37S CLASSIFICATION. Cuap. XIII. 



CHAPTER XIII. 



MUTUAL AFFINITIES OF ORGANIC BEINGS: MOEPHOLOGY : EM- 

 BRYOLOGY: RUDIMENTARY ORGANS. 



Classifiriition. Groups subordinate fn Group? — Natural System— Rnlcs ;ind Difficiiltica 

 in Chissilio.'UiDii. explained on tlio Theory of Descent with Moditicalion — Classi- 

 fication of Vnrieliew— Descent alwavH used in Classification — Analofrical or Adap- 

 tive Characters — Affinities, General. Complex, and liadiatincj— Extinction sepa- 

 rates and defines Groups — Morpliolou'V- between members of the same Class, be- 

 tween parts of the same Individual — Embryoloiry. Laws of. explained by Vari.i- 

 tions not supervening at an early Age, and being inherited at a corresponding 

 Age — Kudimeutary Organs ; their Origin explainuU — Suinniar3'. 



Classijtcation. 



From a very remote period in the history of the world or- 

 ganic beings have resembled each other iu descending degrees, 

 so that they can be classed in groups under groups, litis 

 classiftcation is not arbitrary, like the grouping of the stars in 

 constellations. The existence of groups would have been of 

 simple signification, if one group had been exclusively fitted to 

 inhtibit the land, and another tlie water; one to feed on flesh, 

 another on vegetable matter, and so on ; but the case is widely 

 different in Nature ; for it is notorious how commonly members 

 of even the same sub-group have dilfercnt habits. In the second 

 :ind fourth chapters, on Variation and on Natural Selection, I 

 have attempted to show that within each country it is the 

 Avidel^'-ranging, the much-dilfused and common, that is, the 

 dominant sj^ccies belonging to the larger genera in each class, 

 which vary most. The varieties, or incipient species, thus pro- 

 duced, ultimately become converted into new and distinct spe- 

 cies ; and these, on the principle of inheritance, tend to pro 

 duce other new and dominant species. Consequently, the 

 groups which are now large, and which generally include many 

 dominant sjiecies, tend to go on increasing in size. I further 

 attempted to show that, from the varying descendants of each 

 species t tying to occupy as many and as different places as pos- 



