AKNIYERSAET ADDEESS OE THE PKESIDENT. 75 



or about half of the whole class Aves. The difficulties of classifj-- 

 ing them are so great that no two authors agree as to the number 

 or limits of the families into which they can be divided. They 

 have undoubtedly great powers of migration, and many can adapt 

 themselves to changed conditions, some of the higher forms, for 

 instance, the crows, being omnivorous and ranging all over the 

 world ; but very many genera are restricted in food and range, and 

 appear no better adapted to survive extensive changes than mammals 

 or reptiles are. It may be safely inferred that the Passeres are of 

 more recent origin than other orders of birds, and probably than 

 any other order of Yertebrata. Geological evidence, so far as it is 

 available, coincides with this ; for no remains of the order have been 

 found below the Miocene. It must be remembered, however, that 

 remains of birds from older systems are Yerj rare. 



It will thus be observed that Sclater's regions, adopted by Wallace 

 and others, were chiefly based on what is very probably the most 

 recently developed group of vertebrata, perhaps the most recent in 

 the animal kingdom. 



Huxley's scheme of zoological distribution, to which reference 

 has already been made, was first proposed in a paper on the 

 affinities and distribution of Alecteromorjphce and Ileteromor^hce, or 

 what are commonly known as Gallinaceous birds and their allies ; 

 but it was shown that other groups of the animal kingdom confirm 

 the scheme first suggested by the distribution of these birds, j^ow 

 as Huxley's system differs widely from Sclater's, and as both were 

 suggested by diff'erent orders of the same class (birds*'), it is wise 

 to examine a little more closely how far the distribution of other 

 classes or orders agrees with that of the Passeres. 



I have already noticed the great importance attached by Wallace 

 to the mammalia. But there are serious difficulties in the way of 

 accepting the Passerine regions for mammals. In the first place, the 

 difference between the mammals of the Australian region and those 

 of all the other regions is far greater than the distinctions between 

 the latter, and point, as Huxley has noticed, to the Australian 

 region having been divided from the rest of the world by a barrier 



* Eeiclienow (Zool. Jahrb, hi. p. 671, 1888) has proposed the following 

 regions for birds : — 

 Arctic, 



Western, — North and South America. 

 Eastern, — Africa, Europe, and Asia. 

 Southern, —Australia, New Zealand, New Guinea, &c. 

 Madagascar. 

 Antarctic. 



