THE ORIGIN OF LIFE 269 



are eminently cosmopolitan, occurring over vastly 

 wide areas of sea-bottom, and are very variable, they 

 would afford a better test of theories of derivation 

 than any that can be obtained from the more locally 

 distributed and less variable animals of higher grade. 

 I was much struck with this recently, in examining a 

 series of Foraminifera from the Cretaceous of Mani- 

 toba, and comparing them with the varietal forms 

 of the same species in the interior of Nebraska, 500 

 miles to the south, and with those of the English 

 chalk and 01 the modern seas. In all these different 

 times and places we had the same species. In all 

 they existed under so many varietal forms passing 

 into each other, that in former times every species 

 had been multiplied into several. Yet in all, the 

 identical varietal forms were repeated with the most 

 minute markings alike. Here were at once con- 

 stancy the most remarkable and variations the most 

 extensive. If we dwell on the one to the exclusion 

 of the other, we reach only one-sided conclusions, 

 imperfect and unsatisfactory. By taking both in con- 

 nection we can alone realize the full significance of 

 the facts. We cannot yet obtain such series for all 

 geological time ; but it may even now be worth while 

 to inquire, What do we know as to any mc^dification 



