THE CLASSIFICATION OF BIRDS, 259 
XVIII. Struthiones. 
This last order contains all the Ratite. 
It is absolutely impossible to arrange the Orders which make 
up the Class of Birds in any linear series which shall express 
their affinities. A few such groups may be placed in juxta- 
position, and then follows an inevitable break. On the theory 
of Evolution all the various groups now existing are, as it were, 
diverging twigs from small branches which sprang from larger 
branches, and these from others, and so on, till we come to the 
stem. It would manifestly be impossible so to enumerate the 
twigs of a tree in a linear series, that their linear succession 
should indicate their relative relationships to the trunk whence 
they all sprang. Just as difficult would it be to express the 
genetic relations of Birds by placing them in any linear series 
whatever, and the same may be said of their deeper structural 
resemblances even apart from the theory of Evolution. 
The first Order, Passeriformes, includes by far the greater 
number of birds, and all those spoken of in our introductory 
chapter as Passerine' birds. There are doubtless more than six 
thousand six hundred species. 
Following Mr. Seebohm, we divide this mass into three 
groups, of approximatively equal rank, as swborders, and name 
them: 1. Passeres, 2. Eurylemi, and 3. Trochili. The third 
suborder includes all the Humming-birds and no others. The 
second suborder takes in only the Broadbills and their allies pe 
while the first suborder includes all the other Passerine Birds. 
The characters of these groups are as follows :— 
Subclass I. CARINAT 2. 
Order I. PASSERIFORMES. 
Perching-birds, the young of which are born helpless and 
need to be fed in the nest for many days, yet which hardly 
ever pass through any downy stage*. The hallux is always 
present as a hind toe, is well-developed, separably moveable, and 
furnished with a larger claw than the others. Wing-coverts 
somewhat few in number and rather small; greater coverts 
1 See ante, p. 131. 2 See ante, p. 77. 
3 Thickly coyered with down only in the Lyre-bird (Menwra). 
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