92 EVOLUTION OF TO-DA Y. 



only are required to produce much change. If this 

 were true we would only expect to find evidence of 

 the periods of rest, the periods of change being too 

 brief to give much chance for preservation. While, 

 then, fossils do not show the numerous stages of a 

 slow evolution, it is possible that the fossil record 

 may be in harmony with this saltatory evolution. 



But even with this modified and more favorable 

 form of evolution in mind, the record of paleon- 

 tology cannot be regarded otherwise than as re- 

 markably imperfect. Its imperfection is indeed a 

 necessity for evolution. Nor can there be the 

 slightest doubt as to the teaching of recent years 

 on this matter. All evidence from every source 

 emphasizes the fact that the paleontological record 

 is very imperfect ; that the few animals which we 

 have preserved are almost as nothing compared 

 with the countless myriads which have disappeared 

 and left no trace. Indeed recent years would indi- 

 cate that this imperfection is even greater than 

 assumed by Darwin. The discovery, in quite a 

 number of cases, of a single imperfect specimen 

 of an animal in a bed of rocks whose accumulation 

 must have taken thousands of years, is a slight indi- 

 cation of what we may look for in this direction. 

 The causes of this imperfection are very varied. 

 The chief are as follows: (i) Only those animals 

 which possess some sort of hard skeleton can be 

 preserved as fossils, soft animals leaving almost no 

 impression in the sedimentary rocks. This is 

 demonstrated by the fact that about nine tenths of 

 the orders which are entirely unrepresented in the 



