Xll CONTENTS. 



LETTER XII. 



PAGE 



Their nervous system and senses: happiness of Molluscs, 175, 176: 

 instincts, 176 — 179 : nervous system, 180 — 182 : senses, touch, 182 

 —184: taste, 184: smell, 184—187: sight, 187—196: eyes of the 

 bivalves, 187 : of the Cephalopods, 188 : of the Gasteropods, 189 — 192 : 

 their number and position, 193, 194: not produced by innate desires, 

 194—196: hearing, 197—200 : noises of Mollusca, 200, 201. . 175 



LETTER XIII. 



Their circulating system, 202 — 204 : circulation in the Cephalopods, 

 204—208 : in the Gasteropods, 209—212 : in the Conchifera, 212— 

 214 : in the Tunicata, 214 — 216 : more modern views of the circula- 

 tion in the Mollusca, 216—221 : the pulse in Mollusca, 221, 222 : the 

 blood, 223, 224. . . . . . . .202 



LETTER XIV. 



Their secretions : shell, 225—227 : pearl, 227—233 : colours, 233, 

 234 : mutability of the Cephalopods, 235 — 238 : inky secretions, 238 — 

 241 : purples, 241 — 244 : urinary secretions, 244 — 246 : mucus, 246, 

 247 : phosphorescence, 247—251 : electricity, 251 : heat, 251. . 225 



LETTER XV. 



Their respiration, 252, 253 : vibratile cilia, the functions of, 253 — 

 255: effects of respiration, 255 — 257: can be long suspended, 257: 

 torpidity, 258 — 261 : hybernation, 261 — 266 : relation between respira- 

 tion and locomotion, 267 : relation of respiration to habitat, 267, 268. 252 



LETTER XVI. 



Organs of respiration : pulmoniferous Mollusca, 269, 270 : branchi- 

 ferous Mollusca, 270 : Mollusca with external branchiae, 270 — 272 : with 

 covered branchiae, 273 : with internal branchiae, 273, 274 : branchiae 



