Volume Ii

THE

EVOLUTION THEORY

DR. AUGUST WEISMANN

PROFESSOR OF ZOOLOGY IN THE UNIVERSITY OF FREIBURG IN BREISGAU

TRANSLATED WITH THE AUTHOR'S CO-OPERATION

J. ARTHUR THOMSON

REGIUS PROFESSOR OF NATURAL HISTORY IN THE UNIVERSITY OF ABERDEEN

AND

MARGARET R. THOMSON

ILLUSTRATED

IN TWO VOLUMES

VOL. II

LONDON EDWARD ARNOLD 41 & 43 MADDOX STREET, BOND STREET, W.

1904

All rights reserved

CONTENTS

LECTURE PAGE

XX. REGENERATION 1

XXI. REGENERATION (continued) 23

XXII. SHARE OF THE PARENTS IN THE BUILDING UP OF THE OFFSPRING 37

XXIII. EXAMINATION OF THE HYPOTHESIS OF THE TRANSMISSIBILITY OF FUNCTIONAL MODIFICATIONS 62

XXIV. OBJECTIONS TO THE THESIS THAT FUNCTIONAL MODIFICATIONS ARE NOT TRANSMITTED 80

XXV. GERMINAL SELECTION 113

XXVI. GERMINAL SELECTION (continued) 136

XXVII. THE BIOGENETIC LAW 159

XXVIII. THE GENERAL SIGNIFICANCE OF AMPHIMIXIS 192

XXIX. THE GENERAL SIGNIFICANCE OF AMPHIMIXIS (continued) 210

XXX. IN-BREEDING, PARTHENOGENESIS, ASEXUAL REPRODUCTION, AND THEIR CONSEQUENCES 238

XXXI. THE INFLUENCES OF ENVIRONMENT 265

XXXII. INFLUENCE OF ISOLATION ON THE FORMATION OF SPECIES 280

XXXIII. ORIGIN OF THE SPECIFIC TYPE 299

XXXIV. ORIGIN OF THE SPECIFIC TYPE (continued) 330

XXXV. THE ORIGIN AND THE EXTINCTION OF SPECIES 346

XXXVI. SPONTANEOUS GENERATION AND EVOLUTION: CONCLUSION 364

INDEX 397

LIST OF ILLUSTRATIONS

FIGURE PAGE

35 B (repeated). Hydra viridis, the Green Freshwater Polyp. 4

96. A Planarian cut transversely into nine pieces 6

97. A Planarian which has been divided into two by a longitudinal cut 14

98. The leg of a Crab, adapted for self-mutilation or autotomy 17

99. Regeneration of the lens in a Newt's eye 21

100. Regeneration of Planarians 25

101. A Starfish arm 27

76 (repeated). Diagram of the maturation divisions of the ovum 39

82 (repeated). Fertilization in the Lily 59

91 (repeated). Hind-leg of a Grasshopper 83

102. Brush and comb on the leg of a Bee 84

103. Claw on the leg of a 'Beach-fly' 85

104. Digging leg of the Mole-cricket 86

105. Ovary of a fertile Queen-Ant and ovaries of a Worker 91

106. Three Workers of the same species of Indian Ant 97

107 A, B. Larva of a Caddis-fly 105

107 C. Leptocephalus stage of an American Eel 133

108. Nauplius larva of one of the lower Crustaceans 161

109 A, B. Metamorphosis of one of the higher Crustacea, a Shrimp 162

109 C. Second Zoæa stage 163

109 D, E. Mysis-stage and fully-formed Shrimp 164

70 (repeated). Daphnella 166

110. The largest of the Daphnids (Leptodora hyalina), with summer ova beneath the shell 166

111. Nauplius larva from the winter egg of Leptodora hyalina 167

112. Development of the parasitic Crustacean Sacculina carcini 168, 242

113. The two sexes of the parasitic Crustacean Chondracanthus gibbosus 170

114. Zoæa-larva of a Crab 171

115. Caterpillar of the Humming-bird Hawk-moth Macroglossa stellatarum 178

3 (repeated). Full-grown caterpillar of the Eyed Hawk-moth 178

4 (repeated). Full-grown caterpillar of the Eyed Hawk-moth 179

8 (repeated). Caterpillars of the Buckthorn Hawk-moth 179

116. Development of the eye-spots in the caterpillar of the Elephant Hawk-moth Chærocampa elpenor 180

117. Caterpillar of the Bed-straw Hawk-moth Deilephila galii 181

118. Two stages in the life-history of the Spurge Hawk-moth Deilephila euphorbiæ 182

119. Caterpillar of the Poplar Hawk-moth Smerinthus populi 184

120. A, Symmetrical, and B, asymmetrical curve of frequency 207

121. Life-cycle of Coccidium lithobii 214

122. Conjugation of a Coccidium (Adelea ovata) 216

123. Conjugation of Coccidium proprium 218

79 (repeated). The two maturation divisions of the 'drone eggs' 236

124. Alternation of generations in a Gall-wasp 245

125. The two kinds of galls formed by the species 246

126. Ovipositor and ovum of the two generations of the same species of Gall-wasp 247

127. Life-cycle of the Vine-pest (Phylloxera vastatrix) 249

128. Heterostylism 254

38 (repeated). A fragment of a Lichen 261

129. Aberration of Arctia caja, produced by low temperature 276

130. Skeleton of a Greenland Whale, with the contour of the body 313

131. Peridineæ: species of Ceratium 325