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THE LIFE OF CRUSTACEA
BY
W. T. CALMAN, D.Sc.
WITH THIRTY-TWO PLATES AND EIGHTY-FIVE FIGURES
METHUEN & CO. LTD.
36 ESSEX STREET W.C.
LONDON
_First Published in 1911_
PREFACE
This sketch of the Natural History of the Crustacea deals chiefly with
their habits and modes of life, and attempts to provide, for readers
unfamiliar with the technicalities of Zoology, an account of some of the
more important scientific problems suggested by a study of the living
animals in relation to their environment.
I am indebted to the Trustees of the British Museum for leave to
reproduce certain figures prepared for the "Guide to the Crustacea,
Arachnida, Onychophora, and Myriopoda exhibited in the Department of
Zoology"; also to Sir Ray Lankester, K.C.B., F.R.S., and to Messrs. A.
and C. Black for the use of a number of figures from my volume on
Crustacea in the "Treatise on Zoology," edited by Sir Ray Lankester.
The source of these figures is indicated in the explanation attached to
each. Of the remaining illustrations, some are reproduced from
photographs of specimens in the collection of the British Museum; the
others have been drawn from Nature, or copied from the original figures
of various authors, by Miss Gertrude M. Woodward, to whom I am much
indebted for the care and skill which she has given to their
preparation.
W. T. C.
CONTENTS
CHAPTER PAGE
I. INTRODUCTORY 1
II. THE LOBSTER AS A TYPE OF CRUSTACEA 6
III. THE CLASSIFICATION OF CRUSTACEA 34
IV. THE METAMORPHOSES OF CRUSTACEA 66
V. CRUSTACEA OF THE SEASHORE 88
VI. CRUSTACEA OF THE DEEP SEA 117
VII. FLOATING CRUSTACEA OF THE OPEN SEA 138
VIII. CRUSTACEA OF FRESH WATERS 157
IX. CRUSTACEA OF THE LAND 188
X. CRUSTACEA AS PARASITES AND MESSMATES 207
XI. CRUSTACEA IN RELATION TO MAN 237
XII. CRUSTACEA OF THE PAST 256
APPENDIX:
I. METHODS OF COLLECTING AND PRESERVING CRUSTACEA 271
II. NOTES ON BOOKS 277
INDEX 280
LIST OF ILLUSTRATIONS IN THE TEXT
FIG. PAGE
1. THE COMMON LOBSTER (_Homarus gammarus_), FEMALE,
FROM THE SIDE 7
2. ONE OF THE ABDOMINAL SOMITES OF THE LOBSTER, WITH ITS
APPENDAGES, SEPARATED AND VIEWED FROM IN FRONT 9
3. THIRD MAXILLIPED OF LOBSTER 11
4. WALKING LEGS OF LOBSTER 12
5. APPENDAGES OF LOBSTER IN FRONT OF THIRD MAXILLIPED 13
6. DISSECTION OF MALE LOBSTER, FROM THE SIDE 16
7. GILLS OF THE LOBSTER, EXPOSED BY CUTTING AWAY THE
SIDE-FLAP OF THE CARAPACE (BRANCHIOSTEGITE) 18
8. FIRST LARVAL STAGE OF THE COMMON LOBSTER. x 4 28
9. SIDE-VIEW OF ROSTRUM OF (A) COMMON LOBSTER
(_Homarus gammarus_) AND (B) AMERICAN LOBSTER
(_Homarus americanus_) 32
10. THE "FAIRY SHRIMP" (_Chirocephalus diaphanus_), MALE. x 2 35
11. _Estheria obliqua_, ONE OF THE CONCHOSTRACA 36
12. _Daphnia pulex_, A COMMON SPECIES OF "WATER-FLEA."
MUCH ENLARGED 37
13. SHELLS OF OSTRACODA. MUCH ENLARGED 38
14. _Cyclops albidus_, A SPECIES OF COPEPOD FOUND IN FRESH
WATER 39
15. _Nebalia bipes._ ENLARGED 44
16. _Mysis relicta_, ONE OF THE MYSIDACEA. ENLARGED 47
17. _Gnathophausia willemoesii_, ONE OF THE DEEP-SEA MYSIDACEA.
HALF NATURAL SIZE 48
18. _Diastylis goodsiri_, ONE OF THE CUMACEA. ENLARGED 49
19. _Apseudes spinosus_, ONE OF THE TANAIDACEA. ENLARGED 50
20. A WOODLOUSE (_Porcellio scaber_), ONE OF THE ISOPODA.
ENLARGED 51
21. AN AMPHIPOD (_Gammarus locusta_). ENLARGED 53
22. TWO SPECIES OF CAPRELLIDAE 54
23. _Paracyamus boopis_, THE WHALE-LOUSE OF THE HUMPBACK
WHALE 55
24. _Meganyctiphanes norvegica_, ONE OF THE EUPHAUSIACEA.
TWICE NATURAL SIZE 56
25. LARVAL STAGES OF THE COMMON SHORE CRAB (_Carcinus
maenas_--SEE PLATE IX.) 68
26. LAST LARVAL STAGE OF THE COMMON PORCELAIN CRAB
(_Porcellana longicornis_--SEE FIG. 41, P. 113). x 9 70
27. FIRST LARVAL STAGE OF _Munida rugosa_ (SEE PLATE VI.) x 10 71
28. THE PHYLLOSOMA LARVA OF THE COMMON SPINY LOBSTER
(_Palinurus vulgaris_--SEE PLATE V.). MUCH ENLARGED 72
29. LARVAL STAGES OF THE PRAWN _Penaeus_ (SEE PLATE IV.). x 45 74
30. NEWLY-HATCHED YOUNG OF A CRAYFISH (_Astacus fluviatilis_).
ENLARGED 76
31. YOUNG SPECIMEN OF AN AFRICAN RIVER CRAB (_Potamon
johnstoni_), TAKEN FROM THE ABDOMEN OF THE MOTHER.
MUCH ENLARGED 78
32. EARLY LARVAL STAGE OF A SPECIES OF SQUILLA, PROBABLY
_S. dubia_. x 10 80
33. LARVAL STAGES OF THE BRINE SHRIMP (_Artemia salina_) 81
34. EARLY NAUPLIUS LARVA OF A COPEPOD (_Cyclops_). MUCH
ENLARGED 82
35. LARVAL STAGES OF THE COMMON ROCK BARNACLE
(_Balanus balanoides_--SEE PLATE III.) 83
36. A COMMON HERMIT CRAB (_Eupagurus bernhardus_) REMOVED
FROM THE SHELL 91
37. _Pylocheles miersii_, A SYMMETRICAL HERMIT CRAB 94
38. _Callianassa stebbingi_ (FEMALE), A SAND-BURROWING
THALASSINID FROM THE SOUTH COAST OF ENGLAND.
NATURAL SIZE 103
39. THE COMMON SAND-HOPPER (_Talitrus saltator_), MALE,
FROM THE SIDE. x 3 108
40. A, A PIECE OF A TROPICAL SEA-WEED (_Halimeda_); B, A
CRAB (_Huenia proteus_) WHICH LIVES AMONG THE FRONDS
OF _Halimeda_, AND CLOSELY RESEMBLES THEM IN FORM
AND COLOUR. REDUCED 110
41. THE COMMON PORCELAIN CRAB (_Porcellana longicornis_),
SLIGHTLY ENLARGED, AND ONE OF THE THIRD MAXILLIPEDS
DETACHED AND FURTHER ENLARGED TO SHOW
THE FRINGE OF LONG HAIRS 113
42. A DEEP-SEA LOBSTER (_Nephropsis stewartii_), FROM THE
BAY OF BENGAL. REDUCED 122
43. _Munidopsis regia_, A DEEP-SEA GALATHEID FROM THE BAY
OF BENGAL. REDUCED 123
44. _Thaumastocheles zaleucus._ REDUCED 129
45. A DEEP-SEA CRAB (_Platymaia wyville-thomsoni._) REDUCED 131
46. _Polycheles phosphorus_, ONE OF THE ERYONIDEA, FEMALE,
FROM THE INDIAN SEAS 133
47. _Eryon propinquus_, ONE OF THE FOSSIL ERYONIDEA, FROM
THE JURASSIC ROCKS OF SOLENHOFEN 135
48. _Conchoecia curta_, AN OSTRACOD OF THE PLANKTON. x 40 144
49. _Mimonectes loveni._ A FEMALE SPECIMEN SEEN FROM THE
SIDE AND FROM BELOW, SHOWING THE DISTENDED-BALLOON-LIKE
FORM OF THE ANTERIOR PART OF THE
BODY. x 3 145
50. THE ZOEA LARVA OF A SPECIES OF _Sergestes_, TAKEN BY
THE "CHALLENGER" EXPEDITION. x 25 146
51. THE NAUPLIUS LARVA OF A SPECIES OF BARNACLE OF
THE FAMILY LEPADIDAE, SHOWING GREATLY-DEVELOPED
SPINES. FROM A SPECIMEN TAKEN IN THE ATLANTIC
OCEAN, NEAR MADEIRA. x 11 147
52. _Calocalanus pavo_, ONE OF THE FREE-SWIMMING COPEPODA
OF THE PLANKTON. ENLARGED 148
53. _Copilia quadrata_ (FEMALE), A COPEPOD OF THE FAMILY
CORYCAEIDAE, SHOWING THE PAIR OF LARGE "TELESCOPIC"
EYES. x 20 153
54. _Phronima colletti_, MALE. FROM A SPECIMEN TAKEN IN
DEEP WATER NEAR THE CANARY ISLANDS. x 12 154
55. THE BRINE SHRIMP (_Artemia salina_) 164
56. _Chydorus sphaericus_, A COMMON SPECIES OF WATER-FLEA.
x 50 166
57. A WATER-FLEA (_Daphnia pulex_), FEMALE, WITH EPHIPPIUM
CONTAINING TWO "RESTING EGGS." x 20 167
58. _Bythotrephes longimanus_, FEMALE, WITH EMBRYOS IN THE
BROOD-SAC. x 12 169
59. _Diaptomus coeruleus_, FEMALE. x 25 171
60. _Asellus aquaticus_, FEMALE. x 4 173
61. MAP SHOWING THE DISTRIBUTION OF CRAYFISHES 175
62. A WELL SHRIMP (_Niphargus aquilex_). x 7. 185
63. THE SEA-SLATER (_Ligia oceanica_). ABOUT TWICE NATURAL
SIZE 200
64. STRUCTURE OF THE BREATHING ORGANS OF _Porcellio
scaber_ 202
65. _Armadillidium vulgare._ x 2-1/2 203
66. TWO BRANCHES OF A CORAL (_Seriatopora_) SHOWING
"GALLS" INHABITED BY THE CRAB _Hapalocarcinus
marsupialis_. ON THE RIGHT THE FEMALE CRAB,
EXTRACTED FROM THE GALL AND FURTHER ENLARGED 211
67. _Hyperia galba_, FEMALE. ENLARGED 213
68. A, THE CRAB _Melia tessellata_ CLINGING TO A BRANCH OF
CORAL, AND CARRYING IN EACH CLAW A LIVING SEA-ANEMONE;
B, ONE OF THE CLAWS FURTHER ENLARGED
TO SHOW THE WAY IN WHICH THE ANEMONE IS HELD 216
69. THE COMMON PEA CRAB (_Pinnotheres pisum_), FEMALE.
NATURAL SIZE 217
70. _Cirolana borealis._ ABOUT TWICE NATURAL SIZE 219
71. A, FRONT PART OF BODY OF A PRAWN (_Spirontocaris
polaris_), FROM ABOVE, SHOWING ON THE RIGHT SIDE A
SWELLING OF THE CARAPACE CAUSED BY THE PRESENCE OF THE
PARASITE _Bopyroides hippolytes_ IN THE GILL CHAMBER;
B, THE FEMALE PARASITE EXTRACTED AND FURTHER ENLARGED;
C, THE MALE PARASITE ON SAME SCALE AS THE FEMALE 222
72. A FISH-LOUSE (_Caligus rapax_), FEMALE. x 5 225
73. STAGES OF DEVELOPMENT OF _Lernaea branchialis_. F IS
SLIGHTLY, THE OTHER FIGURES GREATLY, ENLARGED 226
74. STAGES OF THE LIFE-HISTORY OF _Haemocera danae_, ONE
OF THE MONSTRILLIDAE 229
75. FREE-SWIMMING STAGES OF _Sacculina carcini_. MUCH
ENLARGED 232
76. EARLY STAGE OF _Sacculina_ WITHIN THE BODY OF A CRAB 234
77. ROSTRUM AND FORE PART OF CARAPACE, SEEN FROM ABOVE, OF
(A) RED-CLAWED CRAYFISH (_Astacus fluviatilis_) AND
(B) WHITE-CLAWED OR ENGLISH CRAYFISH
(_Astacus pallipes_) 242
78. THE COMMON SHRIMP (_Crangon vulgaris_). NATURAL SIZE 244
79. THE NORWEGIAN DEEP-WATER PRAWN (_Pandalus borealis_),
FEMALE 246
80. THE GRIBBLE (_Limnoria lignorum_). MUCH ENLARGED 254
81. RESTORATION OF A TRILOBITE (_Triarthrus becki_), SHOWING
THE APPENDAGES. UPPER SIDE ON RIGHT, UNDER SIDE ON
LEFT. SLIGHTLY ENLARGED 258
82. _Ceratiocaris papilio_, ONE OF THE FOSSIL PHYLLOCARIDA 262
83. _Pygocephalus cooperi_, FROM THE COAL-MEASURES: UNDER
SIDE OF A FEMALE SPECIMEN, SHOWING THE OVERLAPPING
PLATES OF THE BROOD-POUCH 263
84. THE TASMANIAN "MOUNTAIN SHRIMP" (_Anaspides tasmaniae_),
A LIVING REPRESENTATIVE OF THE SYNCARIDA.
SLIGHTLY ENLARGED 264
85. _Praeanaspides praecursor_, ONE OF THE FOSSIL SYNCARIDA,
FROM THE COAL-MEASURES OF DERBYSHIRE. SLIGHTLY
ENLARGED 265
FULL-PAGE PLATES
PLATE FACING PAGE
I. MALE AND FEMALE LOBSTERS, SHOWING THE DIFFERENCE IN THE
RELATIVE BREADTH OF THE ABDOMEN IN THE TWO SEXES. THIS
FIGURE ALSO ILLUSTRATES THE DISSIMILARITY OF THE LARGE
CLAWS, AND THE FACT THAT THE "CRUSHING CLAW" MAY BE ON
EITHER THE RIGHT OR LEFT SIDE OF THE BODY.
(_From Brit. Mus. Guide_) 26
II. _Apus cancriformis_ FROM KIRKCUDBRIGHTSHIRE. SLIGHTLY
ENLARGED 36
{ GROUP OF SPECIMENS OF THE GOOSE BARNACLE }
{ (_Lepas anatifera_), ONE SHOWING THE CIRRI }
{ EXTENDED AS IN LIFE. NATURAL SIZE. }
III. { (_From Brit. Mus. Guide_) } 42
{ }
{ GROUP OF A COMMON SPECIES OF ACORN-SHELL OR ROCK }
{ BARNACLE (_Balanus balanoides_). NATURAL SIZE }
IV. _Penaeus caramote_, FROM THE MEDITERRANEAN. ABOUT
HALF NATURAL SIZE. (_From Brit. Mus. Guide_) 57
V. THE COMMON SPINY LOBSTER (_Palinurus vulgaris_).
MUCH REDUCED. (_From Brit. Mus. Guide_) 59
VI. _Munida rugosa._ BRITISH. REDUCED 60
VII. THE COMMON HERMIT CRAB, _Eupagurus bernhardus_, IN THE
SHELL OF A WHELK. REDUCED. (_From Brit. Mus. Guide_) 62
VIII. THE "NORTHERN STONE CRAB," _Lithodes maia_. MUCH REDUCED.
THE LAST PAIR OF LEGS ARE FOLDED OUT OF SIGHT IN THE
GILL CHAMBERS. (_From Brit. Mus. Guide_) 63
{ THE COMMON SHORE CRAB (_Carcinus maenas_). REDUCED }
IX. { }
{ _Dromia vulgaris_, CARRYING ON ITS BACK A MASS OF } 68
{ THE SPONGE, _Clione celata_. BRITISH. REDUCED }
X. _Calappa flammea._ BRAZIL. REDUCED 72
XI. THE GIANT JAPANESE CRAB, _Macrocheira kaempferi_. MALE. THE
SCALE OF THE FIGURE IS GIVEN BY A TWO-FOOT RULE PLACED
BELOW THE SPECIMEN. (_From Brit. Mus. Guide_) 76
XII. _Squilla mantis_, FROM THE MEDITERRANEAN. ABOUT ONE-HALF
NATURAL SIZE. (_From Brit. Mus. Guide_) 82
{ A SWIMMING CRAB, _Portunus depurator_. BRITISH. }
{ REDUCED }
XIII. { }
{ A SPIDER CRAB, _Maia squinado_, DRESSED IN FRAGMENTS } 96
{ OF WEEDS. BRITISH. REDUCED }
{ _Corystes cassivelaunus._ MALE (ON LEFT) AND FEMALE }
{ (ON RIGHT). BRITISH. REDUCED }
XIV. { } 100
{ _Albunea symnista_, ONE OF THE HIPPIDEA. INDIAN }
{ SEAS. REDUCED }
{ _Ocypode cursor._ WEST AFRICA. REDUCED }
XV. { }
{ _Gelasimus tangeri._ MALE ABOVE, FEMALE BELOW. } 104
{ WEST AFRICA. REDUCED }
XVI. A DEEP-SEA HERMIT CRAB, _Parapagurus pilosimanus_,
SHELTERED BY A COLONY OF _Epizoanthus_. FROM DEEP WATER
OFF THE WEST OF IRELAND. SLIGHTLY REDUCED 124
XVII. A DEEP-SEA PRAWN, _Nematocarcinus undulatipes_.
SLIGHTLY REDUCED. (_From Brit. Mus. Guide_) 128
XVIII. _Bathynomus giganteus._ ABOUT ONE-HALF NATURAL SIZE.
(_From Lankester's "Treatise on Zoology," after
Milne-Edwards and Bouvier_) 131
{ _Latreillia elegans_, ONE OF THE DROMIACEA WHICH }
{ RESEMBLES A SPIDER CRAB. FROM THE MEDITERRANEAN. }
XIX. { NATURAL SIZE } 155
{ }
{ THE GULF-WEED CRAB, _Planes minutus_. SLIGHTLY }
{ ENLARGED }
{ THE MURRAY RIVER "LOBSTER," _Astacopsis spinifer_. }
XX. { NEW SOUTH WALES. MUCH REDUCED } 177
{ THE LAND CRAYFISH, _Engaeus cunicularis_. TASMANIA. }
{ NATURAL SIZE }
XXI. _Palaemon jamaicensis._ A LARGE FRESHWATER
PRAWN OF THE FAMILY PALAEMONIDAE. WEST
INDIES. MUCH REDUCED 179
XXII. _Atya scabra._ A FRESHWATER PRAWN OF THE
FAMILY ATYIDAE, WEST INDIES. REDUCED 180
{ THE RIVER CRAB OF SOUTHERN EUROPE, _Potamon edule_ }
{ (OR _Telphusa fluviatilis_). REDUCED }
XXIII.{ } 182
{ _Sesarma chiragra._ A FRESHWATER CRAB OF THE FAMILY }
{ GRAPSIDAE. FROM BRAZIL. SLIGHTLY REDUCED }
XXIV. _AEglea laevis._ SOUTH AMERICA. NATURAL SIZE 184
XXV. THE BLIND CRAYFISH OF THE MAMMOTH CAVE OF KENTUCKY,
_Cambarus pellucidus_. NATURAL SIZE 186
{ A WEST INDIAN LAND CRAB, _Gecarcinus ruricola_. }
XXVI. { REDUCED } 190
{ }
{ A LAND HERMIT CRAB, _Coenobita rugosa_. REDUCED }
XXVII. THE COCONUT CRAB, _Birgus latro_. MUCH REDUCED 196
XXVIII. GROUP OF BARNACLES, _Coronula diadema_, ON THE
SKIN OF A WHALE. JAPAN. REDUCED 209
{ _Cymothoa oestrum._ AN ISOPOD PARASITE OF FISH. }
{ SLIGHTLY ENLARGED }
XXIX. { } 220
{ _Sacculina carcini_ ATTACHED UNDER THE ABDOMEN }
{ OF A COMMON SHORE CRAB. REDUCED }
XXX. THE "NORWAY LOBSTER," _Nephrops norvegicus_. ABOUT
ONE-THIRD NATURAL SIZE. (_From Brit. Mus. Guide_) 240
XXXI. THE COMMON EDIBLE CRAB, _Cancer pagurus_. BRITISH.
MUCH REDUCED 248
XXXII. PIECE OF TIMBER FROM RYDE PIER, SHOWING DAMAGE CAUSED
BY _Limnoria_ AND _Chelura_. (_From Brit. Mus. Guide_) 255
THE LIFE OF CRUSTACEA
CHAPTER I
INTRODUCTORY
Everyone has some acquaintance with the animals that are grouped by
naturalists under the name Crustacea. The edible Crabs, Lobsters,
Prawns, and Shrimps, are at least superficially familiar, either as
brought to the table or as displayed in the fishmonger's, and the most
unobservant of seaside visitors must have had his attention attracted by
living specimens of some of the more obtrusive species, such as the
common Shore Crab. Many, however, will be surprised to learn that the
Barnacles coating the rocks on the seashore, the Sand-hoppers of the
beach, and the Woodlice of our gardens, are members of the same class.
Still less is it suspected, by those who have not given special
attention to the subject, that the living species of the group number
many thousands, presenting strange diversities of structure and habits,
and playing important parts in the general economy of Nature.
In addition to those just mentioned, a few Crustacea are sufficiently
well known to be distinguished by popular names, such, for example, as
Crayfish and Hermit Crabs, but for the vast majority no names are
available except those of technical zoology. In the following pages,
therefore, while technical terms have been introduced as sparingly as
possible, the unfamiliarity of the animals themselves makes it needful
to use many unfamiliar names.
In the classification of the Animal Kingdom, the Crustacea form one of
the divisions of a comprehensive group, or Phylum, known as Arthropoda.
The typical members of this group have a more or less firm external
skeleton, the body is divided into segments, there are jointed limbs,
and some of these are modified to serve as jaws. The chief divisions or
classes of the Arthropoda are--(i.) _Insecta_, including Butterflies,
Moths, Bees, Wasps, Flies, Beetles, and the like; (ii.) _Chilopoda_, or
Centipedes; (iii.) _Diplopoda_, or Millipedes[1]; (iv.) _Onychophora_,
including the curious worm-like _Peripatus_; (v.) _Arachnida_, or
Scorpions, Spiders, Mites, and their allies; and (vi.) _Crustacea_.
[1] The Chilopoda and Diplopoda are sometimes regarded as forming a
single class--Myriopoda.
It is not easy to summarize in a few words the characters common to all
Crustacea, and distinguishing them from the other groups of Arthropoda.
As a rough guide to classification, it is useful to remember that an
Insect can generally be recognized by having three pairs of walking
legs, an Arachnid by having four pairs, and a Centipede or Millipede by
having a great many pairs, all nearly alike. The Crustacea, on the other
hand, show great diversity in the number and arrangement of their
walking or swimming legs, but they rarely show any special resemblance
to those of the other large groups of Arthropoda. Thus, for example, a
common species of Woodlouse, _Armadillidium vulgare_, is very similar at
first sight to the Millipede _Glomeris marginata_, but it has only seven
pairs of walking legs, while the Millipede has seventeen or nineteen
pairs.
More precisely, it may be said of the great majority of Crustacea that
they are aquatic animals, breathing by gills or by the general surface
of the body, having two pairs of "feelers," or antennae, on the front
part of the head, and at least three pairs of jaws. Exceptions to each
of these statements will be mentioned in later chapters in dealing with
parasites and other highly modified types. In such cases, however, the
larval or young stages afford indications of affinity, and comparison
with less modified forms enables us to trace a connection with the
typical Crustacea.
The best way to form a conception of a group of animals, however, is not
to attempt in the first place to define its limits, but to begin by
studying the structure of some typical and central species, and
afterwards to note the divergences from this type presented by other
members of the group. Speaking very generally, it may be said that these
divergences are of two kinds. On the one hand there are characters that
have no apparent relation to the animal's habits and mode of life, and
on the other hand there are modifications of structure which are more or
less plainly of use to the animal. It is to characters of the former
class that we look for evidence of an animal's affinities, and it is
upon them that our systems of classification are chiefly based. The
characters of the second class--"adaptive" characters, as they are
called--become of importance when we study the animal "as a going
concern," so to speak, and endeavour to understand how its life is
carried on in relation to its surroundings.
In pursuance of this plan of study, the next chapter will be devoted to
a description of the Common Lobster as a type of the Crustacea. In the
third chapter a survey of the classification of the group will be given;
since, however, the characters on which the classification is based
cannot be explained fully without entering into technical details which
are beyond the scope of this work, this survey will be restricted to
what is necessary for comprehension of the succeeding chapters. In the
fourth chapter some account is given of the young or larval stages of
Crustacea, and of the changes they undergo in the course of
development.
In the next five chapters the Crustacea are classified according to
their habitats, and those living in the shallow waters, the depths, and
the surface of the ocean, in the fresh waters, and on land, are
discussed in turn; while a separate chapter is devoted to the curious
forms that live as parasites on, or as associates with, other animals.
The last two chapters deal respectively with the Crustacea as they
affect man, and with the past history of the group as revealed by fossil
remains.