Xll CONTENTS. 



LETTER XII. 



PAGE 



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

 instincts, 176 179 : nervous system, 180 182 : senses, toueh, 182 

 184: taste, 184: smell, 184187: sight, 187196: eyes of the 

 bivalves, 187 : of the Cephalopods, 188 : of the Gasteropods, 189192 : 

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

 194196: hearing, 197200 : noises of Mollusca, 200, 201. . 175 



LETTER XIII. 



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

 204208 ; in the Gasteropods, 209212 : in the Conchifera, 212 

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

 tion in the Mollusca, 216221 : the pulse in Mollusca, 221, 222 : the 

 blood, 223, 224. . . 202 



LETTER XIV. 



Their secretions : shell, 225227 : pearl, 227 233 : colours, 233, 

 234 : mutability of the Cephalopods, 235238 : inky secretions, 238 

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

 247 : phosphorescence, 247251 : 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 



