GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 135 



iiving; why ancient and extinct forms often tend to fill 

 up gaps between existing forms, sometimes blending two 

 groups, previously classed as distinct, into one; but more 

 commonly bringing them only a little closer together. 

 The more ancient a form is, the more often it stands in 

 some degree intermediate between groups now distinct; 

 for the more ancient a form is, the more nearly it will 

 be related to, and consequently resemble, the common 

 progenitor of groups since become widely divergent. 

 Extinct forms are seldom directly intermediate between 

 existing forms; but are intermediate only by a long 

 and circuitous course through other extinct and different 

 forms. We can clearly see why the organic remains of 

 closely consecutive formations are closely allied; for they 

 are closely linked together by generation. We can clearly 

 see why the remains of an intermediate formation are 

 intermediate in character. 



The inhabitants of the world at each successive period 

 in its history have beaten their predecessors in the race 

 for life, and are, in so far, higher in the scale, and their 

 structure has generally become more specialized; and this 

 may account for the common belief held by so many 

 jjaleontologists that organization on the whole has pro- 

 gressed. Extinct and ancient animals resemble to a 

 certain extent the embryos of the more recent animals 

 belonging to the same classes, and this wonderful fact 

 receives a simple explanation according to our views. 

 The succession of the same types of structure within the 

 same areas during the later geological periods ceases 

 to be mysterious, and is intelligible on the principle of 

 inheritance. 



If then the geological record be as imperfect as many 



— SOIEKCB — 23 



