THE CLASSIFICATION OF BIED3 



DROM!OMORPH.ffi. 



If the Penguins may be supposed to have concentrated their 

 energies upon the task of diving under water like fishes, the 

 Ostriches must be regarded as having done their best to vie with 

 the racehorse in running over land. There can scarcely be any 

 doubt that the Ostriches, like the Penguins, are descended from 

 birds which could fly, and that their wings have ceased to be 

 functional from disuse. At what period they were isolated it is 

 impossible to guess, it may have been before or it may have been 

 after the isolation of the aquincubital birds. Inasmuch as no 

 trace of the loss of a fifth secondary from the imperfect wings of 

 the Ostriches can be detected, and their affinities appear to be 

 most with the quincubital series, it is quite possible that they 

 may represent the survivors of a later branch than that from 

 which the Penguins are descended. Under any circumstances it 

 is scarcely probable that any one will deny them the rank of a 

 Subclass. The idea of dividing all living birds into two subclasses, 

 Ratitge and Carinatae, has been abandoned as unwarranted by the 

 evidence. Whether the Apterygidcc differ sufficiently from the 

 other three families to entitle them to ordinal rank .is an open 

 question. That Dromceus should have lost the ambiens muscle * 

 is not regarded as a sufficient reason for separating it from 

 Casuarius. 



APTERYGIFORMES. 

 30. APTEKYGES. 



It is a matter of opinion how far the Apteryges differ from 

 the Struthiones, but I have placed them in separate Orders in 

 deference to the opinion of Fiirbringer, to whom we are indebted 

 for an enormous collection of facts bearing upon the classification 

 of birds. A few of the characters in which these groups differ 

 from each other are enumerated below. 



* So far as is known, the habits of the Cassowaries and the Rheas resemble 

 those of the Ostriches and Emus, and it is very difficult to imagine any possible 

 reason why it should have been to the advantage of the Ernus to have lost the 

 ambiens muscle that does not equally apply to the -other Dromseomorphas. The 

 only explanation that suggests itself is to assume that Droma : us adopted a terres- 

 trial life somewhat later than the other Di omoeomorphas, so late, indeed, that 

 the last rudiments of the ambiens muscle had been lost bej-ond recall. 



