RESTORATION OF HESPERORNIS. 115 



characters necessary to volant movements, once attained, would appear 

 never to be completely lost, and this alone seems to furnish a crucial test 

 When such suggestive indications are wanting in the skeleton, we may 

 fairly challenge any assumption of previous flight. 



Although Hesperornis may thus, like its Reptilian ancestry, have 

 always been incapable of flight, the anterior limbs may have long continued 

 limited aids to locomotion. Whether used actively in the air, like the 

 wings of the Ostrich, or of young swimming birds, or passively, like the 

 sail-set pinions of a Swan, or later as imperfect paddles, the wings of 

 Hesperornis were certainly not well fitted for diving, and hence they • 

 gradually became useless, and virtually disappeared. We may imagine 

 among the reasons for the gradual loss of wings, the fact that they were 

 too weak to be of much service under water, while from then position they 

 added greatly to the resistance, especially during rapid diving. To diminish 

 this resistance, they would naturally be applied closely to the side, and 

 from such disuse, would gradually suffer atrophy. 



In this great swhnming bird, as thus modified, we have presented to 

 us an interesting problem in animal mechanics. The wings may be 

 regarded as wanting, since the remnant of the humerus was attached 

 closely to the side, as in the Apteryx, if not entirely concealed beneath the 

 skin, like a scapula. The locomotion was therefore entirely performed by 

 means of the posterior limbs, a specialization here seen for the first time in 

 acpiatic birds, recent or fossil. Those who have observed a Penguin or a 

 Loon swimming beneath the water know what a vigorous use such birds 

 then make of their wings, however useless these members may appear to 

 be on land. Not only do the wings, in such a case, assist in the forward 

 movement through the water, but they are of much service in steering. 

 A Penguin, when in swift sub-aqueous flight, can ton around, by the aid 

 of its wings, while moving twice its length. Hesperornis had no such aid, 

 but the legs and feet were far superior, for swimming- and diving-, to those 

 of the Penguins, not merely in power, but in the more perfect adaptive 

 mechanism. This was doubtless the main reason why the posterior limbs 

 of Hesperornis became so predominant. 



