IO8 EVOLUTION OF TO-DAY. 



solution, but has rather increased the difficulty by 

 increasing the extent of that ancient fauna, and 

 making it more like that existing to-day. Various 

 suggestions have been offered in explanation as de- 

 tailed above, which show that the problem is not 

 beyond solution, though they are hardly sufficient 

 to answer the objections. In spite of all, the Silurian 

 fauna is a surprise, and remains an unsolved problem. 



Turning now from these difficulties to positive evi- 

 dence, we next ask whether the recent discoverers 

 have been successful in finding any of the infinite 

 number of connecting links which the theory as- 

 sumes must have existed. And here we find that 

 paleontologists have been successful almost beyond 

 what could have been expected. Naturally it is 

 the vertebrates which have furnished most of the 

 evidence. They form a group which has been de- 

 veloped since the Silurian age, and are, moreover, 

 well adapted for preservation as fossils. Their bones 

 are found in abundance in the later formations, and 

 consequently are not metamorphosed. They are 

 better known and more studied than any other 

 group, and it is not surprising, therefore, that most 

 of our advance in paleontology has been in regard 

 to the vertebrates. The work of Cope, Marsh, and 

 Huxley has been so careful and painstaking, and 

 has been attended with so much success, that the 

 actual history of many of our vertebrates has been 

 accurately traced from fossil specimens. 



It is interesting to compare the state of our 

 knowledge to-day as to these intermediate types, 

 with that which the first edition of the " Origin of 



