A VIEW IN PERSPECTIVE. 163 



fauna. The Quaternary (10) has certainly lasted a 

 great many thousands of years, but in comparison 

 with the immense periods of the earlier ages, it is 

 very short. It was with the Quaternary, indeed with 

 the later part of the Quaternary, that the strictly 

 modern fauna (i. e. the modern species) appeared, 

 and we may say, therefore, that the duration of the 

 present geological age is very short compared with 

 the immense periods of time that have preceded it. 



The modern fauna is regarded as an impoverished 

 one. Of course there seem to be more animals and 

 more species to-day than ever before, but this is due 

 largely to the fact that we have the animals them- 

 selves to study to-day in profusion, while of the past 

 we have only here and there a specimen. In variety of 

 form the geological ages certainly surpassed the pres- 

 ent. There are but few classes in which there has not 

 been such a great extinction of orders in the past 

 that the representatives remaining are to be regarded 

 as fragments. Most of the invertebrates reached 

 their culmination in the geological ages, and many 

 of them have been for a long time on the decline. 

 Even of the vertebrates, every class has been in much 

 higher state of development in the past than at 

 present. The fishes belonged to the Devonian (3), 

 though one order has subsequently greatly expanded 

 since then (bony fishes, in the Cretaceous (8). The 

 amphibians belonged to the Triassic (6), the reptiles 

 to the Jurassic (7), while the mammals existed in 

 greater profusion in the Tertiary than they do to- 

 day. More than one third of the orders of the ver- 

 tebrates have become extinct, and of those that 



