414 Life and Immortality. 



Thus it follows that the animals of any given formation, 

 and the plants as well, where the records are preserved, are 

 more like those of the next formation below and of the next 

 formation above, than they are like any others. This fact of 

 itself is an inexplicable one. But if we believe that the 

 animals and plants of any given formation are, in part at 

 any rate, the lineal descendants of those of the preceding, 

 and the progenitors, also in part at least, of those of the suc- 

 ceeding formation, then the fact is readily comprehensible. 

 So frequently confronted is the palaeontologist with the phe- 

 nomenon of closely-related forms, especially of animals, 

 succeeding one another in point of time, that he is compelled 

 to believe that such forms have been developed from some 

 common ancestral type by some process of evolution. Upon 

 no other theory can we comprehend why the Post-Tertiary 

 mammals of South America should consist of edentates, 

 llamas, tapirs, peccaries, platyrhine monkeys and other forms 

 now characterizing this continent, while those of Australia 

 should be exclusively referable to the order of marsupials ; 

 and on no other view can we explain the common occur- 

 rence of transitional forms of life, filling in the gaps between 

 groups now widely distinct. But, on the other hand, there 

 are facts which point clearly to the presence of some other 

 law than that of evolution, and probably of a deeper and 

 more far-reaching character. No theory of evolution can 

 offer a satisfactory explanation for the constant introduction 

 throughout geological time of new forms of life, which do 

 not appear to be preceded by pre-existent allied types. The 

 graptolites and trilobites have no known predecessors, and 

 leave no known successors. Insects appear suddenly in the 

 Devonian, and spiders and myriopods in the Carboniferous, 

 but all under well -differentiated and highly -specialized 

 forms. With equal apparent suddenness the Dibranchiate 

 Cephalopods show themselves in the older Mesozoic de- 

 posits, and no known type of the Palaeozoic period can 

 be pointed to as a possible ancestor. And so does the 



