CONTENTS. Xlll 



PAGE 



of the Cephalopods, 274 : of the bivalves, 275 277 : of the Brachiopods, 

 277, 278: of the Tunicata, 278284: mixture of function in the lungs 

 and gills, 284 : evidenced in amphibious Mollusca, 284 288. . . 269 



APPENDIX. 



Species of the same genus inhabit different situations, 289 : species 

 found on land, in fresh and in salt water, 290 : fresh water genera with 

 salt water species, 290292 : sea genera with fresh water species, 292 : 

 the same species in salt and fresh water, 293 295. . . . 289 



LETTER XVII. 



Their food and digestive organs : of the Tunicata, 296 299 : of the 

 bivalves, 299304. . . . ... 296 



LETTER XVIII. 



Carnivorous Mollusca : Conchifera, 305 : Pectinibranchial Gastero- 

 pods, 305 : feed on bivalves, 306 : how they perforate the shell, 307 : 

 structure of the proboscis, 308, 309 : Mr. Hancock's discovery, 310 : 

 the Naticse, 310: the Bullse and Aplysise, 311 : the Vitrina and Tes- 

 tacellus, 312314 : the Pteropods, 314 : the Cephalopods, 314323. 305 



LETTER XIX. 



Phytivorous Mollusca, 324 : their proportion to the Zoophagous, 324 : 

 marine tribes, their food, 325 : land tribes, their food, 325, 326 : struc- 

 ture of the mouth and tongue, 326, 328 : of the stomach and alimen- 

 tary canal, 328 331 : of the liver, 331, 332 : gastro-vascular system, 

 332 334 : phytivorous Mollusca are occasionally animal feeders, 334 

 336: time of feeding, 336 338. . . . .. .324 



LETTER XX. 



Reproductive functions : first discovery of their origin from ova, 339 : 

 monoecious Mollusca, 340 350 : production of the Tunicata and their 

 metamorphoses, 340343 : alternating generations, 344 ; the Brachio- 

 poda, 345 : and bivalves, 345 348 ; viviparous bivalves, 348: prolificness 



