CONTENTS. Xlll 



P A G K 



of the Cephalopods, 274 : of the Li valves, 275 — 277 : of the Brachiopods, 

 277, 278 : of the Tunicata, 278—284 : 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, 290—292 : 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, 299—304. . ..... 296 



LETTER XVIII. 



Carnivorous Mollusca : Conchifcra, 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 Naticte, 310: the Bullae and Aplysiae, 311 : the Vitrina and Tes- 

 tacellus, 312—314 : the Pteropods, 314 : the Cephalopods, 314—323. 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, 340—343 : alternating generations, 344 ; the Brachio- 

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



