FORMS ALLIED TO AMMONITES. 



217 



advantage which would be established by selection. If 

 other palaeontologists consider the fluctuations of form 

 accompanying the relaxation of the closed spiral as evinc- 

 ing the decline of the group, no contradiction seems to 

 be imphed, for what was originally used as an ad- 

 vantage by natural selection, proved injurious in its con- 

 sequences. 



As we have seen, the earliest states are obliterated to 



such a degree by curtailment of development that the 

 indication of the nature of the progenitors continually 

 diminishes. But our theory necessarily leads to the 

 conviction that the families within which we have as yet 

 been able to compare Ontogenesis with Phylogenesis, 

 constantly approximate in their origin, and vindicate the 



