The most important part, however, of a zoologist's work is not the giving of instruction, but the labour of original research, to which we have already alluded; not the mere communication of information, but the task of adding to the general store of knowledge; not teaching, but discovery. The work of the man of science is, in fact, within the limits of his own department, the work of seeking after truth. INDEX A. Acoelomata, 37. Adaptation, 13. Alternation of Generations, 57, 137. Amoeba, 35, 45. Amphibia, 152-154. Ancestors, 40, 42. Animalcule (minute animal), 49. Anisopleura, 29. Annelids, 72. Annulosa, 69. Ants, 92. Appendages, 77. Arachnida (spiders), 84. Arthropoda, 33, 76. Ascidians, 33, 44, 135. Asexual reproduction, 55. Atavistic variation, 27. Azygo-branchiata, 29. B. Balanoglossus, 133, 143. Barnacles, 79, 80. Bees, 91. Beetles, 95. Bell Animalcule, 49. Birds, 156. Bivalve shell-fish, 23, 27, 107. Body-cavity, 34, 37, 38. Body-cavity (diagrams), 38, 139. Body-rings, or "segments," 69. Brachiopoda, 33, 43, 44, 117. Bryozoa, 33, 44, 119. Buds, 55. Butterflies, 89, 93. C. Cat, fur of black, 160. Cell, 11. Cell-types, 49. Cephalodiscus, 145. Cephalopoda, 113. Centipedes, 77. Chætopoda, 71. Chalk, 46. Chordata, 33, 44, 135, 143-146. Cilia, 42, 43, 48, 65. Classes, 33. Classification, 30. Classification, tables of, 30, 44, 52, 62, 67, 75, 116, 118, 121, 134, 146, 164, 179. Coelenterata, 33, 44, 53. Coelomata, 37, 44. Cockle, 111. Colony, 57. Corals, 59. Corallines, 56, 58. Corticata (or Infusoria), 47. Crabs, 81. Crocodile, 11. Crustacea, 78-83. Ctenophora, 60, 62. D. Degeneracy, 28, 172-180. Development by metamorphosis (change of form), 41, 89. Development, direct, 45. Dicyemidæ, 34. Diploblastic (two-layered), 34, 36. Diploblastic larva, 41. Duck-mole, 160. E. Earthworm, 74. Earthworm, diagrammatic section of, to show position of body-cavity, 38. Echinodermata, 33, 43, 44, 122. Ectoderm, outer or skin-layer of adult animals and larvæ (corresponding with the epiblast of embryos in the egg), 34, 37, 41, 139. Eleutheroblasteæ (hydroid animals which throw off "free buds"), 56. Embryology, 45. Encrinites, 131. Endoderm, inner or digestive layer of adult animals and larvæ (corresponding with the hypoblast of embryos in the egg), 37, 41, 139. Enteron, 36. Environment, 26. Errantia, or Wandering Annelids, 72. Euthyneura, 100. F. Families, 33. Fertility, 32. Feathers, 157. Feather-stars, 132. Fishes, 150-152. Flagella, 65. Flat-fish, 23. Foraminifera, 46. Frogs, 38, 152. G.