xxxvi THE VOYAGE OF H.M.S. CHALLENGER. 



hemispheres are numerous, and will be still more increased by future investigations. A 

 certain number of the species are no doubt more localised ; those will be chiefly such as 

 have been derived, and are not yet far removed in their organization, from littoral forms. 

 Others, which may be supposed to have been derived from pelagic surface fish, may have 

 been as widely distributed, almost from the beginning of their existence, as their ancestors. 

 At present, however, our knowledge of the actual distribution of deep-sea fishes is much 

 too imperfect to be used as a safe basis for further generalisations. 



