CLEWS IN NATURAL HISTORY. 



21 



kiwi-kiwi (Fig. 4) of New Zealand, a near relative of the ostriches and 

 running-birds in general, represents a still more degraded condition of 

 the organs of flight, for the wing 

 is reduced in size to an extraor- 

 dinary degree, and exists in a 

 highly abortive condition; while 

 only one complete finger is rep- 

 resented in the hand other 

 birds, as a rule, possessing three 

 modified fingers. The logger- 

 headed duck of South America 

 has wings so reduced that it 

 can but "flap along the sur- 

 face of the water," a condition 

 of matters closely imitated among ourselves by the Aylesbury duck 

 although, indeed, the young ducks are able to fly. The wing of the 

 penguin (Fig. 5) is a mere scaly appendage utterly useless for flight, 

 but useful as a veritable fin, enabling it to swim under water with great 

 facility ; and of the auk's wing the same remark holds good. In the 



Fig. 4. 



Fig. 5. 



birds, then, there is ample evidence of deterioration of organs in the 

 rudimentary nature of the wings of many species. How these condi- 

 tions have been brought about is not difficult to explain in most in- 

 stances. In New Zealand, where we find a singular absence of quad- 

 rupeds, wingless birds many being extinct of which the apteryx is a 

 good example, take the place of the four-footed population. In view 

 of an immunity from the attack of other animals, the ground-feeding 

 habits of these birds would become more and more strongly settled as 

 their special way of life ; and, in the pursuit of such habits, the wings, 



