GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 125 



development of these organisms up to the standard -which 

 they had then reached. When advanced up to any given 

 point, there is no necessity, on the theory of natural se- 

 lection, for their further continued progress; though they 

 will, during each successive age, have to be slightly mod- 

 ified, so as to hold their places in relation to slight 

 changes in their conditions. The foregoing objections 

 hinge on the question whether we really know how 

 old the world is, and at what period the various forms 

 of life first appeared; and this may well be disputed. 



The problem whether organization on the whole has 

 advanced is in many ways excessively intricate. The 

 geological record, at all times imperfect, does not extend 

 far enough back to show with unmistakable clearness 

 that within the known history of the world organization 

 has largely advanced. Even at the present day, looking 

 to members of the same class, naturalists are not unani- 

 mous which forms ought to be ranked as highest: thus, 

 some look at the selaceans or sharks, from their approach 

 in some important points of structure to reptiles, as the 

 highest fish; others look at the teleosteans as the highest. 

 The ganoids stand intermediate between the selaceans and 

 teleosteans; the latter at the present day are largely pre- 

 ponderant in number; but formerly selaceans and ganoids 

 alone existed; and in this case, according to the standard 

 of highness chosen, so will it be said that fishes have 

 advanced or retrograded in organization. To attempt to 

 compare members of distinct types in the scale of high- 

 ness seems hopeless; who will decide whether a cuttle- 

 fish be higher than a bee — that insect which the great 

 Von Bare believed to be "in fact more highly organized 

 than a fish, although upon another type"? In the com- 



