PREFACE. IX 



confined to exhibit the grand divisions in philoso- 

 phical connection. As regards, however, the im- 

 portant distinctions of form and aggregation of 

 forms, o£ species and genus, I have thought it right 

 to exercise my own judgment. Wherever I have 

 used the term sub-species, I use it in the sense of a 

 permanent varieti/. The negro is a sub-species of 

 the species man. A sub-species has no independent 

 specific existence, yet has a permanent specific 

 appearance, though passing into, and propagating 

 with the other forms, whether sub-species, or simple 

 varieties included in the particular species to which 

 it belongs. A species, on the other hand, is defined, 

 unalterable, original, approaching, but never unit- 

 ing. Varieties are forms depending on local or 

 accidental causes, diverging from the normal type, 

 but often, and with facility returning to it. As 

 regards character, certain organs are specific in 

 some genera or even families, and generic in others. 

 Thus the eye is specific in the family Naticidae, 

 generic in most of the Gasteropodous tribes. So 

 also with colour and habit. Colour appears to be 

 specific in Natica, generic in Fusus. This law 



