EARLY REPTILIAN FOSSILS. 75 



ters, just as we see the foetus of a high animal 

 passing through various inferior stages before it 

 reach its proper mature character. The lines, 

 moreover, being independent of each other, and 

 not quite uniform as to the stages of animality 

 through which they pass, it follows that, unless we 

 knew of some law governing their different gesta- 

 tive periods, we are not entitled to look for the 

 first occiurence of their various ichthyic, reptilian, 

 and mammalian sections, in any order as regards 

 each other, even though we could be sure (which 

 we are not) that we are surveying a geographical 

 region where they all started fair in the race of 

 progressive organization. Hence it is that, though 

 the batrachia are usually placed by zoologists at 

 the bottom of the list of reptilian orders, I attach 

 little importance to their vestiges being now found 

 so low. All that I think we can expect is, that, 

 in a particular area where we have reason to be- 

 lieve that the lines have started abreast, they should 

 all reach their various grades nearly about one 

 time, or what may be considered as one time com- 

 pared with the whole extent of geological chrono- 

 logy. And such appears to be pretty much the 

 case in those regions which geologists have ex- 

 plored. 



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