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 original name has been accidentally misspelt, either 

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

 properly changed to Sueticum', 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 humana parum cavit natura." 



CHAPTER II. 



ORGANIZATION AND HABITS. 



REPRODUCTIVE SYSTEM. FECUNDITY. HYBRIDISM. PROGRESSIVE 

 DEVELOPMENT. 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 Mollusca 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 ;" 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 Valvatidce being at 



