246 ANIMAL LIFE PAST AND PKESENT 



is the remnant of one that was originally functional 

 does not admit of doubt ; but whether we have to go 

 back to invertebrates before this was the case is, as 

 mentioned in the chapter referred to, still a matter of 

 uncertainty. 



Among birds we may notice many instances of the 

 wings having become rudimentary owing to the disuse 

 of the power of flight. This occurs to a greater or 

 lesser extent throughout the whole of that great group 

 comprising the Ostrich, the Cassowary, the Kiwi, and 

 the extinct Moas (Fig. 46, p. 150) of New Zealand : all 

 the bones of the wing having completely disappeared 

 in the last-named birds. There are also numerous in- 

 stances of the abortion of the wings in that larger 

 group which includes all other birds ; well-known cases 

 being those of the Dodo of Mauritius, the Solitaire of 

 Rodriquez, the Great Blue Water-hen (Notornis) of 

 New Zealand, and the Great Auk ; all of which, with 

 the possible exception of Notornis, have become extinct 

 from their incapacity to fly. 



Insects, again, present us with many instances of 

 rudimentary organs. Thus in the extensive group of 

 Flies (Diptera) the hinder pair of wings, which are 

 found fully developed in the Dragon-Flies (Neuro- 

 ptera), have become aborted into organs like minute 

 drumsticks, projecting from either side of the body, 

 and known as "halteres," or balancers. In the Beetles 

 (Coleoptera), on the other hand, it is the front wings 

 which have been modified not, indeed, so as to be 

 absolutely useless, but so as to serve the purpose of 



