X26 THE GENESIS OF SPECIES. [Chap. 



not ; as also does the distinctness of forms formerly sup- 

 posed to constitute connecting links. For, it must not 

 be forgotten that, if species have manifested themselves 

 generally by gradual and minute modificiitions, then the 

 absence, not in one, but in all cases, of such connecting 

 links, is a phenomenon which remains to be accounted for. 

 It appears then that, apart from f(jrtuitous clianges, 

 there are certain difliculties in the way of accepting ex- 

 tremely minute modifications of any kind, altliougli these 

 difliculties may not be insuperable. Something, at all 

 events, is to be said in favor of tlie opinion tliat sudden 

 and appreciable changes have, from time to time, occurred, 

 however they may have been induced. Marked races have 

 undoubtedly so arisen (some striking instances having been 

 here recorded), and it is at least conceivable tliat such may 

 be the mode of specific manifestation generally, tlie pos- 

 sible conditions as to which will be considered in a later 

 chapter. 



