1 1 8 E VOL UTION OF TO-DA Y. 



preponderance of specialized forms at all times over 

 generalized types, which the descent theory assumes 

 have existed ; the sudden appearance of various 

 highly-developed groups of animals and plants in 

 later times, such as the Teleost fishes and the Di- 

 cotyledonous plants abruptly in the Cretaceous with 

 absolutely no previous indications of their exist- 

 ence; the discrepancies as to the necessary amount 

 of time required for the development of the animal 

 kingdom, as estimated by Darwin, and the probable 

 age of the world as estimated by Sir William Thom- 

 son and others ; all of these difficulties, though 

 partially answered and certainly not unsurmountable, 

 still demand the attention of our scientists. 



On the other hand, the researches since Darwin 

 have proved that our paleontological record is very 

 imperfect, particularly at its beginning, where most 

 of the difficulties occur, and with this conclusion 

 many of them disappear. " As the area over which 

 accurate observations have been carried on extends, 

 and as fossiliferous rocks found in one locality fill 

 up the gaps left in another, the abrupt demarkations 

 between the fauna and flora of different epochs dis- 

 appear," and in numerous cases fossils have been 

 found to bridge over the gaps existing between 

 widely different groups. The patient study of 

 vertebrate fossils, which have left the most com- 

 plete record, has given a very exact history of their 

 development, a history becoming more and more 

 complete with the discovery of every new fossil. 

 The accumulation of the numerous links connecting 

 animals, and the satisfactory explanation which evolu- 



