there 
is very little fusion of neighbour- 
ing zooids, and the amount of true 
coenenchym is so small that it can 
hardly be said to exist at all. 
Bourne ^ has united this genus with 
Telesto into a family Asiphonacea, 
which he joins with the Penna- 
tulida in the order Stelechotokea ; 
but their affinities seem to be closer 
with the Alcyonacea than with the 
Pen natulacea, from which they differ 
in many important characters. 

The genus Alcyonium not only contains the commonest 
British Alcyonarian {A. digitatum), but it is one of the most 
widely distributed genera of all Alcyonaria that occur in .shallow 
water. 

The genera Sarcophytum and Lohopliytuni occur in shallow 
water in the tropics of the old world. The former frequently 
consists of huge toad -stool shaped masses, soft and spongy in 

^ G. C. Bourne. Lankester's Treatise on Zoology, pt. ii. 1900, " Anthozoa," p. 26. 




Fig. 154. — Alcyonium (ligUatmn, a 
single-lobed specimen, with some of 
the zooids expanded. 



348 COELENTERATA ANTHOZOA chap. 

consistency, of a green, brown, or yellow colour. On some reefs 
the colonies of Sarco^jliytum form a very conspicuous feature, and 
from their very slimy, slippery surface, add to the minor dangers of 
wading in these regions. Both genera are dimorphic. Some species 
of the genus Sclerophytum} which occur in the Indian Ocean, are 
so hard and brittle that they might readily be mistaken for a 
Zoantharian coral. This character is due to the enormous 
number of tightly packed spicules borne by the coenenchym. 
Some of these spicules in S. querciforme are 7 mm. x 1'7 mm.; 
the largest, though not the longest {vide p. 335) of any spicules 
occurring in the order. 

Another very important genus occurring on coral reefs, and 
of very wide distribution, is Sjwngodes. This genus forms bushy 
and rather brittle colonies of an endless variety of beautiful 
shapes and colours. Arising from the neck of each anthocodia 
there are one or two long, sharp, projecting spicules, which give 
the surface a very spiny or prickly character. 

The genera Siphonogorgia and Ckironephthya form large 
brittle, branching colonies which might readily be mistaken for 
Oorgonians. The strength of the branches, however, is mainly 
due to the large, densely packed, spindle-shaped spicules at the 
surface of the coenenchym, the long coelenteric cavities of the 
zooids penetrating the axis of both stem and branches. 
Siplionogorgia is usually uniformly red or yellow in colour. 
Cliironephthya, on the other hand, exhibits a great variety of 
colour in specimens from the same reef, and indeed in different 
branches of the same colony. 

Fam. 1. Xeniidae. — Alcyonacea with non- retractile zooids. 
Spicules very small discs, usually containing a relatively small 
proportion of lime. 

Xenia, Savigny ; Indian Ocean and Torres Straits. Hetero- 
xenia, Kolliker ; Eed Sea, Cape of Good Hope, and Torres Straits. 

Fam. 2. Telestidae. — Colonies arising from an encrusting 
membranous or branching stolon. The erect stem and branches 
are formed by the body-walls of two or three zooids only, from 
which secondary zooids and branches of the next order arise. 

Telesto, Lamouroux, widely distributed in warm waters of the 
Atlantic, Pacific, and Indian Oceans. The genus Fascicularia, 
Yiguier, from the coast of Algiers, seems to be related to Telesto, 

' E. M. Pratt, Fauna and Geogr. Maldive Archip. ii. pt. i. 1903, j). 516. 



XIII ALCVONARIA — ALCYONACEA 349 

but the groups of zooids are short, aud do not give ri.se to 
branches. 

Fam. 3. Coelogorgiidae. — The colony arborescent, attaclied hj 
stolon-like processes. The stem formed by an axial zooid with 
thickened body-walls. Branches formed by axial zooids of the 
second order, and branchlets l^y axial zooids of the third order, 
borne either on two sides or in spirals by the main stem. Genus 
Coelogorgia, Zanzibar. 

Fam. 4. Alcyoniidae. — The colonies of this family are usually 
soft and fleshy, and the spicules, evenly distributed throughout 
the coenenchym, do not usually fuse or interlock to form a 
continuous solid skeleton. They may be unbranched or lobed, 
never dendritic in form. The principal genera are : — Alcyonium, 
Linnaeus, cosmopolitan, but principally distributed in temperate 
and cold waters. Alcyonium digitatum is the commonest British 
Alcyonarian. It is found in shallow water, from the pools left at 
low spring tides to depths of 40 or 50 fathoms, at most places 
on the British shores. It is stated by Koehler to descend into 
depths of over 300 fathoms in the Bay of Biscay. There are two 
principal varieties ; one is white or pale pink in the living con- 
dition, and the other yellow. In some localities the two varieties 
may be found in the same pools. Another species, Alcyonium 
glomeratum, placed in a distinct genus {Rhodophyton) by Gray, 
and distinguished from the common species by its red colour and 
long digitate lobes, is found only off the coast of Cornwall. 
Faralcyonium, Milne Edwards ; Mediterranean. Scle7'02)]iytum, 
Pratt ; sometimes dimorphic, Indian Ocean. Sarco2'>hytum, 
Lesson ; dimorphic, principally tropical. Lohopliytxtm, Maren- 
zeller ; dimorphic, tropical. Anthomastus, Verrill ; dimorphic, 
Atlantic Ocean, deep water. Acroj^hytum, Hickson ; dimorphic, 
Cape of Good Hope. 

Fam. 5. Nephthyidae. — Colonies dendritic. Usually soft and 
flexible in consistency. Nephthya, Savigny ; Indian and Pacific 
Oceans. Spongodes, Lesson ; widely distributed in the Indian and 
Pacific Oceans. 

Fam. 6. Siphonogorgiidae. — Colonies often of considerable 
size. Dendritic. Spicules usually large and abundant, giving a 
stiff, brittle consistency to the stem and branches. Siphonogorgia, 
Kolliker ; Ked Sea, Indian, and Pacific tropics. Chironejihthya, 
Wright and Studer ; Indian and Pacific Oceans. Lemnalia, 



350 



COELENTERATA ANTHOZOA 



Gray; Zanzibar. Agaricoides, Simpson;^ Indian Ocean, 400 
fathoms. 

Order IV. Gorgonacea. 

This order contains a very large number of dendritic and 
usually flexible corals occurring in nearly all seas and extending 
from shallow waters to the very great depths of the ocean. A 
large proportion of them are brightly coloured, and as the 
principal pigments are fixed in the spicules, and are therefore 
preserved when the corals are dead and dried, they afford some 
of the most attractive and graceful objects of a natural history 
museum. 

The only character that separates them from the Alcyonacea 
is that they possess a skeletal axis that is not perforated by the 
coelenteric cavities of the zooids. The coelenteric cavities are 
usually short. The order may conveniently be divided into two 
sub-orders. 

Sub-Order 1. Pseudaxonia. 

The axis in this sub-order consists of numerous spicules tightly 
packed together, or cemented together by a substance which is 
probably allied to horn in its chemical composition. This sub- 
stance may l)e considerable in amount, in which case it remains 
after decalcification as a spongy, porous residue ; or it may be so 
small in amount, as in Corallmm, that the axis appears to be 
composed of solid carbonate of lime. The statement is usually 
made that the axis is penetrated by nutritive canals in certain 
genera, but the evidence upon which this is based is unsatisfactory 
and in some cases unfounded. There can be no doubt, however, 
that in some genera the axis is porous and in others it is not, 
and this forms a useful character for the separation of genera. 

Fam. 1. Briareidae. — The medullary substance consists of 
closely packed Ijut separate spicules embedded in a soft horny 
matrix, which is uniform in character throughout its course. 
Nearly all the genera form dendritic colonies of considerable size. 

The principal genera are : — Solenocaulon, Gray ; Indian Ocean 
and North Australia. Many of the specimens of this genus have 
fistulose stems and branches. The tubular character of the stem 
and branches is probably caused by the activity of a Crustacean, 

1 Zool. Anz. xxix. 1905, p. 263. 



ALCYONARIA GORGONACEA 



35 



Alplieus, and may be regarded as of the nature of a gall- 
formation.^ Paragorgia, M. Edwards ; Norwegian fjords, in deep 
water. This genus forms very large tree-like colonies of a ruby- 
red or white colour. It is perhaps the largest of the dendritic 
Alcyonarians. It is dimorphic. Spongioderma, Kolliker ; Cape 
of Good Hope. The surface of this form is always covered by 
an encrusting sponge. IcUigorgia, Eidley ; Torres Straits. The 
stem and branches are compressed and irregular in section. 

Fam. 2. Sclerogorgiidae. — The medullary mass forms a 
distinct axis consisting of closely packed elongate spicules with 
dense horny sheaths. 

Suberogorgia, -Gnij, has a wide distribution in the Pacific 
Ocean, Indian Ocean, and the West Indies. Keroeides, W. and S., 
comes from Japan. 

Fam. 3. Melitodidae. — The axis in this family exhibits a 
series of nodes and internodes (Fig. 155), the former consisting 
of pads formed of a horny substance 
with embedded spicules, the latter of a 
calcareous substance with only traces 
of a horny matrix. The internodes 
are quite rigid, the nodes however give 
a certain degree of flexibility to the A 
colony as a whole. Neither the nodes 
nor the internodes are penetrated by 
nutritive canals, but when dried the 
nodes are porous. 

The principal genera are: — Mditodcs, 
Verrill ; widely distributed in the 
Indian and Pacific Oceans, Cape of 
Good Hope, etc. This genus is in 
some localities extremely abundant and 
exhibits great brilliancy and variety of 
colour. The branching is usually dicho- 
tomous at the nodes. Wrightclla, Gray. 
This is a delicate dwarf form from 
Mauritius and the coast of South 
Africa. Farisis, Verrill ; Pacific Ocean 

from Formosa to Australia but not very common. One species 
from Mauritius. The branches arise from the internodes. 




. 15,">. — Melitodes dichotoma, 
showing the swollen nodes 
and the internodes. 



S. .1. Hicksou, Fauna and Geo<j. Maldivc Archlp. ii. pt. i. 1903, \k 495. 



35 2 COELENTERATA — ANTHOZOA chap. 

Fam. 4. Coralliidae. — The axis is formed by the fusion of 
spicules into a dense, solid, inflexible, calcareous core. 

Corallium, Lamarck. Corallium nolnle, Pallas, the " precious 
coral," occurs in the Mediterranean, chiefly off the coast of North 
Africa, but also on the coasts of Italy, Corsica, Sardinia, and* it 
extends to the Cape Verde Islands in the Atlantic Ocean. C. 
japonicmn, Kisliinouye, called Akasango by the fishermen, occurs 
ott' the coast of Japan, and C. reginae, Hickson, has recently been 
described from deep water otf the coast of Timor.-' The genus 
■ Pleurocorallium, Gray, is regarded by some authors' as distinct, 
but the characters that are supposed to distinguish it, namely, 
the presence of peculiar " opera-glass-shaped spicules," and the 
occurrence of the verrucae on one side of the branches only, are 
not very satisfactory. The following species are therefore placed 
by Kishinouye '^ in the genus Corallium : — C. elatius, Eidley 
(Momoirosango) ; C. konojoi, Kishinouye (Shirosango) ; C. hoshn- 
ensis, K. ; C. sulcatum, K. ; C. inutile, K. ; and G. pusillum, K., — 
•all from the coast of Japan. Of the coral obtained from these 
species, the best kinds of Momoirosango vary in price from £30 
per pound downwards according to the quality. The Shirosango 
is the least valual)le of the kinds that are brought into the 
market, and is rarely exported.^ Three species of Corallium 
(Pleurocorallium) have been described from Madeira,^ and one 
of these, G. johnsoni, has recently been found in 388 fathoms off 
the coast of Ireland.'^ Other species are C. stylasteroides, from 
Mauritius ; G. confusum, Morotf,'' from Sagami Bay in Japan ; and 
an undescribed species obtained by the " Siboga," off Djilolo. 
These corals range from shallow water to depths of 300-500 
fathoms. Pleurocoralloidcs, Moroff, differs from the others in 
having very prominent verrucae and in the character of the 
large spindle-shaped and scale-like spicules. It was found in 
Sagami Bay, Japan. Specimens attributed to the genus Pleuro- 
coralliiim have been found fossil in the white chalk of France, 
but Corallium has been found only in the tertiaries." 

^ Hickson, K. Akad. Wet. Amsterdam, 1905. 

"^ Journ. Imp. Fish. Bureau, Tokyo, xiv. 1, 1904. 

^ Kitahara, Journ. Imp. Fish. Bureau, Tokyo, xiii. 3, 1904. 

* Jolinson, Proc. Zool. Sac. 1899, p. 57. 

^ Hickson, Nature, Ixxiii. 1905, p. 5. 

6 Moroff, Zool. Jahrh. Syst. xvii. 1902, p. 404. 

' Ridley, Proc. Zool. Sac. 1882, p. 231. 



ALCVONARIA GORGONACEA 353 



Sub-Order 2. Axifera. 

The axis in this sub-order may be horny, or horny with a 
core of calcium carbonate, or composed of horn impregnated with 
calcium carbonate, or of nodes of horn alternating with internodes 
of calcium carbonate. It may be distinguished from the axis of 
the Pseudaxonia by the fact that in no case have definite spicules 
been observed to take part in its formation. It has been 
suggested that as the Axifera represent a line of descent distinct 
from that of the Pseudaxonia they should be placed in a separate 
order. Apart from the character of the axis, however, the two 
sub-orders show so many affinities in their general anatomy that 
it is better to regard the two lines of descent as united within 
the Gorgonacean limit. It is very improbable that the two 
groups sprang independently from a stoloniferous ancestor. 

Fam. 1. Isidae. — Tliis family includes all those Axifera 
in which the axis is composed of alternate nodes of horn and 
internodes of calcareous substance. 

There can be little doubt of the close affinities of many of 
the genera of this family with the Melitodidae among the 
Pseudaxonia. In both the coenenchym is thin and the 
coelenteric cavities short. No important differences have been 
observed between the structure of the zooids of the two families, 
and now that we know that the " nutritive canals " of Melitodes 
do not perforate the nodes there is no important difference 
left between the coenosarcal canal systems. The structure and 
method of calcification of the internodes of the two families are 
very similar. The main difference between them is that the 
nodes of the Isidae are purely horny, whereas in the Melitodidae 
the horny substance of tlie nodes contains calcareous spicules. 

The principal genera are : — Isis, Linnaeus ; Pacific Ocean. 
This genus forms substantial fan-shaped colonies with, relatively, 
a thick coenenchym, short stout internodes and black horny 
nodes. Mopsea, Lamouroux ; Coast of Australia. The verrucae 
are club-shaped and are arranged in spiral rows round tlie stem. 
AcancUa, Gray ; principally found in deep water in the Atlantic 
Ocean but also in the Pacific. The internodes are long and the 
branches arise from the nodes. ]\Iost of the species occur in 
deep water, some in very deep water {A. simplex, 1600 to 1700 
fathoms). In this and the following genera the coenenchym is 
VOL. I 2 A 



3 54 COELENTERATA ANTHOZOA chap. 

thin and the zooids imperfectly or not retractile. Ceratoisis, 
Wright ; Atlantic Ocean, extending from shallow to deep water. 
The branches arise from the nodes. Chclidonisis, Studer ; deep 
water off the Azores. Isidella, Gray ; Mediterranean Sea. 
Bathrjgorgia, Wright; off Yokohama, 2300 fathoms. Tliis genus 
is unbranched, with very long internodes and short nodes. The 
zooids are arranged on one side only of the stem. 

Fam, 2. Primnoidae. — This is a well-marked family. The 
axis of the colonies is horny and calcareous. The coenenchym 
and the non-retractile zooids are protected by scale-like spicules, 
which usually overlap and form a complete armour for the pro- 
tection of the soft parts. On the aboral side of the base of each 
tentacle there is a specialised scale, and these fit together, when 
the tentacles are folded over the peristome, to form an operculum. 

The principal genera are : — Primnoa, Lamouroux ; Atlantic 
Ocean, occurring also in the Norwegian fjords. This genus is 
usually found in moderately deep water, 100 to 500 fathoms. 
Primnoella, Gray. This genus seems to be confined to the 
temperate seas of the southern hemisphere. It is unbranched. 
The zooids are arranged in whorls round the long whip-like 
stem. Flumarella, Gray ; southern hemisphere, in moderately 
deep water. This is branched pinnately in one plane. The 
zooids are small and arise at considerable intervals alternately 
on the sides of the branches. Stenella, Gray ; widely distributed 
in deep water. The zooids are large and are arranged in whorls 
of three situated at considerable distances apart. Stachyodes, 
W. and S. ; Fiji, Kermadecs, Azores, in deep water. Colony 
feebly branched. Zooids in regular whorls of five. Other 
genera belonging to this group of Primnoidae are TlunMrcUa, 
Gray, and AmjjhilapJiis, Antarctic seas. 

The following genera are placed in separate sub-families : — 
Callozostro7i, Wright ; Antarctic Sea, 1670 fathoms. The axis 
is procumbent and tlie zooids are thiclcly set in rows on its 
upper surface. Tlie zooids are protected by large imbricate 
scales, of which those of the last row are continued into long 
spine-like processes. Calyjitropliora, Gray ; Pacific Ocean, in 
deep water. The base of tlie zooids is protected by two remark- 
al)ly large scales. Primnoides, W. and S. ; Southern Ocean. 
The opercular scales are not distinctly differentiated and the 
calyx is therefore imperfectly protected. 



XIII ALCYONARIA GORGONACEA 355 

Fam. 3. Chrysogorgiidae.^ — The axis in tliis family is com- 
posed of a ]iorny iibrous substance witli interstratified calcareous 
jiarticles, and it springs from a calcareous plate, which sometimes 
gives off root-like processes. It may be unbranched or branched 
in such a way that the branches of the second, third, and subsc- 
(|uent orders assume in turn the direction of the base of the 
main axis. The axis is frequently of a metallic iridescent 
appearance. The zooids usually arise in a single straight or 
spiral row on the branches, and are not retractile. The 
coenenchym is thin. The spicules vary considerably, Ijut in a 
very large proportion of the species they are thin, oval, or hour- 
glass plates (Fig. 149, 10, p. 336). 

By some authors this family is considered to be the simplest 
and most primitive of the Axifera ; but the delicate character of 
the axis of the main stem and branches, the thinness of the 
coenenchym, the position of the zooids on one side of the branches 
only, and the tenuity of the calcareous spicules may be all 
accounted not as primitive characters, but as special adaptations 
to the life in the slow uniform currents of deep water. 

The principal genera are : — Lepidogorgia, Verrill ; Atlantic 
and Pacific Oceans, 300 to 1600 fathoms. Axis unbranched. 
Zooids large and arranged in a single row. Trichogorgia, 
Hickson ; Cape of Good Hope, 56 fathoms. Colony branching 
in one plane. Zooids numerous and on all sides of the branches. 
Chrysogorgia, D. and M. ; deep water. Axis branched. Spicules 
on the zooids always large. Metallogorgia, Versluys ; Atlantic 
Ocean, 400 to 900 fathoms. Basal part of the stem imbranched 
(mouopodial). Iridogorgia, Yerrill. vSpiral stem and Ijranches. 
PIcurogorgia, Versluys. Axis branched in one plane. Coenen- 
chym thick. Riisea, D. and M. Monopodial stem and thick 
coenencliym. 

Fam. 4. Muriceidae. — Tliis is a large family, exhibiting very 
great variety of haldt. The spicules are often very spiny, ami 
project beyond the surface of the ectoderm, giving the colony a 
rough appearance. A great number of genera have been described, 
l)ut none of them are very well known. The family requires 
careful revision. 

The more important genera are: — Acanthogorgia, Gray; 
principally in deep water in the Atlantic Ocean. The calices arc 

^ For a revision of tliis family, see Versluys, Siborja Expcditic, xii. 1902. 



356 



COELENTERATA — ANTHOZOA 






large, cylindrical, and spiny. Villogorgia, D. and M. ; widely 
distributed. Delicate, graceful forms, with thin coenenchyni. 
Echinomuricea, Verrill ; Muricea, Lamouroux ; Paramuricea, 
Koll ; Acam2')togorgia, W. and S. ; Behryce, Philippi. 

Fam. 5. Plexauridae, — In this family we find some of the 
largest and most substantial Gorgonids. The axis is usually 
black, but its horny substance may be impregnated with lime, 
particularly at the base. The coenenchyni is thick, and the 
zooids are usually completely retractile, and the surface smooth. 

The species of the 
family are princi- 
pally found in 
shallow water in 
warm or tropical 
regions. 

The principal 
genera are: — Eu- 
nicea, Lamouroux. 
The calices are pro- 
minent, and not 
retractile. Plcxaura, 
Lamouroux; Euplex- 
aura, Verrill. Eiini- 
cella, Verrill. With 
an outer layer of 
peculiar torch- 
shaped spicules. The only British species of this order is 
Eunicella cavolini (formerly called Gorgonia verrucosa). It is 
found in depths of 10 to 20 fathoms off the coast of the 
English Channel and west of Scotland. Occasionally specimens 
are found in which a gall-like malformation with a circular 
aperture is seen, containing a Barnacle. Such gall formations, 
common enough in some species of Madreporaria, are rarely 
found in Alcyonaria. 

Fam. 6. Gorgoniidae. — This family contains some of the 
commonest and best-known genera of the order. Tliey usually 
form large flexible branched colonies with delicate horny axes 
and thin coenenchyni. The ^ooids are usually completely 
retractile. 

The principal genera are : — Gorgonia, Linn. This genus 




Fio. 156. — Eunicella cavolini. Some branches of 
dried specimen, showing a gall formed by a Cirripedc 



lars 



ALCVONARIA — GORGONACEA 



357 



includes Gorgonia {Bhipidogorgia) fiabdlum, the well-known fan 
Gorgonia with intimately anastomosing branches, from the warm 
waters of the Atlantic Ocean. The genera Eugorgia, Verrill, and 
Leptogorgia, Milne Edwards, differ from Gorgonia in the char- 
acter of the spicules. In Xipliigorgia, Milne Edwards, from the 
West Indies, the branches are much compressed, forming at 
the edges wing-like ridges, which bear the zoopores in rows. 
Malacogorgia, Hickson, has no spicules. Cape of Good Hope. 

Fam. 7. Gorgonellidae. — In this family the horny axis is 
impregnated with lime. The surface of the coenenchym is 
usually smooth, and the spicules small. The colonies are some- 
times unbranched {Jun- 
cella). In the branching 
forms the axis of the 
terminal branches is 
often very fine and 
thread-like in dimen- 
sions. 

The principal genera 
are : — GorgoneUa, with 
a ramified flabelliform 
axis ; Ctenocella, with 
a peculiar double-comb 
manner of brandling ; 
and Juncella, ' whicli 
forms very long un- 
branched or slightly 
branched colonies, with 
club - shaped spicules. 
All tliese genera are found in shallow water in the tropical or 
semi-tropical regions of the world. Verrucclla is a genus with 
delicate anastomosing branches found principally in the sliallow 
tropical waters of the Atlantic shores. Like many of the Gorgo- 
nacea, with branches disposed in one plane (flabelliform) Verrucella 
frequently carries a considerable number of epizoic Brittle stars, 
which wind their flexible arms round the branches, and thus 
obtain a firm attachment to tlieir host. There is no reason to 
suppose that these Brittle stars are in any sense parasitic, as a 
specimen that bears many such forms sliows no sign of injury or 
degeneration, and it is i)0ssible they may even be of service to 




Fig. 157. — yerrucella guadaloupensis, with an epizoic 
Brittle star {Oph.) of similar colour. 



358 



COELENTERATA ANTHOZOA 



the Verrticella by preying upon other organisms that might be 
injurious. An interesting feature of the association is that the 
Brittle stars are of the same colour as the host, and the knob- 
like plates on their aboral surface have a close resemblance to 
the verrucae (Fig. 157). 



-^ 



Order V. Pennatulacea. 

The Sea-pens form a very distinct order of the Alcyonaria. 
They are the only Alcyonarians that are not strictly sedentary 
in habit, that are capable of independent movement as a whole, 
and exhibit a bilateral symmetry 
of the colony. No genera have 
yet been discovered that can be 
regarded as connecting links between 
the Pennatulacea and the other 
orders of the Alcyonaria. Their 
position, therefore, is an isolated one, 
and tlieir relationships obscure. 

The peculiarities of the order are 
due to the great growth and modi- 
fication in structure of the first 
formed zooid of the colony. This 
zooid (Oozooid, Hauptpolyp, or Axial 
zooid) increases greatly in length, 
develops very thick fleshy walls, 
usually loses its tentacles, digestive 
organs, and frequently its mouth, 
exhibits profound modification of its 
system of mesenteries, and in other 
ways becomes adapted to its func- 
tion of supporting the whole colony. 
Fig. 158.— Diagram of a Sea-pen. L. The axial ZOoid showS from an 

leaves composed of a row of auto- early stage of development a di^'ision 

zooids ; R, rachis ; St., stalk ; T, _ <' ° ^ 

anthocodia of the axial zooid, into two regions : a distal region 
g™!) '"P^""''"''- ^^^^'' ■^""- which produces by gennnation on 
the body-wall numerous secondary 
zooids, and becomes the rachis of the colony ; and a proximal 
region which becomes the stalk or peduncle, and does not pro- 
duce buds (Fig. 158). The secondary zooids are of two kinds: 




ALCVONARIA — PENNATULACEA 



359 




the autozooids and the siphonozooids. The former have the 
ordinary characters of an Alcyonariau zooid, and produce sexual 
cells ; the latter have no tentacles, a reduced mesenteric system, 
and a stomodaeum provided with a very wide siphonoglyph. 

The arrangement of the autozooids and siphonozooids upon 
the axial zooid is subject to great modifications, and affords the 
principal character for the classification of the order. In the 
Pennatuleae the autozooids are arranged in two bilateralh^ 
disposed rows on the rachis, forming 
the leaves or pinnae of the colony (Fig. 
158). The number in each leaf in- 
creases during the growth of the colony 
by the addition of new zooids in regular 
succession from the dorsal to the ventral 
side of the rachis^ (Fig. 159). In 
other Pennatulacea the autozooids are 
arranged in rows which do not unite to 
form leaves {Funiculina), in a tuft at 
the extremity of a long peduncle 
( JJnibellula), scattered on the dorsal side 
of the rachis {RenUla, Fig. 160), or 
scattered on all sides of the rachis 
{Cavernidaria, Fig. 161). In those 
forms in which the autozooids are 
scattered the bilateral symmetry of the 
colony as a whole becomes obscured. 
The siphonozooids may be found on the 

leaves {Ptevoeides), but more frequently between the leaves or 
rows of autozooids, or scattered irregularly among the autozooids. 
Usually the siphonozooids are of one kind only, but in Pen- 
natula miirrayi there is one specially modified siphonozooid at 
the base of each leaf,^ which appears to have some special but 
unknown function. 

In UnibeUula gracilis each siphonozooid bears a single pinnate 
tentacle, and in some other species of the same genus there is 
a tentacle which is not pinnate.'' 

^ Jungersen {Danish Ingolf Exjtcdition, Pennatuliiia, 1904) l:as shown that tliis 
is tlie correct nomenclature of the regions of the raciiis. Xearly all other autliors 
describe the dorsal side as ventral and the ventral as dorsal. 

- S. J. Hickson, Report British Association (Southport Meeting), 1903, p. 688. 

•" ilarshall, Trans. Boy. Soc. Edinb. xxxii. 1883, \k 143. 



Fig. 159. — Diagram of a portiou 
of a rachis of a Sea-pen. ant. 
The rows of autozooids ; 1-6, 
the order of age of the auto- 
zooids composing a leaf ; D, 
the dorsal side of the rachis ; 
.SV, the siphonozooids ; T' the 
ventral side of the rachis. 
(After Jungersen.) 



360 COELENTERATA — ANTHOZOA chap. 

The zooids and coenenchym are usually protected by a crust 
of coloured or colourless, long, smooth, needle -like, calcareous 
spicules, situated principally in the superficial layer, so as to leave 
the subjacent tissues soft and spongy in texture. In some cases 
the spicules are smooth double clubs, rods, discs, or irregular 
granules, and in Sarcoiihyllum, ChuneUa, some species of Umhellula 
and others, there is no calcareous skeleton. The tuberculated 
spindles, so common in other Alcyonaria, are not found in any 
species. In most genera a horny, or calcified horny rod is 
embedded in the central part of the axial polyp, serving as a 
backbone or support for its muscles. It is absent, however, in 
Benilla, and reduced or absent in Cavernidaria. 

The sexual organs are borne by the mesenteries of the auto- 
zooids only, and each colony is either male or female. There is 
no record of hermaphroditism in the order. The eggs contain 
a considerable amount of yolk, and fertilisation is effected in the 
sea-water after their discharge. The segmentation is irregular, 
and the free-swimming ciliated larva (of Benilla) shows the 
rudiments of the first buds from the axial polyp before it settles 
down in the mud. 

The Sea-pens are usually found on muddy or sandy sea- 
bottoms, from a depth of a few fathoms to the greatest depths of 
the ocean. It is generally assumed that their normal position is 
one with the peduncle embedded in the mud and the rachis erect. 
Positive evidence of this was given by Eumphius, writing in 
1741, in the case of Virgularia rumphii and V. juncea at 
Amboina,^ and by Darwin in the case of Stylatula darwinii at 
Bahia Blanca.^ 

"At low water," writes Darwin, "hundreds of these zoophytes 
might be seen projecting like stubble, with the truncate end 
upwards, a few inches above tlie surface of the muddy sand. 
When touched or pulled they suddenly drew themselves in with 
force so as nearly or quite to disappear." 

It is not known whether the Pennatulids have the power of 
moving from place to place when the local conditions become 
unfavourable. It is quite probable that they have this power, 
but the accounts given of the Sea-pens lying flat on the sand do 
not appear to be founded on direct observation. The fable of 

^ Ruiuphius, Amboinschc Rariteitkamer , 1741, p. 64. 
- Darwin, Naturalist' s Voyaije round the World, 1845, p. 99. 



ALCYONARIA PENNATULACEA 



Pcnnatula swimming freely " with iill its delicate transparent 
polypi expanded, and emitting tlieir usual brilliant phosphorescent 
light, sailing through the still and dark abyss by the regular and 
synchronous pulsations of tlie minute fringed arms of the whole 
polypi," appears to be based on a statement made by Bohadsch in 
1761, and picturesque though it be, is undoubtedly erroneous. 

The brilliant pliosphorescence of many species of Pennatulacea 
has been observed by many naturalists, and it is very probable 
that they all exhibit this property to some degree. The phos- 
phorescence appears to be emitted by the mesenteric filaments 
of the autozooids, but it is not yet determined whether the 
phenomenon is confined to these organs or is more generally 
distributed. 

The Pennatulacea are usually devoid of epizoites, but occa- 
sionally the parasitic or semi-parasitic Entomostracan Lamippe is 
found in the zooids. A small crab is also frequently found 
between the large leaves of species of Fteroeides. The most 
remarkable case of symbiosis, however, has recently been observed 
in the form of an encrusting Gymnoblastic Hydroid ^ living on 
the free edge of the leaves of a species of Ptilosarcus. 

The order Pennatulacea is divided into four sections. 

Sect. 1. Pennatuleae. — In this section the colony is distinctly 
liilaterally symmetrical, and the autozooids are arranged in rows 
with their body-walls fused to form leaves. 

The genus Pteroeides, the representative genus of the family 
Pteroeididae, is a fleshy Sea-pen found in shallow sea water in 
the warm waters of the Pacific Ocean and in the Mediterranean. 
It has large leaves with long spiny, projecting spicules, and the 
siphonozooids are borne by the leaves. Pennatula, the represen- 
tative genus of the family Pennatulidae, has a wider distribution 
in area and in depth. Pennatula p]iosp)liorea is a common l)ritish 
species, found in depths of 10 to 20 fathoms in many localities 
off our coasts. It is about 5 inches in length. There are several 
varieties of this species distributed in Atlantic waters. Penna- 
tida grandis is a magnificent species found in Norwegian fjords, 
in the Faeroe Channel, and off the northern coasts of K America, 
in depths of from 50 to 1255 fathoms. Specimens have been 

' To be described in the forthcoming Report on the Pennatulidae of the 
"Siboga" E.xpedition. 



362 COELENTERATA ANTHOZOA chap. 

obtained no less than 2^ feet in length. P. murrayi and P. 
naresi are species of the genvis found at depths of a few hundred 
fathoms in tropical seas. 

The genus Virgularia, belonging to the family Virgulariidae, 
is represented in the British seas by V. mirahilis, a long slender 
Sea-pen found in many localities off the Scottish coasts. 

Sect. 2. Spicatae. — This section includes those Sea-pens in 
which the autozooids are arranged bilaterally on the axial zooid 
in rows or more irregularly, but do not unite to form leaves. It 
is a large section and contains many widely divergent genera. 

The family Funiculinidae is represented on our coasts by 
Funiculina quadrangular is, a long and slender Sea-pen 2 to 3 
feet in length. The autozooids are arranged in oblique rows, 
and the siphonozooids are on the ventral side of the rachis. 
There is one point of special interest in this genus. The 
siphonozooids appear to change as the colony grows and to 
become autozooids. If this is the case it may be more correct to 
describe the genus as devoid of true siphonozooids. 

The fcimily Anthoptilidae contains the species Anthoptilum 
grandifiorum, which has a wide distribution in depths of 130 to 
500 fathoms in the N. and S. Atlantic Ocean. It is perhaps the 
largest of all tlie Pennatulacea, specimens having been obtained 
from the Cape of Good Hope o^^er 4 feet long with expanded 
autozooids, each more than half an inch in length. 

The family Kophobelemnonidae contains a number of forms 
with remarkably large autozooids arranged in irregular rows on 
the two sides of the rachis. The siphonozooids are numerous 
and scattered, and their position is indicated by small papilliforni 
calices on the coenenchym. The surface of these pens is usually 
rough, owing to the presence of numerous coarse projecting 
spicules. Kophohelemno^i occurs in the Mediterranean in deep 
water, off the coasts of Ireland and Scotland, and in other regions. 

The ftimily Umbellulidae contains some of the most remarkable 
and interesting exaui[)les of the deep-sea fauna. The peduncle is 
very long and the rachis stunted and expanded. The autozooids 
are of great size, non-retractile, and arranged in a cluster or 
rosette on the terminal rachis. There is a wide structural range 
between the species. Some species have numerous large spicules, 
others have none. In some species the siphonozooids have a 
single pinnate or digitate tentacle, in others the siphonozooids 



XIII ALCVONARIA — PENNATULACEA 363 

are of the usual type. Umlellula appears to be a somewhat rare 
but cosmopolitan genus in deep water, extending from the Arctic 
to the Antarctic region in water ranging from 200 to 2500 
fathoms. 

The interesting genus Chunella was discovered by the German 
"Valdivia" Expedition at a depth of about 420 fathoms off the 
coast of E. Africa, and subsequently by the Dutch " Siboga " 
Expedition at a depth of about 500 fathoms in the Malay 
Archipelago. According to Kiikenthal,^ this genus with another 
closely allied genus Am'phianthus should form a new section of 
Pennatulacea, the Verticilladeae. Chunella has a long and very 
delicate rachis and peduncle, and the former terminates in a 
single autozooid and has five or six whorls of three autozooids, 
situated at considerable distances from one another. Spicules are 
absent. The full description of this genus has not yet been 
published, but it is clear that it occupies a very isolated position 
in the order. 

Sect. 3. Renilleae. — This section contains a single family 
Renillidae and a single genus Eenilla (Fig. 160). The rachis 



Fig. 160. — Renilla reniformis, a small specinifn (34 mm.), showing the dorsal side of the 
expanded rachis. A, autozooid ; H, tlie mouth of the a.xial zooid ; .v, siplioiiozooid ; 
St, the short stalk. (After Kolliker.) 

is expanded into a ilattencd cordate form set at an angle to the 
peduncle, and the zooids are confined to the dorsal surface, which 
is uppermost in the natural position of the colony. The peduncle 
is short and does not contain an axial skeleton. The colour of 

1 Zool. Anz. XXV. 1902, 11. 302. 



364 COELENTERATA — ANTHOZOA chap, xiii 

this Sea-pen is usually violet when dried or preserved. Specimens 
of Renilla are very abundant in shallow water in some localities 
on the Atlantic and Pacific coasts of N. America, but the genus 
has also been obtained from the Ked Sea and the coast of Australia. 
A popular name for this genus is " Sea pansy." 

Sect. 4. Veretilleae. — This section contains a number of genera 
in which the bilateral arrangement of the zooids is obscured by tlieir 
gradual encroachment on the dorsal side of the axial polyp. The 
rachis and peduncle are t?iiick and fleshy, and the autozooids and 



Si 



Fig. 161. — Cavermilwi la ohesa in uitozooil, "?( '-iphonozooid ; xSY, stalk. 
,Attci KJhkci.) 

siphonozouids are irregularly distriliuted all round the rachis. 
The genus Cavernularia is not uncommonly found in moderate 
depths of water in the Indian and Pacific Ocean, and is distin- 
guished from the other genera by the reduction of the skeletal 
axis. Other genera are Veretillum, Mediterranean and Atlantic 
Ocean, and LUuaria, Indian Ocean. 



CHAPTER XIV 

ANTIIOZOA {coyTINL'ED) : ZOANTHAKIA 

Sub-Class 11. Zoantharia. 

The Zoantharia exhibit a great deal more diversity of form and 
structure than the Alcyonaria. The sub-class is consequently 
difficult to define in a few words, and it may be taken to include 
all the Anthozoa which do not possess the typical Alcyonarian 
characters. 

All the orders, with the exception of the Antipathidea and 
Zoanthidea, contain genera of solitary zooids, and the orders 
Edwardsiidea and Cerianthidea contain no genera that form 
colonies. In the Madreporaria, Zoanthidea, and Antipathidea, 
on the other hand, colonies are formed composed of a very large 
number of individuals which frequently attain to a very great 
size. The term " Sea-anemone " is commonly used in writing 
about the solitary Zoantharia which do not form any skeletal 
structures, and the term " Coral " is applied to all those Zoantharia 
which do form a skeleton. 

In a scientific treatise, however, these popular terms can no 
longer be satisfactorily employed. The " Sea-anemones " exhibit 
so many important differences in anatomical structure that they 
must be placed in at least three distinct orders that are not 
closely related, and the organisms to which the term Coral has 
been applied belong to so many organisms — such as Alcyonaria, 
Hydrozoa, Polyzoa, and even Algae — that its use has become 
indeterminate. 

Whilst these terms must disappear from the systematic part 
of Zoology, they may still be employed, however, in the description 
of a local fauna or coral reef to signify the soft solitary zooids on 

365 



366 COELENTERATA ANTHOZOA chap. 

the one hand, and the organisms, animals or plants, wliich form 
large, massive skeletons of carbonate of lime, on the otlier. 

The form of the solitary zooids and of tlie colony of zooids in 
the Zoantharia, then, may be very divergent. In the Actiniaria 
we find single soft gelatinous zooids of considerable size adherent to 
rocks or half-buried in the sand. Among the Madreporaria we 
find great branching colonies of thousands of zooids supported by 
the copious skeleton of carbonate of lime that they have secreted. 
Among the Antipathidea, again, we find a dendritic skeleton of a 
dark horny substance, formed by a colony of small zooids that 
cover it like a thin bark. The majority of the Zoantharia are, 
like other zoophytes, permanently fixed to the floor of the ocean. 
"Where the embryo settles, there must the adult or colony of 
adults remain until death. Some of the common Sea-anemones 
can, however, glide slowly over the surface on which they rest, and 
thus change their position according to the conditions of their 
surroundings. Others (the Minyadidae) float upside down in the 
sea, and are carriei hither and thither by the currents. Others, 
again (Cerianthus, Edwardsia, Peachia), burrow in the sand or 
mud at the sea-bottom. 

The structure of the zooid varies considerably, but in tlie 
following characters differs from the zooid of the Alcyonaria. 
The tentacles are usually simple finger- 
like processes, and when they bear 
secondary pinnae these can readily 
be distinguished from the rows of 
secondary pinnules of the Alcyonarian 
tentacle. The number of tentacles 
is very rarely eiglit (young Halcamfo), 
and in these cases they are not 
pinnate. The number of tentacles 
may be six (many Antipathidea and 
c ^ some zooids of Madre.'pord), twelve 

Fig 162.-Large (A) and small (Madrcvora), some multiple of six, or 

(B) plumose tentacles of ylc;;;- ^ . -* . ^ ' 

nodendron lyiumosum. Large an indefinite number. In the Tlialas- 
S2fnr! ^f'"'''^] ^^} ^^T°'' sianthidae and some other families of 

tentacles of A. glomeratum. 

(After Haddon.) Actiuiaria the tentacles are plumose, 

but do not exhibit the regular 
pinnate form of the tentacles of Alcyonaria. 

As regards the number of mesenteries, the Zoantharia exhibit 





XIV ZOANTHARIA MESENTERIES 367 

very great variety. It lias been shown tliat there is frequently 
a stage in their development during which there are only eight 
mesenteries. This stage is usually called the Edvxirdsia stage. 
Tliese eight mesenteries are arranged in bikiteral pairs as 
follows: — One pair is attached to the body -wall and reaches 
to tlie dorsal side of the stomodaeuni, and is called the pair of 
dorsal directives ; a corresponding pair attached to the ventral 
side of the stomodaeuni is called the pair of ventral directives. 
The other two pairs are the lateral mesenteries. To these four 
pairs are added, at the close of the Echvardsia stage, two additional 
pairs, making in all twelve mesenteries (cf. Fig. 163). 

These six primary pairs of mesenteries, conveniently called 
the " protocnemes " by Duerden, may be traced in the develop- 
ment and recognised in the adult of the majority of Zoantharia. 
But the number of the mesenteries is usually increased in the 
later stages by the addition of other mesenteries called the 
" metacnemes." The metacnemes differ from the protocnemes 
in that they usually appear in unilateral pairs, that is to say, 
in pairs of which both members arise on the same side of the 
stomodaeum, and the number is very variable throughout the 
group. The space enclosed by a pair of mesenteries is called an 
" entocoele," and the space between two pairs of mesenteries is 
called an " ectocoele." 

The twelve protocnemes are usually complete mesenteries, that 
is to say, they extend the whole distance from the body-wall to 
the stomodaeuni, while the metacnemes may be complete or in- 
complete ; in the latter case extending only a part of the distance 
from the body-wall towards the stomodaeuni. 

We find, therefore, in making a general survey of the anatomy 
of the Zoantharia that there is no general statement to be made, 
concerning the number or arrangement of the mesenteries, which 
holds good for the whole or even for a considerable portion of the 
genera. 

The bands of retractor muscles are, as in the Alcyonaria, 
situated on one face only of the mesenteries (except in the 
Antipathidea and Cerianthidea), but an important character of 
the Zoantharia is that the muscle bands on the ventral pair 
of directives are situated on the dorsal faces of these mesenteries, 
and not on the ventral faces as they are in Alcyonaria. 

In the Edwardsiidea there are only eight complete mesenteries. 



368 



COELENTERATA ANTHOZOA 



but a variable number of other rudimentary and incomplete 
mesenteries have recently been discovered by Faurot.^ In the 
Zoanthidea the mesenteries are numerous, but the order is 
remarkable for the fact that the dorsal directives are incomplete, 
and that, of the pairs of metacnemes that are added, one mesentery 
becomes complete and the other remains incomplete. In most of 
the genera of the Antipathidea there are only ten mesenteries, 
but in Leiopathes there are twelve, and as they bear no bands 




Fill. 163. — Diagrams of transverse sections of 1, Alcyonarian ; 2, Eilwardsia; 3, Ceri- 
anthus ; 4, Zoanthus ; 5, Favia ; 6, Mcidrepora. I)D, the dorsal directive mesen- 
teries ; VD, the ventral directives ; I- VI, tlie protocnemes in order of sequence. 



of retractor muscles it is difficult to determine accurately their 
true relation to the mesenteries of other Zoantharia. 

In the Cerianthidea the mesenteries are very numerous, and 
increase in numbers by the addition of single mesenteries alter- 
nately right and left in the ventral inter -mesenteric chamber 
throughout the life of the individual. These mesenteries do 
not bear retractor muscles. 

In the Actiniaria and Madreporaria, with the exception of 

the genera Madre.pora, Porites, and a few others, there are also 

very many mesenteries. The two pairs of directives are usually 

present, but they may nOt occur in those zooids that are produced 

1 Faurot, Arch. Zool. Expvr. 3rcl ser. iii. 1895, p. 71. 



XIV ZOANTIIARIA MESENTERIES — STOMODAEUM 369 

asexually by tission (see p. 388). The iiietacnemes are fre- 
quently formed in regular cycles, and in many genera appear 
to be constantly some multiple of six (Fig. 163, 5). 

In Madrepora and Porites ^ the two pairs of directives and 
two pairs of lateral protocnemes are complete ; the other two 
pairs of protocnemes are, however, incomplete ; and metacnemes 
are not developed (Fig. 163, e). 

The stomodaeum is usually a flattened tube extending some 
distance into the coelenteric cavity and giving support to the 
inner edges of the complete mesenteries ; in many of the 
Madreporaria, however, it is oval or circular in outline. In 
most of the Actiniaria there are deep grooves on the dorsal and 
ventral sides of the stomodaeum, but in Zoanthidea the groove 
occurs on the ventral side only and in the Cerianthidea on the 
dorsal side only. In the Madreporaria these grooves do not occur 
or are relatively inconspicuous.^ In the Alcyonaria the siphono- 
glyph exhibits a very marked differentiation of the epithelium 
(see Fig. 148, p. 334), and the cilia it bears are very long 
and powerful. It has not been shown that the grooves in 
the Zoantharia show similar modifications of structure, and they 
are called by the writers on Zoantharia the sulci. There is no 
difference in structure, and rarely any difference in size, between 
the dorsal sulcus and the ventral sulcus in the xlctiuiaria, and 
the use of the word — sulculus — for the former is not to be 
commended. 

The mesenteries bear upon their free edges the mesenteric 
filaments. These organs are usually more complicated in 
structure than the corresponding organs of the Alcyonaria, and 
the dorsal pair of filaments is not specialised for respiratory 
purposes as it is in that group. 

In many genera the mesenteric filaments bear long, thread- 
like processes — the " acontia " — armed with gland cells and 
nematocysts which can be protruded from the mouth or pushed 
through special holes (the " cinclides ") in the body-wall. 

The gonads in the Zoantharia are borne upon the sides of the 
mesenteries and are usually in the form of long lobed ridges 
instead of being splierical in form, and situated at the edges of 
the mesenteries as they are in the Alcyonaria. 

' Duerden, ^[nn. Acad. Jrashington, 3rd Ser. viii. 1902. 
'•' Duerden, I.e. p. 43G. 
VOL. I 2 B 



370 COELENTERATA ANTHOZOA chap. 

Nearly all tlie zooids and even the colonies of tlie Zoantharia 
are unisexual, but some species, such as Manicina areolata 
(Wilson), Meandrina lahyrinthica (Duerden), Cerianthus mem- 
hranaceus, and others, are hermaphrodite. Mr. J. S. Gardiner has 
recently given reasons for believing that the genus Flabellum 
is protandrous. 

Skeleton. — The soft tissues of the Zoantliarian zooids may 
be supported or protected by hard skeletal structures of various 
kinds. In the Zoanthidea and the Actiniaria there are many 
species that have no skeletal support at all, and are quite naked. 
These seem to be sufficiently well protected from the attacks of 
carnivorous animals by the numerous nematocysts of tlie 
ectoderm, and perhaps in addition by a disagreeable flavour in 
their tissues. Anemones do not seem to be eaten habitually by 
any fish, but cases have been described of Feachia Jiastata being 
found in the stomach of the Cod, and of Edwardsia in the 
stomach of the Flounder.^ On the Scottish coasts Anemones are 
occasionally used with success as a bait for cod." The body- 
wall of Edwardsia, however, is protected to a certain extent 
by the secretion of a mucous coat in which grains of sand and 
mud are embedded. Some Anemones, such as Urticina, Feachia, 
and others, lie half-buried in the sand, and others form a cuticle, 
like that of Edwardsia, to which foreign bodies are attached. 

Cerianthus is remarkable for constructing a long tube com- 
posed of a felt-work of discharged nematocysts mixed with mud 
and mucus, into which it retires for protection. In the Zoantliidea 
the body-wall is frequently strengthened by numerous and 
relatively large grains of sand, which are passed through the 
ectoderm to lie in the thick mesogloea. 

In the Madreporaria a very elaborate skeleton of carbonate of 
lime is formed. In the solitary forms it consists of a cup-shaped 
outer covering for the base and column of the zooid called the 
" theca," of a series of radial vertical walls or " septa " projecting 
into the intermesenteric chambers carrying the endodermal 
lining of the coelenteric cavity with them, and in some 
cases a pillar, the " columella," or a series of smaller pillars, the 
" pali " projecting upwards from the centre of the base of the 

1 M'Intosh, "The Marine Invertebrates and Fishes of St. Andrews," 1875, pp. 
Sr, 38. 

" M'Intosh, "The Resources of the Sea," 1899, pp. 10, 129. 



XIV ZOANTHARIA SKELETON REPRODUCTION 37 I 

theca towards the stomodaeuin. In the colonial forms the theca 
of the individual zooids is continuous with a common colonial 
skeleton called the " coenosteum." This is solid in the Imper- 
forate corals, and it supports at the surface only a thin lamina 
of canals and superficial ectoderm. In the Perforate corals, 
however, the coenosteum envelopes and surrounds the canals 
during its formation, and thereby remains perforated by a 
network of fine channels. In the colonial Madreporaria the 
skeletal cups which support and protect the zooids are called 
the " calices." 

The skeleton of the Antipathidea is of a different nature. 
It is composed of a horny substance allied to keratin. When 
it is old and thick, it usually has a polished black appearance, 
and is commonly termed " black coral." The surface of this 
kind of coral is ornamented with thorny or spiny projections, 
but it is never perforated by calices or canal systems. It forms 
a solid axis for the branches of the corals, and all the soft parts 
of the zooids and coenosarc are superficial to it. 

It was formerly considered that this type of coral, which 
shows no trace of the shape and form of the living organisms 
that produce it, is of a different character to the calcareous 
skeleton which exhibits calices, septa, pores, and other evidence 
of the living organism, and it was called a " sclerobase " to 
distinguish it from the " scleroderm " of the Madreporaria. 

It is now known that both the sclerobasic skeleton and the 
sclerodermic skeleton are products of the ectoderm, and conse- 
quently these expressions are no longer in general use. 

Asexual reproduction in the Zoantharia may be effected by 
continuous or discontinuous fission or gemmation. 

In the Edwardsiidea, Actiniaria, and Cerianthidea, that is to 
say in the animals popularly known as Sea-anemones, asexual 
reproduction does not commonly occur, but nevertheless a good 
many instances of it are now known in individual genera. In 
Actinoloha {Metriclium), for example, I'arker has described a case 
of complete longitudinal fission, and Duerden states that it 
occurs in the West Indian Anemones AdinotrT/x and Bicordea. 
A still more remarkable form of asexual reproduction known as 
transverse fission has been described in the genus Gonacti7iia} 
In this case, the body of the Anemone becomes constricted in 

1 H. Prouho, Arch. Zool. Ex2)tr. 2nd ser. ix. 1891, p. 247. 



372 COELENTERATA ANTHOZOA chap. 

the middle, a circlet of tentacles is formed below the constriction, 
and division takes place. The upper half floats away with the 
original tentacles and stomodaeum and becomes attached by 
the base in another place ; the lower half remains behind and 
develops a new stomodaeum, mesenteric filaments, and sexual 
organs. In some of the Actiniaria another form of asexual 
reproduction occurs, known as " Pedal laceration." In the 
common British Actinoloha, for example, so often kept in 
aquaria, the pedal disc sometimes spreads on the glass or rock 

upon which the animal 
rests, in the form of a 
thin membrane or film 
",— - of an irregular circular 
shape, nearly twice the 
diameter of the column. 
As the Anemone glides 
along, the film remains 
behind and breaks up 
into a number of hemi- 

FlG. 164.— Longitudinal lission of Actinoloba. Spherical droplctS, which 

(After Agassizan,! Parker.) -^^ ^ ^^^^ ^^^^ develop 

tentacles, a mouth, mesenteries, and the other organs of a 
complete and independent Anemone. A similar method of 
reproduction has been observed in several species of Sagartia. 
A true process of discontinuous gemmation has also been observed 
in Gonactinia, in Corynactis, and in Actinoloha. 

In the Madreporaria, Zoanthidea and Antipathidea, the 
usual method of reproduction to form the colonies is continuous 
gemmation. The new zooids that are added to the colony as 
it grows arise as buds, either from the superficial canals of the 
ccenenchym, or from the base or body-wall of the older zooids. 
In these cases the young zooids acquire the same number of 
mesenteries, and the same characters of the stomodaeum as the 
original parent. Some further particulars of asexual repro- 
duction in the Madreporaria are given on p. 387. 

The sexual reproduction of a great many species of Zoantharia 
has now been observed. The eggs are, as a general rule, ripened 
in batches, and fertilisation is effected before their discharge from 
the body. In some cases the sexual condition is seasonal. In 
temperate climates the generative organs ripen in the spring and 




XIV ZOANTHARIA LARVAE FOOD 373 

summer montlis, and remain small and relatively inconspicuous 
in the colder weather ; but British Sea-anemones, when kept in 
an aquarium and regularly fed, will breed nearly all the year 
round. The corals of the tropics living in warmer water of a 
more regular temperature show considerable variety in their 
breeding habits. Thus Duerden found that colonies of Favia, 
Manicina, Siderastraea and Porites are fertile at nearly all times, 
whereas colonies of 3fadrepora, Orhicella and Cladocora were 
rarely so. In nearly all cases the fertilisation is effected, and 
segmentation of the ovum occurs within the body of the parent, 
the young Zoantharian beginning its independent life as an 
oval or pear-shaped ciliated larva. 

There are a great many cases among the Actiniaria in which 
the embryos are retained within the coelenteron, or in special 
brood pouches of the parent (p. 379), until a stage is reached 
with twelve or more tentacles. 

The oval or pear-shaped larva swims about for a few days or 
hours, and then settles down on its aboral end. In swimming, 
the aboral end is always turned forwards. In the larva of 
Lebrunia coralligens and Bhodactis sancti-thomae, a distinct 
sense organ has been observed upon the aboral extremity, and 
a similar but less distinct organ on the larva of Actinia equina. 
These organs are of considerable interest, as they are probably 
the only specialised sense organs known to occur in the 
Zoantharia. 

The larvae of Zoantharia present, as a rule, very little 
variation from the type described, and live but a short time if 
they fail to find a suitable place for fixation. The colour is 
usually white and opaque, but in some species the endoderm may 
be coloured yellow by Zooxanthellae (cf pp. 86, 125). 

The larvae of the Cerianthidea, however, are remarkable 
and exceptional. After the larva of tliese animals has passed 
tlirough the gastrula stage, a certain number of mesenteries and 
tentacles are formed, and it rises in the water to live a pelagic 
life of some duration. This larva is known as Arachnadis, and 
is not unfrequently found in the plankton. 

The character of the food of the Zoantharia varies with the 
size of the zooids, the occurrence of Zooxanthellae in the 
endoderm, and local circumstances ; but in general it may be 
said to consist mainlv of small livintr animals. 



374 COELENTERATA ANTHOZOA chap. 

Sea-anemones kept in an aquarium will readily seize and 
devour pieces of raw beef or fragments of mussel that are offered 
to them ; but they may also be observed to kill and swallow the 
small Crustacea that occur in the water. "When a living animal 
of a relatively small size comes within range of the tentacles, 
it appears to be suddenly paralysed by the action of the nemato- 
cysts and held fast. The tentacles in contact with it, and 
otliers in the neighbourhood but to a lesser extent, then bend 
inwards, carrying the prey to the moutli. The passage of the 
food through the stomodaeum is effected partly by ciliary, and 
partly by muscular action, and the food is then brought to the 
region of the mesenteric filaments where it is rapidly disinte- 
grated by the digestive fluids they secrete. Any unsavoury or 
undigested portions of the food are ejected by the mouth. 

Very little is known concerning the food of the Madreporariau 
Corals. Many investigators have noticed that the zooids of 
preserved specimens very rarely contain any fragments of animal 
or plant bodies that could possibly be regarded as evidence of 
food. It is possible that many Corals derive a part, perhaps in 
some cases a considerable part, of their nourishment from the 
symbiotic Zooxanthellae (pp. 86, 125) which flourish in the 
endoderm ; but it is improbable that in any case this forms the 
only source of food supply. The absence of food material in 
the cavities of the zooids may perhaps be accounted for by the 
fact that nearly all the Corals are fully expanded, and therefore 
capable of catching their food only at night. Corals are usually 
collected during the daytime, and therefore during the period 
of rest of the digestive organs. 

It is true that nearly all Corals do exhibit Zooxanthellae in 
their endoderm, but there are some species from whicli they 
are nearly or wholly absent, such as Astrangia solitaria and 
Phyllangia americana on the West Indian reefs,^ and the 
Pocilloporidae. The absence of any signs of degeneration in 
the tentacles or digestive organs of those corals with Zooxanthellae 
as compared with those without them suggests, at any rate, that 
the Zooxanthellae do not supply such a large proportion of the 
food necessary for the support of the colonies as to warrant any 
relaxation of the efforts to obtain food by other means. Mr. 
Duerden found that when living Annelids are placed upon the 
^ Duerden, Mem. Acad. Washington, viii. 1902, p. 437. 



XIV ZOANTHARIA EDWARDSIIDEA 37 5 

tentacles of a living Siderastraea — a genus with Zooxanthellae, 
the tentacles at once close upon them and prevent their escape. 
The general conclusion seems to he, therefore, that the Madre- 
porarian Corals feed upon small animals in much the same way 
as the Sea-anemones, whether they have Zooxanthellae or not, 
but that in general they feed only at night. 

Age. — It is known that Sea-anemones kept in an aquarivmi 
and regularly fed will live for a considerable number of years with- 
out showing signs of weakness or failing health. TDalyell kept 
in an aquarium a specimen oi Actinia viesemhryanthemum, which. 
lived for sixty-six years and then died a natural death ; and 
specimens of Sagartia, still living, are known to be about fifty 
years old.^ The unnatural conditions of life in an aquarium may 
have favoured the longevity of these specimens, and it would not 
be reasonable to conclude from these records that the average life 
of a full-grown Anemone on the rocks is more than thirty or 
thirty-five years, and perhaps it is a good deal less. 

As regards the Madreporarian Corals, we know but little con- 
cerning their duration of life. An examination of any living 
coral reef is sufficient to convince an observer that the power of 
asexual reproduction of the colonial forms is not unlimited ; that 
colonies, like individuals, have a definite span of life, and that 
they grow old, senile, and then die a natural death if spared in 
their youth from accident and disease. Mr. Gardiner has 
calculated that the duration of life in solitary Corals like Flabelliim 
is about twenty-four years, in colonial forms such as Goniastraea, 
Prionastraea, Orhicella, and Pocilloi^ora, from twenty -two to 
twenty-eight years. 

Order I. Edwardsiidea. 

This order contains only a few genera and species of small 
size living in shallow water in various parts of the world. In 
external features they closely resemble several genera of the 
Actiniaria, particularly those belonging to the family Hal- 
campidae. The distinguishing character of the order is to be 
found in the system of mesenteries. In all the species only 
eight mesenteries are complete, namely, the first two pairs of 
protocnemes, and the two pairs of directives (Fig. 163, 2), 

^ Ashworth and Annandale, Proc. Roy. Soc. Edinb. xxv. 1904, p. 11. 



Z7^ 



COELENTERATA ANTHOZOA 



and these usually support such large and powerful muscle-bands 
that they appear to be the only mesenteries present. A careful 
examination of transverse sections, however, reveals the fact that 
other mesenteries are present. The fifth and sixth pairs of 
protocnemes seem to be invariably represented, and two or three 
pairs of metacnemes can also be traced in some species. 

The tentacles are variable in number. In Ed'wardsia beau- 
tempsii, for example, they may be 14-16 in number, arranged in 

a single row round the 
oral disc. In E. timida 
they vary from 20 to 24. 
The normal number ap- 
pears to be eight tentacles 
of the first cycle, corre- 
sponding to the eight 
primary inter-mesenteric 
chambers, plus 6 or 12 
tentacles, corresponding 
with the chambers limited 
by the more rudimentary 
mesenteries, — making a 
total of 14 or 20 ten- 
tacles ; but by the sup- 
pression of the two 
primary dorso - lateral 
tentacles, or by the addi- 
tion of tentacles of 
another cycle, the actual 
number is found to vary 
considerably. The 

Edwardsiidea are not 
fixed to the bottom, but are usually found deeply embedded in 
sand, the aboral extremity being pointed and used for burrowing 
purposes. The general colour of the body is yellow or yellowish 
brown, but it is partly hidden by a short jacket of mud or 
sand and mucous secretion. The oral crown frequently shows 
beautiful colours. De Quatrefages relates that in Edwardsia 
leautempsii the oral cone is golden yellow, and the tentacles, 
transparent for the greater part of their extent, terminate in 
opaque points of a beautiful yellowish red colour. 




Fig. 165. 



-Ed'wardsia beautempsii. 
(After de Quatrefages.) 



Nat. size. 



XIV ZOANTHARIA ACTINIARIA 377 

Fam. 1. Edwardsiidae. — Several species of this family have 
been fouiul in the British area. They are very local in their 
distribution, but sometimes occur in great numbers. 

Edwardsia heaiUem2^sii occurs in shallow water near the 
shores of the English Channel and has been found in Bantry 
Bay ; and E. carnca and E. timida have also been found in the 
Channel. E. tccta is a recently described species from the S. 
Irish coast, and E. aUmani and E. goodsiri are found in Scottish 
waters. 

Fam. 2. Protantheidae. — This family, constituted for the 
reception of three remarkable genera, is now usually included in 
the order Edwardsiidea on the ground that not more than eight 
mesenteries are complete. 

The genus Gonactinia exhibits the very exceptional character 
of having a thick layer of muscles in the body -wall (cf. 
Cerianthidea, p. 409), and it is also remarkable for the frequency 
with which it reproduces itself asexually by longitudinal and, 
more rarely, by tranverse fission. It has been found in Norway, 
the Mediterranean, and on the reefs of New Caledonia. The other 
genera of the family are Oractis from California, and Proiantliea 
from the coast of Sweden. 

Order II. Actiniaria. 

This order contains nearly all the animals popularly known 
as Sea -anemones. They are usually found in shallow water, 
attached by a broad basal disc to shells, stones, or sea- weeds. In 
the Halcampidae, however, the aboral extremity ends in a blunt 
point as in the Cerianthidea and Edwardsiidea, and the animals 
live half-buried in sand or mud. The Minyadidae of the southern 
oceans are pelagic in habit, floating near the surface of tlie sea 
with tlie mouth turned downwards. They are supported in the 
water by a bladder, formed by an involution of the pedal disc, 
and filled with gas. 

Many of the Sea-anemones are found in symbiotic association 
with other animals. The common Adamsia of the British coasts 
is found on whelk shells containing hermit crabs. The crab is 
probably protected from the attacks of some of its enemies by 
the presence of the Anemone, which in its turn has the advantage 
of securing some fragments of the food captured and torn to 



378 COELENTERATA ANTHOZOA chap. 

pieces by the crab. The association, therefore, seems to be one 
of mutual advantage to the messmates. It is a noteworthy fact 
that in these associations the species of Sea-anemone associated 
with a particular hermit crab is nearly always constant. Thus 
in the English Channel, Adamsia 2')ciUiata is almost invariably 
found associated with Eupag^irus prideauxii, and Adamsia ron- 
delctii with Eupagurus hernhaoxhis. But, perhaps, the most 
remarkable association of this kind is to be seen in the case of 
the little shore crab of the Indian Ocean, Melia tesselata, which 
invariably holds in each of its large claws a small Sea-anemone. 
Mobius, who originally described this case, relates that when the 
crab is robbed of its Anemone it appears to be greatly agitated, 
and hunts about on the sand in the endeavour to find it again, 
and will even collect the pieces, if the Anemone is cut up, and 
arrange them in its claw.^ 

Another very interesting association is that of certain fish 
and Crustacea with the large Sea -anemones of the tropical 
Australian coast." Thus Stoichactis kenti almost invariably 
contains two or more specimens of the Percoid fish A7nphi23rion 
percula. This fish is remarkable for its brilliant colour, three 
pearly white cross -bands interrupt a ground plan of bright 
orange-vermilion, and the ends of the cross-bands as well as the 
fins are bordered with black. In another species a prawn of 
similar striking colours is found. These companions of the giant 
Anemones swim about among the tentacles unharmed, and when 
disturbed seek refuge in the mouth. It has been suggested that 
these bright and attractive animals serve as a lure or bait for 
other animals, which are enticed into striking distance of the 
stinging threads of the Anemone, but how the commensals escape 
the fate of the animals they attract has yet to be explained. 

In a considerable number of Sea-anemones, such as Actinoloha 
marginata and A. dianthus, some species of Sagartia, Actinia 
cari, Anemonia sulcata, and Calliactis 2^<^'>"ctsiiica, the fertilisa- 
tion of the eggs and their subsequent development take place in 
the sea water.^ In a great many others, such as Bunodes (several 
species), Cereactis aurantiaca, Sagartia troglodytes, Bunodactis 

' For recent experiments on this case, see a forthcoming paper by J. E. Duerdcn 
{P.Z.S.). 

^ Saville Kent, "Great Barrier Reef," London, 1893, p. 14r). 
^ 0. Carlgren, Biolorj. Centralhl. xxi. 1901, p. 480. 



XIV ZOANTHARIA ACTINIARIA 379 

gemmacea, etc., the embryos are discharged into the water from 
the body-cavity of the parent, at a stage with six or twelve 
tentacles. In the Arctic species of the genera Urticina and 
Actinostola, however, the embryos are retained witliin the body 
of the parent until several cycles of tentacles are developed, and 
in Urticina crassicornis the young have been found with the full 
number of tentacles already formed. In Epiactis inolifera from 
Puget Sound, the young Anemones attach themselves to tlie body- 
wall of tlie parent after their discharge, and in Ujnactis mnrsu- 
jnalis, Pseudo2Jhellia arctica, Ejngonactis fecu7ida, and other species 
from cold waters, the young are found in numerous brood sacs 
opening in rows on the body- wall. It is not known for certain 
how these embryos enter the brood sacs, but it is possible that 
each sac is formed independently for a young embryo that has 
settled down from the outside upon the body- wall of the parent. 
The most specialised example of this kind of parental care in the 
Sea-anemones is seen in Marsupifer valdiviae from Kerguelen, in 
which there are only six brood sacs, but each one contains a great 
many (50-100) embryos. 

The wonderful colours of our British Sea-anemones are familiar 
to most persons who have visited the sea-side. The common 
Actinia viesemlryanthemum of rock pools, for example, is of a 
purple red colour. The base is usually green with an azure line. 
Around tlie margin of the disc there are some twenty-five tur- 
quoise blue tubercles. On each side of the mouth there is a 
small purple spot, and the numerous tentacles forming a circlet 
round the mouth are of a pale roseate colour. Nothing could be 
more beautiful than the snowy-white Actinoloha dianthus or the 
variegated Urticina crassicornis. 

Similar wonderful variety and beauty of colour are seen in 
the Sea-anemones of other parts of the world. Thus Saville 
Kent ^ in describing a species of the gigantic Stoichactis of the 
Australian Barrier Eeef says, " the spheroidal bead-like tentacles 
occur in irregularly mixed patches of grey, white, lilac, and 
emerald green, the disc being shaded with tints of grey, while 
the oral orifice is bordered with bright yellow." 

The order Actiniaria contains a large number of families, 
presenting a great variety of external form and of detail in 
general anatomy. The definitions of the families and their 

1 Saville Kent, "The Great Barrier Reef," 1893, p. 144. 



380 COELENTERATA ANTHOZOA chap. 

arrangement in larger groups have presented many difficulties, 
and have led to considerable differences of opinion ; and even now, 
although our anatomical knowledge has been greatly extended, 
the classification cannot be regarded as resting on a very firm 
basis. The families may be grouped into two sub-orders : — 

Sub-Order 1. Actiniixa. — The tentacles are simple and 
similar, and there is one tentacle corresponding to each inter- 
mesenteric chamber (endocoel). 

Sub-Order 2. Stichodactylina. — The tentacles are simple 
and similar, or provided with teat-like or ramified pinnules. One 
or more tentacles may correspond with an endocoel, and there 
may be two kinds of tentacles (marginal and accessory) in the 
same genus. 

Sub-Order 1. Actiniina. 

Fam. 1. Halcampidae. — This family is clearly most closely 
related to the Edwardsiidea. There are, however, twelve complete 
mesenteries of the first cycle, and a second cycle of more or less 
incomplete mesenteries. The tentacles are usually twelve in 
number, but may be twenty or twenty-four. There is no pedal 
disc, but the base is swollen and rounded or pointed at the end. 

The genus Halcam'pa includes a considerable number of small 
species occurring in the shallow waters of the temperate northern 
hemisphere, and of the Kerguelen Islands in the south. Three 
British species have been described, of which Halcainpa chrysan- 
thellum alone is common. The larva with eight tentacles and 
eight mesenteries has been found living on the Medusa 
Thaumantias. 

Peachia is a genus containing Anemones of much larger size 
(10-25 cm.). It is remarkable for the very large siplionoglyph 
on the ventral side of the stomodaeum, prolonged into a 
papillate lip projecting from the mouth called the " conchula." 
The genera Scyto2)liorus from 150 fathoms off Kerguelen and 
Gyractis from Ceylon, although showing some remarkable 
peculiarities of their mesenteric system, appear to be closely 
related to this family. 

Ilyanthus mitchellii is a large Anemone with a vesicular 
base, forty-eight tentacles and mesenteries, occurring in the 
English Channel, but it is not very common. It is usually 



XIV ZOANTHARIA ACTINIARIA 38 1 

placed in a separate family, but is in many respects intermediate 
in character between the Halcampidae and the Actiniidae. 

Fam. 2. Actiniidae. — This family contains some of the 
commonest British Sea-anemones. There is a large flat pedal 
disc by which the body is attached to stones and rocks. The 
body-wall is usually smooth, and not perforated by cinclides. 
The edge of the disc is usually provided with coloured marginal 
tul;)ercles. There are no acontia. 

Actinia. — This genus contains the widely distributed and very 
variable species Actinia mesemhryantliemuvi, one of the commonest 
of the Sea-anemones found in rock pools on the British coast. 
The colours of this species are often very beautiful (see p. 379) 
but variable. 

Ammonia is a genus with remarkably long tentacles which are 
not completely retractile. A. sulcata (sometimes called Anthea 
cereus) is very common in the rock pools of our southern coasts. 

Bolocera tuecliae is, next to Actinoloha dianthus, the largest of 
the British Anemones. It has very much the same colour as the 
common varieties of Actinia, mesembryanthemum, but the body- 
wall is studded with minute, rounded warts. It is found between 
tide marks in the Clyde sea-area, but usually occurs in deeper 
water. 

Fam. 3. Sagartiidae. — This family includes several genera 
with a contractile pedal disc, with the body- wall usually perforated 
by cinclides, and provided with acontia. 

The genera may be arranged in several sub-families dis- 
tinguished by well-marked characters. Among the well-known 
Sea-anemones included in the family may be mentioned : — 

Sagartia troglodytes, a very common British species found in 
hollows in rocks. It is usually of an olive green or olive l)rown 
colour, and the upper third or two-thirds of the body-wall is 
beset with numerous pale suckers. Adamsia ipalliata has a 
white body-wall spotted with bright red patches, and is associated 
with the hermit crab Eupagurns prideauodi. 

Actinoloha (frequently called Metridium) dianthus is con- 
sidered the handsomest of all the British Sea-anemones. It has 
a lobed disc frilled with numerous small tentacles, and is uni- 
formly coloured, creamy-white, yellow, pale pink, or olive brown. 
It lives well in captivity, and sometimes reaches a length of 6 
inches with a diameter of 3 inches (Fig. 164). 



382 COELENTERATA ANTHOZOA chap. 

Aiptasia couchii is a trumpet-shaped Anemone, found under 
stones at low-water mark in Cornwall and the Channel Islands, 
with relatively slight power of retraction. 

Gephyra dohrnii is an interesting species with twelve tentacles, 
which was supposed at one time to form a connecting link between 
the Actiniaria and the Antipathidea. It is found attached to 
the stems and Ijranches of various Hydrozoa and Alcyonaria, 
sometimes in such numbers and so closely set that it gives 
the impression of having formed the substance of its support. 
Haddon ^ has described specimens found on the stems of 
Tubularia from deep water off the south and south-west coasts 
of Ireland. It also occurs in the Mediterranean and the Bay 
of Biscay. 

Fam. 4. Aliciidae. — The members of this family have a large 
flat contractile base and simple tentacles. The body-wall is 
provided with numerous simple or compound outgrowths or 
vesicles, usually arranged in vertical rows. Alicia mirahilis is 
a rare Anemone from Madeira with a very broad base, capable of 
changing its position with considerable activity, and of becoming 
free and floating upside down at the surface of the sea. Other 
genera of the family are Bimodeopsis and Cystiactis. The genus 
Thaumactis, described by Fowler," from the Papeete reefs, has 
many peculiarities, but is probably capable of crawling rapidly 
and of floating at the surface like other members of the family. 
The remarkal:)le Anemone Lebrunia from the West Indies may be 
included in this family. 

Fam. 5. Phyllactidae. — These are distinguished by the 
presence of a broad collar of foliaceous or digitate processes out- 
side the circle of tentacles. The processes have some resemblance 
to the foliaceous tentacles of the Stichodactylinae. They are 
found in the Mediterranean, Eed Sea, and on the shores of the 
Atlantic Ocean, but have not yet been found in the British area. 

Fam. 6. Bunodidae. — This family is characterised by prominent 
\-errucae and tul)ercles of the body-wall. It contains several 
British species, of which Bunodes gemmacea fovind between tide 
marks on our southern shores is fairly common. The very 
common British species Urticina {Tealia) crassicornis is usually 
placed in this family, but exhibits some peculiarities which seem 

^ A. C. Haddon, Trans. Roy. Duhl. Soc. iv. 1889, p. 325. 
2 G. H. Fowler, Quart. Journ. Mia: Sci. xxi.x. 1888, p. 143. 



XIV ZOANTHARIA ACTINIARIA 383 

to warrant its removal to another division of the Actiuiaria. It 
is found in tide pools attached to rocks, but is usually partially 
hidden by adlierent sand or small stones. 

Fam. 7. Minyadidae. — This family contains a number of 
lloating Anemones. The basal disc is folded over to form a gas 
bladder lined by a cuticular secretion. The species are principally 
found in tlie seas of the southern hemisphere. 



Sub-Order 2. Stichodactylina. 

Fam. 1. Corallimorphidae. — In this family the marginal 
cycle of tentacles and accessory tentacles are all of the same kind. 
The accessory tentacles are arranged in radial rows. All the 
tentacles are knobbed at the extremity. The musculature is 
weak. Capnea sanguinea, Corynactis viridis, and Aureliania 
heterocera belong to the British fauna. They are all small 
Anemones of exquisite colours, but are not very common. The 
genus Corallimorphus is principally found in the southern 
hemisphere. 

Fam. 2. Discosomatidae. — The tentacles are all of one kind 
and are very numerous. The mesenteries are also very numerous. 
The sphincter muscle is strong. 

This family includes a rather heterogeneous assembly of forms, 
and will probably require some rearrangement as our knowledge 
increases. Nearly all the species are found in the shallow waters 
of the tropics, and among them are to be found some of the 
largest Anemones of the world. Stoichactis kenti, from the 
Barrier Eeef, is from one to four feet in diameter across the disc. 
In the West Indies these Anemones do not attain to such a great 
size, but Homosticlianthus anemone from Jamaica is sometimes 
8 inches in diameter. 

Fam. 3. Rhodactidae. — In this family the body -wall is 
smooth and the oral disc greatly expanded. The tentacles are 
of two kinds. On the margin there is a single cycle of minute 
tentacles, while on the disc there are numerous tuberculate or 
lobed tentacles. Many of the species of this family are quite 
small, but Actinotryx mussoides from Thursday Island has an 
oral disc 8 inches in diameter. The genera and species are 
widely distributed in the warm, shallow waters of the world. 

Fam. 4. Thalassianthidae. — The tentacles are simple or 



384 



COELENTERATA — ANTHOZOA 



ramified (Fig. 166), aud in some cases very long {Actinodendron 



arloreum). Many of the 
3fegcdactis griffithsi are of 



specimens 
very large 






m 



of A. plicmosuni and 
size, 8 to 12 inches 
in diameter. Of the 
former of these two 
species Saville Kent 
remarks : " The 
colours are lacking 
-f in brilliancy, being 
chiefly represented 
Ijy varying shades 
of light brown and 
white, which are 
probably conducive 
to its advantage by 
assimilating it to 
the tint of its sandy 
bed. When fully 
T. 1^^ . .■ , , 7 , V r .. , extended the com- 

FlG. 166.— Arfnioi/r/iih-nii p]v mnsii ,n. I), disc of attach- 
ment ; Si, siphoiioglyph ; t, t, lobes of the margiual disc pouud tentacles are 
bearing the tentacle.s ; IF body-wall. Height of the elevated tO a height 
column 200 mm. (After Haddon.) o 

of 8 or 10 inches, 
and bear a remarkable resemblance to certain of the delicately 
branching, light brown sea-weeds that abound in its vicinity." 
The same author calls attention to their stinging, which is 
" nearly as powerful as the ordinary stinging nettle." 




Order III. Madreporaria. 

The Madreporaria form a heterogeneous group of Zoantharia 
characterised by a single common feature, the formation of an 
extensive skeletal support of carbonate of lime. In a great 
many cases the skeleton exhibits cups or " calices " into which 
the zooids may be completely or partially retracted, and these 
calices usually exhibit a series of radially disposed vertical 
laminae, the "septa," corresponding with the inter -mesenteric 
spaces of the zooids. Calices and structures simulating septa 
also occur in Helioiwra, which is an Alcyonarian, and in certain 
fossil corals which are probably not Zoantharians. The anatomy 
of the zooids of a great many Madreporaria is now known, and, 



ZOAXTHARIA MADREPORARIA 



385 



although a great deal of work yet remains to be done, it may be 
said tliat tlie Madreporaria exhibit close affinities in structure 
with the Actiniaria. Tlie chief points in the anatomy of the 
zooids are described under tlic different sub-divisions, but a 
few words are necessary in this section to explain the principal 
features exhibited by the skeleton. 

There is no more difficult task tlian the attempt to explain 
upon any one simple plan tlie A'arious peculiarities of the Madre- 
porariau skeleton.^ The authorities upon the group are not agreed 
upon the use of the terms employed, nor are the current theories 




Fig. 167. — Series of diagrams to illustrate tlie structure of tlie Mailreporarian skeleton. 
A, young stage of a solitary eoral with simple protlieea {p.t). B, solitary coral, 
with theca (th), epitheca (e.t), anil prototheca (p.t). C, young stage of colonial coral, 
showing coenosteuni (coe) and theca (th), and the formation of the theca of a bud (b). 
D, two zooids of a more advanced stage of a colonial coral, coe, Coenosteum ; th, 
theca. The black horizontal partitions are the tabulae. E, transverse section of a 
calyx, c, Costa ; col, columella ; d, dissepiment ; r/, septum ; p, pali. 

of the evolution of the skeleton consistent. It is necessary, 
however, to explain the sense in which certain terms are em- 
ployed in the systematic part that follows, and in doing so to 
indicate a possible line of evolution of the more complicated 
compound skeletons from the simple ones. 

There can be no doubt whatever that the whole of the skeleton 
of these animals is formed by the ectoderm, and is external to 
their bodies. If we could get rid of the influence of tradition 
upon our use of popular expressions we should call this skeleton 
a shell. There can be little doubt, moreover, that this skeleton 
is formed by a single layer of specialised ectoderm cells called the 
" calicoblasts." 

^ For a general account of the Madreporarian skeleton, cf. Ogilvie, Phil. Trans, 
noy. Sac. cl.xxxvii. B. 1896. 

VOL. I 2 C 



386 



COELENTERATA ANTHOZOA 



The calicoblasts form, in the first instance, a skeletal plate at 
the aboral end of the coral embryo, which becomes turned up at 
the edges to form a shallow saucer or cup. This cup is called 
the " prototheca." ^ At this stage the body-wall of the living 
zooid may or may not overflow the edge of the prototheca. In 
tlie former case the growth of the rim of the prototheca is 
brought about by the calicoblasts of an inner and outer layer of 
epiblast, and the cup is then called the " theca." In the latter 




Diagram of a vertical FiG. 169. — A young Garyophyllia, viewed from 



sectiou of a young CaryophylUa, 
showing the septa (<S) covered 
with endoderm projecting into 
the coelenteric cavity. M, 
mouth ; St, stomodaeum. (After 
G. von Koch.) 



above, showing the tentacles {t) and tlie 
stomodaeum {St). The letter m points to a 
space between a pair of mesenteries, and 
the darker shading in this place shows a 
septum projecting radially from the wall of 
the theca. (After G. von Kocli.) 



case, the growth of the rim of the prototheca is continued by the 
calicoblasts of one layer of epiblast only, and it is called the 
" epitheca " (Flahcllum). With the continued growth of the tlieca 
the tissues that have overflowed — the " episarc " — retreat from 
the base, and in doing so the ectoderm of the edge and, to 
some extent, the outer side of the episarc secrete a layer of 
epitheca which becomes more or less adherent to the theca. 
Thus the cup may have a double wall, the theca and the epi- 
theca (CaryophylUa). 

With the growth of the theca and epitheca a certain number 
of radially disposed laminae of lime rise from the walls and 
grow centripetally. These are the " septa." Additional ridges on 
1 H. M. Bernard, Ann. Mag. Nat. Hist. (7) xiii. 1904, p. 1. 



XIV ZOANTHARIA — MADREPORARIA 387 

tlie iuner wall of the cup between the septa are called the 
" dissepiments." Corresponding with the septa there may be a 
circle of columns or bands rising from the basal parts of the 
prototlieca — the " \rdli " ; and from the actual centre a single 
column called tlie "columella." The longitudinal ridges on the 
outside of the tlieca, corresponding in position with the septa 
inside, are called the " costae " (Fig. 167, E, c). 

"We may imagine that in the primitive forms that gave rise 
to colonies, the episarc of the primary zooid overflowed on to 
the substance to which it was attached, and gave rise to 
successive layers of epitliecal skeleton, which may be called the 
" coenosteum." The ectoderm at the base of the original prototheca 
is in some corals periodically dragged away from the skeleton, 
and forms another cup or platform of lime at a little distance 
from it — the "tabula." New zooids are developed at some 
distance from the primary one by a process of gemmation in the 
episarc, and independent thecae, septa, etc., are formed in it ; 
the skeleton of tlie new zooid thus originated being connected 
with that of the primary zooid by the coenosteum. 

There are many modifications of this simple description of 
skeleton formation to be considered before a thorough knowledge 
of coral structure can be understood, but sufficient has been said 
to explain the use of the terms that it is necessary to employ in 
the description of the families. When it is necessary to speak 
of the cup in which the zooid is situated without expressing an 
opinion as to the homology of its wall, it is called the calyx. 

There are many forms of asexual reproduction observed in 
the Madreporaria. Of these the most frecjuent is gemmation. 
The buds are formed either on the episarc or on the canals 
running between zooids at the surface of the coenenchym. AVhen 
the young zooids that have been formed by gemmation reach 
maturity they have tlie same characters as their parents. Fission 
occurs in the production of a great many colonies of Madreporaria. 
It occurs occasionally in such genera as Madrepora and Forites, 
where reproduction by gemmation prevails, but it is said that 
gemmation never occurs in those forms such as the Astraeidae 
Fissiparantes where fission is the rule. In fission a division of 
the zooid takes place in a vertical plane passing tlirough the 
stomodaeura and dividing the zooid into two equal parts. In 
some cases these two parts become separated during the further 



388 



COELENTERATA ANTHOZOA 



growth of the coral. In other cases, however, further divisions 
of the stomodaeum occur before the separation of the zooids, and 
then elongated, serpentine polyps are produced (as in Meandrina, 
etc.), which consist of a number of imperfectly separated zooids, 
each with a distinct mouth and stomodaeum but with continuous 
coelenteric cavities. Two kinds of fission must be distinguished 
from each other. In Madrepora and Poriies the plane of fission 
passes dorso-ventrally through the zooids, that is, between the 
dorsal and ventral pairs of directive mesenteries. In these cases 
the zooids produced by fission are similar to the parent form. 





Fig. 170. — Diagrammatic transverse sections oi Porites to illustrate the process of fission. 
A, before division ; B, fission nearly completed. In A four bilateral pairs [a, b, c, d) 
of mesenteries have appeared in the entocoele of the ventral directives ( VD). These 
are increased to six pairs and then fission commences as seen in B, the plane of 
fission passing through the entocoeles of the last pair of secondary mesenteries (/) 
and of the dorsal directives (DD). I, II, V, VI, the protocnemes in the order of 
their development. (After Duerden. ) 

In most Madreporaria, however, the plane of fission appears to 
be more or less at right angles to this, and the resulting zooids 
are unlike the original parent form in having either no directive 
mesenteries at all or only one pair of them. 

The section Fungacea presents us with some exceptional and 
remarkable forms of asexual reproduction. The embryo Fungia 
gives rise to a conical fixed coral called a " trophozooid." The 
upper part of the calyx of this trophozooid expands and becomes 
disc-shaped. This is called the " anthocyathus," and after it has 
reached a certain size it breaks away from the rest of the tropho- 
zooid as an adult Fungia. Several anthocyathi may be formed 
in succession from one trophozooid. This may be described as 
a process of successive transverse fission. In Diaseris the disc 
divides into four quadrants, and each quadrant appears to be 
capable of acquiring the shape and size of the undivided parent. 



ZOANTHARIA MADREPORARIA 



389 



Without doubt a process of sexual reproduction occurs in all 
Madreporaria. In some genera sexual reproduction appears to 
be almost continuous tlirougliout the year ; in others the sexual 
organs are formed only at periods separated by considerable 
intervals of sterility. According to the researches of Duerden 
the Madreporaria appear to 




pirally twisted ^^^^- 1~^- — -^ fixed stage in the development 
of Fuiujia. The trophozooid has Ijecome 
differentiated into a discoid crown, the 
anthocyathus (Cy) and a pedicle, the antlio- 
caulus (C«). (After G. C. Bourne.) 



be usually viviparous, the 
early stages of development 
are passed through within the 
body of the parent, and the 
young coral is discharged 
into the water as a free- 
swimming ciliated larva. The 
larvae are spheroidal, oval, or 
pear-shaped, but change their 
shape a good deal, and some- 
times become elongated, 
straight, or 

rods. The larvae are at first 
dense and opaque, but subse- 
quently they become dis- 
tended by the absorption of water, and more nearly transparent. 
They swim about for one or two days, and then settle down by 
the aboral pole and become fixed. The tentacles are not formed, 
in any species that has yet been observed, during the free- 
swimming stage of existence. 

Distribution of Reef Corals. — The principal reef-forming 
corals reach their greatest size and grow with greatest rapidity 
in the warm, shallow waters of the world, but they are not 
confined to this habitat. A species of Madre2wra has been 
found in the very cold waters of Archangel, and Manicina areolata 
occurs in Simon's Bay, Cape of Good Hope, many degrees south 
of the region of the East African coral reefs. As regards tlie 
distribution of these corals in depth, very little is known at 
present. The face of the growing coral reef that is turned 
towards the open sea is so steep that it has been found 
impossible to determine to wdiat depth the living reef corals 
actually extend. 

The survey of the Macclesfield bank proved that a consider- 
able number of reef corals are to be found alive at depths 



390 



COELENTERATA ANTHOZOA 



ranging from 30 to 50 fathoms.^ To give one example: — In 
the dredging No. 50, depth 32 to 35 fathoms, living examples of 
the following genera of corals were obtained : Madreijora, 
Montijwra, Fsammocora, Favonia, and Astraeojwra. 

Coral Reefs and Atolls. — In many regions of the tropical 
seas, hanks and islands are found which are built up of blocks of 
coral, coral detritus, and altered or modified limestone. These 
are the famous coral reefs of which so much has been said and 
written during the last half-century. There can be little doubt 
that the superficial strata of these formations are entirely due 
to the action of coral-forming animals and plants living in warm, 
shallow sea-water. 

Three classes of coral reefs are usually recognised : the 
" fringing reefs " which follow the contour of the coast at a distance 

of a few hundred yards, 
^^ and are separated from 

the beach at low tide by 
sand flats or a shallow 
lagoon ; the " barrier 
reefs," following the con- 
tour of the coast less 
regularly than the fring- 
ing reefs, but at a much 
greater distance, and 
separated from the beach 
by a lagoon of sufficient 
depth to serve as a 
harbour for ships of great 
size ; and, finally, the 
" atolls," which are ring- 
shaped, or broken circlets 
of low islands enclosing 
a lagoon which is, in 
some cases, of consider- 
able depth. 
It was observed by the early surveyors that in many cases 
the sea-bottom slopes downwards steeply or almost precipitously 
from the outer edge of the barrier reefs and atolls to very great 

' "Report on the Results of Dredging on the Macclesfield Bank," Admiralty 
Meport, 1894. 




Fig. 172. — Plan of Minikoi Atoll in Laccadive Archi- 
pelago. ^1, the land elevated above the level of 
high-water mark ; Ch, the boat channel ; 5 fm, 
the five fathom line ; If in, the two fathom line ; 
L. tlie lagoon with a maximum depth of 7 fathoms ; 
R, the reef continuing the circle on the east side 
of the atoll, awash at high tides. (After Stanley 
Gardiner. ) 



CORAL REEFS 39 I 



depths — to depths, in fact, at which reef- forming corals do not 
live. 

It seems ohvious, tlierefore, that tlie atolls and barrier-reefs 
are resting upon some stratum which could not possibly have 
been formed by reef-building organisms at the same relative 
position it has now, and the questions arose. What is the sub- 
stratum and how was it formed ? 

If this stratum is a coral rock, it is clear that it must have 
been formed at a time when it was nearer to the surface of the 
sea than it is now, and that it must have subsided subsequently 
to greater depths. If, on the other hand, it is a primitive rock, 
we must assume that in such regions as the Indian Ocean and 
the South Pacific, where the archipelagoes of atolls extend for 
hundreds of miles, there are chains of mountain ranges with 
peaks reaching to a uniform level beneath the surface of the sea. 
" But we cannot believe that a broad mountain summit Jies buried 
at the depth of a few fathoms beneath every atoll, and nevertheless 
that throughout the immense areas above named not one point 
of rock projects above the level of the sea. Tor we may judge 
of mountains beneath the sea by those on land, and where can 
we find a single chain, much less several such chains many 
hundred miles in length, and of considerable breadth, with broad 
summits attaining the same height from within 120 to 180 feet ? " ^ 

To account for the observed facts of the atolls and barrier- 
reefs, Darwin conceived and expounded the subsidence theory. 
According to this theory, the regions where atolls now occur were 
at one time dry land, or an archipelago of volcanic islands 
surrounded by fringing reefs of the ordinary type. A gradual 
subsidence of the land took place, and the area of the land 
diminished ; but the area enclosed by the coral reefs did not 
diminish in a corresponding degree, and the young corals growing 
on the debris of the older ones as they sank continued the 
growth of the reef in a direction nearly vertical to the sea- 
bottom. The fringing reefs thus became barrier reefs, and they 
were separated from the land by a lagoon of considerable depth. 
Finally, when the mountain peaks disappeared beneath the 
waves, a ring-shaped reef or atoll was all that was left to mark 
the position of the former land. 

The fundamental assumption in the subsidence-theory is that 
' C. Darwin, Coral Reefs, 3rd edition, 1889, p. 125. 



392 



COELENTERATA ANTHOZOA 



the substratum of the coral reefs and islands is coral-formed 
limestone. To test the truth of this assumption an expedition 
was sent out to obtain, by boring, evidence of the character of 
the substratum of a typical atoll. The island of Funafuti in tlie 
Ellice group of the Pacific Ocean was selected, and after several 
attempts a successful boring was made to a depth of 1114 feet. 
The material from the boring was found to consist of rocks or 
sands entirely derived from the calcareous skeletons of marine 
Invertebrate animals and calcareous Algae.^ Moreover, in the 
cores from various depths down to the lowermost the fossilised 




Fig, 173. — Section of the outer edge of one of the Maldive Atolls. A, foundation of 
primitive roclc cut down by the currents ; B, upgrowth of the rim l>y the deep-sea-, 
intermediate depth- and (B') reef-organisms ; C, extension outwards l)y means of 
the talus slope ; D, lagoon. Scale in fathoms. (After Stanley Gardiner.) 

skeletons of the common genera of recent corals, and very few or 
no representatives of genera of corals now extinct were discovered. 
These facts, therefore, prove the justice of Darwin's assumption 
as to the nature of the substratum — and give support to the 
subsidence-theory as applied to this particular island. A strong 
opinion has, however, been expressed by several authors of recent 
years that the subsidence-theory cannot account for the formation 
of all the atolls and barrier reefs that have now been investigated, 
and alternate hypotheses have been put forward to account for" 
particular cases. The main chain of the Maldive Archipelago 
in the Indian Ocean, for example, presents special difficulties to 
the acceptance of the subsidence-theory as one of general applica- 
tion.^ The main chain of these islands is more than 300 miles 
long, and lies at right angles to the monsoon currents of the 



' For the details of these borings, see " The Atoll of Funafuti," Royal Society 
of London, 190-1. 

2 For further information, sec J. Stanley Gardiner, Thr Fauna and Geography 
of the Maldive, and Laecadive Archipcleujoes, vol. i. pt. ii. 1002, p. 172. 



CORAL REEFS FOSSIL MADREPORARIA 393 



Indian Ocean. Here the action of the currents appears to have 
cut down a great tract of land to form a plateau more than 100 
fathoms in de]ith. The outer rim of this plateau may liave 
grown in height by the deposit of the skeletons of surface- 
swimming animals, and the skeletons of deep-sea corals, until it 
reached a le^^el where reef-forming .corals can thrive. A certain 
number of channels would be retained and even deepened as the 
rim grew up, and thus the coral would eventually reach the 
surface not as a single large atoll, but as a series of coral islands. 
When the coral reef has thus reached the surface and cannot 
grow farther in height, it spreads radially like a fairy ring on 
the talus formed by broken corals that have fallen down the 
slopes. The central parts, no longer protected by living organ- 
isms, are continually subject to the solvent action of the sea water 
penetrating the porous substratum, and sink to form the lagoon. 

It is not only in the reefs of the Indian Ocean, however, but 
in many of the archipelagoes of the Pacific Ocean, where there is 
evidence of very extensive elevation of the land areas in the 
neighbourhood of atolls and barrier reefs, that the subsidence- 
theory does not satisfactorily account for all the observed facts. 
It appears probable, therefore, that although a gradual subsidence 
of the land may have been the primary cause of coral reef 
formation in some areas, similar reefs may have been formed in 
other areas by other natural methods. 

Fossil Corals. — A great number of the genera of corals found 
in the newer Tertiary deposits, and a smaller number of those occur- 
ring in the older Tertiary and Cretaceous strata clearly belong to 
families now represented by recent corals. In the earlier strata, 
however, fossils are found which cannot be placed in our system 
with any degree of certainty. Attempts have been made from 
time to time to arrange these corals in their proper positions by 
tlie careful study and comparison of their skeletal features, but 
the reasons given are not convincing. The genus Syringopora, 
and the families Favositidae, Heliolitidae, and Coccoseridae have 
been noticed in the chapter on Alcyonaria (pp. 343-346). The 
family Zaphrentidae will be noticed when dealing with the order 
Zoanthidea. 

Among the families of fossil corals of uncertain position which 
may still be included in the order Madreporaria, the more 
important are : — 



394 COELENTERATA ANTHOZOA chap. 

Cyathophyllidae, a family of solitary and colonial corals with 
numerous radially arranged septa, extending from tlie Silurian to 
the Carboniferous limestone. It includes the genera Cyatho- 
'phyllum, which was very abundant in Devonian times, and 
LWiostrotion, which, in tlie times of tlie formation of the 
Carboniferous limestone, occurred in continuous masses extending 
over great areas of the sea-bottom. The Cyathophyllidae may 
possibly be ancestral to the representatives of both Astraeidae 
and Fungiidae, which appeared in tlie Triassic strata. 

The Cyathaxoniidae form a family of solitary turbinate or 
horn-shaped corals, with septa showing a regular, radial arrange- 
ment, and may have been the ancestors of the modern family 
Turbinoliidae. They have the same geological range as the 
Cyathophyllidae. 

The Oystiphyllidae. — This family consists of solitary corals 
with very tliin septa ; the interseptal spaces are filled with 
an abundant vesicular substance called the " stereoplasm." The 
systematic position of this family is very doubtful, as the 
structure is evidently much destroyed, but by some authors it is 
supposed to be ancestral to the family Eupsammiidae. 

These three families, together with the Zaphrentidae (p. 40 G), 
were formerly grouped together as the Tetracoralla or Eugosa. 

Sub-Order 1. Entocnemaria. 

Madreporaria forming perforate coralla, with calices that do 
not project above, or project only slightly above the surface of tlie 
coenosarc. The zooids of each colony are usually small and 
crowded. The mesenteries arise in bilateral pairs, and the 
increase in their number takes place in the chamber between the 
ventral or the dorsal pairs of directives. The corals included in 
this order are among the most important of tlie reef -builders. 
On many of the recent coral reefs they occur in enormous 
numbers and of great individual size. But although so prevalent 
upon recent reefs, they appear to have played a far less important 
part in the formation of the reefs of the early Tertiary times, and 
in the reefs of times antecedent to the Tertiary they were rare or 
absent. 

Judging from the structure of the skeleton and the palaeonto- 
logical history alone it might be thought that the Entocnemaria 



XIV ZOANTHARIA MADREPORARIA 395 

represent the most recent types of Madreporarian structure, but 
the anatomy of the zooids points to a contrary conclusion. The 
zooids are of very simple structure ; the mesenteries are found 
only in bilateral pairs, and all the new mesenteries formed after 
the protocnemes originate in one of the directive chambers. 
These are characters indicating a very ancient history, suggesting 
affinities with the Edwardsiidea on the one hand, and some 
ancient type of Cerianthidea on the other. There can be little 
doubt that it was owing to the evolution of a porous skeleton of 
rapid growth that these corals have caught up and passed the 
Astraeidae and other more specialised forms in the struggle for 
predominance on the coral reefs. 

Fam. 1. Madreporidae. — The calices of the corallum are 
small and contain a few perfectly distinct septa. The coenosteum 
is porous and contains a plexus of the coenosarcal canals, which 
connects the cavities of neighbouring zooids. This fjxmily is 
divided into a number of sub-families, but it is only necessary 
here to mention the peculiarities of a few of the well-known 
genera. 

Madrepora. — This genus is represented by an immense number 
of forms on the coral reefs of both the old and new world. 
Attempts have been made at various times to divide these forms 
into specific groups, and a large number of species have been 
defined and named. The differences between these species, how- 
ever, are such as may be due to varying conditions of life upon 
the reefs and not to characters transmitted from generation to 
generation by heredity. There can be no doubt that when our 
knowledge of the soft tissues of these corals is extended the 
number of species will be greatly reduced. There are, however, 
three principal forms of growth or fctcics in the genus. 

1. The flabellate or palmate colonies with large flat or concave 
fronds, radiating from an encrusting base : Forma j^fdmata. 

2. Much branched colonies, several branches radiating obliquely 
from a common centre : Forma iirolifera. 

3. Large and more erect colonies, less branched except towards 
the periphery : Forma cervicornis. 

On some reefs one of these forms of growth predominates, and 
for miles the reef seems to be built up mainly of corals of this 
shape. On other reefs two or sometimes all three of these forms 
may be found within a stone's throw of one another. Notwith- 



396 COELENTERATA ANTHOZOA chap. 

standing the difficulty of distinguishing the species, the genus 
itself is quite well defined. The calices project slightly from the 
surface of the branches and contain six septa, of which the pair 
that is parallel with the axis of the branch is the strongest. 
This strong pair of septa can usually be well seen when a slender 
branch of a Madrepore is examined by a lens by transmitted 
light. At the apex of each branch there is a terminal zobid and 
in the skeleton an apical calyx. The terminal zooid is (in some 
species at least) different from the lateral or radial zooids. The 
former is radially symmetrical and has six long equal digitiform 
tentacles, the latter have usually twelve tentacles, of which six 
are larger than the others. These tentacles alternate, but tliey 
are so arranged on the disc as to give a distinctly bilateral 
appearance to the zooids. 

The colour of the West Indian Madrepores appears to be 
entirely due to Zooxanthellae (pp. 86, 125). They are lighter 
or darker shades of brown, sometimes becoming green, yellow, 
or orange. On the Australian barrier reef and other reefs of 
the eastern seas the growing points of the branches are variable 
and often brilliantly coloured, emerald green, violet, or red ; 
giving some of the most wonderful colour effects for which the 
reef pools are famous. The cause of these brilliant apical 
colours has not yet been ascertained. 

The genus is found in shallow water of all seas of the tropical 
belt except on the western side of the continent of America. 

Montipora. — In this genus the calices are small and situated 
in depressions in the coenosteum, and there are six, sometimes 
twelve, septa of approximately equal size. There is no terminal 
calyx at the apex of the branches. This is a genus of very variable 
form and wide distribution in all tropical seas except on the 
shores of the Atlantic Ocean. 

Turhinaria. — This genus is usually cup-shaped or foliaceous 
and twisted in form. The septa may be six to thirty in 
number. Some of the species of this genus attain to a very 
great size in favourable localities. There is a specimen in the 
British Museum that is 16 feet in circumference and weighed, 
when dried, 1500 lbs. 

Fam. 2. Poritidae. — The corallum is usually encrusting, 
foliaceous, lobed or tufted, rarely dendritic. The whole skeleton 
is built up of a system of trabeculae and stout cross bars, and in 



XIV ZOANTHARIA MADREPORARIA 397 

section the limits of the calices are not well defined. The septa 
are represented by twelve trabeculae. The zooids are small and 
are usually provided with twelve tentacles. The most important 
genus is Porites, which is so abundant on many reefs that it 
may be said to rival Madrepora itself in the luxuriance of its 
growth. On the Australian barrier reef a species of Porites 
builds up coralla over twenty feet in length and as many in 
height. According to Saville Kent they are usually found on 
the outer side of the reef and form a basis of support for the 
high-level Madreporas and other corals.^ 

The colours of Porites are very variable and often beautiful. 
In Jamaica ^ the prevailing colours are bright blue, pale yellow, 
and yellowish green. In Australia the colours are less brilliant 
perhaps, but among the prevailing tints are light or bright lilac, 
a delicate pink, dark yellow, and brown. The genus Porites 
occurs in Eocene and Miocene deposits, and is now found on all 
the more important coral reefs of the world. 

The genus Alveopora is usually placed with the Poritidae. 
According to Bernard,^ however, its affinities with this family are 
remote, and it is more closely related to the Favositidae (see 
p. 344). The walls of the calices are contiguous and the septa 
are reduced to rows of spines, as in the Favositidae. It is found 
in shallow water in the Pacific, the Indian Ocean, and the Eed 
Sea. 

Sub-Order 2. Cyclocnemaria. 

Madreporaria forming perforate or imperforate coralla. Solitary 
or colonial. The zooids have usually a large number of mesenteries 
arranged in two or more cycles. The mesenteries beyond the 
protocnemic pairs arise in unilateral pairs in chambers other 
than those between the directives. 

Sect. 1. Aporosa. — Cyclocnemaria in which tlie theca and 
septa are not perforated. The zooids of the colonial forms may 
communicate by means of superficial canals of the coenosarc, or 
they may be in contact with one another only at their edges. 

Several ffimilies are included in this section, of which the 
more important are : — 

^ Saville Kent, "Great Barrier Reef," 1893, p. 185. 

- Duerden, Mem. Ac. Washington, viii. 1902, p. 550. 

' H. M. Bernard, Journ. Linn. Soc. Zool. x.Kvi. 1897, p. -195. 



398 COELENTERATA ANTHOZOA chap. 

Fam. 1. Turbinoliidae. — The corals included in this family 
are mostly solitary forms attached to foreign objects, or living 
partly embedded in sand. In some cases a small colony is 
formed by gemmation. 

The genus Fkibcllum is a solitary coral of a compressed top 
shape. It has a large number of septa arranged radially on the 
cup-wall. This cup-wall is not a true theca but an epitlieca. 
In some forms root-like tubes grow out from the sides of the 
cup near its base and may serve to support the coral on solid 
objects. In some remarkably fine specimens recently obtained 
from the Persian Gulf these tubes served to attach the coral to 
a telegraph cable. FlahcUum seems to be cosmopolitan in its 
distribution. It is usually found in deep or moderately deep 
water, l)ut some specimens have been dredged in water of 2 to 9 
fathoms. 

Caryoi^liyllia is a conical coral fixed by a slightly expanded 
base. The cup-wall is a true theca covered below by an epitheca. 
There is a spongy columella surrounded by a single circle of 

pali. There is one British species, 

i^'^^*^HA4'i^^^^ 6'. smithii. It is found attached 

-^fffl/fl?i iMlllf/ ^° shells at a depth of about thirty 

AxaIIiIt^^^ fi^thoms near the Eddystone Light- 

^^^^^= < - - - ^ ^. i.r ^^gBg ]-^Q^sg and in other localities in 

^j ^"^^^ the English Channel. It also 

Fig. 174.— Side view of Truchocijathus occurs between tide marks in the 

imstatiis, with exsert septa, well- gci^y Islands, and is found off the 

marked costae (c), and -with three f^,, t , 

spinous projections (8p) at the base SllCtlands, On the West COast of 

formed by outgrowths from primary Scotland, and the SOuth-west of 

costae. (Alter G. C. Bourne.) ' 

Ireland. The genus is widely dis- 
tributed and extends from shallow water to depths of 1500 
fathoms. Caryophyllia sometimes occurs in clusters which have 
the appearance of an incipient colony. This may be due to the 
embryos fixing themselves upon tlie epitheca of existing indi- 
viduals and developing there. It is doubtful whether the species 
ever reproduce asexually either l)y gemmation or by fission. 
When the zooid is fully expanded it projects some distance 
above the corallum and shows a very transparent body-wall 
with a crown of some fifty tentacles. Each tentacle terminates 
in a globose head (Fig. 169) charged with nematocysts. The 
general colour is pale pink, and there is a broad brown circle 



XIV ZOANTHARIA MADREI'ORARIA 399 

round the mouth. Large specimens may be three-quarters of an 
inch in diameter. 

Turhinolia is a common Eocene fossil genus found in England 
and France, and is stated to occur in the Caribbean Sea. The 
columella stands up like a stylet and the septa are " exsert," i.e. 
project above the rim of the theca. 

Trocliocyathus is a genus with well-marked " costae " occurring 
in tropical shallow water (Fig. 174). 

Fam. 2. Oculinidae. — Colonial forms, dendritic or encrusting, 
with relatively large and rather prominent calices separated by 
considerable stretches of compact coenosteum. The zooids bear 
a crown of ten to forty-eight or more capitate tentacles. 

Neohelia has a fistulose stem lined internally by a horny 
membrane. There seems to be some reason for supposing that 
this membrane is formed by the zooids themselves. A similar 
membrane is found in the fistulose stems of Amphihelia and 
perhaps other Oculinidae. If this membrane is really formed 
by the activity of the corals it forms an exception to the general 
rule that the skeleton of the Madreporaria is entirely calcareous. 
Others maintain, however, that this memljrane is formed by the 
Chaetopod worms which are found in the tubes, and that the 
fistulose stem of the coral is formed by folding round and 
encrusting the horny tubes of the worm. Neohdia is found in 
the Pacific Ocean.^ 

Lo2)hohclia is a genus forming dendritic colonies of consider- 
able size. The calices have thick walls and are very deep. 
lAyphohelia prolifera has been found in deep water ofl' the 
island of Skye and in other localities off the west coast of 
Seotland. It is also not uncommon in some of the Norwegian 
fjords and in other parts of the world. 

Oculina is another widely distributed genus found in the 
shallow tropical waters of the West Indies, the Indian and 
Pacific Oceans. It forms dendritic colonies of considerable size. 
The calices are usually arranged in a spiral manner on the 
branches. The colour of the West Indian species is stated to 
be light or dark brown when alive. The tentacles are arranged 
in three cycles, and are usually twenty-four in number. Asexual 
reproduction takes place by budding at the apex of the branches. 

Fam. 3. Astraeidae. — This is a very large fcimily, and 

' E M. Pratt, U'illey's Zoological Itcsults, pt. v. 1900, \). 501. 



40O COELENTERATA ANTHOZOA chap. 

authorities are not agreed as to its limits or classificaticn. 
Excluding the simple forms for the present, the family may 
be said to be distinguished by having the calices so closely 
crowded that there is little or no coenosteum between them. 
The corallum is compact and massive, unless bored and perforated 
by algae, worms, and other coral- destroying organisms. 

The genera of Astraeidae that form colonies may be divided 
into two groups : the Gemmantes and the Fissiparantes. In 
the group Gemmantes asexual reproduction is effected by gemma- 
tion, and each zooid of a colony is a distinct individual with two 
pairs of directive mesenteries. Anioug the best known of recent 
corals included in this group may be mentioned Galaxca. In 
this genus there is a good deal more coenosteum between tlie 
calices than tliere is in most of the Astraeidae. The calices are 
long and project some distance above the coenosteum. Tlie 
septa are exsert. In Galaxca esperi examined by Fowler^ there 
are twelve septa, twelve pairs of mesenteries, and twenty-four 
tentacles, of whicli twelve are very small and twelve rather 
larger. The colour is green or brown. The genus is found in 
shallow water in the tropics of the old world. 

In Astrangia solitaria the zooids are either isolated or more 
generally united by thin strands of perithecal tissue to form 
encrusting colonies. The septa are not exsert as in Galaxea. 
Six are prominent and belong to the first cycle, six smaller ones 
form a second cycle, and an incomplete third and fourth cycle 
may be seen. Corresponding with each septum there is a 
tentacle. The tentacles of the innermost cycle are the longest 
(3 mm. in length). All the tentacles terminate in a knobbed 
apex. The living zooids are colourless throughout, or display 
only very delicate tints within restricted areas." This genus 
occurs principally on the coasts of the American continent, 
extending as far south as the Straits of Magellan. Otlier 
well-known genera of Astraeidae Gemmantes are Orhicclla, 
Cladocora, Phyllangia. 

In the group Fissipaeantes asexual production takes place 
by fission without the production of morphologically complete 
zooids. The tentacles, mesenteries, and septa, when fission is 
established, are not arranged in regular hexameral cycles, and no 

1 G. H. Fowler, Quart. Journ. Micr. Sci. xxx. 1890, p. 410. 
- J. E. Duerdcii, 3fem. Ac. Washiiujton, viii. 1902, p. 553. 



XIV ZOANTIIARIA — NFADREPORARIA 40 1 

new directive mesenteries arise. In sijrue cases very large corals 
are formed, and, if our conception is correct, these must be 
regarded, not as a colony of zooids, but as a single individual 
zooid divided into a considerable number of incompletely sepa- 
rated parts. Among the well-known genera belonging to this 
group are Euphyllia, Mussa, Meandriyia, Coeloria, Favia, and 
Goniastraca. 

In such genera as Eu^lujUia the parts of the colony become 
separated by deep grooves, and have the superficial appearance of 
being distinct individuals ; but in the Brain-coral Coeloritt and 
others the surface of the coral presents a series of more or less 
bent or curved grooves, each with a row of slit-shaped mouths 
and bordered by rows of tentacles. 

A number of genera of solitary corals united in the sub-family 
Trochosmiliacea are generally included in the family Astraeidae. 
The study of their skeletal characters has suggested^ that they 
are more closely allied to the Turbinoliidae. The principal genera 
thus transferred would be Trochosmilia, Placosmilia, Parasmilia, 
and Asterosmilia. As these genera and their allies are nearly 
all extinct, and nothing is known of the structure of the living 
zooids, their removal from the Astraeidae may be regarded as 
not fully justified. 

Fam. 4. Pocilloporidae. — The general anatomy of the zooids 
of this family of corals has some resemblance to that of the 
Entocnemaria, and it is possible that they will eventually find a 
place in our classification near to, if not actually within that 
group. The fact, however, that the skeleton is imperforate is 
sufficient for the present to justify the inclusion of the family 
in the section Aporosa. There are but two genera at present 
known, and in both of them the zooids have twelve tentacles, 
twelve mesenteries, and only two mesenterial filaments. The 
zooids are connected together by an elaborate system of canals 
running in the superficial coenosarc. The calices are bilaterally 
symmetrical, and in Seriatopora the septa which are parallel 
with the axis of the branch are united in the centre of the 
calyx, and are very much larger than the others, as in Madrei^ora. 
In all these characters the family shows aftinities with the 
Entocnemaria. In the characters of the skeleton, which is 
im])erforate and tabulate, the affinities are rather with the 

' M. Ogilvie, Trans. Roy. Soc. clx.\xvii. B. 1896. 
VOL. I 2 U 



402 



COELENTERATA ANTHOZOA 



Cyclocnemaria. The two genera are widely distributed on the 
coral reefs of the old world, and in some localities are very 
abundant. Neither genus is found in the West Indies. They 
are both of recent origin, but FociUo2Jora occurs in the Miocene. 
It is a remarkable feature of the family that both genera may 
be attacked by the gall-forming crab HcqKilocarcinus. From 
some reefs nearly all the Pocilloporidae show crab-galls on a 
large number of their branches, whereas other Madreporaria are 
free from them. 







f-T-, ?^ *«-*'' yy. 









Fig. 175. — A portion of a colony of Poc«7%jom from Fig. 176. — A single calyx of 
the Maklive Archipelago. Focillopom septata, showing 

Co, the columella ; S, S, the 
septa ; Th, the theca wall. 
(After Gardiner.) 



Pocillopora is a coral that forms encrusting masses, rising 
into lobes or branches of considerable size, terminating in blunt 
apices. Seriatopora is much more slender and ramified, the 
branches terminating in sharp points. 

Sect. 2. Fungacea. — This section of Cyclocnemaria con- 
tains a number of solitary and colonial corals of very varied 
form united in the possession of a number of cross-bars called 
" synapticula " connecting the septa, and thereby giving strength 
to the calyx apart from any increase in the thickness of the calyx- 
wall. The family Fungiidae shows many peculiarities which 
separate it very distinctly from both . the Cyclocnemaria and 
the Aporosa. The Eupsammiidae, however, approach the Cycle- 



XIV ZOANTHARIA MADREPORARIA 403 

cnemaria in many respects, and tlie Plesiofungiidae form a con- 
necting link with tlie Astraeidae. It is very probable that this 
section had a dual origin, and therefore does not represent a 
single line of descent. 

Fam. 5. Plesiofungiidae. — This family is related .to the 
Aporosa in the possession of septa that are generally solid 
and imperforate, and to the Astraeidae in particular in the 
possession of dissepiments. They differ from them, however, 
in the presence of synapticula and in certain peculiarities of 
the tentacles. 

The genus Siderastraea has recently been studied by Duerden.^ 
The colony is usually massive and encrusting in habit. The zooids 
when expanded do not rise much above the level of the corallura. 
The tentacles are short and are arranged in irregular cycles on the 
disc. They terminate in knobbed extremities, and those of the 
inner cycles are bifurcated. The colour of S. sicleraea is reddish- 
brown when alive. Siderastraea is found in shallow water on 
the coral reefs, and is widely distributed. 

In Agaricia the colony is more foliaceous. The tentacles are 
rudimentary or small. The colour of the living zooids is very 
similar to that of Siderastraea. Epistrelophylhitn is a solitary 
coral, from the Jurassic series, belonging to the family. 

Fam. 6. Fungiidae. — Fungia is an unattached solitary coral 
of a flat disc-like shape with very numerous exsert imperforate 
septa. It is frequently of considerable size (six to twelve 
inches in diameter). On many of the coral reefs of the old 
world it is extremely abundant, and consequently it is one 
of the commonest corals of our collections. When alive the 
corallum is almost hidden by the disc, which is studded all 
over wdth very numerous long tentacles." The colour varies 
in different species, but is usually brown. One species on the 
Australian barrier reef, F. crassitentacidata, is of a dark olive 
green colour, the tentacles terminating in white knobs. 

The free adult Fungias are derived from a fixed stock called 
the trophozooid, from which the young Fungias are detached by 
transverse fission (see p. 388). The thecal wall of the young 
Fungia when detached from the trophozooid is perforated, but 

' "The Coral Siderastraea," Carnegie Inst. No. 20, 'Washington, 1904. 
- The reader is referred to the excellent pliotograjihs of living Fungias in 
Saville Kent's " Great Barrier Reef," 1893, pi. xxiv. i>. 160. 



404 COELENTERATA ANTHOZOA 



the pores become largely filled up during the later growth of the 
coral. 

There are several genera of colonial Fungiidae of less frequent 
occurrence, such as HoJomitra, Herpetolltha, and Cryptalacin. 

Fam. 7. Cycloseridae. — These are solitary or colonial 
Fungacea with an imperforate theca. Bathyactis occurs at 
great depths, Diaseris, shallow water on coral reefs. 

Fam. 8. Plesioporitidae. — The septa in this family are 
trabeculate and perforate, resembling in this respect the septa 
of Poritidae. LeptophjiUia, 3Iicrosolena, extinct. 

Fam. 9. Eupsammiidae. — -This family of perforate corals is 
usually placed with the Madreporidae and Poritidae in the old 
group Perforata. The researches of Fowler and Gardiner have 
shown that the arrangement of the mesenteries is that of the 
Cyclocnemaria, and the presence of synapticula connecting the 
septa suggests affinities with the Fungacea. The synapticula 
of the Eupsammiidae, however, are peculiar in being arranged, 
not in a vertical series, but alternately with one another or 
quite irregularly in position. The members of this family are 
solitary or colonial in habit. 

Stephanojjhyllia is a flattened disc-shaped coral, with per- 
forate and dentate septa, found in the Pacific Ocean and as a 
fossil in various strata since Cretaceous times. 

In Le2)tope7ms, from depths of about 1500 fathoms, the per- 
forations are much larger than in the last-named genus, and the 
skeleton is reduced to a system of slender trabeculae. 

BJwdojysammia has a conical shape, and gives rise by gemma- 
tion to a number of young zooids, which remain attached for 
some time to the parent form before becoming free. 

Among the colonial genera are DeiidrophyUia, Coenopsammia, 
and the well-known Mediterranean senus Astroides. 



Order IV. Zoanthidea. 

This order of Zoantharia consists of a number of solitary or 
colonial Anemones that do not form a skeleton of horn or 
carbonate of lime, and are distinguished from the Actiniaria by 
the peculiar arrangement of their mesenteries. 

Fam. 1. Zoanthidae. — Sphenopus is a solitary coral and 
terminates aborally in a small sucker-like base, by wliich it may 



XIV ZOANTIIAKIA ZOANTHIDEA 4O5 

be attached to foreign bodies. The genera Gemmaria and 
Isanrtis inchide solitary forms. 

In the majority of the species of Zoanthids, however, a basal 
encrusting stolon is formed, which may be thick and fleshy or 
membranous, or may consist of a plexus of bands from which 
several zooids rise and on which the new buds are formed. 

The tentacles are numerous, simple, usually short, and 
arranged in one or two circles on the margin of the dise. 
Most Zoantliidae are encrusted with sand, shell fragments, or 
sponge spicules, but Zoanthus and Isaurus are naked. The 
foreign particles that form the incrustation are firmly attached 
to the ectoderm, and as a rule many of them sink down into 
the mesogloea to give additional support to the body-wall. It 
is the presence of so much incorporated sand that frequently 
gives these Zoantharia such a very brittle character. The 
stomodaeum usually exhibits a well-marked ventral siphonoglyph. 
The mesenteries consist of a pair of complete ventral directives, 
a pair of incomplete dorsal directives, while of tlie remaining 
protocnemes the lateral mesenteries which are first and second 
in the order of appearance are complete, the sixth is incomplete, 
whereas the fifth is complete in the Macrocneminae and incom- 
plete in the Brachycneminae. Duerden ^ has found in specimens 
of three species that the arrangement of the mesenteries is 
" brachycnemic " (the sixth protocneme imperfect) on one side 
and " macrocnemic " (the sixth protocneme perfect) on the other. 
The metacnemes appear in the spaces between the sixth 
protocnemes and the ventral directives in unilateral pairs, of 
which one becomes complete and tlie other always remains 
incomplete (Fig. 163, 4, p. 368). 

The Zoanthidae are usually dioecious, but hermaphroditism 
undoubtedly occurs in the genera Zoanthus and Isaurus. Little 
is known of their development, but a larval form discovered by 
Semper off the Cape of Good Hope, of cylindrical shape, with an 
opening at each end and distinguished by a longitudinal band of 
cilia running from one end to the other, is probably the larva 
of a Zoanthid. It is commonly known as Semper's larva. Other 
larvae provided with a ring of cilia have also been attributed to 
this group. 

A great many Zoanthidae are epizoic in liabit. Thus several 

' Trans. Jloij. Hoc. l>uU. <'2) vi. 189S, ji. 331. 



4o6 



COELENTERATA — ANTHOZOA 



species of Epizoanthvs form colonies on the shells of Gasteropods 
inhabited by hermit crabs. Parazoanthus tunicans is found on 
the stem of a Plumularia ; Parazoanthus separatus, from Jamaica, 
is associated with a sponge. The base of the bundle of long 
spicules of the Sponge Hyalonema (p. 204) is almost invariably 
sheathed by a colony of Einzoanthus stellaris. 

The only genera occurring within the British area are 
Epizoanthus (with six species), Parazoanthus (with four species), 
and Zoantlius sulcatus. 

Of the species of Ejnzoanthus, E. incrustatus is fairly common, 
in depths of twenty to eighty fathoms on all our coasts, and is 

frequently commensal with 
different species of hermit 
crabs, while E. p)agurip)hilns 
is found in much deeper 
water off the west coast of 
Ireland and is always com- 
mensal with hermit cral)s. 
Parazoanthus anguicomus is 
found at depths of a hundred 
fathoms off the Shetlands 
and west of Ireland, and is 
Fig \li.~Zianthns maujiiiuiayi, i small usually associated with vari- 

colon> The tentacles are shown some sDCcies of SnonCTCS 

what contracted by the preservative. Each ^^^^ specieb OL opuu^^eb. 
zooiil is about 25 mm. in length. (After Gcrardia SavaUa is the 

""^''°''-^ largest " black coral " of the 

Mediterranean. The colony begins by encrusting the stem of 
one of the Gorgoniidae, but soon surpassing its support in 
growth, it forms a basal horny skeleton of its own and builds 
up very large branching colonies. A specimen in the British 
Museum,^ from twenty fathoms off the island Negropont, is two 
metres high and two metres wide. The genus appears to be 
related anatomically to Parazoajithus. 

Fam. 2. Zaphrentidae. — This family of Palaeozoic corals is 
usually placed with the Turbinoliidae or in the separate group 
Tetracoralla. Recently Duerden " has given reasons, based on 
the method of increase of the septa in Lo2)hop]iyllum, for believ- 
ing that their affinities lie rather with the Zoanthidae than 

1 F. J. Bell, Trans. Zool. Soc. xiii. pt. ii. 1891, p. 87. 
2 J. E. Duerden, Ann. Mag. Nat. Hist. (7) ix. 1902, p. 381. 




XIV ZOANTHARIA ANTIPATHIDEA 407 

with the jMadreporaria. They are solitary turbinate corals, with 
numerous septa exhibiting a distinct bilateral symmetry in 
arrangement. Zcqihrentis, Loi^hoiihyllum. 

Order V. Antipathidea = Antipatharia. 

The members of this order can readily be distinguished from 
all other Zoantharia by the presence of a horny axial skeleton 
(sclerobase) and the absence of any spicules of calcium carbonate. 
The skeleton is covered by a thin bark which consists of a number 
of simple, naked zooids united at their edges. The zooids bear six 
tentacles, or if there are more than six, six large prominent 
tentacles. In most genera there are but ten mesenteries, in 
others twelve. In Cladojmthes only six mesenteries are found. 
The skeleton of the Antipathidea is simple in Stichopathes and 
Cirripathes, but in all other genera it is ramified. The ramifica- 
tion is usually profuse and irregular. The horny substance of 
which it is composed is free from any deposit or infiltration 
of lime. The surface of the younger branches is beset with 
numerous short spines, the number and arrangement of which are 
characters largely used in the determination of species. The basal 
parts of the main axis and the thicker branches are frequently 
bare, the zooids having died and become disintegrated. In these 
cases the spines wear away and the skeleton appears to be smooth. 
The presence of spines on some of the branches is, however, 
generally sufficient to enable the naturalist to distinguish a dried 
Antipathid from the axis of a Gorgonid, with which alone it 
might be confounded. 

There are six complete mesenteries in each zooid, but as they 
bear no retractor muscles it is not certain that they represent the 
first six protocnemes of other Zoantharia. In a great many 
species the zooids are oval in shape, the longer diameter being 
parallel with the axis of the branch. The mouth and stomodaeum 
are compressed and at right angles to this diameter. It is usually 
assumed that the mesenteries attached to the angles of the stomo- 
daeum are the directives, and that the remaining pair, which is 
axial in direction, corresponds with the first pair of protocnemes. 
The axial pair of mesenteries is frequently very well developed 
and alone bears the gonads. When other mesenteries are formed 
they always arise in bilateral pairs between the axial mesenteries 



408 COELENTERATA ANTHOZOA chap. 

and the directives. The tentacles correspond with the inter- 
mesenteric chambers. In some genera there is a constriction of 
the zooid between the pairs of the tentacles on each side of the 
axial mesenteries and the directive tentacles. This gives tliem 
the appearance of a division into three zooids with two tentacles 
apiece, one with a mouth and two without a mouth ; and as 
the mouthless parts alone bear the gonads on the single axial 
mesentery, they have been called the " gastrozooids " and " gono- 
zooids " respectively. This must not be regarded, however, as a 
case of true dimorphism, as the cavities of the so-called gastro- 
zooid and gonozooids are continuous. 

The Antipatharia are widely distributed in nearly all the great 
seas of the world. Some species are found in shallow water in 
the tropics, but most of them occur in depths of fifty to five 
hundred fathoms. The genus Batliypathes is only found at 
enormous depths ranging from 1070 to 2900 fathoms. Speci- 
mens of Ci7'ripathes spiralis, Antipathella gracilis, and another 
species have recently been obtained in deep water off the west 
coast of Ireland,^ but these are the only Antipatharia known to 
occur within the British area. 

The very simple structure of the Antipatharia is usually 
attributed to degeneration. On this view the Antipathidae with 
only six complete mesenteries are the most modified, whereas 
the Leiopathidae with twelve mesenteries are more closely related 
to the ancestral forms, and Gephyra dohrnii (see p. 382) is a link 
connecting the order with the Actiniaria. 

There is no reason, however, for supposing that Gepltyra 
is specially related to this order, and, as pointed out recently 
by Koule,- the simple structure of the zooids of the Antipa- 
thidea is more easily explained if they are regarded as primitive 
forms. 

Gerardia (p. 406), from the Mediterranean, forms a horny 
axial skeleton like that of the Antipathidea, but this genus is 
probably a Zoanthid. 

Fam. 1. Antipathidae. — In this family the zooids have six 
tentacles and six or ten mesenteries. It includes nearly all the 
familiar genera, such as Sticlwpathes, Cirripathes, Antipathes, 
AntiioatheUa, Cladopathcs, and Bathypiathes. Schizopathes and 

1 Hickson, Xaturc, Ixxiii. 1905, i>. 5. 
- L. Roule, JJuU. Mas. Uciano'jr. Monaco, 1904, \i. 3. 



XIV ZOANTHARIA CEKIANTHIDEA 409 

its allies dccurring in deep water are the forms regarded liy 
Brook as dimorphic. 




Fig. 178. — A poition ot a linuch ot ixti/ ft]i s tn iHttmsis, showing three zooid.s and 
the honn ixi-^ lies t ^^lth thuiii like inojections (Aftei Sthult/e. j 

Fam. 2. Leiopathidae. — This family includes the single 
genus Leiopathes of the Mediterranean Sea. It is distinguished 
from the others by the |)resence of twelve mesenteries. 

Fam. 3. Dendrobrachiidae. — This family also consists of a 
single genus, Uendrohrachia, from 400 fathoms in the South 
Atlantic. It is distinguished by having pinnate retractile 
tentacles. 

Order VI. Cerianthidea. 

This order contains the remarkable Sea-anemone called Ceri- 
anthiis. Two of the species have been placed in separate genera, 
but they do not appear to be of more than sub-generic rank. 
Cerianthus has a long cylindrical body with a double crown of 
numerous long tentacles at the oral extremity and tapering to a 
blunt point or rounded at the aboral extremity. 

There are numerous mesenteries, which increase in number by 
the addition of bilateral pairs, arising only in the ventral 
inter-mesenteric space throughout the greater part, if not the whole, 
of the life of the zooid. The right mesentery of each young pair 
is always more advanced than the left, so that the mesenteries 
have the appearance of arising alternately right and left. None 
of the mesenteries bear conspicuous bands of retractor muscles. 
The movements of the body are effected by a thick band of 
longitudinal fibres lying between the ectoderm and the mesogloea 
in the body-wall. 

The absence or very slight development of muscles on the 
mesenteries renders it difficult to recognise the homologues of the 
protocnernes of other Zoantharia in the adult. From the 
evidence of embryology, however, it seems certain that the six 
dorsal pairs of mesenteries represent the protocnernes (Fig. 163, 3, 
p. 368) and the others are metacnemes. 



4IO 



COELENTERATA ANTHOZOA 



The stomodaeum exhibits a single long deep siphonoglyph, 
which is probably dorsal in position. 

There are two tentacles to each inter-niesenteric space, one 
being marginal and the other circumoral. The gonads are borne 
upon alternate mesenteries, and both ova and spermatozoa are 
produced by the same individual. 

The ectoderm of Cerianthus is remarkable for the immense 
number of nematocysts and gland cells. The latter secrete a 




Fig. 179.— CVn/?)// 



/ C lo ir J ml \\\i\\ teutieks amnilatefl pink and 

\1 out 3o cm 111 kii^th (Atter Andres ) 



quantity of mucus which binds the threads of the discharged 
nematocysts into a sticky feltwork and this secures particles of 
sand and mud, the whole forming a long tube in which the animal 
freely moves. This tube is often of considerable thickness. It 
is tough and resistant, smooth inside but ragged and muddy 
outside. It is often many times the length of the animal's body. 
The embryo of Cerianthus is set free before the completion of 
segmentation, and it gives rise to a floating pelagic larva known 
as Arachnactis. It has a variable number of tentacles and 
mesenteries accordimi to its awe, but when it reaches a size of 



XIV ZOANTHARIA — CERIANTHIDEA 4II 

al^out 15 mm. in length it has developed characters which are 
sufticient to determine its position as a Cerianthid. 

The genus Ccrianthus appears to be widely distributed. 
C. mcmhranaceus is the common species in the Mediterranean Sea, 
but a smaller species has been described from Naples under the 
name C. oligoi)odus by Cerfontaine. C. americanns occurs on 
the eastern coasts of North America. The British and North 
European species is C. lloydii, but another species, C. vogti, has 
been found at a depth of 498 fathoms in the North Sea. C. 
nohilis is a gigantic species supposed to be about 1 foot in length 
when complete, from Torres Straits. 

C. hathymetricus of Moseley, placed by Andres in the genus 
Bathyanthvs, is a species of small size (25 mm.), obtained by the 
" Challenger " from a depth of 2750 fathoms in the North 
Atlantic. It exhibits a remarkable prolongation of the stomo- 
daeum into the coelenteron in the form of a sack which con- 
tained food. Moseley described a species of Cerianthvs, 6 inches 
long, living on the coral reef at Zebu in the Philippines fully 
expanded in the tropical sunshine. 

Several species of Arachnactis larvae have been described. 
Of these Arachnactis lloydii appears to be undoubtedly the 
larva of C. lloydii. The adult forms of Arachnactis cdhida from 
various stations in the Atlantic Ocean and of Arachnactis 
americana are not known. The larva of Cerianthus memhranacens 
has been called Dianthea nohilis, and is characterised by the great 
length of the column, by the general opacity of all parts of the body, 
and by the precocious appearance of the median marginal tentacle. 
A considerable number of remarkable pelagic larvae have been 
described by van Beneden ^ from the Atlantic Ocean, and pro- 
visionally assigned by him to five different genera. The adult 
forms of these larvae are not known, l)ut they are probably 
members of this order. 

' E. van Beneden, Lcs Anthozoaires de la Plankton Expedition, Kiel, 1898. 



CHAPTER XV 



CTENOPHOEA 



The Ctenophora are spherical, lobed, thimble-shaped, or band- 
like animals, usually very transparent and gelatinous in structure. 
They are exclusively marine, and are found floating at or near 
the surface of the sea. 

Although they are generally classified with the Coelenterata, 
they are regarded by some authors as having closer affinities 
with the Polyclad Turbellaria (cf. Vol. II. p. 7). They agree, 
however, with neither of these divisions in their essential 
characters, and the only way to indicate and emphasise their 
unique position is to place them in a separate Phylum, 

They differ from all the Coelenterata in the absence of 
nematocysts, and in the presence in development of a definite 
mesoblast. The character from which they derive their name, 
Ctenophora, is the presence on the surface of bands of swimming 
plates. The plates are called the " combs " (/cret?, gen. KTev6<; = 
a comb) or " ctenophoral plates." They occur in all genera included 
in the Phylum except in Coeloplana (Fig. 183, p. 422). 

Another peculiarity of all Ctenophora (except the Beroidae) 
is the presence, at some stage in the life-history, of two long 
and extremely contractile tentacles. There is also a well- 
developed sense-organ (statocyst) in the centre of the aboral 
area of the body. 

The Ctenophora differ from the Turbellaria in tlie presence 
of the combs and of the two long tentacles, in the position and 
relative importance of the statocyst, and, with the exception of 
Coeloplana, in the general characters of the alimentary canal. 

Shape. — Several of the Ctenophora are conical or spherical 
in shape, but exhibit at the pole where the mouth is situated 



CTENOPHORA 



413 



(Fio-. 180, J/) a slight conical projection, and at the opposite 
))ole where the sense-organ is placed a slight depression (Ah). 
In others, the sides of the body are drawn out into a pair of 
wing -like lobes (Lobata), and the body is considerably flattened 
or compressed (Fig. 181). The Cestoidea have a long flattened 
ribbon- or band-shape (Fig. 182), and the Platyctenea (Fig. 183) 
are flattened in the oro- 
apical axis and exhibit 
a well-marked distinc- 
tion between the dorsal 
and ventral surfaces. 
The shape of Bcroc is 
that of a hollow cone 
or thimljle. 

Ctenophoral plates, 
— In many Ctenophora 
eight lines can be 
traced, like the lines of 
longitude on a globe, 
from the area of the 
sense-organ to the base 
of the mouth-cone or 
hypostome. In the 
course of these lines 

are situated the Cteno- ^iq, iso.—Hormi2)hora plumosa. ^6, position of the 

phoral plates. In some aboral sense-organ ; Ct, rib of ctenophoral plates ; 

, , ,1 M, month ; t. tentacle, with two kimls of pinnae. 

species they extend (After Chun. l 
along the greater part 

of these lines of longitude, but in others they are more restricted. 
That part of the line that bears the plates is called the " rib " or 
" costa." These plates or combs form the principal organs of loco- 
motion of the Ctenophores. They consist of a row of cilia fused 
at the base (cf. p. 141) to form the plate, but free at the ex- 
tremity where they form the comlvlike edge. They are alternately 
raised, by a rapid contractile action, and then slowly flattened 
down again. The plates are raised in succession from the aboral 
to the oral end of each rib, and the appearance given to the bands 
in the living animal is that of a series of waves travelling down 
the lines of longitude from the sensory area towards the mouth. 
The effect of these rhythmic movements of the combs is to 




414 CTENOPHORA 



drive the animal slowly tlirough the water with the oral cone 
forwards. In some Ctenophores the costffi are phosphorescent.^ 

Tentacles. — In all the Ctenophora, except the Beroidae and 
the adult stages of Lobata and Cestoidea, there is a single pair 
of tentacles. They are attached to the base of a blind funnel- 
shaped pit which opens to the exterior near the equator of the 
animal's body. The pits are on opposite sides of the body, 
and the plane which passes through them both vertically divides 
the body into approximately equal parts. It is called the 
" tentacular " or " transverse " plane (Fig. 180). The plane at 
right angles to this, which also passes tlirough the mouth and 
statocyst, is called the " sagittal " plane. 

The tentacles are solid, and in the Cydippidae, of con- 
siderable lengtli. During life they are usually extended, and 
trail behind the animal as it progresses through the water. 
But they are extremely contractile, and when the animal is 
alarmed are suddenly withdrawn into the shelter of the tentacular 
pits. Each tentacle usually bears a row of short pinnae. The 
surfaces of the tentacles and of their pinnae are crowded with 
remarkable cells which carry little globules of an adhesive 
secretion, and are called the glue-cells or " colloblasts." These 
cells stick to any foreign body they touch, and may be drawn 
out some distance from the tentacle, but they remain attached 
to it by a long spiral thread which unwinds as the cell is pulled 
out. Although the colloblasts have the function of catching 
prey similar to that of the nematocysts of Coelenterata, they 
are true animal cells and are not therefore homologous with 
nematocysts, which are the cell products of the cnidoblasts." 

The Lobata and Cestoidea pass through a stage in develop- 
ment called the Cydippiform or Mertensia stage, when they 
possess a single pair of long tentacles similar to those described 
above. In the adult condition, however, these tentacles are 
absent, and their functions are performed by numerous small 
accessory tentacles or tentilla arranged in rows on definite lines 
along the body- wall. 

Sense-organ. — At the aboral pole of the Ctenophore there 
is a hard granulated calcareous body, the " statolith." This is 

1 A. W. Peters, Journ. Expcr. Zool. ii. (1) 1905, p. 103. 

- Cnidol)lasts are stated by Chun to occur on the tentacles of Euchlora ; and 
batteries of " nettle cells " by Abbott on the tentacles of Caeloplana. 



STRUCTURE 415 



supported by four tufts of fused cilia, and is usually covered by 
a dome of delicate protoplasmic texture, which is believed to be 
formed by a fusion of cilia. The dome enclosing the statolith 
is called the " statoeyst." 

Supporting the statoeyst tliere is a circular or oval area of 
ciliated epithelium which is usually supposed, but on insufticient 
evidence, to be specially sensory in function. Extending from 
this area in the sagittal plane tliere are two strips of ciliated 
epithelium called the " polar fields." 

The aboral sense-organ of the Ctenophora is one of the most 
characteristic organs of the Phylum. The aboral pole of the 
]\Iedusae of Coelenterata is usually devoid of any special modi- 
fication of the ectoderm of the bell, and in the Tiarid genus 
Stomatoca the little tassel at the aboral pole of the Medusa 
cannot in any sense be regarded as a homologue of the sense- 
organ of the Ctenophore. If the aboral sense-organ of the 
Ctenophora can be compared with that of any other group of 
animals, it would be with the statoeyst of many of the 
Turbellaria, such as that of Convoluta, but it is far more 
satisfactory to regard it as an organ peculiar to the Ctenophora 
and as having no true relationship with any sense-organ found 
in other animals. 

Alimentary Canal. — The mouth of the Cydippiform 
Ctenophores opens into a sac-like chamber called the " stomo- 
ilaeum," flattened in the sagittal plane and stretching from the 
oral pole as far as the centre of the bod}'. The stomodaeum 
passes into a chamber flattened in the transverse plane called the 
" infundibulum." From the infundibulum a narrow tube passes 
in the direction of the aboral pole called the " intestine," and 
from the extremity of this four short tubes pass to the sides 
of the polar fields at the place where these fields join the sensory 
area. Two, or, in some cases, all four of these tubes open to the 
exterior ; but they do not appear to serve the purpose of ejecting 
the undigested portions of the food, which usually pass to the 
exterior by the mouth as in Coelenterata and Turbellaria. 

From the lateral extremities of the infundibulum four pairs 
of tubes pass to the equatorial region of the body, where each one 
joins a longitudinal vessel which runs immediately beneath the 
epithelium supporting the ribs. These are called the longitudinal 
or " sub-costal " canals. From the infundibulum there also 



41 6 CTENOPHORA 



passes a single pair of blind canals, the " paragastric canals," 
one on each side of the stoniodaeum, to end in the oral cone. 

In the Lobata the paragastric canals communicate with the 
longitudinal canals under the transverse costae,^ and send long- 
blind processes into the lobes. In the Cestoidea the arrange- 
ment of the canals is considerably modified in adaptation to the 
needs of the ribbon-like body. In the Beroidae the paragastric 
and longitudinal canals are in communication by a peripheral 
network of canals, and in the Platyctenea there is also a net- 
work of canals but without any definite longitudinal vessels. 

Sexual Organs. — Most of the Ctenophora are undoubtedly 
hermaphrodite, Ijut Willey was unable to find ova in some of his 
specimens of Ctenoplana that were producing spermatozoa. In 
the Cydippidea the ova are produced on one side of the longitu- 
dinal canal and the spermatozoa on the other. Each longitudinal 
canal therefore performs the functions of a hermaphrodite gland. 
When the sexual cells are ripe they escape into the infundi- 
bulum and are discharged by the mouth. In Ctenoplana there 
are definite and direct male genital ducts. 

The ova are very small when discharged and undergo com- 
plete segmentation in the sea water. The development of the 
Cydippidea is really direct, but there is a stage passed through 
in which the tentacles are relatively very prominent and 
situated close to the aboral pole, and this stage is very different 
in appearance from the adult. In the Lobata and Cestoidea 
there is, however, a definite larval stage, of the general appear- 
ance of a Mertensia, and during this stage fertile eggs and 
spermatozoa are formed and set free. 

Distribution. — Ctenophora are found at the surface of 
nearly all seas, and many of the genera have a cosmopolitan 
distrilnition. Some of the Lobata, the Cestoidea, and the 
Platyctenea are more commonly found in the warmer regions of 
the world. Pleurohrachia jjileus, Bolina infundihulum, Beroe 
ovata, and B. cucumis occur off the British coast. 

Most of the Ctenophora are from 5 to 20 mm. in diameter, 
but Be7'oe reaches the length of 90 mm., Eucharis multicornis 

^ The two costae that are seen in the niidrlle when the Ctenophoie is viewed in 
the transverse plane, as in Figs. 180 and 181, and the corresponding costae on the 
opposite side are called the "transverse" costae; the other four are called the 
" sagittal " costae. 



XV TKNTACULATA CVDIPriDEA 417 

a height of 250 mm., and Cestus veneris has been found no less 
than 1^ metres from one extremity to the other. 

Ctenophores usually go about in shoals, and in the^ case of 
Beroe cucumis and Eucharis inulticornis the shoals may be of 
very great extent. Fleurobrachia iiileus of the British coasts 
is often found at the end of the season (July) as a series of 
isolated individuals ; but in June they occur in small shoals, 
swimming so close together that they will choke a tow-net in a 
very short space of time. 



CLASS I. TENTACULATA 

Ctenophora provided with a pair of tentacles in the larval 
stages only or in both larval and adult stages. 



Order I. Cydippidea. 

This order includes a number of splierical or oval Ctenophores, 
with a pair of tentacles retractile into deep tentacular pits in the 
adult stage. 

Fam. 1. Mertensiidae. — The body is compressed in the trans- 
verse plane, and the riljs on the transverse areas are longer than 
those on the sagittal areas. The family includes the genus 
BucJd or a, which occurs in the Mediterranean and in the northern 
part of the Atlantic Ocean. In Charistephane there are only two 
enormous ctenoplioral plates in each of the longitudinal tracts. 
These plates are so broad that they almost meet laterally to 
form two continupus circlets round tlie body of the animal. This 
genus is found in the Mediterranean, but a few specimens have 
also been obtained in the Atlantic. 

In Tinerfe the body is almost cylindrical, and there is a pair 
of kidney-shaped swellings at the sides of the aboral pole. It 
has a pale blue colour, and is found in the Guinea and south 
equatorial currents of the Atlantic Ocean. 

The name Mertensia has been given to several forms tnat are 
undoubtedly the young stages of genera belonging to the Lobata, 
but Chun retains the name M. ovum for a species which is very 
abundant in the Arctic currents of the North Atlantic. 

Fam. 2. Callianiridae. — Two or four wing-like processes, into 

VOL. I 2 E 



41 8 CTENOPHORA 



which the longitudinal canals extend, are found at the aboral 
pole. CaUia7iira has two of these processes arranged in the 
transverse plane, and Lophoctenia has four. Callianira is found 
in the Mediterranean and in the Atlantic from the Arctic to the 
Antarctic waters. 

Fam. 3. Pleurobrachiidae. — The body is almost spherical 
in form, and the eight ribs are equal in length. 

This family includes the genus Pleurohrachia, in which the 
ribs extend for a considerable distance along the lines of longi- 
tude of the spherical body, but do not reach either the oral or 
the aboral areas. P. pileus is the commonest Britisli Ctenophore, 
and may be found in shoals in May, June, and July at the 
surface of the sea or cast up on the sand as the tide ebbs. It is 
widely distributed in the North Atlantic waters. F. rhodopis of 
the Mediterranean has rather shorter ribs than P. j^Heus. Two 
new species have recently been described from the Malay 
Archipelago.^ Hormiphora (Fig. 180, p. 413) differs from 
Pleurohrachia in having much shorter ribs, and in possessing two 
kinds of pinnae on the tentacles, those of the ordinary kind and 
others much larger and sometimes palmate in character. This 
genus has a world-wide distribution. 

In Lampetia and Euplokamis the body is more cylindrical in 
shape than it is in the other genera, but the ribs and subjacent 
longitudinal canals extend up to the margin of the aboral field. 
Both these genera occur in the Mediterranean, but Lampetia is 
also found in the Malay Archipelago. 



Order II. Lobata. 

The body is considerably flattened in the transverse plane, 
and the sagittal areas are extended into the form of two wide 
peristomial lobes. The oral ends of the areas between the 
transverse and sagittal ribs are extended to form four flaps, called 
the "auricles." There are no tentacles nor tentacle -sheaths 
of the ordinary kind in the adult form ; but numerous tentilla, 
similar in some respects to the pinnae of the tentacles of other 
Ctenophora, form a fringe round the margin of the auricles and 
the peristome. A single pair of long, filamentoiis, non-retractile 
tentacles arise from the sides of the peristomium in Eucharis 

^ F. Mosser, " Ctenoi)horeii der Siboga Expedition," Leiden, 1903. 



TENTACULATA — LOIJATA 



419 



multicornis. These tentacles have no sheaths, and do not bear 
pinnae. T4iey are probably not homologous with those of other 
Ctenophora. 

The characters that separate tlie families of Lobata are chiefly 
those of varying size, shape, and position of the peristomial lobes 
and auricles. In the Lesueuriidae the peristomial lobes are rudi- 
mentary ; in the other families they are moderately or very large. 
In the Bolinidae the auricles are short, but in most of the other 
families they are long and ribbon-like. In Eucharis they can 
be spirally twisted in repose. 

The modifications of the external form seen in the Lobata 
are accompanied by some modifications of the internal structure 
Among these, perhaps the 
most interesting is a 
communication between 
the transverse longi- 
tudinal and the para- 
gastric canals, and the 
long convoluted tubes 
given off to the peri- 
stomial lobes by the 
sagittal longitudinal 
canals. Very little is 
known about the life- 
history and development 
of most of the Lobata, 
but Chun has shown 
that in Uucharis and 
Bulina there is a Cydip- 
piforni larval stage which 
produces ripe ova and spermatozoa. This is followed by a period 
of sterility, but when the adult characters are developed they 
become again sexually mature. To this series of sexual pheno- 
mena the name " Dissogony " is given. 

The order contains only fifteen genera, but they are usually 
arranged in the following eight families : — 

1. Lesueuriidae. Lesueuria. 

2. Bolinidae. Bolina, Bolinopsis. 

3. Deiopeidae. Deiopea. 

4. Eurhamphaeidae. Eurhamphaea. 




Fig. ISl. — Ocyroe crystallina. Ah, aboral sense- 
organ ; an, auricle ; Can, diverticiiluni from the 
])aragastric canal passing into peristomial lobe ; 
Ct, costae ; M, mouth ; Par, paragastric canal 
passing outwards to join one of the transverse 
subcostal canals ; P.L, peristomial lobe ; u\ wart- 
like tubercles on the lobe. (After Mayer.) 



420 CTENOPHORA 



5. Eucharidae. Eucharis. 

6. Mnemiidae. Mmmia, Mneviio2ms. 

7. Calymmidae. Ctdymma. 

8. Ocyroidae. Ocyroe. 

Most of these Gteuopliores occur in the warm and tropical seas ; 
but Bolina is found occasionally at Plymouth in the month of 
May, on the west coast of Ireland, and at other stations on the 
British coasts. Eucharis is regarded as one of the most beautiful 
of the Phylum. A swarm, some miles in length, of large speci- 
mens of E. multicornis was met by the Plankton Expedition in 
the south equatorial current of the Atlantic during the month 
of September. 

Order III. Cestoidea. 

In this order the body is so much compressed in the trans- 
verse plane and elongated in the sagittal plane tliat it assumes 
the shape of a long narrow band or ribbon. The tentacular 
sheaths are present but the tentacles are degenerate in the adult. 
The tentacular functions are performed by numerous tentilla 
situated in long grooves extending along the whole length of the 
oral side of the band-like body. The transverse ribs are reduced ; 
the sagittal ribs extend along the whole of the aboral side. 

Fam. Cestidae. — This is the only family of the order. 
Cestm veneris, the Venus's girdle of the Mediterranean Sea, is 
also found in the Atlantic Ocean, and specimens belonging to the 




Fit;. 182.— Cesfus 2}ecte7ialis. Ah, aboral sense-organ ; Ct, the sagittal v\\>s ; 
M, nioutli. (After Bigelow.) 

same genus, but probably to a different species, occur as far north 
as the White Sea. Some of the larger specimens are consider- 
ably over 1 metre in length. 

C. pectenalis was found in abundance off one of the Maldive 
Islands,^ and differs from C. veneris in having a large and pro- 
1 H. B. Bigelow, Bull. Mus. Comp. Zool. xxxix. 1904, p. 267. 



XV TENTACULATA — CESTOIDEA PLATVCTENEA 42 I 

minent orange patch at each eud of tlie body. It is said to be 
extremely graceful in the water, moving with slow, ribbon-like 
undulations, and shining in the sunlight with a violet iridescence. 
Vexillum, from the Mediterranean Sea and Canary Islands, is 
rather more pointed at the extremities than Cestus, and differs 
from it in some important anatomical characters. 

Order IV. Platyctenea. 

This order has been constituted for two remarkable genera, 
in which the oro-apical axis is so much reduced that distinct 
dorsal and ventral surfaces can be distinguished. 

There is a single pair of long milky-white tentacles capable 
of complete retraction into tentacular sheaths. 

Fam. 1. Ctenoplanidae. — Ctenoplana was discovered by 
Korotneff in 1886 floating with the Plankton off the coast of 
Sumatra. In 1896 Willey ^ discovered fom- specimens on a 
cuttle - bone floating off the coast of New Guinea. To these 
authors we are indebted for the only accounts of this animal 
that have been published. 

AVhen the Ctenoplfuia is creeping on the bottom of a dish 
or with its dorsal side downwards on the surface film of the 
water, it has the form of a flattened disc with a notch on each 
side. On the upper or dorsal surface eight short rows of cteno- 
phoral plates may be seen, and in a position corresponding with 
the two notches in the margin of the body are situated the two 
sheaths from which the long pinnate tentacles protrude. In the 
exact centre of the dorsal surface is situated the statolith, 
supported by stiff processes from adjacent cells ; and forming a 
circlet round the statolith there is a row of short ciliated tentacles. 
These tentacles, however, when examined carefully in the living 
animal, are found to be arranged in two sets of about nine in 
each, separated by narrow gaps on each side, the gaps corre- 
sponding in position with the axis through the tentacles. 

When the animal is swimming it assumes a helmet-shape by 
depressing the sides of the body like a pair of flaps on the 
tentacular axis, and then the ctenophoral plates come into play and 
produce the progressive movements of the animals. The pinnate 
tentacles are opaque white in colour, and have peculiar serpentine 

1 Quart. Journ. Mkr. Sci. xxxix. 1897, p. 323. 



422 



CTENOPHORA 



movements. Very little is known at present concerning many 
details of the internal anatomy, but there is one point of con- 
siderable theoretical interest — namely, the presence of definite 
male genital ducts. 

Three of Dr. Willey's specimens were mottled with a green 
pigment, whereas his fourth specimen and Korotneff's only speci- 
men were mottled with a red pigment. It has yet to be deter- 
mined whether the differences which have been observed in tlie 
individual specimens are of specific value. 

Fam. 2. Coeloplanidae. — Coeloplana was originally discovered 
by Kowalevsky in tlie Red Sea, but has recently been found by 
Abbott ^ on the coast of Japan. 

The Japanese species are found principally on encrusting 
Algae, Zostera, Ifelohesia, etc., which they resemble very closely 

in colour. The Red Sea species is, 

according to Kowalevsky, ciliated 
all over, but the Japanese species 
are ciliated only on tlie ventral 
surface. As in Ctenoplana, the 
body of Coeloplana is a flattened 
^^^ disc with a notch at each end of 

the tentacular axis, when creeping ; 
^j ^j-ii but Codojylana does not swim, nor 

" at any time does it assume a 

helmet -shape. The tentacles are 
very long and of a chalky-white 
colour. They can be retracted into 
^'^ lj> tentacle-sheaths. When the animal 

'Flu,. 18B.— Coeloplana mitsukurii, iioat- ig excited it thl'OWS Out the whole 
iii2f at the surface of the sea with , , i • i i r i -i. £i 

the dorsal side downwards. T, T, tentacle m a cloud ol whitc fiia- 

the tentacles expanded. (After nicnts, "and to watch it at SUCh 

Alibott.) . - . , 1 . • 

a time, shooting out and retracting 
the tentacles, moving along the side of the aquarium like a 
battleship in action is truly a remarkable spectacle." " On the 
dorsal side of the body there is a series of processes which are 
called the dorsal tentacles. The statolith is very small, and 
is not surrounded by sensory processes as it is in Ctcnoplana. 
There are no ctenophoral plates. The colours of the Japanese 

^ Annot. Zooloij. Jupon. iv. ]it. iv. 1902, p. 100. 
" A'obott, I.e. p. 106. 




NUDA 423 



species are scarlet or carmine red and dirty brown or brownish 
yellow. They are from 1 to 2 centimetres in diameter. 



CLASS II. NUDA 

Ctenophora without tentacles. 

Fam. Beroidae. — Beroe, the only genus of this family and 
class, differs from other Ctenophora in several important par- 
ticulars. There are no tentacles, and the stomodaeum is so large 
that the body-form assumes that of a thimble with moderately 
thick walls. The infundibulum is small. The paragastric and 
longitudinal canals give rise to numerous ramifications which 
form a network distributed throughout the surface of the body. 
The statolith is unprotected by a dome, and the polar fields are 
bordered by a number of small branching papillae. The eight 
ribs extend for nearly the whole length of the body. Beroe is 
almost cosmopolitan, and is frequently found at the surface of 
the sea in great numbers. B. ovata is found off the Shetlands, 
Hebrides, and west coast of Ireland, but is rare on the east coast 
of the British Islands and in the English Channel. At Valencia 
it is common in August and September, and sometimes reaches 
the great size of 90 mm. in length by 50 mm. in breadth. It is 
usually of a pale pink colour. 

Appendix to Ctenophoea 

Hydvoctena salenskii has recently been discovered by Dawy- 
doff ^ floating with the Plankton off the island Saparua in the 
Malay Archipelago. It is claimed to be a connecting link 
between the Ctenophora and the Medusae of the Hydrozoa. 

In external features it is like one of the Narcomedusae, 
having a transparent jelly-like bell with a wide bell-moutli 
guarded by a velum (Fig. 184, I^. There are only two simple but 
solid tentacles (t), provided with tentacle-sheaths, but inserted 
on opposite sides of the bell — not on the margin, but, as in the 
Ctenophore, at a level not far removed from the aboral pole. 
At the aboral pole there is a minute pore surrounded by a high 
ciliated epithelium bearing an orange pigment. This leads into 

1 ZooL Anz. .\xvii. 1904, p. 223. 



424 



CTENOPHORA 



a short blind canal, which terminates in an ampulla bearing two 
statoliths supported by elastic processes from the ampullar 
epithelium. 

The sub-umbrellar cavity extends for a distance of about one- 
half the height of the bell. The mouth (3T), which opens into 
this cavity, leads into a wide cavity that gives off a short blind 
canal to the side of each tentacular sheath, and a straight tube 
that leads straight to the statocyst, where it also ends blindly. 




Fig. 184. 



-Hydroctena salenskii. ah, Aboral organ ; M, manubrium ; ty tentacle ; 
T', velum. (After Dawydolt.) 



There are no radial canals and no ring canal at the margin of 
the umbrella. There are also no ctenophoral plates. In the 
absence of any information concerning the position of the genital 
glands, the character of the epithelium of the tentacles and the 
development, we are not justified in regarding Hydroctena either 
as a Ctenophore or as a connecting link between the Cteno- 
phora and the Hydromedusae. It may be regarded simply as a 
Craspedote Medusa, probably related to the Narcomedusae, with 
a remarkable aberrant aboral sense-organ. 



ECHINODERMATA 



E. W. MacBEIDE, M.A., F.RS. 

Formerly Fellow of St. John's College 
Professor of Zoology in McGill University, Montreal. 



425 



CHAPTER XVI 

ECHINODERMATA INTRODUCTION CLASSIFICATION ANATOMY 

OF A STAKFISH SYSTEMATIC ACCOUNT OF ASTEROIDEA 

The name Echinodermata ^ means literally " spiny -skinned," 
and thus brings into prominence one very conspicuous feature 
of most of the animals belonging to this phylum. All, it is true, 
do not possess spines ; but with one or two doubtful exceptions, 
all have calcareous plates embedded in the skin, and these plates, 
in many cases, push out projections which raise the skin into 
corresponding elevations, which are called the spines. The 
spines are, like tlie other plates, inside the skin, and to s})euk of 
an Echinoderm living in its shell, as we speak of a Snail, is a 
serious error. The shell of a Mollusc is fundamentally a 
secretion poured forth from the skin, and is thus entirely 
external to the real living parts ; but the plates and spines of 
an Echinoderm may be compared to our own bones, which are 
embedded deeply in tlie flesh. Hence the name ossicle (little 
bone) is used to designate these organs. 

Besides the possession of these spines, Echinoderms are 
characterised by having their organisation -pervaded by a 
fundamental radial symmetry. The principal organs of the 
body are repeated and are arranged like the spokes of a wheel 
round a central axis instead of being, as, for example, in 
Chaetopoda, arranged behind one another in longitudinal series. 

In addition to these striking peculiarities, Echinoderms 
possess a most interesting internal organisation, being in this 
respect almost exactly intermediate between the Coelenterata, 

^ The name seems first to have been used by Klein in 1734, "Naturalis 
dispositio Echinodermatum " (Danzig). Leuckart about 1850 first established 
Ecliinodermata as a primary division of the animal kingdom. 

427 



428 ECHINODERMATA 



and the higher Invertebrata. Like so many of the latter, the 
Echinodennata have an anus, that is, a second opening to tlie 
alimentary canal through which indigestible material is rejected ; 
like them also, they have a body-cavity or coelom surrounding 
the alimentary canal — from the lining of which the genital cells 
are developed. On the other hand, there is no definite circulatory 
system, nor any specialised excretory organ, and the nervous 
system exhibits no concentration which could be called a brain, 
and is, moreover, in close connexion with the skin. In all 
these points the Echinodermata resemble the Coelenterata. 

One of the most characteristic features of the internal 
anatomy of Ecliinodermata is the presence of a peculiar series 
of organs, known collectively as tlie water-vascular system or 
hydrocoel. This is really a special division of the coelom 
or liody -cavity which takes on the form of a ring-shaped canal 
embracing the mouth, from which are given off long radial 
canals, usually five in number, running to the more peripheral 
parts of the body.^ Each radial canal carries a double series of 
lateral branches, which push out the skin so as to appear as 
appendages of the body. These appendages are known as 
tentacles or tube-feet ; they are both sensory and respiratory 
in function, and often in addition, as the name tube-foot 
indicates, assist in locomotion. As a general term for these 
appendages, to be applied in all cases without reference to their 
function, the name podium has l)een suggested and will be 
employed here. A system of canals, in many ways resembling 
the water-vascular system, is found in Brachiopoda, Gephyrea 
and Polyzoa, but the peculiarity of Echinodermata is the way 
in which it is ke})t filled with fluid. From the ring-canal in the 
interval (or interradius) between two radial canals, a vertical 
canal, termed the stone-canal, is given off, which communicates 
with the exterior l)y means of a sieve-like plate, the madre- 
porite, pierced l)y fine canals. These canals and the stone-canal 
itself are lined with powerful cilia, which produce a strong inward 
current, and keep the water- vascular system tensely filled with 
sea water. 

The phylum includes the familiar Starfish and Sea-urchins, 
which in sheltered spots are found between tide-marks ; the 

^ In the Synaptidae the radial canals although present in the young are lost 
in the adult (Ludwig, 1892, in Bronn's Tkier-Iieich, Bd. ii. Abt. 3, Bach i. p. 460). 



XVI HABITS AND DISTRIBUTION 429 

Brittle Stars and Sea-cucumbers, which can be dredged up from 
below low-water mark, and lastly the beautiful Feather-stars, of 
which there are comparatively few species still living, although 
huge beds of limestone are composed of the remains of fossil 
Feather-stars, 

One species of Sea-cucumber (Sy/utpta siniiUs) ^ is said to enter 
brackish water in the mangrove swamps of the tropics ; but, 
with this exception, the whole phylum is marine. A few species 
can endure partial exposure to the air when left bare l)y the 
receding tide, but the overwhelming majority are only found 
beneath low-water mark, and a considerable number live in the 
deepest recesses of the ocean. 

Their distribution is, no doubt, partly determined by food, 
a number of species being strictly confined to the neighbourliood 
of the shore. On the other hand, since a xevy large number 
of species live on the layer of mud impregnated with animal 
remains which forms the superficial layer of the deposit covering 
the sea-lioor, it is not surprising to learn that many have an 
exceedingly wide range, since this deposit is very widely dis- 
tributed. Another equally important factor in determining 
distribution is wave-disturbance, and it is surprising to learn 
to what a depth this extends. Off the west coast of Ireland a 
large wave literally breaks on a submerged rock 15 fatlioms 
beneath the surface. Speaking generally, it is useless to look 
for Echinoderms on an exposed coast, and the same species, 
which in the sheltered waters of the Clyde are exposed at low 
water, must be dredged up from 20 to 30 fathoms outside 
Plymouth Sound. 

The ordinary collector is attracted to the group chiefly by 
the regularity and beauty of the patterns produced by the radial 
symmetry, l)ut to the scientific zoologist they are interesting from 
many other points of view. Differing widely nevertheless from 
the higher Invertebrata in their symmetry when adult, they have 
as larvae a marked bilateral symmetry, and the se(;ondary 
development of the radial symmetry constitutes one of the most 
remarkable life-histories known in the animal kingdom. 

Then again, owing to the possession of ossicles, the Ecliino- 
dermata are one of the few groups of Invertebrata of which 
abundant remains occur fossilised. In attempting, therefore, to 

' Luihvig, A<c. cif. \>. 'MtJ. 



430 ECHINODERMATA ELEUTHEROZOA chap. 

decipher the past history of life from the fossil record, it is 
necessary to have an exact and detailed knowledge of Echinoderni 
skeletons and their relation to the soft parts. Lastly, the 
internal organisation of Echinoderms throws valuable light on 
the origin of the complicated systems of organs found in the 
higher animals. 

Echinodermata are divided into two great sub-phyla, which 
must have very early diverged from one another. These are : — 

(1) Eleutherozoa, (2) Pelmatozoa.^ 

The sub-phylum Pelmatozoa, to which the living Feather- 
stars (Crinoidea) and the majority of the known fossil species 
belong, is characterised by the possession of a fixing organ placed 
in the centre of the surface opposite the mouth — the aboral 
surface as it is called. Ordinarily this organ takes on the 
form of a jointed stalk, but in most modern species it is a little 
knob with a tuft of rooting processes, termed cirri. In the 
other sub-phylum, the Eleutherozoa, no such organ is found, 
and the animals wander about freely during their adult life, 
though for a lirief period of their larval existence they may be 
fixed by a stalk -like protuberance arising from the oral 
surface. 

SUB-PHYLUM I. ELEUTHEEOZOA 

The Eleutherozoa are divided into four main classes, between 
which no intermediate forms are found amongst the living species, 
though intermediate types have been found fossil. 

The four classes into which the Eleutherozoa are divided 
are defined as follows : — 

(1) Asteroidea (Starfish). — " Star "-shaped or pentagonal 
Eleutherozoa with five or more triangular arms, not sharply 
marked off from the central disc. The mouth is in the centre 
of one surface, called from this circumstance the "oral " ; the anus 
is in the centre of the opposite surface, termed the " aboral." 
From the mouth a groove runs out on the under surface of each 

^ This classification is substantially that suggested by Jeti'rey Bell, Catalogue 
of British Echinoderms in the British Museum, 1892, except that Bell separates 
Holothuroidea from all others. Reasons will be given later for regarding Holo- 
thuroidca as modified Echinoidea. 



CLASSIFICATION ASTEROIDEA 43 I 



arm towards its tip, termed the " ambulacral " groove. Projecting 
from the ambulacral groove are found tlie podia or tube-feet, the 
organs of movement and sensation of the animal. 

(2) Ophiuroidea (Brittle Stars). — Eleutherozoa, in which the 
body consists of a round disc with long worm-like arms inserted 
in grooves on its under surface. No anus is present, and the 
ambulacral grooves are represented by closed canals. The podia 
are merely sensory and respiratory, locomotion being effected by 
muscular jerks of the arms. 

(3) Echinoidea (Sea-urchins). — Globular or disc-shaped 
Eleutherozoa, in wliich the skeleton forms a compact cuirass 
except for a short distance round the mouth (peristome) and 
round the anus (periproct). The ambulacral grooves are 
represented Ijy canals which, like meridians of longitude on a 
school-globe, run from the neighbourhood of the mouth to near 
the aboral pole of the body. The spines are large and movably 
articulated with the plates. The animals move by means of 
podia and spines, or by means of the latter only. The anus is 
usually situated at the aboral pole, but is sometimes displaced 
towards the side, or even on to the ventral surface. 

(4) Holothuroidea (Sea - cucumbers). — Sausage - shaped 
Eleutherozoa, in which the skeleton is represented only by 
isolated nodules of calcium carbonate, and in which the body- 
wall is highly muscular. The mouth and anus are situated at 
opposite ends of the body, and the ambulacral grooves (repre- 
sented by closed canals) run from near the mouth to the 
proximity of the anus. Movement is accomplished by means of 
the podia, aided by worm-like contractions of the body. 



CLASS I. ASTEEOIDEA ' (Staiifisii) 

The Starfish derive their name from their resemblance in 
shape to the conventional image of a star. The body consists 
of broad triangular arms (generally five in number) which 
coalesce in the centre to form a disc. The skin is soft and 

^ Gr. darrip, a "star" ; elSos, " form." Linnaeus established the genus ^s/cnas in 
1766. Joliannes Miiller in 1842 used the name " Asteriden," and in System der 
Astcriden, 1842, by Miiller and Troschel, the foundation of our knowledge of the 
group was laid. 



43 2 ECHINODERMATA — ASTEROIDEA chap. 

semi-transparent, permitting the skeleton to be easily detected ; 
this consists of a mesh-work of rods or plates, leaving between 
them intervals of soft skin. In a living Starfish it can be seen 
that many of these soft places are raised up into finger-like 
outgrowths, which are termed " papulae " or " dermal gills," 
through the thin walls of which an active interchange of gases 
with the surrounding water takes place, and the animal obtains 
in this way the oxygen necessary for its respiration. 

Very few and feeble muscle-fibres exist in the body-wall, and 
the movements of the arms, as a whole, are very slow and limited 
in range. There is a membranous lip surrounding the mouth, 
from which five broad grooves run outwards, one on the under- 
side of each arm. These are termed the " ambulacral grooves." 
Each groove is A-shaped, and its sides are stiffened by a series of 
rod-like ossicles called the " ambulacral ossicles." 

The animal progresses by the aid of a large number of trans- 
lucent tentacles, termed " tube-feet " or "podia," which are attaclied 
to the walls of the ambulacral grooves. 

Anatomy of a Starfish. — As an introduction to the study of 
the anatomy not only of Starfish but of Echinodermata as a 
whole, we select Astcrias ruhens, the common Starfish of the 
British coasts, which in many places may be found on the beach 
near low-water mark. 

External Features. — In this species (Fig. 185) the skeleton 
is a net- work of rod-like plates, leaving wide meshes between 
them, through which protrude a perfect forest of transparent 
papulae. From the points of junction of the rods arise short 
blunt spines surrounded by thick cushions of skin. The surfaces 
of these cushions are covered with a multitude of whitish specks, 
which, on closer inspection, are seen to have the form of minute 
pincers, each consisting of two movable blades crossing eacli other 
below and articulated to a basal piece. Tliese peculiar organs are 
termed " pedicellariae " (Fig. 186), and their function is to keep 
the animal clean by seizing hold of any minute organisms which 
would attempt to settle on the soft and delicate skin. When 
irritated the blades open and then snap together violently, and 
remain closed for a long time.^ These actions are brought about 
by appropriate muscles attaching the blades to the basal piece. 

^ Uexkiill, "Die Physiologie der Pedicellarien," Zeitschr. f. Biol, xxxvii. 1899, 
p. 356. 



ANATOMY OF A STARFISH — PEDICELLARIAE 



433 



The 

fixin 

and 

pose 

into 



last-n.imed ossicle increases the certainty of the grip by 
g tlie lower parts of each blade in the same vertical plane, 
preventing lateral slipping, so tliat it serves the same pur^ 
as the pivot in a pair of scissors 
a groove on the side of this piece. 



Each blade, in fact, fits 
The muscles which close 



mad. 




^^^r.^^^^-^?^^^..},,^ .^ 



s;-^ - ^--^^ 



S^ 



'^Si^ 



fOr 



kjH-*''2> 



-j^j, anus 



w 

Fio. 185. — Asterias rnbens, seer 



, - i, dorsal spines. 






m 

m 

from the aboral surface, x 1. mad, Madreporite. 



the blades arise from the lower ends (handles) of the blades, 
and are united below to form a common muscular string which 
attaches the whole organ to one of the plates of the skeleton. 
An attempt of the victim to tear the pedicellaria out is resisted 
by the contraction of this string, which thus brings about a 
closer grip of tlie blades. In order that the blades may open 
they must first be lifted out of the grooves on the basal piece — 
this is effected by special lifting muscles. The opening is 
VOL. I 2 F 



434 



ECHINODERMATA ASTEROIDEA 



brought about by muscles extending from the " handle " of one 

blade to the upper part of the other. 

Scattered about amongst the papulae between the cushions 

are other pedicellariae of a larger size in which the blades do 

not cross one another (Fig, 186, B). 

In the space or " interradius " between two arms, on the aboral 

surface, there is found a button-shaped ossicle. This is covered 

with fine grooves, and 
from a fancied resemb- 
lance between it and 
some forms of coral it 
has received the name 
" madreporite " (Fig. 
1S5, mad). The bottoms 
of the grooves are per- 
forated by capillary 
canals lined by fiagella, 
through the action of 
which water is con- 
stantly being intro- 
duced into the water- 



/^ 




Fig. 1S6. — -View of pedicellariae of .1. glacialls. A, 
Crossed form, x 100. 1, Ectoderm covering the 
whole organ ; 2, basal piece ; 3, auxiliary muscle VaSCUlar SyStCm. 
closing the blades ; 4, muscle lifting right blade out The anUS is situated 

of the groove ; 5, handle of left blade ; 6, muscles 

closing the blades, and uniting to form 7, the near the centre of the 
muscular string attaching the pedicellaria to the viYj-pgv surface of the 
skeleton. B, straight form, x 10. 1, Basal piece ; ^^ 

2, blades ; 3 and 4, muscles closing the blades ; disC, but it is SO minute 
5, muscle opening the blades. (From Cuenot.) ^^ ^^ require carcful 

inspection in order to discover its position (Fig. 185). 

On the under side of the animal the most conspicuous features 
are the five ambulacral grooves which radiate out from the 
" peristome," a thin membranous area surrounding the central 
mouth. The grooves are filled with the tube-feet, which are 
closely crowded together and apparently arranged in four rows. 

Skeleton. — The sides of the ambulacral grooves are 
stiffened by the rod-like "ambulacral ossicles." To the outer 
ends of these are articulated a set of shorter rods termed the 
" adambulacral ossicles " which carry each two or three rod -like 
spines, the " adambulacral spines," the skin covering which bears 
numerous pedicellariae (Fig. 187, P>). When the animal is 
irritated the edges of the groove are brought together, and tliese 



ASTER IAS SKELETON 



435 



spines then form a trail is- work covering and protecting the 
delicate tube- feet; the numerous pedicellariae are then in a 
position to make it unpleasant for any intruder. The closure of 
the groove is effected by means of powerful muscles connecting 
each ambulacral ossicle with its fellow. There are also feebler 







m 






c^er- 







Fig. 187. — A, Asterias rubens, seen from the oral surface, drawn from a living specimen. 
X 1. B, an adambulacral spine, showing three straight pedicellariae ; C, a tube- 
foot expanded and contracted. 

muscles connecting these plates with their successors and pre- 
decessors, which enable the 'arm to be bent downwards in a 
vertical plane. It is raised by a muscular band running along 
the dorsal wall of the coelom to the point of the arm. 

When the series of ambulacral and adambulacral ossicles is 
followed inwards towards the mouth it is seen that the first 
ambulacral ossicle is closely fixed to the second, but is widely 



436 ECHINODERMATA — ASTEROTDEA chap. 

separated from its fellow, remaining, however, connected with 
the latter by a powerful adductor muscle. In consequence of the 
separation of this pair of ossicles each is brought into closer 
contact with the corresponding ossicle in the adjacent radius, to 
which it is connected by a muscle called the abductor. The 
first adambulacrals in adjacent radii are also brought into closer 
contact and carry long spines which, when the ambulacral 
grooves are contracted, project like a grating over the mouth. 
In the order of Asteroidea to which Asterias belongs, the adam- 
bulacrals themselves do not project much, but in all other cases 
they form prominent mouth-angles, so that the opening of the 
mouth becomes star-shaped (Fig. 211, p. 483). 

Except in the case of the ambulacral and adambulacral plates 
little regular arrangement is to be detected in the ossicles of the 
skeleton which, as has already been mentioned, form a mesh- 
work. If, however, the arm be cut open and viewed from the 
inside it will be seen that the edge is strengthened above and 
below by very thick, powerful, rod-like plates. These are called 
the " supero-marginal " and " infero-marginal " ossicles ; they are 
not visible from the outside, since they are covered by a thick 
layer of the body- wall containing other smaller plates (Fig. 190, 
marg). In many genera, however, they are exposed, and form a 
conspicuous edging to the arm above and below. In many 
genera, also, there are three conspicuous series of plates on the 
back of each arm, viz. a median row, called " carinals " {car., 
Fig. 191), and two lateral rows, termed " dorso-laterals " {d.lat., 
Fig. 191). These three rows, with the two rows of marginals, 
one of ambulacrals, and one of adambulacrals on each side (11 
rows in all), constitute the primitive skeleton of the arm, and 
appear first in development. 

The structure of all these elements of tlie skeleton is the 
same. They may be described as scaffoldings of carbonate of 
lime, interpenetrated by a mesh-work of cells fused with one 
another, by which the carbonate of lime has been deposited. The 
matrix in which the ossicles lie is a jelly-like substance traversed 
by a few bands of fibres which connect the various rods with one 
another. This jelly is almost fluid in the fresh state, but when 
heated forms a hard compound, possibly allied to mucin, which 
will turn the edge of a razor. 

When the covering of tlie back is dissected off the coelom is 



ASTER IAS — COELOM 437 



opened. This is a spacious cavity which apparently surrounds 
the alimentary canal and extends into the arms. It has, how- 
ever, its own proper wall, which is called the " peritoneum," both 
on the outer side, where it abuts on the skin, and on the inner 
side, where it comes in contact with the wall of tlie alimentary 
canal. The outer wall is called the " somatic peritoneum," and it 
is possible to dissect off the rest of the body-wall and leave it 
intact ; the inner wall, from its close association with the 
alimentary canal, is termed the " splanchnic peritoneum." This 
wall can only be distinguished in microscopic sections from that 
of the alimentary canal, to which it is closely applied. 

The coelom is filled witli a fluid, which is practically sea 
water with a little albuminous matter in solution. Through the 
thin walls of the papulae oxygen passes into this fluid, whence it 
easily reaches the inner organs, since they are all in contact 
with some part of the coelomic wall. Similarly CO2 is absorbed 
by the coelomic fluid from all parts of the body, and diffuses 
through the papulae to the surrounding water. 

The Starfish possesses no definite kidney for getting rid of 
nitrogenous waste. In most of the higher animals w^th a well- 
developed coelom it has been proved that the kidney is simply a 
specialised portion of the coelom, and in many cases some parts 
of the coelomic wall still retain their excretory functions, which 
apparently the whole originally possessed. In the Starfish and 
in Echinodermata generally this primitive state of affairs is still 
retained. From the cells forming the coelomic wall, cells are 
budded off into the fluid, where they swim about. These cells 
from their movements are called amoebocytes. If a substance 
such as indigo-rcarmine, which when introduced into the tissues 
of the higher animals is eliminated by the kidney, is injected 
into the Starfish, it is found soon after to be vigorously absorbed 
by the amoebocytes. These later accumulate in the dermal 
branchiae, through the thin walls of which they make their way ^ 
to the outside, where they degenerate. 

The coelom is indented Ijy five folds, which project inwards 
from the interradii. These folds are called the " interradial 
septa " ; they are stiffened by a calcareous deposit, which is not, 
however, sufficiently dense to constitute a plate. In one of the 

" Durham, "Wandering Cells in Echinoilermata," Quart. J. Mlcr. Sci. xxxiii. 
1S91, pp. 81 et scq. 



438 



ECHINODERMATA ASTEROIDEA 



septa the axial sinus and stone-canal (see below) are embedded. 
These septa are to be regarded as areas of lateral adhesion 
between the arms. 

The alimentary canal consists of several distinct portions. 
The mouth leads by a narrow neck called tlie "oesophagus" into 




Fig. 188.— View of upper half of a specimen of Asterias rubens, which has been 
split liorizontally into two halves. o,x.c, Axial sinus ; g.d, genital duct ; oe, cut end 
of the oesophagus, the narrow neck of the stomach ; py, pyloric sac ; p^J.c, pyloric 
caeca ; r, rectum ; r.i% rectal caeca; sept, interradial septum ; st.c, stomach lobe. 

a voluminous baggy sac termed the " stomach," which is produced 
into ten short pouclies, two projecting into each arm. The 
stomach leads in turn by a wide opening into a pentagonal 
flattened sac, the " pyloric sac," which lies above it. Each angle 
of the pyloric sac is prolonged into a tube — the so-called " pyloric 
duct " — running out into the arm, where it immediately bifurcates 
into two forks, each beset by a large number of small pouches 



ASTERIAS ALIMENTARY CANAL FOOD 



439 



and attached to the dorsal wall of the coelom by suspensory 
bands of membrane called mesenteries. These ten forks are called 
" pyloric caeca " ; they are of a deep green colour owing to the 
pigment in their wall. Beyond the pyloric sac the alimentary 
canal is continued as the slender " rectimi " to the anus. The 
rectum gives off two small branched pouches of a brown colour 
called " rectal caeca." This comparatively complicated form of 
alimentary canal is related to the nature of the food of the animal 
and the method it employs to capture its prey. 

The favourite food^ of Asterias consists of the common bivalves 



v.^V. '\^l^ 








Fjo. 1S9. — View of a Starfish (Echinas(er) devouriug a Mussel. 1. The madreporite. 



of the coast, notably of the Mussel {Mytilus edulis). There is, 
however, no animal which it will not attack if it is fortunate 
enough to be able to catch it. The Starfish seizes its prey by 
the tube-feet, and places it directly under its mouth, folding its 
arms down over it in umbrella fashion. The muscles which run 
around the arms and disc in the body-wall contract, and the 
pressure thus brought to bear on the incompressible fluid con- 
tained in the coelom, forces out the thin membranous peristome 
and partially turns the stomach inside out. The everted edge of 
the stomach is wrapped round the prey. 

^ Starfish are most destructive on oyster-beds, and hence possess considerable 
negative economic value. 



440 ECHINODERMATA ASTEROIDEA chap. 

Soon the bivalve is forced to relax its muscles and allow the 
valves to gape. The edge of the stomach is then inserted between 
the valves and applied directly to the soft parts of the prey 
which is thus completely digested. When the Starfish moves 
away nothing but the cleaned shell is left behind. If the bivalve 
is small it may be completely taken into the stomach, and the 
empty shell later rejected through the mouth. 

It was for a long time a puzzle in what way the bivalve was 
forced to open. Schiemenz ^ has, however, shown that when the 
Starfish folds itself in umbrella-like form over the prey it holds 
on to the substratum by means of the tube-feet of the distal 
portions of the arms, whilst, by means of the tube-feet belonging 
to the central portions, it drags apart the valves by main force. 
He has shown experimentally: (1) that whilst a bivalve may be 
able to resist a sudden pull of 4000 grammes it will yield to a 
pull of 900 grammes long continued; (2) that a Starfish can 
exert a pull of 1350 grammes; (3) that a Starfish is unable to 
open a bivalve unless it be allowed to raise itself into a hump, 
so that the pull of the central tube-feet is at right angles to the 
prey. A Starfish confined between two glass plates walked about 
all day carrying with it a bivalve which it was unable to open. 

The lining of the stomach is found to consist very largely of 
mucus-forming cells, which are swollen with large drops of mucus 
or some similar substance. It used to be supposed that this 
substance had some poisonous action on the prey and paralysed 
it, but the researches of Schiemenz show that this is incorrect. 
If when an Asterias is devouring a bivalve another be offered to 
it, it will open it, but wi],l not digest it, and the victim shows no 
sign of injury but soon recovers. The cells forming the walls 
of the pyloric sac and its appendages are tall narrow cylindrical 
cells crowded with granules which appear to be of the nature of 
digestive ferment. This substance flows into the stomach and 
digests the captured prey. 

A very small amount of matter passes into the rectum and 
escapes by the anus, as the digestive powers of the Starfish are 
very complete. The rectal caeca are lined by cells which secrete 
from the coelomic fluid a brown material, in all probability an 
excretion, which is got rid of by the anus. 

^ Mitth. dcs dcutschen Seefischervercins, xii. 1896, p. 102, and J. Mar. Biol. Ass. 
iv. 1895-97, p. 266. 



XVI ASTERIAS WATER-VASCULAR SYSTEM 44 I 

When the meal is finished the stomach is restored to its 
former place by the action of five pairs of retractor muscles, one 
pair of which originates from the upper surface of the ambulacral 
ossicles in each arm and extends to the wall of the stomach, 
where they are inserted (Fig. 190, ret). 

The tube-feet, which are at once the locomotor and the prin- 
cipal sensory organs of the Starfish, are appendages of that peculiar 
system of tubes known as the water-vascular system, which is 
derived from a part of the coelom cut olf from the rest during 
the development of the animal. This system, as already men- 
tioned, consists of (1) a narrow " ring-canal," encircling the mouth 
and lying on the inner surface of the membranous peristome ; 

(2) a radial canal leaving the ring-canal and running along the 
under surface of each arm just above the ambulacral groove ; 

(3) a vertical stone-canal running from the madreporite down- 
wards to open into the ring-canal in the interspace between two 
arms. The madreporite is covered externally by grooves lined with 
long cilia, and is pierced with narrow canals of excessively fine 
calibre, the walls of which are also lined by powerful cilia. Most of 
these narrow canals open below into a main collecting canal, the 
stone-canal, but some open into a division of the coelom termed 
the axial sinus, with which also the stone-canal communicates by a 
lateral opening. The cavity of the stone-canal is reduced by the 
outgrowth from its walls of a peculiar Y-shaped projection, the 
ends being rolled on themselves in a complicated way (Fig. 190, B). 
The walls of the canal consist of a layer of very long narrow cells, 
which carry powerful flagella, and outside this of a crust of 
calcareous deposit, which gives rigidity to the walls and has 
suggested the name stone-canal. 

The tube-feet are covered externally by ectoderm, inside which 
is a tube in connexion with the radial water-vascular canal. This 
latter is lined by flattened cells, which in the very young Star- 
fish are prolonged into muscular tails ; in the older animal these 
tails are separated off as a distinct muscular layer lying between 
the ectoderm and the cells lining the cavity of the tube. The 
tube-foot is prolonged inwards into a bulb termed the " ampulla," 
which projects into the coelom of the arm and in consequence is 
covered outside by somatic peritoneum. Just where the ampulla 
passes into the tube -foot proper the organ passes downwards 
between two of the powerful ambulacral ossicles which support 



442 



ECHINODERMATA ASTEROIDEA 



the ambulacral groove, and a little below this spot a short 
transverse canal connects the tube-foot with the radial canal 
which lies beneath these ossicles (Fig. 191). 

The tube-feet are, therefore, really a double row of lateral 




•"5>>;m 



190. — A, view of the under half of a specimen of Asterias rubens, which has been 
horizontally divided into two halves. B, enlarged view of the axial simis, stone- 
canal and genital stolon cut across. amb.oss, Ambulacral ossicle ; amp. 
ampullae of the tube-feet ; ax.s, axial sinus ; gon, gonad ; ff.stol, genital stolon ; 
marg, marginal ossicle ; nerv.circ, nerve ring ; oe, cut end of oesophagus ; pst, peri- 
stome ; ret, retractor muscle of the stomach ; sept, iuterradial septum ; stone c, 
stone-canal ; T. Tiedemann's body ; vxv.r, water-vascular ring-canal. 

branches of the radial canal. The appearance of being arranged 
in four rows is due to the fact that the transverse canals connect- 
ing thein with the radial canal are alternately longer and shorter 
so as to give room for more tube-feet in a given length of the 
arm. Each tube-foot ends in a round disc with a slightly 
tliickened edge. The radial canal terminates in a finger-shaped 



ASTERTAS TUBE-FEET 



443 



appendage, called the median tentacle, at the base of which is 
the eye. 

The manner in which tliis complicated system acts is as 
follows : — When the tube-foot is to be stretched out the ampulla 
contracts and drives the fluid downwards. The contraction of 
the ampulla is brought about by muscles running circularly 
around it. The tube-foot is thus distended and its broad flattened 
end is brought in contact with the surface of the stone over 
which it is moving and is pressed close against it. The muscles of 
the tube-foot itself, which are arranged longitudinally, now com- 
mence to act, and the pressure of the water preventing the tearing 




Fig. 191. — Diagrammatic cross- 
section of the arm of a 
Starfish, adamh, Aflambii- 
lacral ossicle ; amh, ambu- 
lacral ossicle ; amp, ampulla 
of tube - foot ; branch, 
papula ; ear, carinal plate ; 
d.lat, dorso-lateral plate ; 
inf. mar g, infero - marginal 
plate ; p.br, peribranchial 
space ; jxd, pedicellaria ; 
s.marg, supero - marginal 
plate. The nervous ridge 
between the bases of the 
tube-feet and the two peri- 
haemal canals above this 
ridge are shown in the figure 
but not lettered. 



away of the sucker from the object to which it adheres, the 
Starfish is slowly drawn forward, whilst the fluid in the tube-foot 
flows back into the ampulla. 

If each tube-foot were practically water-tight, then each would 
be entirely independent of all the rest, and it would not be easy 
to suggest a reason for the presence of the complicated system 
of radial canals and stone-canal. Just at the spot, however, 
where the transverse canal leading from the radial canal enters 
the tube- foot there is a pair of valves which open inwards and 
allow fluid to pass from the radial canal into the tube-foot but 
prevent any passing outwards in the reverse direction. The 
presence of these valves renders it probable that the tube-foot is 
not quite water-tight ; that when it is distended under the 
pressure produced by the contraction of the muscles of the 
ampulla, some fluid escapes through the permeable walls ; and 



444 ECHINODERMATA ASTEROIDEA chap. 

that the loss thus suffered is made up by the' entry of fresh fluid 
from the radial canal. The radial canal in turn draws from the 
ring-canal, and this last is supplied Ijy the stone-canal, the 
cilia of which keep up a constant inward current. 

In the fluid contained in the water-vascular system, as in the 
coelomic fluid, there are amoebocytes floating about. These are 
produced in short pouclies of the ring-canal, nine in number, 
which are called after their discoverer " Tiedemann's bodies " 
(Fig. 190, T). From the cells lining these the amoebocytes are 
budded off. 

The nervous system of the Starfish is in a very interesting 
condition. The essential characteristic of all nervous systems is 
tlie presence of the " neuron," a cell primitively belonging to an 
epithelium but which generally has sunk below the level of the 
others and lies amongst their bases. This type of cell possesses 
a round body produced in one direction into a long straight 
process, the " axon," whilst in the other it may have several 
root-like processes, or " dendrites," which may spring from a 
common stem, in which case the neuron is said to be " bipolar." 
The axon is often distinguished as a " nerve-fibre " from the round 
body which is termed the " nerve-cell." This is due to the fact 
that for a long time it was not recognised that these two strvic- 
tures are parts of a whole. 

Now at the base of the ectoderm all over the body of the 
Starfish there is to be found a very fine tangle of fibrils ; these 
are to be found partly in connexion with small bipolar neurons 
lying amongst them and partly with isolated sense-cells scattered 
amongst the ordinary ectoderm cells. This nervous layer is, 
however, very much thickened in certain places, so as to cause 
the ectoderm to project as a ridge. One such ridge is found at 
the summit of each ambulacral groove running along the whole 
under surface of the arm and terminating in a cushion at 
the base of the median tentacle of the water-vascular system. 
This ridge is called tlie radial nerve-cord. The five radial 
nerve -cords are united by a circular cord, the nerve -ring, 
which appears as a thickening on the peristome surrounding 
the mouth. 

The sense-organs of the Starfish are chiefly the discs of the 
tube-feet. Eound the edges of these there is a special aggrega- 
tion of sense-cells ; elsewhere, as in the skin of the back, only 



ASTERIAS NERVOUS SYSTEM 



445 



isolated sense-cells are fouiul, and it becomes impossible to speak 
of a sense-organ. 

A prolongation of the radial nerve -cord extends outwards 
along one side of each tube-foot. This is often spoken of as 
the " pedal nerve," but the term nerve is properly retained for 
a mere bundle of axons such as we find in the higher animals, 
whereas the structure referred to contains the bodies of nerve- 
cells as well as their outgrowths or cell-fibres and is therefore a 
prolongation of the nerve-cord. 



st.c. \ -^ 




Fig. 192. — Diagrammatic longitudinal Keetion through a young Asteroid passing through 
the tip of one arm and the middle of the opposite interradius. This diagram is 
generalised from a section ol Asterina gihbosa. ab, Aboral sinus ; ax, axial sinus ; 
ax^, basal extension of axial sinus forming the inner perihaemal ring-canal ; br, 
hranchia = gill = papula ; g.r, genital rachis ; mp, madreporite ; musc.tr, muscle 
uniting a pair of ambulacral ossicles; nerv.circ, nerve -ring; 7i.r, radial nerve- 
cord ; oc, eye-pit ; oss, ossicles in sliin ; p.br, peribranchial sinus ; p.c, pore canal ; 
perih (on the right), perihaemal radial canal, (on the left), outer perihaemal ring- 
canal ; py, pyloric caecum ; red, rectum ; rect.caec, rectal caeca ; sp, spines ; st.c, 
stone-canal ; t, median tentacle terminating radial canal ; w.v.r, water -vascular 
radial canal. The genital stolon (not marked by a reference line) is seen as an 
irregular band accompanying the stone-canal, its upper end projects into a small 
closed sac, also unmarked, which is tlie ri'jht hydrocoele or niadreporic vesicle. 



At the base of the terminal tentacle the radial nerve-cord 
ends in a cushion. This cusliion is called the " eye," for it is 
beset with a large number of cup -shaped pockets of the 
ectoderm. Each pocket is lined partly by cells containing a 
bright orange pigment and partly by visual cells each of which 
ends in a small clear rod projecting into the cavity of the pit 
(Fig. 193, A, vis.r). The pit is apparently closed by a thin sheet 
of puticle secreted by the most superficial cells. 

An exposed nervous system and simple sense-organs such as 
the Starfish possesses lend themselves admirably to the purposes 



446 



ECHINODERMATA ASTEROIDEA 



of physiological experinieut, and so Starfish have been favourite 
" corpora vilia " with many physiologists. 

The light-perceiving function of the eye is easily demon- 
strated. If a number of Starfish be put into a dark tank 
which is illuminated only by a narrow beam of light they will 
be found after an interval to have collected in the space reached 
by the beam of light.^ If all the median tentacles but one be 

.removed this will 
still be the case ; if, 
however, they are 
all removed the 
Starfish will exhibit 
indifference to the 
light. 

If the under sur- 
face of a Starfish 
be irritated by an 
electric shock or a 
hot needle, or a 
drop of acid, the 
tube - feet of the 
affected area will be 
strongly retracted, 
and this irritation 
will be carried by 
the pedal nerves to 
the radial nerve- 
with the re- 
sult that finally all 
the tube-feet in the 
groove will be retracted and the groove closed by the action of 
the transverse muscle connecting each ambulacral ossicle with 
its fellow. If, on the other hand, the back of a Starfish be 
irritated this may produce a contraction of the tube-feet if the 
irritation be strong, but this will be followed by active alternate 
expansions and contractions, in a word, by endeavours to move. 
Preyer " by suspending a Starfish ventral surface upward, by 







Fig. 193. — A, longitudinal section of a single eye-jiit of 
Asterias. s.ii, Nucleus of supporting cell ; vis.n, nucleus 
of visual cell ; vis.r, visual rod. B, view of the terminal cord 
tentacle showing the eye-pits scattered over it. (After 
Pfeffer.) 



^ Romanes, "Jellyfish, Starfish, and Sea Urchins," Intern. Scientific Scries, 1885, 
pp. 320, 321 ; Preyer, " Bewegungen von Stelleriden," Mitth. Zool. Stat. Neapcl, 
vii. 1886-87, p. 22. 



- Preyer, loc. cit. p. 49. 



ASTERIAS PHYSIOLOGY OF NERVOUS SYSTEM 447 



means of a siiiall /iuc plate to wliicli a string was attached 
which passed through a liole bored in the back and tlirough the 
mouth, caused movements of tliis description whicli lasted for 
hours. Irritation of the back causes also activity of the local 
pediceUariae, which open their valves widely and then close 
them with a snap in the endeavour to seize the aggressor. 

The uninjured Starfish in moving pursues a definite direction, 
one arm being generally directed forwards, but this may be any 
one of the five. The tube-feet of this arm are directed forwards 
when they are stretched out, by the slightly unequal contraction 
of the longitudinal muscles of opposite sides of the foot, which 
persists even when the circular muscles of the ampulla are 
contracting. They thus may be said to swing parallel to 
the long axis of the arm. The tube-feet of the other arms 
assist in the movement, and hence swing obliquely with 
reference to the long axis of the arm to which they belong, 
although they move parallel to the general direction in which 
the Starfish is moving. A change in the direction of the swing 
of the tube-feet will bring about a change in the direction of the 
movement of the animal as a whole. If now the connexion of 
each radial nerve-cord with the nerve-ring be cut through, each 
arm will act as a separate Starfish and will move its tube-feet 
without reference to the movement of those in the other arms, 
so that the animal is pulled first one way and then another 
according as the infiuence first of one arm and then of another 
predominates. Similarly, when a Starfish is placed on its back, 
it rights itself by the combined action of the tube-feet of all the 
arms, extending them all as widely as possible, those which first 
catch hold being used as the pivot for the turning movement. 
If, however, the radial nerve-cords are cut through, each arm 
tries to right itself and it is only by chance that the efforts of 
one so predominate as to turn the whole animal over. From 
these experiments it is clear that the nerve-ring acts as co- 
ordinator of the movements of the Starfish, that is to say as its 
brain. 

If a section be taken across tlie arm of a Starfish (Fig. 191), 
it will be seen that between the V-shaped ridge constituting the 
radial nerve-cord and the radial water-vascular canal there are 
two canals lying side by side and separated from one another by 
a vertical septum. These canals are not mere splits in the sub- 



448 ECHINODERMATA ASTEROIDEA chap. 

stance of the body-wall, but have a well-defined wall of flattened 
cells. They are termed, for reasons which will be explained 
subsequently, perihaemal canals, and tliey open into a circular 
canal called the " outer periliaennd ring," situated just beneath the 
water - vascular ring - canal (Fig. 192, perih). These canals 
originate as outgrowths from the coelom. From their upper 
walls are developed tlie muscles which connect the pairs of 
ambulacral ossicles and close the groove, and also those which 
connect each ossicle with its successor and predecessor and help 
to elevate or depress the tip of the arm. 

In most of the higher animals the processes of many of the 
ganglion-cells are connected together in bundles called " motor 
nerves," which can be traced into contact with the muscles, and 
thus the path along which the stimulus travels in order to evoke 
movement can clearly be seen. No such well-defined nerves can 
be made out in the case of the Starfish, and it is therefore 
interesting when exceptionally the paths along which stimuli 
travel to the muscles can be traced. This can be done in the 
case of the muscles mentioned above. Whereas they originate 
from the dorsal walls of the perihaemal canals, ganglion-cells 
develop from the ventral walls of these canals, which are in close 
contact with the nerve-cord, so that the nervous system of the 
Starfish is partly ectodermic and partly coelomic in origin. 
Stimuli reaching the ectodermic ganglion-cells are transmitted 
by them to the nervous part of the wall of the perihaemal canal 
and from that to the muscular portion of the same layer of cells. 

Besides the radial perihaemal canals and their connecting 
outer perihaemal ring there are several other tubular extensions 
of the coelom found in the body-wall. These are : — 

(1) The " inner perihaemal canal," a circular canal in close 
contact with the inner side of the outer perihaemal canal 
(Fig. 19 2, ax^). 

(2) The " axial sinus " (ax) a wide vertical canal embedded in 
the body-wall outside the stone-canal. This canal opens into the 
inner perihaemal canal below ; above it opens into several of 
the pore-canals and into the stone-canal. The separation of the 
axial sinus from the rest of the coelom is tlie remains of a feebly 
marked metamerism in the larva. 

(3) The " madreporic vesicle," a closed sac embedded in the 
dorsal body-wall just under the madreporite. This sac by its 



XVI ASTERIAS PERIHAEMAL AND VASCULAR SPACES 449 

history in the larva appears to be a rudimentary counterpart of 
the water-vascular system, since this organ in correspondence 
with the general bilateral symmetry of the larva is at first 
paired. Into this a special process of the genital stolon projects. 

(4) The "aboral sinus" (Fig. 192, ab), a tube embedded in 
the dorsal body-wall running horizontally round the disc. The 
aboral sinus surrounds the genital rachis (see p. 452) and gives 
off into each arm two branches, the ends of which swell so as 
to surround the genital organs. It has no connexion with the 
axial sinus though the contrary has often been stated by Ludwig.^ 

(5) The " peribranchial spaces," circular spaces which sur- 
round the basal parts of the papulae (Fig. 1^2, p. hr). 

Besides these, large irregular spaces have been described as 
existing in the body-wall by Hamann " and other authors, but 
for various reasons and especially because they possess no definite 
wall they appear to be nothing more than rents caused by the 
escape of CO2 gas during the process of decalcifying, to which 
the tissues of the Starfish must be subjected before it is easy to 
cut sections of them. 

• The question as to whether or not there is a blood system in 
the Starfish has an interesting history. It must be remembered 
that the examination of the structure of Echinodermata was first 
undertaken by human anatomists, who approached the subject 
imbued with the idea that representatives of all the systems of 
organs found in the human subject would be found in the lower 
animals also. So the perihaemal canals were originally described 
as blood-vessels. Later, Ludwig ^ discovered a strand of strongly 
staining material running in each septum which separates the 
two perihaemal canals of the arm. Each of these radial strands 
could be traced into connexion with a circular strand interposed 
between the outer and the inner perihaemal ring-canals. This 
circular strand again came into connexion with a brown, lobed 
organ, lying in the wall of the axial sinus, and this in turn 

' Bronn's Thier-Reich, Bd. ii. Abt. 3, Buch ii. Seesternc, p. 617. 

2 BeitriUje zur Histologie der Echinodermen , Jena, 1889. Such sfjaces are always 
to be seen in Asterina gibbosa when preserved with corrosive sublimate or other 
acid reagents, but are absent when it is preserved with osmic acid and Mueller's 
fluid. Though corrosive sublimate is usually regarded as a neutral salt, its aqueous 
solution decomposes with tlie production of a certain amount of free hydrochloric 
acid. 

' "Beitriige zur Anatomic der Asteriden," Zeitschr. wiss. Zool. xxx. 1877, pp. 
122 ct seq. 

VOL. I 2 G 



450 ECHINODERMATA ASTEROIDEA chap. 

joined at its upper end a circular cord of pigmented material 
adhering to the dorsal wall of the coelom (lying in fact within 
the aboral sinus), from which branches could be traced to the 
generative organs. Ludwig concluded that he had at last dis- 
covered the true blood-vessels, though the facts that the radial 
strands and the oral circular strand absorbed neutral carmine 
strongly and that the vertical and aboral strands were pig- 
mented, constituted a very slender basis on which to found such 
a conclusion. The colour apparently appealed to the imagination, 
and it is undoubtedly true that the " plasma " or blood-fluid of 
other animals often absorbs stain strongly. 

The strands were accordingly named "radial blood-vessels," 
" oral blood-ring," " aboral blood-ring " ; and the brown vertical 
strand was called the " heart," although no circulation or pulsa- 
tions had ever been observed. When later investigations 
revealed the fact that the so-called heart was practically solid, 
the term "central blood -plexus" was substituted for heart, 
although it was still regarded as the central organ of the system. 
The name " perihaemal " was given to the spaces so called because 
they surrounded the supposed blood-vessels. 

In order to come to a satisfactory conclusion on the matter 
some general idea as to the fundamental nature and function of 
the blood-vessels in general must be arrived at. Investigations 
made on various groups of animals, «uch as Annelida, Mollusca, 
Crustacea, Vertebrata, show that at an early period of develop- 
ment a considerable space intervenes between the alimentary canal 
and the ectoderm, which is filled with a more or less fluid jelly. 
Into this cavity, the so-called " primary body-cavity " or " archi- 
coel," amoebocytes, budded from the ectoderm or endoderm or both, 
penetrate. In this jelly with its contained amoebocytes is to be 
found the common rudiment both of the connective tissue and of 
the blood system. The resemblance of the archicoele and its 
contents to the jelly of a Medusa is too obvious to require special 
insistence on, and therefore in the Coelenterata it may be stated 
that there is to be found a tissue which is neither blood system 
nor connective tissue but is the forerunner of both. 

In the higher animals as development proceeds the jelly 
undergoes differentiation, for some of the amoebocytes become 
stationary and connected with their pseudopodia so as to form 
a protoplasmic network. A portion of this network becomes 



XVI ASTERIAS — "BLOOD-VESSELS" GENITAL STOLON 45 I 

altered into tough fibres, but a portion of each strand remains 
living, and in this way the connective tissue is formed. In the 
interstices of the network of fibres a semi-fluid substance (the 
unaltered jelly) is found, and this is traversed by free, wandering 
amoebocytes. In other places the jelly becomes more fluid and 
forms tlie plasma, or liquid of the blood, whilst the amoebocytes 
form the blood corpuscles. The blood system thus arises from 
regions of the archicoel where fibres are not precipitated. 

Now in the Starfish the whole substance of the body-wall inter- 
vening between the ectoderm and the coelomic epithelium really 
represents the archicoel. The formation of fibres has, it is true, 
proceeded to a certain extent, since there are interlacing bundles 
of these, but there are left wide meshes in which amoebocytes 
can still move freely. Apart from the skeleton, therefore, the 
tissues of the body-wall of the Starfish do not exhibit much 
advance on those of a Jellyfish. If anything is to be compared 
to the blood system of the higher animals it must be these 
meshes in the connective tissue. From observations made on 
other Echinoderms it appears probable that the colour of the 
skin is due to amoebocytes loaded with pigment wandering 
outwards through the jelly of the body -wall and disintegrating 
there. The strands regarded as blood-vessels by Ludwig are 
specially modified tracts of connective tissue in which fibres are 
sparse, and in which there are large quantities of amoebocytes 
and in which the " jelly " stains easily. Cuenot ^ suggests that 
they are placed where new amoebocytes are formed ; this is quite 
possible, and in this case they ought to be compared to the 
spleen and other lymphatic organs of Vertebrates, and not to 
the blood-vessels." 

The organ regarded as the heart, however, belongs to a 
different category : it is really the original seat of the genital 
cells and should be termed the " genital stolon." Careful sections 
show that at its upper end it is continuous with a strand of 
primitive germ-cells which lies inside the so-called aboral blood- 

^ "Cont. a rfitude anat. des Asturides," Arch. Zool. Exp. (2) v. his, 1887, p. 104. 

"^ The analogy of Echinoidea (see p. 529) might suggest tliat, like the lacteals in 
man, these strands were channels along which the products of digestion diffused 
outward. No connexion, liowever, between the oral ring and the alimentary- 
canal has been made out, nor do there a])pear to be such strands developed in the 
proximity of the wall of the digestive tube. A connexion between the aboral ring 
and the rectum through a mesenteric cord has been asserted, but this is doubtful. 



452 ECHINODERMATA ASTEROIDEA chap. 

vessel, and is termed the " genital rachis " (Fig. 192, g.r). The 
germ-cells are distinguished by tlieir large nuclei and their 
granular protoplasm. The genital organs are only local swellings 
of the genital rachis, and from the shape of some of the germ- 
cells it is regarded as highly probable that the primitive germ- 
cells wander along the rachis and accumulate in the genital 
organs. The genital rachis itself is an outgrowth from the 
genital stolon, and this latter originates as a pocket-like ingrowth 
of the coelom into the wall separating it from the axial sinus ; 
when fully formed it projects into and is apparently contained 
in this latter space. 

Not all the cells forming the genital stolon become sexual 
cells. Many degenerate and become pigment-cells, a circumstance 
to which the organ owes its brown colour. In very many species 
of Starfish many of the cells of the genital rachis undergo a 
similar degeneration, and hence is produced the apparent aboral 
blood-vessel. Further, the rachis is embedded in connective 
tissue which has undergone what we may call the " lymphatic " 
modification, and this for want of a better name we call the 
" aboral " blood-ring. 

The size of the genital organs varies with the season of the 
year ; they are feather-shaped, and attached to the genital rachis 
by their bases, but project freely into the coelom of the arm. 
From their great variation in size and also from the shape of 
some of the cells in the genital rachis, Hamann concludes that as 
each period of maturity approaches fresh germ-cells are formed 
in the rachis and wander into the genital organ and grow there 
in size. It is probable that the aboral end of the genital stolon 
is the seat of the formation of new germ-cells. 

In the Starfish, therefore, as in other animals with a well- 
defined coelom, the genital cells ultimately originate from the 
coelomic wall. 

The genital ducts are formed by tlie burrowing outwards of 
the germ-cells. When it is remembered that tlie fundamental 
substance of the body-wall is semi-fluid jelly, this process will be 
better understood. 

When the ova and spermatozoa are ripe, they are simply shed 
out into the sea and fertilisation occurs there. The development 
is described in Chapter XXI. The free-swimming larval period 
lasts about six weeks. 



EXTERNAL CHARACTERS 453 



Having described a single species with some degree of fulness, 
we must now give some account of the range of variation of 
structure met with in the group. 

Number of Arms. — In the overwhelming majority of Star- 
fish the number of arms is 5, but deviations from this rule are 
met with not only as individual variations, but as the character- 
istics of species, genera, and even families. 

The number 5 is rarely diminished, but amongst a large 
collection of specimens of Asterina gihhosa, belonging to the 
author, some 4-rayed individuals are met with. One species of 
Culcita, C. tetragona, is normally 4-rayed. 

On the other hand the number 5 is often exceeded. The 
families Heliasteridae and Brisingidae are characterised by 
possessing numerous (19-25) arms. In the normally 5 -rayed 
family Asteriidae FycnojJodia has 2 2 arms ; and in the Solaster- 
idae the genera Rhipidaster and Solaster are characterised by 
possessing 8 and 11-15 arms respectively; whilst Korethraster 
and Periholaster have only 5. The common Starfish of the Gulf 
of St. Lawrence, Asterias polaris, is 6-rayed, whilst most of the 
other species of the same genus are 5 -rayed, though 6 rays are 
often met with as a variation. 

In some species the fact that the number of arms exceeds 5 
seems to be connected with the power of multiplication by trans- 
verse fission. Thus Ludwig ^ has shown that in Asterias tenuispina 
the number of arms is usually 7, but sometimes 5, 6, or 8, and 
that in most cases the arms are arranged in two groups — one 
consisting of small arms, the other of large. 

Shape. — Apart from the varying number of arms, differences 
in the shape of the Starfish are due to two circumstances : — 

(1) The proportion of breadth to length of arm ; and 

(2) The amount of adhesion between adjacent arms. 

The adhesion can go so far that the animal acquires the 
shape of a pentagonal disc. This is the case for instance in Cul- 
cita. The fact that the Ijody of this animal is really composed 
of adherent arms is at once made clear when the coelora is opened. 
This space is found to be divided up by inwardly projecting folds 
called interradial septa, which are stiffened by calcareous deposits 
and represent the conjoined adjacent walls of two arms. 

' "Die Echinodermen des Golfes von Neapel," Fauna u. Flora G. xon Neapcl, 
xxiv. Monogr. 1897, pp. 349-351. 



454 ECHINODERMATA ASTEROIDEA chap. 

In the family Heliasteridae the mutual adhesion between the 
arms has gone on merely to a slight extent, for the interradial 
septa are still double. 

Skeleton. — Most of the schemes of classification have been 
founded on the skeleton, largely because the greater number of 
species have only been examined in the dried condition, and 
little is known of their internal anatomy or habits. There is, 
however, this justification for this procedure, that the habits and 
food of the species (with the exception of the Paxillosa) which 
have been observed in the living condition appear to be very 
iniiform, and that it is with regard to the skeleton that Asteroidea 
seem to have split into divergent groups through -adopting 
different means of protecting themselves from their foes. 

The description of the various elements of the skeleton will 
be arranged under the following heads : — (a) Main framework ; 
(b) Spines ; (c) Pedicellariae ; (d) Ambulacral skeleton. 

(«) Main Framework. — The type of skeleton which supports 
the body-wall of Asterias is called reticulate. As already indi- 
cated it consists of a series of rods bound together by bundles of 
connective-tissue fibres so as to form a mesh-work. This is a very 
common type of aboral skeleton, but in a large number of Starfish 
a different type occurs, consisting of a series of plates which may 
fit edge to edge, leaving between them only narrow interstices, as 
in the Zoroasteridae, or which may be placed obliquely (as in 
Asterina) so that they imbricate or overlap one another. In a very 
large number of Asteroidea the supero- and infero-marginal ossicles 
are represented by squarish plates even when the rest of the 
skeleton is reticulate ; this is the so-called " phanerozonate " 
structure, the term " cryptozonate " being used when the marginals 
are rod-like and inconspicuous. In other cases (Ganeriidae) the 
whole skeleton of the ventral surface is made of tightly fitting 
plates, whilst the aboral skeleton is either reticulate or made of 
imbricating plates. Lastly, the skeleton mfiy be represented only 
by nodules forming the bases of paxillae (see p. 455), as in the 
Astropectinidae, or may be entirely absent over wide areas 
(Brisingidae). 

{h) Spines. — The spines vary more than any other part of 
the skeleton. They may be close set and small, or few and 
large, and often bear spines of the second order, or spinelets, 
attached to them. In Asterias atid its allies they are com- 



SPINES 



455 



paratively short, blunt tubercles, covered with thick skin. In 
the Echinasteridae and Asterinidae they are short and blunt, 
but they are very numerous and thick set. In the Solasteridae 
they are long, and arranged in bundles diverging from a 
common base. Such bundles may be termed sheaves, and 
starting from an arrangement like this, two distinct lines of 
modification may be traced. Thus (1) the members of a sheaf 
become connected by a web of skin, so that the sheaf becomes an 
umbrella, and successive umbrellas may adhere, so that a supra- 




M 


mi 


'^<' i0 


^,i^^. 


Ufl 


A ■;., 




Fig, 194. — Views of portions of the aboral surface of diflferent genera of Asteroidea 
in order to show the main varieties of skeleton. A, Solaster, showing spines arranged 
in sheaves ; B, Pteraster, showing webs forming supra-dorsal membrane supported 
by diverging spines ; C, Astropecten, showing paxillae ; D, Nardoa, showing uniform 
plating of granules. x 8. (After Sladen.) 



dorsal tent is formed (a structure characteristic of the Pter- 
asteridae), or (2) the members of a sheaf may become arranged 
in a circle round a central vertical axis so that a structure like a 
capstan is produced, which is called a " paxilla " (characteristic of 
Astropectinidae, Porcellanasteridac, and Archasteridae). Tlie 
axis,^ 'as shown by its development, represents the plate which 
bore the bundle of spines. Again, the skeleton may consist of 
plates with a close covering of granules (Pentagonasteridae, etc.). 
Lastly, in Porania spines are absent, the plates being deeply 
embedded in a thick leathery skin. 

^ Ludwig, "Die Ecliinodernien dcs Golfes von Neapol," pp. 63, 69. 




456 ECHINODERMATA ASTEROIDEA chap. 

(c) Pedicellariae. — These are to be looked on as spines of 
the second order. In Asterina and its allies they are not 
present, but groups of little spines arranged in twos and threes, 
each group being attached to a special small plate, are scattered 
over the aboral surface ; and these on irritation approach one 
another, and represent the rudiment out of which pedicellariae 
have been developed. The most perfect form, termed " forci- 
pulate," in which there is a basal ossicle, is found in Asteriidae, 
Brisingidae, Heliasteridae, Pedicellasteridae, Zoroasteridae, Stich- 
asteridae. There are two varieties of forcipulate pedicellariae, 

the " crossed " and the " straight," 
which have been described on 
p. 432. In all other cases the 
pedicellariae are devoid of the 
basal ossicle, and the two or more 
spinelets forming the jaws are 
directly attached to one of the 
main plates of the skeleton. 

The simplest variety is termed 
Fig i95.-Differeut forms of pedicel- » pectinate " ; thcse pedicellariae 

lanae (excluding the forcipulate form, ^ ' ^ 

for which see Fig. 186). A, pecti- are composcd of two parallel 

nate; B pectinate; C yalvate ; D, ^^^^,^ ^f g^^j^ -^^g OppOSCd tO 
pmcer-shaped ; E, alveolate, from the ^ '^ ^ 

side ; F, alveolate, from above, x 10. each Other. They are found in 
(After siaden.) ^-^^ Archastcridae, and are hardly 

more advanced in structure than the groups of spines found 
in Asterina. In Leptogonaster and its allies there are pincer- 
shaped pedicellariae composed of two curved rods articulating 
with one of the plates of the skeleton, and also " alveolate " 
pedicellariae, composed of two short prongs which are im- 
planted on a concave tubercle borne on one of the plates of 
the skeleton. In the Antheneidae every plate of the ventral 
surface bears a large " valvate " pedicellaria consisting of two 
horizontally elongated ridges, which can meet one another. It 
is possible that valvate pedicellariae have been derived from a 
pectinate form in which successive spinules of one row have 
become adherent. 

{d) Ambulacral Skeleton. — In every case, whether spines 
are developed elsewhere or not, the adambulacral plates bear 
spines. Where the spines are elsewhere represented by granules 
{Nardoa and its allies) (Fig. 194, D) the adambulacral spines are 



XVI SKELETON PAPULAE WATER-VASCULAR SYSTEM 457 

short and blunt. The terms " monacanthid " and " diplacanthid " 
are used to express the occurrence of one or two rows of spines 
respectively on each adambulacral plate. 

In the Zoroasteridae the adambulacral plates are curved, and 
are alternately convex and concave towards the ambulacral 
groove, so that this groove presents a wavy outline. 

In the description of Asterias it was pointed out that the 
first adambulacral plates in adjacent radii are closely approxi- 
mated to one another, and bear spines which can to some extent 
form a trellis-work over the mouth. In very many species not 
only is this the case, but the plates themselves project inwards 
over the mouth so as to form prominent " mouth-angles." This 
is not the case in the Asteriidae or the allied families. 

Papulae. — In Asteriidae and many allied families these 
organs are found both on the upper and under surface of the 
disc, but in another large group consisting of Astropectinidae, 
Pentacerotidae, and allied families, papulae are only borne on 
the dorsal surface, and, in some cases, are restricted to a few 
groups at the base of the arms. In most Asteroidea the papulae 
are arranged singly, that is to say, each occupies one of the 
interspaces between the plates of the skeleton, but in Asterias 
and some other genera they are arranged in tufts of two or 
three. 

Water -vascular System. — In its general structure this 
system of organs is very constant, the two most important 
variations being found, one, in Asteriidae and a few allied 
families, and the other, in the Astropectinidae and the families 
allied to them. 

The first of the variations alluded to concerns the number of 
the tube-feet in a radius. In Asterias and its allies these are 
so Jiumerous that there is not room for them one behind the 
other, but they follow one another in a zigzag line, the trans- 
verse canals connecting them with the radial canals being 
alternately longer and shorter. In this way the appearance of 
four rows of tube-feet is produced, and the advantage of this 
increase in number can be recognised by any one who has 
compared the quick movements of Asterias and the slow ones 
of a Crihrella, for instance. 

The second important variation referred to is the complete 
loss of the sucker of the tube-foot, and, concomitantly, the loss 



458 



ECHINODERMATA ASTEROIDEA 



of the power of climbing. Starfish which have undergone this 
change live on sandy bottoms and run over the surface of the 
sand. They are also incapable of forcing asunder the valves of 
Molluscs, and hence are compelled to swallow tJieir prey whole. 

" Polian vesicles," or stalked sac-like outgrowths of the water- 
vascular ring, are absent from the Asteriidae, but are found in 
many families — the Asterinidae, Solasteridae, Astropectinidae, 
for example. They project outwards from the water-vascular 
ring in the interradii ; when there are several present in one 
interradius they often arise from a common stalk. Cuenot 

believes that their sole func- 




FlG. 



tion, like that of Tiedemann's 
bodies, is to produce amoebo- 
cytes, but this appears unlikely. 
It is more probable that they 
act as store-houses of fluid for 
the water- vascular ring. 

The stone -canal is rarely 
repeated, but this occurs in the 
aberrant genus Acantliaster, 
where there may even be several 
in one interradius, and each 



show the Polian vesicles, ftwi?, Ampullae stOllC-Canal haS EU axial sinUS, 



-Dissection 



Gtenodiscus to 



of the tube -feet ; nerv.circ, nerve-ring; 
Pol, Polian vesicle ; sept, interradial 
septum ; stone c, stone-canal ; T, Tiede- 
mann's body ; w.v.r, water -vascular 
ring. X 1. 



genital stolon, and madreporite 
annexed to it. According to 
Cuenot, in Astcrias, when 6- 
rayed specimens occur in a 
species normally 5 -rayed, there are two stone-canals, suggesting 
that the repetition of stone-canals is a suppressed effort at multi- 
plication by division. This is also true of Uchinaster, but in 
Ophidiaster two madreporites may occur in an individual with five 
arms. In the Asterinidae the Y-shaped fold which projects into 
the cavity of the stone-canal is feebly developed, whereas in the 
Pentacerotidae it meets the opposite side of the stone-canal, and 
in Culcita gives out branches which reduce the cavity of the 
canal to a series of channels. In Echinasteridae and some 
Asterinidae, and in Astropectinidae and Pentacerotidae the 
ampullae become so deeply indented as to be almost divided 
into two, so that each tube-foot has virtually two ampullae. 

The alimentary canal has a remarkably constant structure. 



XVI ALIMENTARY CANAL REPRODUCTION 459 

The only important variation from the type, as described in 
Astcrias, is found amongst the Astropectinidae and Porcellanas- 
teridae, where the anus is wanting. In Astropecten the rectum 
and the rectal caeca still persist, but in Luidia even these have 
disappeared. The rectal caeca are remarkably variable structures. 
In Aster ias there are two, but in Pentacerotidae there are five 
forked caeca, in Asterina five simple caeca, and in the Echin- 
asteridae and Astropectinidae one large flat slightly 5-lobed 
caecum. In the Asterinidae the pyloric caeca are remarkable 
for the size of tlie enlarged basal portion in each radius, which 
serves as a reservoir for the juices secreted by the branched 
forks of the caecum. In Porcellanaster pacijicus the pyloric 
caeca are vestigial, and in Hyphalaster moseri they are absent.^ 

The genital organs are, as we have seen, outgrowths from 
radial branches of the genital rachis. In most species, as in 
Asterias, they are limited to a single cluster of tubes on each 
branch of the rachis, but in the Astropectinidae and Pentacero- 
tidae each branch gives rise to a large number of clusters, 
arranged in longitudinal series, each cluster having its inde- 
pendent opening to the exterior. 

Asexual reproduction, as a regular occurrence, is not common 
amongst Asteroidea. If, however, a Starfish loses some of its 
arms, it has the power of regenerating the missing members. 
Even a single arm will regenerate the whole Starfish. Now in 
some cases (Astropectinidae, Linckiidae) Starfish will readily snap 
off their arms on irritation. In TAnchia this occurs at regular 
intervals and the separated arm forms a new individual. In one 
of the Asterinidae, Asterina wega, a small Starfish with seven 
arms, transverse fission regularly occurs, a portion with three 
arms separating from one with four. The same is believed to 
occur in two species of Asterias, and as has already been pointed 
out, the repetition of the madreporite and stone-canal is, in many 
cases, possibly connected with this tendency to transverse fission. 

Classification of Asteroidea. 

Whilst there is considenil)le agreement amongst the authorities 
as to the number of families, or minor divisions of unequivocal 

^ Ludwig, "Scientific Results of the Expedition of the 'Alliatross' to the Tropical 
Pacific"— "Asteroidea," 1905, pp. 91, 103. 



460 ECHINODERMATA ASTEROIDEA chap. 

relationship, to be found in the class Asteroidea, there has been 
great uncertainty both as to the number and limits of the orders 
into which the class should be divided, and also as to the limits 
of tlie various species. The difficulty about the species is by no 
means confined to the group Echinodermata ; in all cases where 
the attempt is made to determine species by an examination of a 
few specimens of unknown age there is bound to be uncertainty ; 
the more so, as it becomes increasingly evident that there is no 
sharp line to be drawn between local varieties and species. In 
Echinodermata, however, there is the additional difficulty that 
the acquisition of ripe genital cells does not necessarily mark the 
termination of growth ; the animals can continue to grow and at 
the same time slightly alter their characters. For this reason 
many of the species described may be merely immature forms. 
In proportion, however, as the collections from various localities 
increase in number and size, difficulties connected with species 
will tend to disappear. 

The disputes, however, as to the number of orders included in 
the Asteroidea proceed from a different cause. The attempt to 
construct detailed phylogenies involves the assumption that one 
set of structures, which we take as the mark of the class, has 
remained constant, whilst others which are regarded as adaptive, 
may have been developed twice or thrice. As the two sets of 
structures are often of about equal importance it will be seen 
to what an enormous extent the personal equation enters in the 
determination of these questions. 

Where, as in Asteroidea, the internal organisation is very 
imiform, the best method of classification is to take as our basis 
the different methods in which the demands of the environment 
have been met. It is in this way, we hold, that divergence of 
character has been produced, for whilst species may differ in 
trifling details, families and orders differ in points of functional 
importance. The fact that one of the orders may have sprung 
from several allied species instead of one may be admitted, and 
at the same time the hopelessness of trying to push phylogenetic 
inference into details asserted. 

Sladen, in his Monograph of the Asteroidea collected by the 
" Challenger " expedition, took for the basis of his system the 
presence or absence of distinct pavement-like marginal plates 
along the edges of the arms and the restriction of the papulae to 



CLASSIFICATION 46 1 



the aboral surface, or their distribution over the whole surface of 
the body. What connexion, if any, the presence of these pave- 
ment-like plates has with the habits it is impossible to say, but 
it is unlikely to be of the high importance with which it was 
regarded by Sladen, for in the same family we have genera with 
inconspicuous marginals {Asterina) and others with conspicuous 
marginals (Palmi2)es). The restriction of the papulae to the 
back also varies within the same family (Linckiidae), and 
whilst, on the whole, it is perhaps a primitive arrangement, 
it is in many cases connected with burrowing habits, which 
can scarcely be deemed to have been the original mode of life 
of the class. 

A far better basis is supplied by the system of Perrier,^ who 
divides the Asteroidea into five orders according to the character 
of the dorsal skeleton ; and this classification really corresponds 
with the different habits assumed by groups of Asteroidea in 
order to meet what must be regarded as one of their chief dangers, 
viz. assaults by other animals, especially parasites, on their soft 
and delicate skins. Since the food (so far as is known) of all 
Asteroidea is more or less similar, the great differentiating factor 
in their development must have been the means they adopt to 
shelter themselves from their enemies, Perrier's classification, 
which we shall adopt, is as follows : — 

Order 1. Spixulosa. — Asteroidea in which the plates of the 
dorsal skeleton bear spines arranged singly or in groups. The 
tube-feet have suckers and there are no pedicellariae. Marginals 
sometimes conspicuous, sometimes rod-like. 

Order 2. Velata. — Asteroidea in which the dorsal surface 
of the animal is concealed from view by a false membrane com- 
posed of the webs of skin stretched between diverging groups of 
spines united at the base with one another. No pedicellariae. 
Tube-feet with suckers. 

Order 3. Paxillosa. — Asteroidea in which the dorsal surface 
is beset with paxillae (upright spines bearing two or three 
circles of horizontal spinelets). Pedicellariae, when present, few,, 
and never of the forcipulate variety ; often absent. JMarginals 
large. Papulae only on dorsal surface. Tube-feet mostly devoid 
of suckers. 

Order 4. Valvata. — Asteroidea in which the dorsal surface 

' lies. sci. Exi^td. Traraillenr et Talisman, " Ecliinodermes," 1894, pp. 10-15. 



462 ECHINODERMATA ASTEROIDEA chap. 

is protected by plates covered with a mail of minute granules. 
Pedieellariae of the valvate or alveolate type. Marginals large. 

Order 5. Forcipulata. — Asteroidea in which the dorsal 
surface is beset with small spines surrounded by numerous for- 
cipulate pedieellariae. Tube-feet with suckers and arranged in 
four rows. Marginals rod-like and inconspicuous. 

Order I. Spinulosa. 

This is by far the most primitive order of Asteroidea. The 
tube-feet are arranged in two rows only, and there is no special 
means of protecting the back, other than the small close-set 
plates bearing spines, with which it is covered. In some cases, 
as Asterina, these spines have a tendency to converge when 
irritated, and thus act somewhat like pedieellariae. This cir- 
cumstance suggests strongly the manner in which pedieellariae 
have been developed from small groups of spines. The order is 
divided into six families, of which four have common represen- 
tatives on the British coast. 

Fam. 1. Echinasteridae. — Spinulosa in which the aboral 
skeleton is composed of close set plates bearing comparatively 
small spines. This family is represented on the British coasts 
by the beautiful scarlet Starfish Crihrella {Henricia) sanguino- 
lenta. It is also found on the Norwegian coast and on the east 
coast of North America. On the Pacific coast it is replaced by 
a larger species, C. laeviuscula. The narrow ambulacral grooves 
and sluggish movements at once distinguish it from the Starfish 
described as the type. Indeed, all the Spinulosa seem to 
be slow in their movements in contrast to the comparatively 
active Asterias and its allies. Crihrella is remarkable for its 
large eggs, which have a rapid development. The larva never 
swims at the surface but glides only for a short time over 
the bottom. Echinaster is an allied genus in which each 
plate bears a single somewhat enlarged spine. It possesses 
on the skin of the aboral surface numerous pits lined by 
glandular walls, which probably secrete a poisonous fiiuid which 
defends it. Acanthaster has thorny spines, more than ten arms, 
and several stone-canals and madreporites. 

Fam. 2. Solasteridae. — Spinulosa in which the aboral skeleton 
is a network of rods. Spines arranged in diverging bundles 



SPINULOSA 463 



(sheaves) attached to a basal button. This family includes the 
well-known " Sun-stars," with numerous arms and a wide peris- 
tome. There are two species found on both sides of the Atlantic. 
Solastcr yapposus, with thirteen or fourteen arms and long bundles 
of spines on the dorsal surface, which is of an orange colour 
variegated with yellow, and S. endeca with eleven rays and shorter 
spines and of a reddisli violet colour. Bhipidaster has eight arms. 
Some genera have, however, only five arms, as, for instance, 
Feribolaster and Korethrastcr (Fig. 197). In this family there 




Fig. litT. — Korethrastcr hisjiidi's. x 2. (From Wyville Tlionisoii.) 

are conspicuous " Polian vesicles " attached to the water-vascular 
ring. 

Fam. 3. Asterinidae. — Spinulosa in which the aboral skeleton 
consists of overlapping plates, each bearing a few small spines. 
The common British representative of this family is the small 
Asterina gihhosa, in which the arms are short and stout and of 
somewhat unequal length. This Starfish differs from most of its 
allies in being littoral in its habit. At low tide on the south 
and west coasts of England it can be found on the underside of 
stones feeding on the Sponges and Ascidians with which they are 
covered. Like Crihrella sanguinolenta this species has a modified 
development. The larva resembles that of Crihrella, and the 
larval staue only lasts a1»out a week. Owinrj to the fact that 



464 ECHINODERMATA ASTEROIDEA chap. 

Asterina lays its eggs in accessible localities, its development 
has been more thoroughly worked out than that of any other 
species. Fahnijjes memhranaceus, an animal of extraordinary 
thinness and flatness, is sometimes dredged up off the coast of 
Britain in deeper water. Its arms are so short that the general 
form is pentagonal. The infero-marginal plates are long and 
rod-like, and form a conspicuous border to the body when viewed 
from below. 

Fam. 4. Poraniidae. — Spinulosa allied to the Asterinidae but 
possessing a thick gelatinous body-wall in which the plates and 
spines are buried, the marginals forming a conspicuous border to 
the body. This family is represented in British waters only by 
Porania pulvillus, a cushion-shaped Starfish with very short arms 
and of a magnificent reddish-purple colour. It is occasionally, 
but rarely, exposed at low tide. 

Fam. 5. Ganeriidae. — Spinulosa allied to the Asterinidae but 
distinguished by the large marginals and by the fact that the 
skeleton of the oral surface consists of plates each bearing a few 
large spines. Ganeria, Ifarginaster. 

Fam. 6. Mithrodidae. — Spinulosa with a reticulate aboral 
skeleton. The spines are large and blunt, covered with minute 
spinules. Ifithrodia, sole genus. 

These last two families are not represented in British waters. 

Order II. Velata. 

This is a very extraordinary group of Starfish, about the 
habits of which nothing is known, since they all live at very 
considerable depths. Their nearest allies amongst the Spinulosa 
must be looked for amongst the Solasteridae. If the sheaves of 
spines with which the latter family are provided were to 
become adherent at their bases, and connected with webs of skin 
so as to form umbrella-like structures, and if then these umbrellas 
were to become united at their edges, we should have a supra- 
dorsal membrane formed such as is characteristic of the order. 

Fam. 1. Pythonasteridae. — Velata in which each sheaf of 
spines is enveloped in a globular expansion of the skin and is not 
united with the neighbouring sheaves. Pythonaster, sole genus. 

Fam. 2. Myxasteridae. — Velata with numerous arms in 
which the sheaves of spines are long and form with their con- 



VELATA 



465 







^m. 















''^^p^^ 



Fig 198.— Aboral view of Ptemster stelli/er. mars, Dorsal V.rood-pouch. 
X U. (From Sladen.) 




Fig m.-Ol■^lyi^■^y oUIymenasterpellucidus. x 1. (From Wyville Thomson.) 

2 H 
VOL. I 



466 ECHINODERMATA — ASTEROIDEA chap. 

necting " umbrellas " web-like expansions which do not fuse with 
one another. Myxaster, sole genus, 

Fam. 3. Pterasteridae. — Velata in which the membranes 
supported by the sheaves of spines are united so as to form a 
continuous supra-dorsal tent. The Pterasteridae are represented 
in British waters by a single species, Pteraster militaris, which 
is occasionally dredged in deep water off the British coast, and is 
found also in the Norwegian fjords and off the east coast of 
Canada. This interesting Starfish has five short, blunt arms, and 
its general appearance at first sight recalls that of Asterina. 
Closer inspection reveals the " false back." The anus is sur- 
rounded by five fan-like valves, supported by spines (Fig. 198), 
underneath which is a space in which the young complete their 
development, Pteraster being one of the genera in which the 
normal larval form is not developed. The tendency towards the 
union of adjacent spines by webs is deeply rooted in the organisa- 
tion of the animal. It is seen on the under side where the spines 
borne by the ventral plates are united so as to form transverse 
combs. In Hymenaster (Fig. 199) the spines borne by the ventral 
plates are long and free. 

Order III. Paxillosa. 

This is an exceedingly well-marked order. The armature of 
the upper surface consists of paxillae. These organs as already 
mentioned are probably to be traced back to sheaves of spines 
like those of the Solasteridae. The same end as that striven 
after in the case of the Velata has been attained, but in a 
different way. The horizontal spinelets of the paxillae meet one 
another and form a close-fitting mail which is almost as efficient 
a protection as the webs and umbrellas of the Velata. Pedi- 
cellariae are occasionally present, but they are always of the 
pectinate or piucer variety, never forcipulate. 

Fam. 1. Archasteridae. — Paxillosa in which the anus is 
still retained and in which the tube-feet have suckers. 

The Archasteridae are a most interesting family. Thus 
Pararchaster has no true paxillae, but only small isolated groups 
of spines. The pectinate pedicellariae are composed each of two 
parallel rows of somewhat smaller spines. The members of this 
family are to some extent intermediate in structure between the 



PAXILLOSA 



467 



Spiiiulosa, such as Echinasteridae, and the other families of the 
Paxillosa — some genera, indeed, might almost be classed as 
Spinulosa. At the same time they are apparently closely allied 
with the more primitive Valvata such as Astrogonium and its allies, 
some of which have paxillae on the upper surface ; although the 
retention of the anus and of the suckers on the tube-feet (in 




Fig. 200.— Aboral view of Archaster hifrons. x |. (From Wyville Tboinsou.) 

which characters they agree with the Archasteridae) distinguishes 
them from the more typical Paxillosa, in which both anus and 
suckers are lost. Archaster (Figs. 200, 201). Leptogonaster. 

Fam. 2. Astropectinidae. — Paxillosa which have lost the 
anus, but which possess neither aboral protuberance nor inter- 
radial grooves. The marginal plates are thick, covered with 
spinules and placed horizontally. The tube-feet have no suckers. 

This family is the only one of the order which occurs in 
British waters, where it is represented by two genera, Astropecten, 
and Luidia. In Astr(ypecten tlie inferior marginal plate is in 



468 ECHINODERMATA — ASTEROIDEA chap. 

immediate contact with the adambulacral, whilst in Luidia it 
is separated from it by a small intermediate plate. 

Astropecten irregularis is a very common species on the coast 
of Britain, and a study of its habits when in captivity has 
thrown a great deal of light on many obscure points in the 
anatomy of the Paxillosa, Owing to the loss of suckers it is 




Fig. 201. — Oral view of Arduister bifrous. x f. (From Wyville Thomson. ) 



unable to climb over rocks and stones like the ordinary species, 
but it runs over the surface of the hard sand in which it lives 
by means of its pointed tube-feet. The arms are highly 
muscular, and the animal when laid on its back rights itself by 
throwing the arms upwards and gradually overbalancing itself. 
The loss of suckers has also rendered Astropecteii and its 
allies incapable of feeding in the manner described in the case 
of Asterias ruhens. They are unable forcibly to open the valves 
of shell-fish, and the only resource left to them is to swallow 
their prey whole. The mouth is consequently wide, and the 



PAXILLOSA 



469 



unfortunate victims, once inside the stomach, are compelled by 
suffocation to open sooner or later, when they are digested.^ 

Many interesting experiments have lieen made on AstroiJccten 
by Preyer and other 
investigators, but one im- 
portant fact '" has escaped 
their notice, that Astro- 
pecten, when at rest, lies 
buried in the sand, whilst 
the centre of the aboral 
surface is raised into a cone 
which projects above the 
surface. On the sides of 
this cone the few papulae 
which this species possesses 
are distributed. This rais- 
ing of the aboral surface 
is obviously an expedient 
to facilitate respiration. 
It loosens the sand over 
the region of the papulae, 
and thus allows the water 
to have access to them. 

We can thus understand ■ ^-'. \,\/ i x ^-^^^^ ,adamb. 

how the restriction of the _ 
papulae to the dorsal sur- "' 
face, so characteristic of the 
Paxillosa, is not always as 
Sladen imagined, a primi- 
tive characteristic, but often 
an adaptation to the bur- 
rowing habits which in all y\q 
probability are character- 
istic of the whole order. 
In both Luidia and Astro- 
pecten Cuenot has described short spines covered with cilia in 




202. — Oral view of Psilaster acuminatus. 
X J. adamb, Adamlnilacral spines ; pax, 
jmxillae ; })od, pointed tube -feet devoid of 
sucker. (.■Xfter Sladen. ) 



^ Schienienz (reference on p. 440 n.). 

- Tills fact was discovered bj- Dr. E. J. Allen, Director of the Plymouth Bio- 
logical Station, who pointed it out to the author during the latter's sojourn at the 
station in 1899. 



470 



ECHINODERMATA ASTEROIDEA 



the interspaces between the marginal plates, these also subserve 

respiration by 
drawing a current 
of water over the 
gills. Fsilaster 
(Fig. 202). 

Fam. 3. Por- 
cellanasteridae. 
— Paxillosa which 
have lost the anus. 
There is a conical 
prominence in the 
centre of the dor- 
sal surface termed 
the epiproctal 
cone, and in the 
interradial angles 
there are vertical 
grooves bordered 
by folds of mem- 
brane produced 
into papillae, the 
so-called " cribri- 
form organs." The 
marginal plates 
are thin and form 
the vertical border 
of the thick disc. 
The tube - feet 
have no suckers. 

Comparing the 
Porcellanasteridae 
with the Astro- 
pectinidae we see 
at once that the 
" epiproctal cone " 
is a permanent 
representative of the temporary aboral elevation in Astrojjecten, and 
we are inclined to suspect that the cribriform organs are grooves 
lined with cilia which keep up a respiratory current like the ciliated 




Fig. 203. — Porcellanaater caernleus. A, aboral view ; B, oral 
view. X 1. (From Wyville Thomsou.) 



VALVATA 471 



spines of Luidia. In all probability the Porcellanasteridae are 
more habitual burrowers than even the Astropectinidae. 

Ctenodiscus (Fig. 196), a genus in which there is a short 
epiproctal cone and numerous feeble cribriform organs in each 
interradius, is found in deep water north of the Shetland Islands. 
Porcellanaster (Fig. 203) is a more typical genus, with one large 
cribriform organ in each interradius. Hyphalaster has long 
arms, on which the supero-marginal plates meet above. 

Order IV. Valvata. 

The Starfish included in this order are characterised by the 
absence of prominent spines and by the superficial covering of 
minute granules. The skeleton consists, in most cases, of 
plates, and these plates with their covering of granules probably 
represent the first stage in the evolution of paxillae. 

The tube -feet possess well-developed suckers. No members 
of this order can properly be said to be British. 

Fam. 1. Linckiidae. — Valvata with long arms, the marginals 
being developed equally throughout the whole length. These Star- 
fish are distinguished by their long narrow arms and small disc. 
It is possible that these forms, so different in many respects from 
the other fiimilies of the order, have been directly derived from 
the long-armed Echinasteridae. Oj^hidiast&i^ Nardoa, Linckia. 

Fam. 2. Pentagonasteridae. — Valvata with short arms, the 
marginals being especially developed at the base and in the 
interradial angles. The aboral skeleton consists of close-fitting 
plates. Pentagonaster (Fig. 204), Astrogonium. 

Fam. 3. Gymnasteridae. — Valvata allied to the foregoing 
but distinguished by pdssessing a very thick skin in whicli the 
plates are completely l)uried. Dermasterias, Asteroj)sis. 

Fam. 4. Antheneidae. — Valvata with short arms. The 
dorsal skeleton is reticulate and each ventral plate bears one 
or several large valvular pedicellariae (Fig. 195, C). Ifijij^asfei-ias, 
Goniaster. 

Fam. 5. Pentacerotidae. — Valvata with arms of moderate 
length. The doisal slceletoii is reticulate but the ventral plates 
bear only small pedicellariae or none. The upper marginals are 
smaller than the ventral ones. 

The Pentacerotidae include both short-armed and louff-ai'med 



47: 



ECHINODERMATA ASTEROIDEA 



forms. Amongst the former is Culcita, in which tlie body is a 
pentagonal disc, all outer trace of the arms being lost ; Pentaceros 
is a long-armed form. 

The family Pentagonasteridae furnishes the key to the 
understanding of most of the forms contained in this order. It 
contains genera such as Astrogonium which possess on the back 
unmistakable paxillae, whilst on the under surface they have the 




-TTTrrCy, 








Fig. 204. — Pentar/onastcr jajjon icus. 



(After Sladen.) 



characteristic covering of granules ; these genera seem to be 
closely allied to the short-armed species of the Archasteridae, 
from which they are distinguished chiefly l)y the granular 
covering of the marginals. From a study of tliese cases it 
seems clear that the plates of the dorsal skeleton of tlie Valvata 
correspond to the supporting knobs of the paxillae much 
broadened out, and the granules correspond to the spinelets of 
the paxillae increased in number and diminished in size. 



FORCIPULATA 473 



As mentioned above, Ludwig has proved that the paxillae 
develop in the life-liistory of the individual out of ordinary 
plates, the axis of the paxilla reja-esenting the plate. 

Order V. Forcipulata. 

This order, which includes the most highly developed mem- 
bers of the class Asteroidea, is at once distinguished by the 
possession of forcipulate pedicellariae which, as we have seen, 
possess a well-marked basal piece with which the two plates 
articulate. The pedicellariae are consequently sharply marked 
off from the spinelets, and no intermediate forms occur. The 
first conjoined adambulacrals, which in other orders form the 
" teeth " or mouth-angles, do nut here project beyond the first 
pairs of ambulacral plates. 

Fam. 1. Asteriidae. — Forcipulata in which the tube-feet are 
apparently arranged in four rows. Aljoral skeleton a loose 
reticulum. 

The general features of the family Asteriidae ha^'e been ex- 
plained in the description of Asterias ruhens (p. 432). There are 
five well-marked species of the genus found on the British coasts. 
Of these A. glacialis is found chiefly in the south-western parts of 
the English Channel. It is a large Starfish of a purplish-grey 
colour, with large spines surrounded by cushions of pedicellariae 
arranged in one or two rows down each arm. A. mueUeri 
resembles the foregoing species, but is of much smaller size, and 
is further distinguished by having straight pedicellariae in the 
neighbourhood of the ambulacral groove only. It is found on the 
east coast of Scotland, and carries its comparatively large eggs 
about with it until development is completed. A. ruhens is the 
commonest species, and is found on both east anil west 
coasts. Its colour is a l)right orange, but varies to almost a 
straw colour. It is at once distinguished from the foregoing 
species by the spines of the dorsal surface, which are small and 
numerous, an irregular line of somewhat larger ones being some- 
times seen down the centre of each arm. A. murrayi is a 
peculiar species restricted to the west coast of Scotland and 
Ireland. It has flattened arms, with vertical sides, and only 
three rows of small spines on the dorsal surface. It is of a 
violet colour. A. Iiisjnda is also a western species. It is a 



474 ECHINODERMATA ASTEROIDEA chap. 

small Starfish with short stout arms ; there are no straight 
pedicellariae, and only a few sharp spines on the dorsal surface. 

On the eastern coast of North America there are several 
species of Asterias, of which the most noteworthy is the 6- 
rayed A. polaris of the Gulf of St. Lawrence. This species 
exhibits a marvellous range of colour-variation, ranging from 
bluish-violet through purple to red and straw-coloured. This 
variation seems to show that colour, as such, is of no importance 
to the animal, but probably depends on some compound of 
slightly varying composition which is being carried by the 
amoebocytes towards the exterior. On the Pacific coast there is 
a rich fauna of Starfish, among which we may mention as members 
of this family Asterias ochracea, a large violet species, so strong 
that it requires a severe wrench to detach it from the rock, and 
Pycnopodia with twenty-two arms. 

Fam. 2. Heliasteridae. — Forcipulata allied to the Asteriidae, 
but with very numerous arms and double interradial septa. 
Heli<ister. 

Fam. 3. Zoroasteridae. — Forcipulata with the tube-feet in 
four rows at the base of the arm, in two rows at the tip. Aboral 
skeleton of almost contiguous plates bearing small spines or 
flattened scales. Zoroaster, Pholidaster. 

Fam. 4. Stichasteridae. — Forcipulata with the tube-feet in 
four rows. Aboral skeleton of almost contiguous plates covered 
with granules. Stichaster, Tarsastcr. 

The Stichasteridae and Zoroasteridae have acquired a super- 
ficial resemblance to some of the long-armed Valvata, from which 
they are at once distinguished by their pedicellariae. It would 
be exceedingly interesting if more could be found out concerning 
the normal environment of these animals ; it might then be 
possible to discover what is the cause of the assumption of this 
uniform mail of plates. 

Fam. 5. Pedicellasteridae. — Forcipulata with two rows of 
tube-feet. The aboral skeleton bears projecting spines surrounded 
by cusliions of straiglit pedicellariae. Pcdicellaster, Coronaster. 

Fam. 6. Brisingidae. — Forcipulata with numerous arms and 
only two rows of tube - feet. Aboral skeleton largely rudi- 
mentary and confined to the base of the arms. The small blunt 
spines are contained in sacs of skin covered with pedicellariae. 

The Brisingidae, including Brisinga and Odinia, are a very 



FOSSIL ASTEROIDEA 



475 



remarkable family, chiefly on account of the sinallness of the 
disc and of the extraordinary length of the arms. The arms 
have what we must consider to have been the primitive arrange- 
ment, since there is no lateral adhesion between them, and inter- 




-Aboral \'iew of Odin 



(After Perrier.) 



brachial septa are consequently entirely absent. The reduction 
of the skeleton is a very marked peculiarity and, like the ten- 
dency to the reduction of the skeleton of deep-sea fish, may 
stand in some relation to the great pressure under which the 
animals live. 



Fossil Asteroidea. 

The Asteroidea occur somewhat plentifully as fossils. In the 
Lower Jurassic Asterias, Astyojiecten, Luidia, Solaster, and Goni- 
aster have already made their appearance. In the Cretaceous 



476 



ECHINODERMATA ASTEROIDEA 



Pentaceros appears. In the older rocks occur a number of forms of 
different character from any now existing. Of these Asiridosoma 
(Fig. 206), with short lancet-shaped arms sharply distinguished 
from the disc and continued along its under surface, seems to be 
intermediate between Asteroidea and Ophiuroidea. The skeleton 
of the arm is composed of alternating ambulacral ossicles bordered 
by adambulacral ossicles, which are at the same time marginals 
and sharply distinguished from the marginals forming the edge 
of the disc. Palaeaster, on the other hand, is a true Asteroid ; 
there are marginals distinct from the adambulacrals, but the disc 
is reduced to its smallest dimensions, there being only one plate 




Fig. 206. — Three views oi Aftpidosoma, a fossil Asteroid. A, oral view ; B, aboral view 
of one arm ; C, enlarged view of a portion of the ambnlacral groove, adamb, 
Adainbnlacral plate ; amb, ambulacral plate ; marg, marginal plate ; pod, aperture 
for extension of tube-foot. 



on the ventral side of each interradius. There are a number of 
genera {Palaeocoma, for instance) with a large disc and very short 
arms and very shallow ambulacral grooves ; all have alternating 
ambulacral plates. Some genera appear to have had the madre- 
porite on the ventral surface of an interradius. On the other 
hand, in the Devonian occurs Xenaster, which was a fairly normal 
Asteroid, with pavement-like marginals, deep ambulacral grooves, 
and broad arms. 

Thus it will be seen that already in Jurassic times the three 
orders, Forcipulata, Paxillosa, and Spinulosa were differentiated 
from each other, but how these are related to the older Palaeozoic 
forms it is at present impossible to say. 



CHAPTER XVII 

ECHINODERMATA (cOXTIXCED) : OPHIUROIDEA = BRITTLE STARS 

CLASS II. OPHIUEOIDEA 

The second class of Eleutherozoa are familiarly known as 
'• Brittle Stars," on account of their tendency, when seized, to 
escape by snapping off an arm, although this habit is by no 
means confined to them, l)ut is shared in a marked degree by 
many Asteroidea, such as Luidia, for instance. Like the 
Asteroidea, they are " starfish," that is to say, they consist of 
a disc and of arms radiating from it ; but the scientific name 
Ophiuroidea really expresses the great dominating feature of 
their organisation. Literally it signifies " Snake-tail " (o<^i9, 
snake; ovpd, tail), and thus vividly describes the wriggling, 
writhing movements of the long thin arms, by means of which 
the Ophiuroid climbs in and out of the crevices between the 
stones and gravel in which it lives. This feature, viz. the 
effecting of movement by means of muscular jerks of the arms, 
instead of by the slow protrusion and retraction of the tube- 
feet, is the key to the understanding of most of the points 
wherein the Brittle Stars differ from the true Starfish. 

Asteroidea and Ophiuroidea agree in the common ground- 
plan of their structure, that is, they both possess arms ; but 
the most obvious difference in their outer appearance is that 
whereas in Asteroidea the arms merge insensibly into the difc, 
in Ophiuroidea the disc is circular in outline and is sharply 
marked off from the arms. Closer inspection shows that in the 
Ophiuroid the arms are continued inwards along grooves, which 
run on the under surface of the disc, and that they finally 
coalesce to form a buccal framework surrounding the mouth. In 

477 



478 



ECHINODERMATA — OPHIUROIDEA 



the very young Ophiuroid the arms melt into a small central 
disc, as in the Starfish, but the disc of the adult is made up of 




Fig. 207. — Aboral view of Ophiotkrix fragilis. x 1. r, Radial plate. 



a series of iuterradial dorsal outgrowths which meet one another 
above the arms. 



ANATOMY OF OPHIOTHRIX 



479 



One of the coiiiiiionest British Ophiuroids is Oj)]iiot}irix 
fragilis (Figs. 207, 208), which is found in swarms in sluillow 
water off tlie west coast of England and Scothmd. We may 
therefore select it as tlie type, and, since the arm is the most 
characteristic organ of an Ophiuroid, we may commence by study- 
ing it. Speaking generally, an Ophiuroid eitlier drags itself 
forward by two arms and pushes itself by the other three 
(Fig. 207),^ or else it drags itself by one and pushes with the other 
four (Fig. 217). The arms during tliis process are bent into 
characteristic curves, by tl)e 

straightening of whicli in the ...■ P 

posterior arms the animal is 
pushed onwards, whilst the 
intensification of these curves 
in the anterior arms causes 
the animal to be dragged 
forwards. The grip of the 
arm on tlie substratum is 
chiefly in the distal portion 
of the curve. The alteration 
of the curvature is due to the 
contraction of the muscles on 
one side of the arms. There 
is no ambulacral groove such 
as is found on the under side 
of the arms of all Asteroidea, 

for the arm is completely ensheathed b}' four series of plates, an 
upper row of dorsal plates, an under row of ventral plates, 
and two lateral rows of lateral plates. The last named, which 
in all probability correspond to the adambulacral plates of 
Starfish, bear each a transverse row of seven spines witli 
roughened surfaces ; tliese enable the animal to get a grip on 
the substratum over which it moves. The podia in Ophiuroidea 
are termed " tentacles " ; they are totally devoid of suckers, 
being simple conical papillae used as sense-organs, and are of 
little, if any, service in locomotion. They issue from openings 
called " tentacle -pores " situated between the edges of the 




Fig. 208.— Oral view of the disc of Ophiothrix 
fragilis. g.b. Opening of the geuital bursa ; 
m.p, madrepoiite ; ^wrf, podia ; t.p, tooth- 
papillae ; v.p, ventral plates of the arms. 
X 1. 



' This li^furc does not show tlie animal's attitude during forward progression 
quite correctly. The tips of the two anterior arms should be bent outwards, not 
inwards as in the figure. 



48o 



ECHINODERMATA — OPHIUROIDEA 



ventral aiul lateral plates, guarded each by a valve-like plate 
called the " tentacle -scale." In Ophiothrix they are covered 
with sense-organs, each consisting of a hillock -like elevation of 
the ectoderm, in which are cells carrying long stiff sense-hairs. 
In most Ophiuroids such organs are not present, though 
abundant scattered sense-cells occur, and the outer surface of 
the tube-feet and the lining of certain pockets called " genital 
bursae" (Fig. 208, g.h) are the only portions of the surface 
where the ectoderm persists. Everywhere else, although present 



upper arm plate. 




-3 — 9P- 
tentacle 'P ^ ■ nervrad 
scales underarm ., 

plate perih. 

Fig. 209. — Diagrammatic transverse section of the arm of an Ophiuroid. coe, Dorsal 
coelomic canal ; ed, ectoderm covering the tube-foot ; ep, epiueural canal ; gang.p, 
pedal ganglion ; L, nerve-cor<l ; viusc, longitudinal muscles attaching one vertebra 
to the next ; nerv.rad, radial nerve -cord ; perih, radial perihaemal canal ; pud, 
podium (tube-foot) ; sp, lateral spines ; w.v.r, radial water-vascular canal. 

in the young, it disappears, leaving as remnants a few nuclei 
here and tliere attached to the under side of the cuticle.^ 

The greater part of the section of the arm is occupied by a 
disc-like ossicle called the " vertebra." Each vertebra articulates 
with its predecessor and successor by cup-and-l)all joints, and it 
is connected to each of them by four powerful longitudinal 
muscles. Above, its outline is notched by a groove, in which 
lies an extension of the coelom of the disc (Fig. 209, coe), but 
contains no outgrowth of the alimentary canal, as is the case in 
Asteroidea. The vertebra is also grooved below, and in this 
lower groove are contained the radial water - vascular canal 

' In the more primitive Opliiuroidea (Streptophiurae) it jiersists all over the 
body ; in Cladophiurae it is found on the central part of the disc. 



OPHIOTHRIX VERTEBRAE 



481 



(Fig. 209,?r.?'.r), and below it perihaemal canals as in Asteroidea ; 
below this again the radial nerve -cord (X), and beneath this 
again a canal called the " epineural canal " (e^;), which represents 
the missing ambulacral groove. This canal in the very young 
Brittle Star is an open groove, but becomes closed by the 
approximation of its edges. The vertebra, which has a double 
origin, represents a pair of fused ambulacral ossicles. In 
Ophiohdus these are only slightly adherent to one another 
(Fig. 216). 



cr 




210. — Proximal and distal views of the three types of vertebra found amongst 
Ophiuroidea. A, Ophioteresis, a type of the Streptophiurae (after Bell), x 24 ; 
B, Astroschema, a type of the Cladophiurae (after Lyman), x 10 ; C, Ojjhiarachna, 
a type of the Zygophinrae (after Ludwig), x 3. The upper figure in all cases 
represents the distal aspect, the lower the proximal aspect of the vertebra, v.g, 
Ventral groove. 



When the surface of a vertebra is examined it is found that 
it can be divided into a thin border, to which are attached the 
four muscles by which it is connected to its successor and pre- 
decessor, and a central portion, on which are situated the 
knobs and pits, by means of which it articulates with the next 
verteljra. 

The simultaneous contraction of the two upper muscles 
causes the arm to bend upwards. The contraction of the two 
lower bend it downwards, whilst a sideward movement is effected 
by the contraction of the upper and lower muscle of the same 
side. On the proximal surface of the central portion of the 
vertebra there is a central knolj and two ventro-lateral knobs, 

VOL. I 2 I 



482 ECHINODERMATA — OPHIUROIDEA chap, 

a median ventral pit and two dorso-lateral pits, and on tlie 
distal surface there are pits corresponding to the knohs on the 
proximal side and vice versa (Fig. 210, C). These knobs and 
pits restrict the movement of one vertebra on the next, so that 
although the arms can undergo an unlimited amount of flexion 
from side to side, they cannot be rolled up in the vertical plane. 
AVhen the under surface of the vertebra is examined there is 
seen on each side of the central groove two round holes, a 
distal and a proximal. The distal pair are for the passage of the 
canals connecting the radial water-vessel with the tentacles, 
these canals traversing the substance of the vertebra for a part of 
their course ; the proximal pair are for nerves going to the 
longitudinal muscles, which likewise perforate part of the 
ventral border of the vertebra. 

In order to understand the anomalous circumstance that the 
canals going to the tentacles actually perforate the vertebrae, it 
must be clearly borne in mind that tlie basis of tlie body-wall 
in all Echinoderms is a mass of jelly with amoebocytes in it, to 
which we must assign the power of secreting carbonate of lime, 
and all we have to assume in the case of Ophiuroids is that 
calcification spread outwards from tlie original ambulacral 
ossicles into the surrounding jelly, enclosing any organs that 
happened to traverse it. 

When the ossicles of the arm are followed inwards towards 
the mouth, they are seen to undergo a profound modification, so 
as to form, by union with tlie corresponding ossicles of adjacent 
arms, a structure called the mouth-frame. The general character 
of this modification is similar to that affecting the first ambulacral 
and adambulacral ossicles in the arms of an Asteroid, but in 
the Ophiuroid the change is much more profound. The first 
apparent vertebra consists of two separated halves, and each is 
fused with the first adambulacral (lateral) plate, which in turn is 
firmly united with the corresponding plate in the adjoining arm. 
Thus is formed the "jaw," as the projection is called. The 
extensions of the mouth-cavity between adjacent jaws are termed 
" mouth-angles." To the apex of each jaw is attached a plate 
bearing a vertical row of seven short blunt spines called " teeth " 
(Fig. 212, p). The plate is called the " torus angularis " (Fig. 211, 
T), and on its ventral edge there is a tuft of spines which are termed 
" tooth-papillae " (Fig. 208, i'.p). On the upper aspect of the jaw 



OPHIOTHRIX MOUTH-SKELETON 



483 



are a pair of plates termed " peristomial plates." Tliese discs — 
of which there are two in each radius, one on each jaw which 
flanks the radius — possibly represent the separated halves of the 
first vertebra, the apparent first vertebra being really the second. 
On the flank of the jaw there is dorsally a groove for the water- 



A^ 



A^ 



^d4y, Asteroid 



A3 



f^c:\ 




"^m 


'^.\ 


A4 


H 



Ophiuroid 




Fig. 211. — Diagrams to 
show the moditication 
of the ambulacral and 
adambxilaeral ossicles 
to form the armature 
of the mouth. A, Aste- 
roid ; B, Ophiuroid. 
A^-A^, the first four 
aiul)ulacra ossicles ; 
A(\-Ad^, the first four 
adamljulacral ossicles ; 
Jj, the first plate of 
the interradius (in the 
Ophiuroid the scutum 
huccale) ; P, the spines 
borne by the jaw (in 
the Ophiuroid the 
teeth) ; T, the torus 
angularis ; W, the 
water - vascular ring ; 
Wr, the radial water- 
vessel ; 7, //, the first 
two pairs of tube-feet. 
(After Ludwig.) 



vascular ring and nerve-ring (Fig. 212, n.r), and beneath this a 
groove for the first tentacle and a pore for the second, both of 
which spring directly from the ring-canal ; below these, in most 
Ophiuroidea, but not in Ophiothrix, there is a row of blunt 
triangular spines called " mouth -papillae " (Fig. 212, j9^). 

The words "jaw " and " tooth " are misleading. There is no 
evidence that the jaws of a Brittle Star are ever used for crushing 
food, but by means of the muscles attaching them to the first 



484 ECHINODERMATA OPHIUROIDEA chap. 

complete vertebra in the arm they can be rotated downwards 
so as greatly to enlarge the mouth, and again rotated upwards 
and inwards, when they form an excellent strainer to prevent 
the entrance of coarse particles. To permit this extensive 
movement the articulatory facets on tlie proximal surface of the 
first vertebra have been much modified ; the median knob and 
pit have disappeared, and the dorso-lateral pits are raised on to 
the surface of processes, so that there are in all four processes, 
two of which articulate with one half of a jaw. 

The mouth can be narrowed and the jaws forced inwards 



A? 



A^-' 




}. 212. — Lateral view of 
moutli - frame of Ophi- 
arachna incrassata. x 4. 
A^l, peristomial plate, 
possibly the half of the 
tirst vertebra ; .4-, the 
half of the second verte- 
bra ; .4^, the third verte- 
bra ; /'"', pores for pair 
of tentacles ; gen, genital 
scale lying beside open- 
ing of genital bursa ; 
muse, longitudinal nuiscles 
connecting vertebrae ; 7i.r, 
groove for nerve-ring ; ^j, 
tooth ; ^J^, mouth-papilla ; 
t, torus angularis. (After 
Ludwig.) 



towards the centre hy the simultaneous contraction of five 
muscles (ynusc. tr, Fig. 213) each, which unite the two halves of 
a jaw. 

Turning now to the skeleton of the disc, we notice that 
dorsally it consists of a closely -fitting mosaic of small plates, 
which are usually concealed from view by a covering of minute 
spines. Opposite the insertion of each arm there are, however, 
a pair of large triangular plates (" radials "), which extend out- 
wards to the periphery and strengthen it, much as the ribs do in 
an umbrella. These radial plates are always exposed, in Ophio- 
tlivix, even when the rest of the dorsal plates are concealed by 
spines. On the under surface there is a similar plating ; but 
adjoining the jaws are five large, more or less rhomboidal, plates. 



XVII OPHIOTHRIX DISC ALIMENTARY CANAL ' 485 

termed " scuta buecalia " (Fig. HI 1, </^ ), on one of which open tlie 
few niadreporic pores wliich tlie animal possesses. Attaclied to 
the sides of the scuta buecalia are the " lateral mouth shields," 
which are in fact the adambulacral plates belonging to the second 
pair of ambulacral plates which form the main mass of the jaws. 
Further out, on the under side of the disc, there is, on each side 
of each arm, a long narrow slit — tlie opening of the genital bursa 
(Fig. 208, (jl)), so that there are ten genital bursae. The 
"genital bursa" (Fig. 214) is a sac lined by ciliated ectoderm 
projecting into the interior of the disc. It is called genital 
because the openings of the genital organs are situated on its 
surface ; its main function, however, is respiratory, the cilia 
bringing about a constant inward current of fresh sea-water, 
the oxygen contaiiied in which diffuses through the thin wall 
of the sac into the coelomic fluid. The opening of the bursa is 
strengthened on its radial side by a rod-like ossicle, the " genital 
plate," and on its interradial side by an ossicle called the 
"genital scale" (Fig. 212, ge%), and in Oi^hiothrix the outer end 
<jf the radial plate articulates with the outer end of the genital 
plate. Muscles connect the two plates running on either side 
of the articulation. 

Observations on Oj^hiothrix^ show that in this species at any 
rate the radial plates can be raised or lowered. Wlien they are 
raised the centre of the disc is lifted into a cone and water is 
sucked into the genital bursae, whereas when they are lowered 
the bursae are compressed and water is expelled. This forced 
respiration appears to come into play when tlie supply of oxygen 
is getting scanty. 

The alimentary canal of Opliiotlirix is a simple flattened 
sac (Fig. 213). It is devoid of an anus and cannot be everted 
through the mouth. There is a horizontal pouch given off into 
each interradial lobe of the disc. The sac is attached to the 
dorsal wall of the coeloni by numerous mesenteries, fibrous cords 
traversing tlie coelomic cavity and clothed on the outer side by 
coelomic epithelium. To the mouth-frame it is attached by a 
circular membrane, whicli we have reason for believing is a 

^ How far this form of respiratory mecliaiiisni is distributed amongst Opliiurids 
it is imiJossible to say. It was first observed by me in tlie case of Ophiothrix 
frayUis at Plymouth in 1905, but since then I have found it in Ophiuru ciliaris 
and in Amphiura squancaia