THE
CAMBRIDGE NATURAL HISTORY
EDITED BY
S. F. HARMER, Sc.D., F.R.S., Fellow of King’s College, Cambridge;
Keeper of the Department of Zoology in the British Museum (Natural
History)
AND
A. E. SHIPLEY, M.A., Fellow and Tutor of Christ’s College, Cambridge;
Reader in Zoology in the University
VOLUME IV
[Illustration: Signet]
MACMILLAN AND CO., LIMITED
LONDON · BOMBAY · CALCUTTA
MELBOURNE
THE MACMILLAN COMPANY
NEW YORK · BOSTON · CHICAGO
ATLANTA · SAN FRANCISCO
THE MACMILLAN CO. OF CANADA, LTD.
TORONTO
CRUSTACEA
By GEOFFREY SMITH, M.A. (Oxon.), Fellow of New College, Oxford;
and the late W. F. R. WELDON, M.A. (D.Sc., Oxon.), formerly Fellow
of St. John’s College, Cambridge, and Linacre Professor of Human
and Comparative Anatomy, Oxford
TRILOBITES
By HENRY WOODS, M.A., St. John’s College, Cambridge; University
Lecturer in Palaeozoology
INTRODUCTION TO ARACHNIDA, AND KING-CRABS
By A. E. SHIPLEY, M.A., F.R.S., Fellow and Tutor of Christ’s
College, Cambridge; Reader in Zoology
EURYPTERIDA
By HENRY WOODS, M.A., St. John’s College, Cambridge; University
Lecturer in Palaeozoology
SCORPIONS, SPIDERS, MITES, TICKS, ETC.
By CECIL WARBURTON, M.A., Christ’s College, Cambridge; Zoologist
to the Royal Agricultural Society
TARDIGRADA (WATER-BEARS)
By A. E. SHIPLEY, M.A., F.R.S., Fellow and Tutor of Christ’s
College, Cambridge; Reader in Zoology
PENTASTOMIDA
By A. E. SHIPLEY, M.A., F.R.S., Fellow and Tutor of Christ’s
College, Cambridge; Reader in Zoology
PYCNOGONIDA
By D’ARCY W. THOMPSON, C.B., M.A., Trinity College, Cambridge;
Professor of Natural History in University College, Dundee
MACMILLAN AND CO., LIMITED
ST. MARTIN’S STREET, LONDON
1909
All the ingenious men, and all the scientific men, and all the
fanciful men, in the world, with all the old German bogypainters into
the bargain, could never invent ... anything so curious, and so
ridiculous, as a lobster.
CHARLES KINGSLEY, _The Water-Babies_.
For, Spider, thou art like the poet poor,
Whom thou hast help’d in song.
Both busily, our needful food to win,
We work, as Nature taught, with ceaseless pains,
Thy bowels thou dost spin,
I spin my brains.
SOUTHEY, _To a Spider_.
Last o’er the field the Mite enormous swims,
Swells his red heart, and writhes his giant limbs.
ERASMUS DARWIN, _The Temple of Nature_.
PREFACE
The Editors feel that they owe an apology and some explanation to the
readers of _The Cambridge Natural History_ for the delay which has
occurred in the issue of this, the fourth in proper order, but the last
to appear of the ten volumes which compose the work. The delay has been
due principally to the untimely death of Professor W. F. E. Weldon, who
had undertaken to write the Section on the Crustacea. The Chapter on the
Branchiopoda is all he actually left ready for publication, but it gives
an indication of the thorough way in which he had intended to treat his
subject. He had, however, superintended the preparation of a number of
beautiful illustrations, which show that he had determined to use, in
the main, first-hand knowledge. Many of these figures have been
incorporated in the article by Mr. Geoffrey Smith, to whom the Editors
wish to express their thanks for taking up, almost at a moment’s notice,
the task which had dropped from his teacher’s hand.
A further apology is due to the other contributors to this volume. Their
contributions have been in type for many years, and owing to the
inevitable delays indicated above they have been called upon to make old
articles new, ever an ungrateful labour.
The appearance of this volume completes the work the Editors embarked on
some sixteen years ago. It coincides with the cessation of an almost
daily intercourse since the time when they “came up” to Cambridge as
freshmen in 1880.
S. F. HARMER.
A. E. SHIPLEY.
_March 1909._
CONTENTS
PAGE
SCHEME OF THE CLASSIFICATION ADOPTED IN THIS VOLUME xi
CRUSTACEA
CHAPTER I
CRUSTACEA
GENERAL ORGANISATION 3
CHAPTER II
CRUSTACEA (_continued_)
ENTOMOSTRACA—BRANCHIOPODA—PHYLLOPODA—CLADOCERA—WATER-FLEAS 18
CHAPTER III
CRUSTACEA ENTOMOSTRACA (_continued_)
COPEPODA 55
CHAPTER IV
CRUSTACEA ENTOMOSTRACA (_continued_)
CIRRIPEDIA—PHENOMENA OF GROWTH AND SEX—OSTRACODA 79
CHAPTER V
CRUSTACEA (_continued_)
MALACOSTRACA: LEPTOSTRACA—PHYLLOCARIDA: EUMALACOSTRACA: SYNCARIDA—
ANASPIDACEA: PERACARIDA—MYSIDACEA—CUMACEA—ISOPODA—AMPHIPODA:
HOPLOCARIDA—STOMATOPODA 110
CHAPTER VI
CRUSTACEA MALACOSTRACA (_continued_)
EUMALACOSTRACA (_CONTINUED_): EUCARIDA—EUPHAUSIACEA—COMPOUND EYES—
DECAPODA 144
CHAPTER VII
CRUSTACEA (_continued_)
REMARKS ON THE DISTRIBUTION OF MARINE AND FRESH-WATER CRUSTACEA 197
CHAPTER VIII
CRUSTACEA (_continued_)
TRILOBITA 221
ARACHNIDA
CHAPTER IX
ARACHNIDA—INTRODUCTION 255
CHAPTER X
ARACHNIDA (_continued_)
DELOBRANCHIATA = MEROSTOMATA—XIPHOSURA 259
CHAPTER XI
ARACHNIDA DELOBRANCHIATA (_continued_)
EURYPTERIDA = GIGANTOSTRACA 283
CHAPTER XII
ARACHNIDA (_continued_)
EMBOLOBRANCHIATA—SCORPIONIDEA—PEDIPALPI 297
CHAPTER XIII
ARACHNIDA EMBOLOBRANCHIATA (_continued_)
ARANEAE—EXTERNAL STRUCTURE—INTERNAL STRUCTURE 314
CHAPTER XIV
ARACHNIDA EMBOLOBRANCHIATA (_continued_)
ARANEAE (_CONTINUED_)—HABITS—ECDYSIS—TREATMENT OF YOUNG—MIGRATION—
WEBS—NESTS—EGG-COCOONS—POISON—FERTILITY—ENEMIES—PROTECTIVE
COLORATION—MIMICRY—SENSES—INTELLIGENCE—MATING HABITS—FOSSIL
SPIDERS 338
CHAPTER XV
ARACHNIDA EMBOLOBRANCHIATA (_continued_)
ARANEAE (_CONTINUED_)—CLASSIFICATION 384
CHAPTER XVI
ARACHNIDA EMBOLOBRANCHIATA (_continued_)
PALPIGRADI—SOLIFUGAE = SOLPUGAE—CHERNETIDEA = PSEUDOSCORPIONES 422
CHAPTER XVII
ARACHNIDA EMBOLOBRANCHIATA (_continued_)
PODOGONA = RICINULEI—PHALANGIDEA = OPILIONES—HABITS—STRUCTURE—
CLASSIFICATION 439
CHAPTER XVIII
ARACHNIDA EMBOLOBRANCHIATA (_continued_)
ACARINA—HARVEST-BUGS—PARASITIC MITES—TICKS—SPINNING MITES—
STRUCTURE—METAMORPHOSIS—CLASSIFICATION 454
CHAPTER XIX
ARACHNIDA (APPENDIX I)
TARDIGRADA—OCCURRENCE—ECDYSIS—STRUCTURE—DEVELOPMENT—AFFINITIES—
BIOLOGY—DESICCATION—PARASITES—SYSTEMATIC 477
CHAPTER XX
ARACHNIDA (APPENDIX II)
PENTASTOMIDA—OCCURRENCE—ECONOMIC IMPORTANCE—STRUCTURE—DEVELOPMENT
AND LIFE-HISTORY—SYSTEMATIC 488
PYCNOGONIDA
CHAPTER XXI
PYCNOGONIDA 501
INDEX 543
SCHEME OF THE CLASSIFICATION ADOPTED IN THIS VOLUME
_The names of extinct groups are printed in italics._
=CRUSTACEA= (p. 3).
=ENTOMOSTRACA= (p. 18).
──────────┬───────────┬───────────┬──────────────────────────┬─────────────────
Divisions.│ Orders. │Sub-Orders.│ Tribes. │ Families.
──────────┼───────────┼───────────┴──────────────────────────┼─────────────────
│=Bran- │ │Branchipodidae
│ chiopoda=│=Phyllopoda= (pp. 19, 35) │ (pp. 19, 35).
│ (p. 18) │ │
│ „ │ „ │Apodidae (pp. 19,
│ │ │ 36).
│ „ │ „ │Limnadiidae
│ │ │ (pp. 20, 36).
──────────┼───────────┼───────────┬───────────┬──────────────┼─────────────────
│ │=Cladocera=│Calyptomera│Ctenopoda │
│ „ │ (p. 37) │ (pp. 38, │ (p. 51) │Sididae (p. 51).
│ │ │ 51) │ │
│ „ │ „ │ „ │ „ │Holopediidae
│ │ │ │ │ (p. 51).
──────────┼───────────┼───────────┼───────────┼──────────────┼─────────────────
│ „ │ „ │ „ │Anomopoda │Daphniidae
│ │ │ │ (p. 51) │ (p. 51).
│ „ │ „ │ „ │ „ │Bosminidae
│ │ │ │ │ (p. 53).
│ „ │ „ │ „ │ „ │Lyncodaphniidae
│ │ │ │ │ (p. 53).
│ │ │ │ │Lynceidae =
│ „ │ „ │ „ │ „ │ Chydoridae
│ │ │ │ │ (p. 53).
──────────┼───────────┼───────────┼───────────┴──────────────┼─────────────────
│ „ │ „ │Gymnomera (pp. 38, 54) │Polyphemidae
│ │ │ │ (p. 54).
│ „ │ „ │ „ │Leptodoridae
│ │ │ │ (p. 54).
──────────┬───────────────────────┬───────────┬──────────────┬─────────────────
Divisions.│ Orders. │Sub-Orders.│ Tribes. │ Families.
──────────┼───────────┬───────────┼───────────┼──────────────┼─────────────────
│=Copepoda= │=Eucope- │=Gymnoplea=│Amphascan- │Calanidae
│ (p. 55) │ poda= │ (p. 57) │ dria (p. 57)│ (p. 57).
│ │ (p. 57) │ │ │
──────────┼───────────┼───────────┼───────────┼──────────────┼─────────────────
│ │ │ │Heterar- │Centropagidae
│ „ │ „ │ „ │ thrandria │ (p. 58).
│ │ │ │ (p. 58) │
│ „ │ „ │ „ │ „ │Candacidae
│ │ │ │ │ (p. 60).
│ „ │ „ │ „ │ „ │Pontellidae
│ │ │ │ │ (p. 60).
──────────┼───────────┼───────────┼───────────┼──────────────┼─────────────────
│ │ │=Podoplea= │Amphar- │Cyclopidae
│ „ │ „ │ (p. 61) │ thrandria │ (pp. 61, 62).
│ │ │ │ (p. 61) │
│ „ │ „ │ „ │ „ │Harpacticidae
│ │ │ │ │ (pp. 61, 62).
│ „ │ „ │ „ │ „ │Peltiidae
│ │ │ │ │ (p. 63).
│ „ │ „ │ „ │ „ │Monstrillidae
│ │ │ │ │ (p. 63).
│ „ │ „ │ „ │ „ │Ascidicolidae
│ │ │ │ │ (p. 66).
│ „ │ „ │ „ │ „ │Asterocheridae
│ │ │ │ │ (p. 67).
│ „ │ „ │ „ │ „ │Dichelestiidae
│ │ │ │ │ (p. 68).
──────────┼───────────┼───────────┼───────────┼──────────────┼─────────────────
│ „ │ „ │ „ │Isokerandria │Oncaeidae
│ │ │ │ (p. 69) │ (p. 69).
│ „ │ „ │ „ │ „ │Corycaeidae
│ │ │ │ │ (p. 69).
│ „ │ „ │ „ │ „ │Lichomolgidae
│ │ │ │ │ (p. 70).
│ „ │ „ │ „ │ „ │Ergasilidae
│ │ │ │ │ (p. 71).
│ „ │ „ │ „ │ „ │Bomolochidae
│ │ │ │ │ (p. 71).
│ „ │ „ │ „ │ „ │Chondracanthidae
│ │ │ │ │ (p. 72).
│ „ │ „ │ „ │ „ │Philichthyidae
│ │ │ │ │ (p. 73).
│ „ │ „ │ „ │ „ │Nereicolidae
│ │ │ │ │ (p. 73).
│ „ │ „ │ „ │ „ │Hersiliidae
│ │ │ │ │ (p. 73).
│ „ │ „ │ „ │ „ │Caligidae
│ │ │ │ │ (p. 73).
│ „ │ „ │ „ │ „ │Lernaeidae
│ │ │ │ │ (p. 74).
│ „ │ „ │ „ │ „ │Lernaeopodidae
│ │ │ │ │ (p. 75).
│ „ │ „ │ „ │ „ │Choniostomatidae
│ │ │ │ │ (p. 76).
──────────┼───────────┼───────────┴───────────┴──────────────┼─────────────────
│ „ │=Branchiura= (P. 76) │Argulidae
│ │ │ (p. 76).
──────────┼───────────┴───────────┬──────────────────────────┼─────────────────
│=Cirripedia= (p. 79) │=Pedunculata= (p. 84) │Polyaspidae
│ │ │ (p. 84).
│ „ │ „ │Pentaspidae
│ │ │ (p. 87).
│ „ │ „ │Tetraspidae
│ │ │ (p. 88).
│ „ │ „ │Anaspidae
│ │ │ (p. 89).
──────────┼───────────────────────┼──────────────────────────┼─────────────────
│ „ │=Operculata= (p. 89) │Verrucidae
│ │ │ (p. 91).
│ „ │ „ │Octomeridae
│ │ │ (p. 91).
│ „ │ „ │Hexameridae
│ │ │ (p. 91).
│ „ │ „ │Tetrameridae
│ │ │ (p. 92).
──────────┼───────────────────────┼──────────────────────────┴─────────────────
│ „ │=Acrothoracica= (p. 92).
│ „ │=Ascothoracica= (p. 93).
│ „ │=Apoda= (p. 94).
│ „ │=Rhizocephala= (p. 95).
──────────┼───────────────────────┴──────────────────────────┬─────────────────
│=Ostracoda= (p. 107) │Cypridae
│ │ (p. 107).
│ „ │Cytheridae
│ │ (p. 107).
│ „ │Halocypridae
│ │ (p. 108).
│ „ │Cypridinidae
│ │ (p. 108).
│ „ │Polycopidae
│ │ (p. 109).
│ „ │Cytherellidae
│ │ (p. 109).
=MALACOSTRACA= (p. 110).
=LEPTOSTRACA= (p. 111)
=Phyllocarida= (p. 111).
──────────┬───────────┬───────────────────────┬──────────────┬─────────────────
Divisions.│ Orders. │ Sub-Orders. │ Tribes │ Families.
──────────┴───────────┴───────────────────────┴──────────────┴─────────────────
=EUMALACOSTRACA= (p. 112).
=Syncar- │ │Anaspididae
ida= │=Anaspidacea= (p. 115) │ (p. 115).
(p. 114)│ │
„ │ „ │Koonungidae
│ │ (p. 117).
──────────┼──────────────────────────────────────────────────┼─────────────────
=Per- │ │Eucopiidae
acarida=│=Mysidacea= (p. 118) │ (p. 118).
(p. 118)│ │
„ │ „ │Lophogastridae
│ │ (p. 119).
„ │ „ │Mysidae (p. 119).
──────────┼──────────────────────────────────────────────────┼─────────────────
„ │=Cumacea= (p. 120) │Cumidae (p. 121).
„ │ „ │Lampropidae
│ │ (p. 121).
„ │ „ │Leuconidae
│ │ (p. 121).
„ │ „ │Diastylidae
│ │ (p. 121).
„ │ „ │Pseudocumidae
│ │ (p. 121).
──────────┼───────────┬──────────────────────────────────────┼─────────────────
„ │=Isopoda= │=Chelifera= (p. 122) │Apseudidae
│ (p. 121) │ │ (p. 122).
„ │ „ │ „ │Tanaidae
│ │ │ (p. 122).
──────────┼───────────┼──────────────────────────────────────┼─────────────────
„ │ „ │=Flabellifera= (p. 124) │Anthuridae
│ │ │ (p. 124).
„ │ „ │ „ │Gnathiidae
│ │ │ (p. 124).
„ │ „ │ „ │Cymothoidae
│ │ │ (p. 126).
„ │ „ │ „ │Cirolanidae
│ │ │ (p. 126).
„ │ „ │ „ │Serolidae
│ │ │ (p. 126).
„ │ „ │ „ │Sphaeromidae
│ │ │ (p. 126).
──────────┼───────────┼──────────────────────────────────────┼─────────────────
„ │ „ │=Valvifera= (p. 127) │Idotheidae
│ │ │ (p. 127).
„ │ „ │ „ │Arcturidae
│ │ │ (p. 127).
──────────┼───────────┼──────────────────────────────────────┼─────────────────
„ │ „ │=Asellota= (p. 127) │Asellidae
│ │ │ (p. 128).
„ │ „ │ „ │Munnopsidae
│ │ │ (p. 128).
──────────┼───────────┼──────────────────────────────────────┴─────────────────
„ │ „ │=Oniscoida= (p. 128).
──────────┼───────────┼───────────┬──────────────────────────┬─────────────────
„ │ „ │=Epicarida=│=Cryptoniscina= (pp. 129, │Microniscidae
│ │ (p. 129) │ 130) │ (p. 130).
„ │ „ │ „ │ „ │Cryptoniscidae
│ │ │ │ (p. 130).
„ │ „ │ „ │ „ │Liriopsidae
│ │ │ │ (p. 130).
„ │ „ │ „ │ „ │Hemioniscidae
│ │ │ │ (p. 130).
„ │ „ │ „ │ „ │Cabiropsidae
│ │ │ │ (p. 130).
„ │ „ │ „ │ „ │Podasconidae
│ │ │ │ (p. 130).
„ │ „ │ „ │ „ │Asconiscidae
│ │ │ │ (p. 130).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │ „ │=Bopyrina= (pp. 129, 130, │Dajidae (p. 130).
│ │ │ 132) │
„ │ „ │ „ │ „ │Phryxidae
│ │ │ │ (p. 130).
„ │ „ │ „ │ „ │Bopyridae
│ │ │ │ (pp. 130, 133).
„ │ „ │ „ │ „ │Entoniscidae
│ │ │ │ (pp. 130, 134).
──────────┼───────────┼───────────┴──────────────────────────┼─────────────────
„ │ „ │=Phreatoicidea= (p. 136) │Phreatoicidae
│ │ │ (p. 136)
──────────┼───────────┼──────────────────────────────────────┼─────────────────
„ │=Amphipoda=│=Crevettina= (p. 137) │Lysianassidae
│ (p. 136) │ │ (p. 137).
„ │ „ │ „ │Haustoriidae
│ │ │ (p. 137).
„ │ „ │ „ │Gammaridae
│ │ │ (p. 138).
„ │ „ │ „ │Talitridae
│ │ │ (p. 139).
„ │ „ │ „ │Corophiidae
│ │ │ (p. 139).
──────────┼───────────┼──────────────────────────────────────┼─────────────────
„ │ „ │=Laemodipoda= (p. 139) │Caprellidae
│ │ │ (p. 139).
„ │ „ │ „ │Cyamidae
│ │ │ (p. 140).
──────────┼───────────┼──────────────────────────────────────┴─────────────────
„ │ „ │=Hyperina= (p. 140).
──────────┼───────────┴──────────────────────────────────────┬─────────────────
=Hoplo- │ │Squillidae
carida= │=Stomatopoda= (p. 141) │ (p. 143).
(p. 141)│ │
──────────┼──────────────────────────────────────────────────┼─────────────────
=Eucarida=│=Euphausiacea= (p. 144) │Euphausiidae
(p. 144)│ │ (p. 144).
──────────┼───────────┬───────────┬──────────────────────────┼─────────────────
„ │=Decapoda= │=Macrura= │Nephropsidea (p. 154) │Nephropsidae
│ (p. 152) │ (p. 153) │ │ (p. 154).
„ │ „ │ „ │ „ │Astacidae
│ │ │ │ (p. 157).
„ │ „ │ „ │ „ │Parastacidae
│ │ │ │ (p. 157).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │ „ │Eryonidea (p. 157) │Eryonidae
│ │ │ │ (p. 158).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │ „ │Peneidea (pp. 158, 162) │Peneidae
│ │ │ │ (p. 162).
„ │ „ │ „ │ „ │Sergestidae
│ │ │ │ (p. 162).
„ │ „ │ „ │ „ │Stenopodidae
│ │ │ │ (p. 162).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │ „ │Caridea (pp. 158, 163) │Pasiphaeidae
│ │ │ │ (p. 163).
„ │ „ │ „ │ „ │Acanthephyridae
│ │ │ │ (p. 163).
„ │ „ │ „ │ „ │Atyidae (p. 163).
„ │ „ │ „ │ „ │Alpheidae
│ │ │ │ (p. 163).
„ │ „ │ „ │ „ │Psalidopodidae
│ │ │ │ (p.164).
„ │ „ │ „ │ „ │Pandalidae
│ │ │ │ (p. 164).
„ │ „ │ „ │ „ │Hippolytidae
│ │ │ │ (p. 164).
„ │ „ │ „ │ „ │Palaemonidae
│ │ │ │ (p. 164).
„ │ „ │ „ │ „ │Glyphocrangonidae
│ │ │ │ (p. 164).
„ │ „ │ „ │ „ │Crangonidae
│ │ │ │ (p. 164).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │ „ │Loricata (p. 165) │Palinuridae
│ │ │ │ (p. 167).
„ │ „ │ „ │ „ │Scyllaridae
│ │ │ │ (p. 167).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │ „ │Thalassinidea (p. 167) │Callianassidae
│ │ │ │ (p. 167).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │=Anomura= │Galatheidea (p. 168) │Aegleidae
│ │ (p. 167) │ │ (p. 169).
„ │ „ │ „ │ „ │Galatheidae
│ │ │ │ (p. 169).
„ │ „ │ „ │ „ │Porcellanidae
│ │ │ │ (p. 170).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │ „ │Hippidea (p. 170) │Albuneidae
│ │ │ │ (p. 171).
„ │ „ │ „ │ „ │Hippidae
│ │ │ │ (p. 171).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │ „ │Paguridea (p. 171) │Pylochelidae
│ │ │ │ (p. 180).
„ │ „ │ „ │ „ │Paguridae
│ │ │ │ (p. 180).
„ │ „ │ „ │ „ │Eupagurinae
│ │ │ │ (p. 180).
„ │ „ │ „ │ „ │Pagurinae
│ │ │ │ (p. 180).
„ │ „ │ „ │ „ │Coenobitidae
│ │ │ │ (p. 181).
„ │ „ │ „ │ „ │Lithodidae
│ │ │ │ (p. 181).
„ │ „ │ „ │ „ │Hapalogastorinae
│ │ │ │ (p. 181).
„ │ „ │ „ │ „ │Lithodinae
│ │ │ │ (p. 181).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │=Brachyura=│Dromiacea (p. 183) │Dromiidae
│ │ (p. 181) │ │ (p. 184).
„ │ „ │ „ │ „ │Dynomenidae
│ │ │ │ (p. 184).
„ │ „ │ „ │ „ │Homolidae
│ │ │ │ (p. 184).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │ „ │Oxystomata (p. 185) │Calappidae
│ │ │ │ (p. 187).
„ │ „ │ „ │ „ │Leucosiidae
│ │ │ │ (p. 188).
„ │ „ │ „ │ „ │Dorippidae
│ │ │ │ (p. 188).
„ │ „ │ „ │ „ │Raninidae
│ │ │ │ (p. 188).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │ „ │Cyclometopa (p. 188) │Corystidae
│ │ │ │ (p. 190).
„ │ „ │ „ │ „ │Atelecyclidae
│ │ │ │ (p. 190).
„ │ „ │ „ │ „ │Cancridae
│ │ │ │ (p. 191).
„ │ „ │ „ │ „ │Portunidae
│ │ │ │ (p. 191).
„ │ „ │ „ │ „ │Xanthidae
│ │ │ │ (p. 191).
│ │ │ │Thelphusidae =
„ │ „ │ „ │ „ │ Potamonidae
│ │ │ │ (p. 191).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │ „ │Oxyrhyncha (p. 191) │Maiidae (p. 193).
„ │ „ │ „ │ „ │Parthenopidae
│ │ │ │ (p. 193).
„ │ „ │ „ │ „ │Hymenosomatidae
│ │ │ │ (p. 193).
──────────┼───────────┼───────────┼──────────────────────────┼─────────────────
„ │ „ │ „ │Catometopa (p. 193) │Carcinoplacidae
│ │ │ │ (p. 195).
„ │ „ │ „ │ „ │Gonoplacidae
│ │ │ │ (p. 195).
„ │ „ │ „ │ „ │Pinnotheridae
│ │ │ │ (p. 195).
„ │ „ │ „ │ „ │Grapsidae
│ │ │ │ (p. 196).
„ │ „ │ „ │ „ │Gecarcinidae
│ │ │ │ (p. 196).
„ │ „ │ „ │ „ │Ocypodidae
│ │ │ │ (p. 196).
=TRILOBITA= (p. 221).
Families
_Agnostidae_ (p. 244).
_Shumardiidae_ (p. 245).
_Trinucleidae_ (p. 245).
_Harpedidae_ (p. 245).
_Paradoxidae_ (p. 246).
_Conocephalidae_ = _Conocoryphidae_ (p. 247).
_Olenidae_ (p. 247).
_Calymenidae_ (p. 247).
_Asaphidae_ (p. 249).
_Bronteidae_ (p. 249).
_Phacopidae_ (p. 249).
_Cheiruridae_ (p. 250).
_Proëtidae_ (p. 251).
_Encrinuridae_ (p. 251).
_Acidaspidae_ (p. 251).
_Lichadidae_ (p. 252).
=ARACHNIDA= (p. 255).
=DELOBRANCHIATA = MEROSTOMATA= (pp. 258, 259).
───────────────────┬────────────────┬────────────────┬─────────────────
Orders. │ Sub-Orders. │ Families. │ Sub-Families.
───────────────────┴────────────────┼────────────────┼─────────────────
=Xiphosura= (pp. 258, 259, 276) │Xiphosuridae │Xiphosurinae
│ (p. 276) │ (p. 276).
„ │ „ │Tachypleinae
│ │ (p. 276).
────────────────────────────────────┼────────────────┴─────────────────
_Eurypterida = Gigantostraca_ │_Eurypteridae_ (p. 290).
(pp. 258, 283) │
=EMBOLOBRANCHIATA= (pp. 258, 297).
=Scorpionidea= (pp. 258, 297) │Buthidae │Buthinae
│ (p. 306) │ (p. 306).
„ │ „ │Centrurinae
│ │ (p. 306).
────────────────────────────────────┼────────────────┼─────────────────
„ │Scorpionidae │Diplocentrinae
│ (p. 306) │ (p. 307).
„ │ „ │Urodacinae
│ │ (p. 307).
„ │ „ │Scorpioninae
│ │ (p. 307).
„ │ „ │Hemiscorpioninae
│ │ (p. 307).
„ │ „ │Ischnurinae
│ │ (p. 307).
────────────────────────────────────┼────────────────┴─────────────────
„ │Chaerilidae (p. 307).
────────────────────────────────────┼────────────────┬─────────────────
„ │Chactidae │Megacorminae
│ (p. 307) │ (p. 308).
„ │ „ │Euscorpiinae
│ │ (p. 308).
„ │ „ │Chactinae
│ │ (p. 308).
────────────────────────────────────┼────────────────┴─────────────────
„ │Vejovidae (p. 308).
„ │Bothriuridae (p. 308).
────────────────────────────────────┼──────────────────────────────────
=Pedipalpi= (pp. 258, 308) │Thelyphonidae (p. 312).
„ │Schizonotidae = Tartaridae
│ (p. 312).
────────────────────────────────────┼────────────────┬─────────────────
│Tarantulidae = │Tarantulinae
„ │ Phrynidae │ (p. 313).
│ (p. 312) │
„ │ „ │Phrynichinae
│ │ (p. 313).
„ │ „ │Charontinae
│ │ (p. 313).
────────────────────────────────────┼────────────────┴─────────────────
=Araneae= (pp. 258, 314) │Liphistiidae (p. 386).
────────────────────────────────────┼────────────────┬─────────────────
│Aviculariidae = │Paratropidinae
„ │ Mygalidae │ (p. 387).
│ (p. 386) │
„ │ „ │Actinopodinae
│ │ (p. 387).
„ │ „ │Miginae (p. 387).
„ │ „ │Ctenizinae
│ │ (p. 388).
„ │ „ │Barychelinae
│ │ (p. 389).
„ │ „ │Aviculariinae
│ │ (p. 389).
„ │ „ │Diplurinae
│ │ (p. 390).
────────────────────────────────────┼────────────────┴─────────────────
„ │Atypidae (p. 390).
„ │Filistatidae (p. 391).
„ │Oecobiidae = Urocteidae (p. 392).
„ │Sicariidae = Scytodidae (p. 393).
„ │Hypochilidae (p. 393).
„ │Leptonetidae (p. 393).
„ │Oonopidae (p. 393).
„ │Hadrotarsidae (p. 394).
────────────────────────────────────┼────────────────┬─────────────────
„ │Dysderidae │Dysderinae
│ (p. 394) │ (p. 394).
„ │ „ │Segestriinae
│ │ (p. 395).
────────────────────────────────────┼────────────────┴─────────────────
„ │Caponiidae (p. 395).
„ │Prodidomidae (p. 395).
────────────────────────────────────┼────────────────┬─────────────────
„ │Drassidae │Drassinae
│ (p. 396) │ (p. 396).
„ │ „ │Clubioninae
│ │ (p. 397).
„ │ „ │Liocraninae
│ │ (p. 397).
„ │ „ │Micariinae
│ │ (p. 397).
────────────────────────────────────┼────────────────┴─────────────────
„ │Palpimanidae (p. 398).
„ │Eresidae (p. 398).
„ │Dictynidae (p. 398).
„ │Psechridae (p. 399).
„ │Zodariidae = Enyoidae (p. 399).
„ │Hersiliidae (p. 400).
„ │Pholcidae (p. 401).
────────────────────────────────────┼────────────────┬─────────────────
„ │Theridiidae │Argyrodinae
│ (p. 401) │ (p. 402).
„ │ „ │Episininae
│ │ (p. 402).
„ │ „ │Theridioninae
│ │ (p. 403).
„ │ „ │Phoroncidiinae
│ │ (p. 404).
„ │ „ │Erigoninae
│ │ (p. 404).
„ │ „ │Formicinae
│ │ (p. 405).
„ │ „ │Linyphiinae
│ │ (p. 405).
────────────────────────────────────┼────────────────┼─────────────────
„ │Epeiridae │Theridiosomatinae
│ (p. 406) │ (p. 407).
„ │ „ │Tetragnathinae
│ │ (p. 407).
„ │ „ │Argiopinae
│ │ (p. 408).
„ │ „ │Nephilinae
│ │ (p. 408).
„ │ „ │Epeirinae
│ │ (p. 408).
„ │ „ │Gasteracanthinae
│ │ (p. 409).
„ │ „ │Poltyinae
│ │ (p. 410).
„ │ „ │Arcyinae
│ │ (p. 410).
────────────────────────────────────┼────────────────┼─────────────────
„ │Uloboridae │Dinopinae
│ (p. 410) │ (p. 410).
„ │ „ │Uloborinae
│ │ (p. 410).
„ │ „ │Miagrammopinae
│ │ (p. 411).
────────────────────────────────────┼────────────────┴─────────────────
„ │Archeidae (p. 411).
„ │Mimetidae (p. 411).
────────────────────────────────────┼────────────────┬─────────────────
│Thomisidae │Thomisinae =
„ │ (p. 412) │ Misumeninae
│ │ (p. 412).
„ │ „ │Philodrominae
│ │ (p. 413).
„ │ „ │Sparassinae
│ │ (p. 414).
„ │ „ │Aphantochilinae
│ │ (p. 414).
„ │ „ │Stephanopsinae
│ │ (p. 414).
„ │ „ │Selenopinae
│ │ (p. 414).
────────────────────────────────────┼────────────────┴─────────────────
„ │Zoropsidae (p. 415).
„ │Platoridae (p. 415).
────────────────────────────────────┼────────────────┬─────────────────
„ │Agelenidae │Cybaeinae
│ (p. 415) │ (p. 415).
„ │ „ │Ageleninae
│ │ (p. 416).
„ │ „ │Hahniinae
│ │ (p. 416).
„ │ „ │Nicodaminae
│ │ (p. 416).
────────────────────────────────────┼────────────────┴─────────────────
„ │Pisauridae (p.416).
„ │Lycosidae (p. 417).
„ │Ctenidae (p. 418).
„ │Senoculidae (p. 418).
„ │Oxyopidae (p. 419).
„ │Attidae = Salticidae (p. 419).
────────────────────────────────────┴──────────────────────────────────
=Palpigradi= (pp. 258, 422).
───────────────────┬────────────────┬──────────────────────────────────
=Solifugae = │ │
Solpugae= │ │Galeodidae (p. 428).
(pp. 258, 423) │ │
───────────────────┼────────────────┼────────────────┬─────────────────
„ │ │Solpugidae │Rhagodinae
│ │ (p. 429) │ (p. 429).
„ │ │ „ │Solpuginae
│ │ │ (p. 429).
„ │ │ „ │Daesiinae
│ │ │ (p. 429).
„ │ │ „ │Eremobatinae
│ │ │ (p. 429).
„ │ │ „ │Karshiinae
│ │ │ (p. 429).
───────────────────┼────────────────┼────────────────┴─────────────────
„ │ │Hexisopodidae (p. 429).
───────────────────┼────────────────┼────────────────┬─────────────────
=Chernetidea = │ │ │
Chernetes = │ │Cheliferinae │Cheliferidae
Pseudoscorpiones=│ │ (p. 436). │ (p. 436)
(pp. 258, 430) │ │ │
„ │ │ „ │Garypinae
│ │ │ (pp. 436, 437).
„ │ │ „ │Obisiinae
│ │ │ (pp. 436, 437).
───────────────────┼────────────────┼────────────────┴─────────────────
=Podogona = │ │
Ricinulei= │ │Cryptosteinmatidae (p.440).
(pp. 258, 439) │ │
───────────────────┼────────────────┼──────────────────────────────────
=Phalangidea = │=Cyphophthalmi= │
Opiliones= │ (p. 447) │Sironidae (p. 448).
(pp. 258, 440) │ │
───────────────────┼────────────────┼──────────────────────────────────
│=Mecostethi = │
„ │ Laniatores= │Phalangodidae (p. 448).
│ (p. 448) │
„ │ „ │Cosmetidae (p. 449).
„ │ „ │Gonyleptidae (p. 449).
───────────────────┼────────────────┼────────────────┬─────────────────
│=Plagiostethi = │Phalangiidae │Sclerosomatinac
„ │ Palpatores= │ (p. 449) │ (p.449).
│ (p. 449) │ │
„ │ „ │ „ │Phalangiinae
│ │ │ (p. 450).
───────────────────┼────────────────┼────────────────┴─────────────────
„ │ „ │Ischyropsalidae (p. 451).
„ │ „ │Nemastomatidae (p. 451).
„ │ „ │Trogulidae (p. 452).
───────────────────┼────────────────┼──────────────────────────────────
=Acarina = Acari = │=Vermiformia= │Eriophyidae = Phytoptidae
Acaridea= │ (p. 464) │ (p. 464).
(pp. 258, 454) │ │
„ │ „ │Demodicidae (p. 465).
───────────────────┼────────────────┼────────────────┬─────────────────
„ │=Astigmata= │Sarcoptidae │Sarcoptinae
│ (p. 465) │ (p. 466) │ (p. 466).
„ │ „ │ „ │Analgesinae
│ │ │ (p. 466).
„ │ „ │ „ │Tyroglyphinae
│ │ │ (p. 466).
───────────────────┼────────────────┼────────────────┴─────────────────
„ │=Metastigmata= │Oribatidae (p. 467).
│ (p. 467) │
───────────────────┼────────────────┼────────────────┬─────────────────
„ │ „ │=Ixodoidea= │Argasidae
│ │ (p. 468) │ (p. 469).
„ │ „ │ „ │Ixodidae
│ │ │ (p. 469).
───────────────────┼────────────────┼────────────────┼─────────────────
„ │ „ │Gamasidae │Gamasinae
│ │ (p. 470) │ (p. 470).
„ │ „ │ „ │Dermanyssinae
│ │ │ (p. 471).
───────────────────┼────────────────┼────────────────┴─────────────────
„ │=Heterostigmata=│Tarsonemidae (p. 471).
│ (p. 471) │
───────────────────┼────────────────┼──────────────────────────────────
„ │=Prostigmata= │Bdellidae (p. 471).
│ (p. 471) │
„ │ „ │Halacaridae (p. 472).
„ │ „ │Hydrachnidae (p. 472).
───────────────────┼────────────────┼────────────────┬─────────────────
„ │ „ │Trombidiidae │Limnocharinae
│ │ (p. 472) │ (p. 472).
„ │ „ │ „ │Caeculinae
│ │ │ (p. 472).
„ │ „ │ „ │Tetranychinae
│ │ │ (p. 472).
„ │ „ │ „ │Cheyletinae
│ │ │ (p. 473).
„ │ „ │ „ │Erythraeinae
│ │ │ (p. 473).
„ │ „ │ „ │Trombidiinae
│ │ │ (p. 473).
───────────────────┼────────────────┼────────────────┴─────────────────
„ │=Notostigmata= │Opilioacaridae (p. 473).
│ (p. 473) │
Orders.
=TARDIGRADA= (pp. 258, 477).
=PENTASTOMIDA= (pp. 258, 488).
=PYCNOGONIDA = PODOSOMATA = PANTOPODA= (p. 501).
Families.
Decolopodidae (p. 531).
Colossendeidae = Pasithoidae (p. 532).
Eurycididae = Ascorhynchidae (p. 533).
Ammotheidae (p. 534).
Rhynchothoracidae (p. 535)
Nymphonidae (p. 536).
Pallenidae (p. 537).
Phoxichilidiidae (p. 538).
Phoxichilidae (p. 539).
Pycnogonidae (p. 539).
CRUSTACEA
CHAPTERS I and III-VII
BY
GEOFFREY SMITH, M.A. (OXON.)
Fellow of New College, Oxford
CHAPTER II
BY
THE LATE W. F. R. WELDON, M.A. (D.SC. OXON.)
Formerly Fellow of St. John’s College, Cambridge, and Linacre Professor
of Human and Comparative Anatomy, Oxford
CHAPTER I
CRUSTACEA—GENERAL ORGANISATION
The Crustacea are almost exclusively aquatic animals, and they play a
part in the waters of the world closely parallel to that which insects
play on land. The majority are free-living, and gain their sustenance
either as vegetable-feeders or by preying upon other animals, but a
great number are scavengers, picking clean the carcasses and refuse that
litter the ocean, just as maggots and other insects rid the land of its
dead cumber. Similar to insects also is the great abundance of
individuals which represent many of the species, especially in the
colder seas, and the naturalist in the Arctic or Antarctic oceans has
learnt to hang the carcasses of bears and seals over the side of the
boat for a few days in order to have them picked absolutely clean by
shoals of small Amphipods. It is said that these creatures, when crowded
sufficiently, will even attack living fishes, and by sheer press of
numbers impede their escape and devour them alive. Equally surprising
are the shoals of minute Copepods which may discolour the ocean for many
miles, an appearance well known to fishermen, who take profitable toll
of the fishes that follow in their wake. Despite this massing together
we look in vain for any elaborate social economy, or for the development
of complex instincts among Crustacea, such as excite our admiration in
many insects, and though many a crab or lobster is sufficiently uncanny
in appearance to suggest unearthly wisdom, he keeps his intelligence
rigidly to himself, encased in the impenetrable reserve of his armour
and vindicated by the most powerful of pincers. It is chiefly in the
variety of structure and in the multifarious phases of life-history that
the interest of the Crustacea lies. Before entering into an examination
of these matters, it will be well to take a general survey of Crustacean
organisation, to consider the plan on which these animals are built, and
the probable relation of this plan to others met with in the animal
kingdom.
The Crustacea, to begin with, are a Class of the enormous Phylum
Arthropoda, animals with metamerically segmented bodies and usually with
externally jointed limbs. Their bodies are thus composed of a series of
repeated segments, which are on the whole similar to one another, though
particular segments may be differentiated in various respects for the
performance of different functions. This segmentation is apparent
externally, the surface of a Crustacean being divided typically into a
number of hard chitinous rings, some of which may be fused rigidly
together, as in the carapace of the crabs, or else articulated loosely.
Each segment bears typically a pair of jointed limbs, and though they
vary greatly in accordance with the special functions for which they are
employed, and may even be absent from certain segments, they may yet be
reduced to a common plan and were, no doubt, originally present on all
the segments.
Passing from the exterior to the interior of the body we find, generally
speaking, that the chief system of organs which exhibits a similar
repetition, or metameric segmentation, is the nervous system. This
system is composed ideally of a nervous ganglion situated in each
segment and giving off peripheral nerves, the several ganglia being
connected together by a longitudinal cord. This ideal arrangement,
though apparent during the embryonic development, becomes obscured to
some extent in the adult owing to the concentration or fusion of ganglia
in various parts of the body. The other internal organs do not show any
clear signs of segmentation, either in the embryo or in the adult; the
alimentary canal and its various diverticula lie in an unsegmented
body-cavity, and are bathed in the blood which courses through a system
of narrow canals and irregular spaces which surround all the organs of
the body. A single pair, or at most two pairs of kidneys are present.
The type of segmentation exhibited by the Crustacea is thus of a limited
character, concerning merely the external skin with its appendages, and
the nervous system, and not touching any of the other internal
organs.[1] In this respect the Crustacea agree with all the other
Arthropods, in the adults of which the segmentation is confined to the
exterior and to the nervous system, and does not extend to the
body-cavity and its contained organs; and for the same reason they
differ essentially from all other metamerically segmented animals,
_e.g._ Annelids, in which the segmentation not only affects the exterior
and the nervous system, but especially applies to the body-cavity, the
musculature, the renal, and often the generative organs. The Crustacea
also resemble the other Arthropoda in the fact that the body-cavity
contains blood, and is therefore a “haemocoel,” while in the Annelids
and Vertebrates the segmented body-cavity is distinct from the vascular
system, and constitutes a true “coelom.” To this important distinction,
and to its especial application to the Crustacea, we will return, but
first we may consider more narrowly the =segmentation= of the Crustacea
and its main types of variation within the group. In order to determine
the number of segments which compose any particular Crustacean we have
clearly two criteria: first, the rings or somites of which the body is
composed, and to each of which a pair of limbs must be originally
ascribed; and, second, the nervous ganglia.
Around and behind the region of the mouth there is very little
difficulty in determining the segments of the body, if we allow
embryology to assist anatomy, but in front of the mouth the matter is
not so easy.
In the Crustacea the moot point is whether we consider the paired eyes
and first pair of antennae as true appendages belonging to two true
segments, or whether they are structures _sui generis_, not homologous
to the other limbs. With regard to the first antennae we are probably
safe in assigning them to a true body-segment, since in some of the
Entomostraca, _e.g._ _Apus_, the nerves which supply them spring, not
from the brain as in more highly specialised forms, but from the
commissures which pass round the oesophagus to connect the dorsally
lying brain to the ventral nerve-cord. The paired eyes are always
innervated from the brain, but the brain, or at least part of it, is
very probably formed of paired trunk-ganglia which have fused into a
common cerebral mass; and the fact that under certain circumstances the
stalked eye of Decapods when excised with its peripheral ganglion[2] can
regenerate in the form of an antenna, is perhaps evidence that the
lateral eyes are borne on what were once a pair of true appendages.
Now, with regard to the segmentation of the body, the Crustacea fall
into three categories: the Entomostraca, in which the number of segments
is indefinite; the Malacostraca, in which we may count nineteen
segments, exclusive of the terminal piece or telson and omitting the
lateral eyes; and the Leptostraca, including the single recent genus
_Nebalia_, in which the segmentation of head and thorax agrees exactly
with that of the Malacostraca, but in the abdomen there are two
additional segments.
It has been usually held that the indefinite number of segments
characteristic of the Entomostraca, and especially the indefinitely
large number of segments characteristic of such Phyllopods as _Apus_,
preserves the ancestral condition from which the definite number found
in the Malacostraca has been derived; but recently it has been clearly
pointed out by Professor Carpenter[3] that the number of segments found
in the Malacostraca and Leptostraca corresponds with extraordinary
exactitude to the number determined as typical in all the other orders
of Arthropoda. This remarkable correspondence (it can hardly be
coincidence) seems to point to a common Arthropodan plan of
segmentation, lying at the very root of the phyletic tree; and if this
is so, we are forced to the conclusion that the Malacostraca have
retained the primitive type of segmentation in far greater perfection
than the Entomostraca, in some of which many segments have been added,
_e.g._ Phyllopoda, while in others segments have been suppressed, _e.g._
Cladocera, Ostracoda. It may be objected to this view of the primitive
condition of segmentation in the Crustacea that the Trilobites, which
for various reasons are regarded as related to the ancestral
Crustaceans, exhibit an indefinite and often very high number of
segments; but, as Professor Carpenter has pointed out, the oldest and
most primitive of Trilobites, such as _Olenellus_, possessed few
segments which increase as we pass from Cambrian to Carboniferous
genera.
The following table shows the segmentation of the body in the
Malacostraca, as compared with that of _Limulus_ (cf. p. 263), Insecta,
the primitive Myriapod _Scolopendrella_, and _Peripatus_. It will be
seen that the correspondence, though not exact, is very close,
especially in the first four columns, the number of segments in
_Peripatus_ being very variable in the different species.
TABLE SHOWING THE SEGMENTATION OF VARIOUS ARTHROPODS
┌──┬──────────────┬───────────┬────────────┬─────────────┬────────────┐
│ │Malacostraca. │_Limulus._ │ Insecta. │ Myriapoda. │_Peripatus._│
│ │ │ │ │ (_Scolopen- │ │
│ │ │ │ │ drella_). │ │
├──┼──────────────┼───────────┼────────────┼─────────────┼────────────┤
│ 1│Eyes │Median eyes│Eyes │ │ │
│ 2│1st antennae │Rostrum │Antennae │Feelers │Feelers │
│ 3│2nd antennae │Chelicerae │Intercalary │ │ │
│ │ │ │segment │ │ │
│ 4│Mandibles │Pedipalpi │Mandibles │Mandibles │Mandibles │
│ 5│1st maxillae │1st walking│Maxillulae │Maxillulae │1st jaw-claw│
│ │ │legs │ │ │ │
│ 6│2nd maxillae │2nd „ │1st maxillae│1st maxillae │2nd jaw-claw│
│ │ │ „ │ │ │ │
│ 7│1st │3rd „ │2nd maxillae│2nd maxillae │1st leg │
│ │maxillipede │ „ │ │ │ │
│ 8│2nd │4th „ │1st leg │1st leg │2nd „ │
│ │maxillipede │ „ │ │ │ │
│ 9│3rd │Chilaria │2nd „ │2nd „ │3rd „ │
│ │maxillipede │ │ │ │ │
│10│1st ambulatory│Genital │3rd „ │3rd „ │4th „ │
│ │ │operculum │ │ │ │
│11│2nd „ │1st │1st │4th „ │5th „ │
│ │ │gill-book │abdominal │ │ │
│12│3rd „ │2nd „ │2nd „ │6th „ │6th „ │
│13│4th „ │3rd „ │3rd „ │6th „ │7th „ │
│14│5th „ │4th „ │4th „ │7th „ │8th „ │
│15│1st abdominal │5th „ │5th „ │8th „ │9th „ │
│16│2nd „ │No │6th „ │9th „ │10th „ │
│ │ │appendages │ │ │ │
│17│3rd „ │ „ │7th „ │10th „ │11th „ │
│18│4th „ │ „ │8th „ │11th „ │12th „ │
│19│5th „ │ „ │9th „ │12th „ │13th „ │
│20│6th „ │ „ │10th „ │Reduced limbs│14th „ │
│21│ [4] │ „ │ │Cercopods │ [5] │
│ │Telson │Telson │Telson │Telson │Telson │
└──┴──────────────┴───────────┴────────────┴─────────────┴────────────┘
The =appendages= of the Crustacea exhibit a wonderful variety of
structure, but these variations can be reduced to at most two, and
possibly to one fundamental plan. In a typical Crustacean, besides the
paired eyes, which may be borne on stalks, possibly homologous to highly
modified limbs, there are present, first, two pairs of rod-like or
filamentous antennae, which in the adult are usually specialised for
sensory purposes, but frequently retain their primitive function as
locomotory limbs even in the adult, _e.g._ Ostracoda; while in the
Nauplius larva, found in almost all the chief subdivisions of the
Crustacea, the two pairs of antennae invariably aid in locomotion, and
the base of the second antennae is usually furnished with sharp biting
spines which assist mastication. Following the antennae is a pair of
mandibles which are fashioned for biting the food or for piercing the
prey, and posterior to these are two pairs of maxillae, biting organs
more slightly built than the mandibles, whose function it is to lacerate
the food and prepare it for the more drastic action of the mandibles. So
far, with comparatively few exceptions, the order of specialisation is
invariable; but behind the maxillae the trunk-appendages vary greatly
both in structure and function in the different groups.
As a general rule, the first or first few thoracic limbs are turned
forwards toward the mouth, and are subsidiary to mastication; they are
then called maxillipedes; this happens usually in the Malacostraca, but
to a much less extent in the Entomostraca; and in any case these
appendages immediately behind the maxillae never depart to any great
extent from a limb-like structure, and they may graduate insensibly into
the ordinary trunk-appendages. The latter show great diversity in the
different Crustacean groups, according as the animals lead a natatory,
creeping, or parasitic method of life; they may be foliaceous, as in the
Branchiopoda, or biramous, as in the swimming thoracic and abdominal
appendages of the Mysidae, or simply uniramous, as in the walking legs
of the higher Decapoda, and the clinging legs of various parasitic
forms.
Without going into detailed deviations of structure, many of which will
be described under the headings of special groups, it is clear from the
foregoing description and from Fig. 1 (p. 10), that three main types of
appendage can be distinguished: first, the foliaceous or multiramous;
second, the biramous; and, third, the uniramous.
We may dismiss the uniramous type with a few words: it is obviously
secondarily derived from the biramous type; this can be proved in detail
in nearly every case. Thus, the uniramous second antennae of some adult
forms are during the Nauplius stage invariably biramous, a condition
which is retained in the adult Cladocera. Similarly the uniramous
walking legs of many Decapoda pass through a biramous stage during
development, the outer branches or exopodites of the limbs being
suppressed subsequently, while the primitively biramous condition of the
thoracic limbs is retained in the adults of the Schizopoda, which
doubtless own a common ancestry with the Decapoda. The only Crustacean
limb which appears to be constantly uniramous both in larval and adult
life is the first pair of antennae.
We are reduced, therefore, to two types—the foliaceous and biramous. Sir
E. Ray Lankester,[6] in one of his most incisive morphological essays,
has explained how these two types are really fundamentally the same. He
compares, for instance, the foliaceous first maxillipede (Fig. 1, A), or
the second maxilla (Fig. 1, B) of a Decapod, _e.g._ _Astacus_, with the
foliaceous thoracic limb of _Branchipus_ (Fig. 1, D), and with the
typically biramous first maxillipede of a Schizopod (Fig. 1, F).
In each case there is present, on the outer edge of the limb, one or
more projections or epipodites which are generally specialised for
respiratory purposes, and may carry the gills. The 6th and 5th “endites”
in the foliaceous limb (Fig. 1, D) are compared with the exopodite and
endopodite respectively of the biramous limb, while the endites 4–1 of
the foliaceous limb are found in the basal joints of the biramous limb.
Lankester presumes that the biramous type of limb throughout has been
derived from the foliaceous type by the suppression of the endites 1–4,
as discrete rami, and the exaggerated development of the endites 5 and
6, as above indicated.
[Illustration:
FIG. 1.—Appendages of Crustacea (=A-G=) and Trilobita (=H=). =A=,
First maxillipede of _Astacus_; =B=, second maxilla of _Astacus_;
=C=, second walking leg of _Astacus_; =D=, thoracic limb of
_Branchipus_; =E=, first maxillipede of _Mysis_; =F=, first
maxillipede of _Gnathophausia_; =G=, thoracic limb of _Nebalia_;
=H=, thoracic limb of _Triarthrus_. _bp_, basipodite; _br_, bract;
_cp_, carpopodite; _cxp_, coxopodite; _cx.s_, coxopoditic setae;
_dp_, dactylopodite; _end_, endopodite; _ep_, epipodite; _ex_,
exopodite; _ip_, ischiopodite; _mp_, meropodite; _pp_, propodite;
1–6, the six endites.
]
The essential fact that the two types of limb are built on the same plan
may be considered as established; but it may be urged that the biramous
type represents this common plan more nearly than the foliaceous. It is,
at any rate, certain that in the maxillipedes of the Decapoda we witness
the conversion of the biramous type into the foliaceous by the expansion
of the basal joints concomitantly with the assumption by the
maxillipedes of masticatory functions. Thus in the Decapoda the first
maxillipede is decidedly foliaceous owing to the expanded “gnathobases”
(Fig. 1, A, _bp_, _cxp_), and the second maxillipedes are flattened,
with their basal joints somewhat expanded and furnished with biting
hairs; but in the “Schizopoda” (_e.g._ _Mysis_) the first maxillipede is
a typical biramous limb, though the expanded gnathobases in some forms
are beginning to project (Fig. 1, E), while the limb following, which
corresponds to the second maxillipede of Decapods, is simply a biramous
swimming leg. Besides this obvious conversion of a biramous into a
foliaceous limb, further evidence of the fundamental character of the
biramous type is found, first, in its invariable occurrence in the
Nauplius stage, which does not necessarily mean that the ancestors of
the Crustacea possessed this type of limb in the adult, but which does
imply that this type of limb was possessed at some period of life by the
common ancestral Crustacean; and, second, the limbs of the Trilobita, a
group which probably stands near the origin of the Crustacea, have been
shown by Beecher to conform to the biramous type (Fig. 1, H).
Furthermore, the thoracic limbs of Nebalia, an animal which combines
many of the characteristics of Entomostraca and Malacostraca, and is
therefore considered as a primitive type, despite their flattened
character, are really built upon a biramous plan (Fig. 1, G).
In conclusion, we may point out that this view of the Crustacean limb,
as essentially a biramous structure, agrees with the conclusion derived
from our consideration of the segmentation of the body, and points less
to the Branchiopoda as primitive Crustacea and more to some generalised
Malacostracan type.
So far we have shortly dealt with those systems of organs which are
clearly affected by the metameric segmentation of the body; we must now
expose the condition of the =body-cavity= to a similar scrutiny. If we
remove the external integument of a Crustacean, we find that the
internal organs do not lie in a spacious and discrete body-cavity, as is
the case in the Annelids and Vertebrates, but that they are packed
together in an irregular system of spaces (“haemocoel”) in communication
with the vascular system and containing blood. In the Entomostraca and
smaller forms generally, a definite vascular system hardly exists,
though a central heart and artery may serve to propel the blood through
the irregular lacunae of the body-cavity; but in the larger Malacostraca
a complicated system of arteries may be present which pour the blood
into fairly definitely arranged spaces surrounding the chief organs.
These spaces return the blood to the pericardium, and so to the heart
again through the apertures or ostia which pierce its walls.
This condition of the body-cavity or haemocoel is reproduced in the
adults of all Arthropods, but in some of them by following the
development we can trace the steps by which the true coelom is replaced
by the haemocoel. In the embryos of all Arthropods except the Crustacea,
a true closed metamerically segmented coelom is formed as a split in the
mesodermal embryonic layer of cells, distinct from the vascular system.
During the course of development the segmented coelomic spaces and their
walls give rise to the reproductive organs and to certain renal organs
in _Peripatus_, Myriapoda, and Arachnida (nephridia and coxal glands),
but the general body-cavity is formed as an extension of the vascular
system, which is laid down outside the coelom by a canaliculisation of
the extra-coelomic mesoderm. In the embryos of the Crustacea, however,
there is never at any time a closed segmented coelom, and in this
respect the Crustacea differ from all other Arthropods. The only clear
instance in which metamerically repeated mesodermal cavities have been
seen in the embryo Crustacean is that of _Astacus_; here Reichenbach[7]
states that in the abdomen segmental cavities are formed which
subsequently break down; but even in this instance no connexion has been
shown to subsist between these embryonic cavities and the reproductive
and excretory organs of the adult.
Since the connexion between the coelom and the excretory organs is
always a very close one throughout the animal kingdom, interest
naturally centres upon the =renal organs= in Crustacea, and it has been
suggested that these organs in Crustacea represent the sole remains,
with the possible exception of the gonads, of the coelom. Since, at any
rate, a part of the kidneys appears to be developed as a closed sac in
the mesoderm, and since they possess a possible segmental value, this
suggestion is plausible; but, on the other hand, since there are never
more than two pairs of kidneys, and since they are totally unconnected
with the gonads or with any other indication of a segmented coelom, the
suggestion remains purely hypothetical.
The renal organs of the Crustacea, excluding the Malpighian tubes
present in some Amphipods which open into the alimentary canal, and
resemble the Malpighian tubes of Insects, consist of two pairs—the
antennary gland, opening at the base of the second antenna, and the
maxillary gland, opening on the second maxilla. These two pairs of
glands rarely subsist together in the adult condition, though this is
said to be the case in _Nebalia_ and possibly _Mysis_; the antennary
glands are characteristic of adult Malacostraca[8] and the larvae of the
Entomostraca, while the maxillary glands (“shell-glands”) are present in
adult Entomostraca and larval Malacostraca, that is to say, the one pair
replaces the other in the two great subdivisions of the Crustacea. The
shell-gland of the Entomostraca is a simple structure consisting of a
coiled tube opening to the exterior on the external branch of the second
maxilla, and ending blindly in a dilated vesicle, the end-sac. The
antennary gland of the Malacostraca is usually more complicated: these
complications have been studied especially by Weldon,[9] Allen, and
Marchal[10] in the Decapoda. In a number of forms we have a tube opening
to the exterior at the base of the second antenna, and expanding within
to form a spacious bladder into which the coiled tubular part of the
kidney opens, while at the extremity of this coiled portion is the
vesicle called the end-sac. This arrangement may be modified; thus in
_Palaemon_ Weldon described the two glands as fusing together above and
below the oesophagus, the dorsal commissure expanding into a huge sac
stretching dorsally down the length of the body. This closed sac with
excretory functions thus comes to resemble a coelomic cavity, and the
view that it is really coelomic has indeed been upheld.
A modified form of this view is that of Vejdovský, who describes a
funnel-apparatus leading from the coiled tube into the end-sac of the
antennary gland of Amphipods; he regards the end-sac alone as
representing the coelom, while the funnel and coiled tube represent the
kidney opening into it.
Not very much is known of the development of these various structures.
Some authors have considered that both antennary and maxillary glands
are developed in the embryo from ectodermal inpushings, but the more
recent observations of Waite[11] on _Homarus americanus_ indicate that
the antennary gland at any rate is a composite structure, formed by an
ectodermal ingrowth which meets a mesodermal strand, and from the latter
are produced the end-sac and perhaps the tubular excretory portions of
the gland with their derivatives.
With regard to the possible metameric repetition of the renal organs, it
is of interest to note that by feeding _Mysis_ and _Nebalia_ on carmine,
excretory glands of a simple character were observed by Metschnikoff
situated at the bases of the thoracic limbs.
The _alimentary canal_ of the Crustacea is a straight tube composed of
three parts—a mid-gut derived from the endoderm of the embryo, and a
fore- and hind-gut formed by ectodermal invaginations in the embryo
which push into and fuse with the endodermal canal. The regions of the
fore- and hind-gut can be recognised in the adult by the fact of their
being lined with the chitinous investment which is continued over the
external surface of the body forming the hard exoskeleton, while the
mid-gut is naked. The chitinous lining of fore- and hind-gut is shed
whenever the animal moults. In the Malacostraca, in which a complicated
“gastric mill” may be present, the chitinous lining of this part of the
gut is thrown into ridges bearing teeth, and this stomach in the crabs
and lobsters reaches a high degree of complication and materially
assists the mastication of the food. The gut is furnished with a number
of secretory and metabolic glands; the so-called liver, which is
probably a hepatopancreas, opening into the anterior end of the mid-gut,
is directed forwards in most Entomostraca and backwards in the
Malacostraca, in the Decapoda developing into a complicated branching
organ which fills a large part of the thorax. In the Decapoda peculiar
vermiform caeca of doubtful function are present, a pair of which open
into the gut anteriorly where fore-passes into mid-gut, and a single
asymmetrically placed caecum opens posteriorly into the alimentary tract
where mid- passes into hind-gut.
The disposition of these caeca, marking as they do the morphological
position of fore-, mid-, and hind-gut, is of peculiar interest owing to
the variations exhibited. From some unpublished drawings of Mr. E. H.
Schuster, which he kindly lent me, it appears that in certain Decapods,
_e.g._ _Callianassa subterranea_, the length of the mid-gut between the
anterior and posterior caeca is very long; in _Carcinus maenas_ it is
considerable; in _Maia squinado_ it is greatly reduced, the caeca being
closely approximated; while in _Galathea strigosa_ the caeca are greatly
reduced, and the mid-gut as a separate entity has almost disappeared.
The relation of these variations to the habits of the different crabs
and to their modes of development is unknown.
The =reproductive organs= usually make their appearance as a small
paired group of mesodermal cells in the thorax comparatively late in
life; and neither in their early development nor in the adult condition
do they show any clear signs of segmentation or any connexion with a
coelomic cavity. The sexes are usually separate, but hermaphroditism
occurs sporadically in many forms, and as a normal condition in some
parasitic groups (see pp. 105–107). The adult gonads are generally
simple paired tubes, from the walls of which the germ-cells are
produced, and as these grow and come to maturity they fill up the
cavities of the tubes; special nutrient cells are rarely differentiated,
though in some cases (_e.g._ Cladocera) a few ova nourish themselves by
devouring their sister-cells (see p. 44). The oviducts and vasa
deferentia are formed as simple outgrowths from the gonadial tubes,
which acquire an opening to the exterior; they are usually poorly
supplied with accessory glands, the epithelium of the canals often
supplying albuminous secretions for cementing the eggs together, while
the lining of the vasa deferentia may be instrumental in the formation
of spermatophores for transferring large packets of spermatozoa to the
female. In the vast majority of Crustacea copulation takes place, the
male passing spermatophores or free spermatozoa into special receptacles
(spermathecae), or into the oviducts of the female. The spermatophores
are hollow chitinous structures in which the spermatozoa are packed;
they are often very large and assume characteristic shapes, especially
in the Decapoda.
The spermatozoa show a great variety of structure, but they conform to
two chief types—the filiform, which are provided with a long whip-like
flagellum; and the amoeboid, which are furnished with radiating
pseudopodia, and are much slower in their movements. The amoeboid
spermatozoa of some of the Decapoda contain in the cell-body a peculiar
chitinous capsule, and Koltzoff[12] has observed that when the
spermatozoon has settled upon the surface of the egg the chitinous
capsule becomes suddenly exceedingly hygroscopic, swells up, and
explodes, driving the head of the spermatozoon into the egg. We cannot
enter here into a description of the embryological changes by which the
egg is converted into the adult form. Crustacean eggs as a whole contain
a large quantity of yolk, but in some forms total segmentation occurs in
the early stages, which is converted later into the pyramidal type,
_i.e._ the blastomeres are arranged round the edge, and the yolk in the
centre is only partly segmented to correspond with them. The eggs during
the early stages of development are in almost all cases (except
Branchiura, p. 77, and _Anaspides_, p. 116) carried about by the female
either in a brood-pouch (Branchiopoda, Ostracoda, Cirripedia,
Phyllocarida, Peracarida), or agglutinated to the hind legs or some
other part of the body (Copepoda, Eucarida), or in a chamber formed from
the maxillipedes (Stomatopoda). Development may be direct, without a
complicated metamorphosis, or indirect, the larva hatching out in a form
totally different to the adult state, and attaining the latter by a
series of transformations and moults. The various larval forms will be
described under the headings of the several orders.
The =respiratory organs= are typically branchiae, _i.e._ branched
filamentous or foliaceous processes of the body-surface through which
the blood circulates, and is brought into close relation with the oxygen
dissolved in the water. In most of the smaller Entomostraca no special
branchiae are present, the interchange of gases taking place over the
whole body-surface; but in the Malacostraca the gills may reach a high
degree of specialisation. They are usually attached to the bases of the
thoracic limbs (“podobranchiae”), to the body-wall at the bases of these
limbs, often in two series (“arthrobranchiae”), and to the body-wall
some way above the limb-articulations (“pleurobranchiae”). In an ideal
scheme each thoracic appendage beginning with the first maxillipede
would possess a podobranch, two arthrobranchs, and a pleurobranch, but
the full complement of gills is never present, various members of the
series being suppressed in the various orders, and thus giving rise to
“branchial formulae” typical of the different groups.
After this brief survey of Crustacean organisation we may be able to
form an opinion upon the position of the Crustacea relative to other
Arthropoda, and upon the question debated some time ago in the pages of
_Natural Science_[13] whether the Arthropoda constitute a natural group.
The Crustacea plainly agree with all the other Arthropoda in the
possession of a rigid exoskeleton segmented into a number of somites, in
the possession of jointed appendages metamerically repeated, some of
which are modified to act as jaws; they further agree in the general
correspondence of the number of segments of which the body is
primitively composed; the condition of the body-cavity or haemocoel is
also similar in the adult state. An apparently fundamental difference is
found in the entire absence during development of a segmented coelom,
but since this organ breaks down and is much reduced in all adult
Arthropods, it is not difficult to believe that its actual formation in
the embryo as a distinct structure might have been secondarily
suppressed in Crustacea.
The method of breathing by gills is paralleled by the respiratory
structures found in _Limulus_ and Scorpions; the transition, if it
occurred, from branchiae to tracheae cannot, it is true, be traced, but
the separation of Arthropods into phyletically distinct groups of
Tracheata and Branchiata on this single characteristic is inadmissible.
On the whole the Crustacea may be considered as Arthropods whose
progenitors are to be sought for among the Trilobita, from whose near
relations also probably sprang _Limulus_ and the Arachnids.