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demn. It is indeed well nigh incredible that any such 

 strictures could ever have heen advanced; for it must 

 surely have occurred to the most superficial inquirer, 

 that genera, after all, cannot he homogeneous, — seeing 

 that they are necessarily composed of detached species, 

 no two of which are precisely similar, even in the few 

 structural details which may have been accidentally 

 chosen for generic diagnostics. How is it possible, 

 therefore, that mere groups, even though they be in 

 accordance with Nature, should be so far isolated and 

 uniform iq their character as to occupy an analogous 

 position to that of the absolutely independent species (of 

 distinct origins) which they severally contain ? 



Taking the preceding considerations into account, the 

 question will perhaps arise, — How then is a genus to be 

 defined? To which I may reply that, were I asked 

 whether genera had any real existence in the animate 

 world, my answer woidd be that they imdoubtedly have, 

 •. — though not in the sense (which is so commonly 

 supposed) of abrupt and disconnected groups. I con- 

 ceive them to be gradually formed nuclei, through the 

 gathering together of creatures which more or less 

 resemble each other, around a central type : they are 

 the dilatations (to use our late simile) along a chain 

 which is itself composed of separate, though dififerently 

 shaped links, — the links being the actual species them- 

 selves, and the swellings, or nodes, the slowly developed 

 genera into which they naturally fall. When I say 



I 



