PEDIGREES AND RELATIONSHIPS 31 



Although this number largely exceeds that of the Amphibia 

 (frogs, toads, salamanders, etc.), which was 633 in 1882, and 

 now, perhaps, approaches 700, it is incomparably inferior to that 

 of the other three great vertebrate classes. For instance, so 

 long ago as the year 1870, Dr. A. Giinther estimated the number 

 of known species of fishes at 9000, and at the present day the 

 estimate would be very much larger. As regards birds (in 

 which, it should be observed, species are often separated on 

 slight characters), the number in the passerine and " picarian " 

 groups alone was given in 190c as 6487. Of mammals (to 

 which the same remark applies) considerably over 7000 species, 

 inclusive of extinct forms, were catalogued in 1899 by Dr. E. L. 

 Trouessart, and the number has since been increased. 



One feature is very noticeable in all the five vertebrate 

 classes, namely the predominance in point of numbers of one 

 particular order or group at the present day ; the great majority 

 of the representatives of such orders being of comparatively 

 small bodily size, although to a certain extent fishes and, among 

 reptiles, snakes form exceptions in the latter respect. 



Thus in the class Pisces we have the Teleostomi (bony 

 fishes), in the Amphibia the Ecaudata (frogs and toads), in the 

 Reptilia the Squamata (lizards and snakes), in Aves the 

 Passeres (perching birds), and in Mammalia the Rodentia 

 (rodents), as the overwhelmingly predominant group in point 

 of numbers. Each one of these groups, it should be added, is 

 of a highly specialised and essentially modern type. 



