CONTENTS. xi 



Invertebrates. 



Mollusca : Cephalopods, gastropods, 163; acephala, 164. Arthro- 

 pods : Simple eye, 164 ; compound eyes of insects and crustaceans, 

 165 ; origin of compound eye, 167. 



Evolution of the Eye. 



(1) Invertebrate eye, 167. Steps of evolution illustrated, 168. (2) 

 Vertebrate eye, 170. Several steps of evolution illustrated, 171. 

 Transition from the invertebrate to the vertebrate eye, 172. Further 

 evolution of the vertebrate eye, 173. 



SECTION VII. 



Sense of Hearing and its Organ, the Ear. 



Structure of human ear, exterior ear, mid-ear, 174. Ossicles, in- 

 terior ear, or labyrinth, 176. Bony labyrinth, membranous labyrinth, 

 178. Membranous cochlea, 179. Mode of action of the whole, dis- 

 tinctive functions of the parts, 181. 



Comparative Morphology and Physiology of the Ear. 



Mammals, birds, reptiles, 183. Fishes, invertebrates, insects, 184. 

 Crustacea, mollusca, 185. Mosquito, 186. Diagram illustrating suc- 

 cessive simplification, 187. 



SECTION VIII. 

 Lower Senses. 



Sense of Smell. — Nostril, 188 Smelling, 190. Comparative phys- 

 iology of smell, keenness of smell, how judged of, 191. Invertebrates, 

 193. 



Sense of Taste. — Analysis of this sense, mixed with feeling, with 

 smell, 194. Examples of pure tastes, 195. Papilla: of the tongue, 

 196. Comparative physiology of taste, 197. 



Sense of Touch. — Analysis of this sense, mixture of many sensa- 

 tions, 198. General sensibility vs. special sense of touch, general or- 

 gan of this sense, 199. Special organ, 200. Minimum tactile, double 

 tactile images, 201. Comparative physiology of touch in vertebrates, 

 202 ; in invertebrates, 203. 



SECTION IX. 



The Voice and its Organ, the Larynx. 



(1) The Simple Voice : Larynx, its position and relation, 204. 

 Structure, 206. Glottis and vocal cords, 207. Their action in vocali- 

 zation, 208. Muscles of the larynx and how they act, 209. (2) Song : 

 Larynx as a musical instrument, 210. (3) Speech, 211 ; Vowel 

 sounds, 212. Consonants, 213. 



