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 original 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. 



ORGAJ^IZATION AND HABITS. 



REPEODLTTIVE 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 POAVERS. 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 f' w^hile 

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

 indiA'idual being at the same time male and female, but 

 incapable of fertilizing itself. Some of these even change 

 their sex at diff'erent periods, — the ValvatidcB being at 



