STKUTHIONES 495 



other birds forbid us to assume this without any further- 

 argument. 



While the Struthiones present collectively and individually 

 a larger number of important differences from other birds, 

 their organisation is essentially on the plan of that of the 

 remaining members of the class. To take only one at the 

 same time one of the most striking of these correspondences 

 in anatomical structure, the respiratory organs may be con- 

 sidered. It is hardly too much to say that there are not even 

 differences of detail in the arrangement of the lungs and air 

 sacs among the struthious birds. Professor HUXLEY ex- 

 ploded some years ago the idea that the oblique septa of the 

 Apteryx were more like the mammalian diaphragm than the 

 corresponding structures of other carinate or ratite birds. It 

 is inconceivable that there should be this minute correspond- 

 ence of detail with detail, if we are to assume with some 

 that the struthious birds have arisen from a totally different 

 stock from that which produced the carinates. They would 

 derive the former from the dinosaurs and the latter from the 

 pterodactyles. 



The existing struthious birds are the genera Strutliio, 

 Afro-Arabian in range; Rhea, South American ; Droma'iis, 

 Australia; Apteryx, New Zealand ; and Casuarius, Australian 

 region. The structure of these living members of the group 

 will be considered first, after which some account will be 

 given of the Dinornithidae and other extinct and undoubted 

 members of the group, as well as of a few dubious forms 

 which have been placed here rather because they do not 

 definitely fit in anywhere in particular than from their 

 obvious affinities with the Struthiones. 



The genus Strutliio appears to contain two species, the 

 more common Struthio camelus and the Somaliland S. 

 molijbdophanes. The ostrich has two toes, Nos. III. and 

 IV. There is no oil gland. The pterylosis, continuous in 

 the adult bird, show's two distinct apteria in the embryo, as 

 has been shown by Miss LINDSAY.' In the young chick 



1 ' On the Avian Sternum,' P. Z. S. 1885, p. 684. See also W. MARSHALL, 

 ' Beobachtungen iiber das Verhiiltniss der Federn,' &c., Zool. Gart. xvi. (1875), 



