XXIV 



INTRODUCTION. [CH. 



The general rule is not to alter the name which has 

 been first given to any species, in order to establish a con- 

 ventional right of priority and to prevent confusion. But 

 this rule is not without an exception — especially where 

 the origmal name has been accidentally misspelt, either 

 by the author or printer. Thus " Suediense " has been 

 properly changed to Suecicum ; and '' Syndosmya " ought 

 to be replaced by Syndesmia. Such trivial corrections 

 are necessary in the works of our best authors ; and in 

 those which have largely benefited the cause of science, 



" non ego paucis 



Offendar maculis, quas aut incuria fudit 

 Aut humaua parum cavit natura." 



CHAPTER II. 



ORGANIZATION AND HABITS. 



REPaODUCTIYE SYSTEM. FECUI^DITY. HYBRIDISM. PEOGRESSIYE 



DETELOPJIENT. ORGANS OF SIGHT HEARING SMELL LOCO- 

 MOTION. FOOD. SIZE. HABITAT. CARE OF YOUNG. SOCIA- 

 BILITY. ESTIVATION AND HIBERNATION. NESTS. MODES OF 



ATTACK AND DEFENCE. RENEWAL OF PARTS. PHOSPHORES- 

 CENCE. PERFORATING POWERS. OCCASIONAL APPEARANCE AND 



DISAPPEARANCE. TENACITY OF LIFE. AGE. RESUME. 



Reproductive system. — The modes of propagation 

 among the Mollusoa are various. In the case of uni- 

 valves, many of them [e, g, the Whelk tribe) have distinct 

 sexes, and are what botanists term " dioecious f while 

 most of the land-snails are nearly ^^ monoecious," each 

 individual being at the same time male and female, but 

 incapable of fertilizing itself. Some of these even change 

 their sex at different periods, — the Valvatidae being at 



