AVES 275 



wings increased in size and effectiveness as motor organs, as shown in 

 Fig. 148, E, F, G, H. 



Gregory's compromise theory of the origin of flight is perhaps 

 more nearly acceptable than any of those hitherto given, and is here- 

 with presented in his own words: 



" The pro-aves were surely quick runners, both on the ground and 

 in the trees, but it is not clear whether the upright position was first 

 attained upon the ground or in the trees. The very early acquired 

 habit of perching upright on the branches, as shown by the consoli- 

 dated instep bones, grasping first digit and strong claws of Archmop- 

 teryx. Their slender arms ended in three long fingers provided with 

 large claws which were at first doubtless used in climbing. These 

 active pro-aves contrasted widely in habits with their sluggish remote 

 reptilian forebears. In pursuit of their prey they jumped lightly from 

 branch to branch and finally from tree to tree, partly sustained by the 

 folds of skin on their arms and legs and later by the long scale-feathers 

 of the pectoral and pelvic ' wings' and tail. That they held the arms 

 and legs perfectly still throughout the gliding leap appears doubtful, 

 for all recent animals that do that have never attained true flight. I 

 cannot avoid the impression that a vigorous downward flap of the 

 arms even before they become efficient wings, would assist in the 

 'take-off' for the leap, and that another flap just before landing would 

 check the speed and assist in the landing." 



Diving Origin of Flight. — So far as the writer is aware, no one 

 has proposed a theory of flight involving the idea that flight may 

 have originated in connection with soaring over the water and diving 

 after fish. Yet there are certain considerations that strongly support 

 such a conception. According to this view the pro-aves used the fore 

 limbs, together with their membranes and elongated scales (possibly 

 also the similar structures of the legs), as planes to aid in diving. The 

 value of such accessories is obvious; the dive being more definitely 

 directed, the descent being made flatter so as to carry the diver 

 farther out from shore, and the force of the plunge being eased up 

 sufficiently to avoid shock. If the wings were flapped more or less a 

 longer glide out over the water could be made, and possible circhng 

 movements could be made over the water while searching for fish. 

 It would appear therefore that the use of the pro-wings as planes in 

 diving would serve as useful a function as in running or leaping from 

 bough to bough. 



