CHAPTER VI.. The Distribution and the ætiology of the Crayfishes • 288

The Distribution and the Ætiology of the Crayfishes • 288

NOTES • 347

BIBLIOGRAPHY • 357

INDEX • 363

LIST OF WOODCUTS.

Frontispiece. THE COMMON CRAYFISH, Astacus fluviatilis, (MALE)

1. Astacus fluviatilis. SIDE VIEW OF THE MALE • 6

2. — — DORSAL VIEWS OF MALE AND FEMALE • 18

3. — — VENTRAL VIEWS OF MALE AND FEMALE • 21

4. — — THE GILLS • 26

5. — — DISSECTION FROM THE DORSAL SIDE (MALE) • 28

6. — — LONGITUDINAL VERTICAL SECTION OF THE ALIMENTARY CANAL • 29

7. — — A GASTROLITH OR “CRAB’S EYE” • 30

8. — — ATTACHMENT OF YOUNG TO SWIMMERET OF MOTHER • 41

9. — — STRUCTURE OF THE STOMACH • 53

10. — — LONGITUDINAL SECTION OF THE STOMACH • 56

11. — — ROOF OF THE STOMACH, FROM WITHIN • 60

12. — — DISSECTION FROM THE SIDE (MALE) • 62

13. — — ALIMENTARY CANAL FROM ABOVE • 65

14. — — BLOOD CORPUSCLES • 68

15. — — TRANSVERSE SECTION OF THORAX • 70

16. — — THE HEART • 72

17. — — STRUCTURE OF THE GILLS • 76

18. — — THE GREEN GLAND • 83

19. — — MUSCULAR TISSUE • 91

20. — — MUSCLES OF CHELA • 93

21. — — ARTICULATION OF ABDOMINAL SOMITES • 97

22. — — MUSCULAR SYSTEM • 100

23. — — NERVE FIBRES • 102

24. — — NERVE GANGLIA • 103

25. — — NERVOUS SYSTEM • 104

26. — — OLFACTORY AND AUDITORY ORGANS • 114

27. — — AUDITORY SAC • 117

28. — — STRUCTURE OF EYE • 119

29. — — DIAGRAM OF EYE • 123

30. — — FEMALE REPRODUCTIVE ORGANS • 129

31. — — MALE REPRODUCTIVE ORGANS • 130

32. — — STRUCTURE OF OVARY • 131

33. — — STRUCTURE OF TESTIS • 132

34. — — SPERMATOZOA • 134

35. — — THE LAST THORACIC STERNUM IN THE MALE AND FEMALE • 136

36. — — TRANSVERSE SECTION OF ABDOMEN • 142

37. — — ABDOMINAL APPENDAGES • 144

38. — — CONNECTION BETWEEN THORAX AND ABDOMEN • 151

39. — — CEPHALOTHORACIC STERNA AND ENDOPHRAGMAL SYSTEM • 153

40. — — OPHTHALMIC AND ANTENNULARY SOMITES • 156

41. — — THE ROSTRUM • 157

42. — — A SEGMENT OF THE ENDOPHRAGMAL SYSTEM • 159

43. — — LONGITUDINAL SECTION OF CEPHALOTHORAX • 162

44. — — THE THIRD MAXILLIPEDE • 164

45. — — THE FIRST AND SECOND MAXILLIPEDES • 166

46. — — THE SECOND AMBULATORY LEG • 169

47. — — THE MANDIBLE AND MAXILLÆ • 171

48. — — THE EYE-STALK, ANTENNULE, AND ANTENNA • 172

49. — — BLOOD CORPUSCLES • 176

50. — — EPITHELIUM • 178

51. — — CONNECTIVE TISSUE • 179

52. — — MUSCULAR TISSUE • 181

53. — — MUSCULAR TISSUE • 182

54. — — NERVE GANGLIA • 188

55. — — NERVE FIBRES • 189

56. — — CUTICULAR TISSUE • 191

57. — — SECTIONS OF EMBRYOS • 208

58. — — EARLIER STAGES OF DEVELOPMENT • 210

59. — — LATER STAGES OF DEVELOPMENT • 216

60. — — NEWLY HATCHED YOUNG • 220

61. Astacus torrentium, Astacus nobilis, and Astacus nigrescens. COMPARATIVE VIEWS OF THE CARAPACE, THIRD ABDOMINAL SOMITE, AND TELSON • 233

62. — —, — —, and — — COMPARATIVE VIEWS OF THE FIRST AND SECOND ABDOMINAL APPENDAGES OF THE MALE • 245

63. Cambarus Clarkii • 248

64. Parastacus brasiliensis • 250

65. Astacoides madagascarensis • 251

66. DIAGRAM OF THE MORPHOLOGICAL RELATIONS OF THE Astacidæ • 253

67. Homarus vulgaris • 258

68. Parastacus, Nephrops, and Palæmon. PODOBRANCHIÆ • 259

69. Nephrops norvegicus • 260

70. Palinurus vulgaris • 262

71. Palæmon jamaicensis • 269

72. Cancer pagurus • 273

73. Penæus • 281

74. Cancer pagurus. DEVELOPMENT • 282

75. Astacus leptodactylis • 301

76. Australian Crayfish • 307

77. MAP OF THE DISTRIBUTION OF CRAYFISHES • 309

78. Cambarus. WALKING LEG • 312

79. Palæmon jamaicensis • 329

80. Pseudastacus pustulosus and Eryma modestiformis • 340

81. Hoploparia longimana • 342

THE CRAYFISH:

AN INTRODUCTION TO THE STUDY OF ZOOLOGY.