CHAP, xxr XEW ZEALAIND 481 



plumes. In the cassowary these wing-feathers are reduced 

 to long spines like porcupine-quills, while even in the 

 Apteryx, the minute external wing bears a series of nearly 

 twenty stiff quill-like feathers.^ These facts render it 

 almost certain that the struthious birds do not owe their 

 imperfect wings to a direct evolution from a reptilian type, 

 but to a retrogi'ade development from some low form of 

 winged birds, analogous to that which has produced the 

 dodo and the solitaire from the more highly-developed 

 pigeon-tyf)e. Professor Marsh has proved, that so far back 

 as the Cretaceous period, the two great forms of birds — 

 those with a keeled sternum and fairly-developed wings, 

 and those with a convex keel-less sternum and rudimentary 

 wings — already existed side by side ; while in the still 

 earlier Archa3opteryx of the Jurassic period we have a bird 

 with well-developed wings, and therefore probably with a 

 keeled sternum. We are evidently, therefore, very far 

 from a knowledge of the earliest stages of bird life, and our 

 acquaintance Avith the various forms that have existed is 

 scanty in the extreme ; but we may be sure that birds 

 acquired wings, and feathers, and some power of flight, 

 before they developed a keeled sternum, since we see that 

 bats with no such keel fly very well. Since, therefore, the 

 struthious birds all have perfect feathers, and all have 

 rudimentary wings, which are anatomically those of true 

 birds, not the rudimentary fore-legs of reptiles, and since 

 we know that in many higher groups of birds — as the 

 pigeons and the rails — the wings have become more or less 

 aborted, and the keel of the sternum greatly reduced in 

 size by disuse, 'it seems j^robable that the very remote 

 ancestors of the rhea, the cassowary, and the apteryx, were 

 true flying birds, although not perhaps provided with a 

 keeled sternum, or possessing very great powers of flight. 

 But in addition to the possible ancestral power of flight, 

 we have the undoubted fact that the rhea and the emu 

 both swim freely, the former having been seen swimming 

 from island to island off the coast of Patagonia. This, 

 taken in connection with the wonderful aquatic ostrich of 

 the Cretaceous period discovered by Professor Marsh, opens 

 1 See fig. in Trans, of N. Z. Institute, Vol. III., plate Vlh. fig. 2. 



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