416 THE GREBES 



THE GREBES 



[W. P. PYCRAFT] 



By common consent the Grebes and Divers are now regarded as 

 nearly related, very ancient types displaying a quite remarkable 

 degree of adaptation in their environment. And this is nowhere so 

 strikingly manifest as in the skeleton, though in this respect they also 

 display some striking differences. But we are concerned here rather 

 with the external characters and the habits of these two types. 



Both Grebes and Divers are carnivorous, and mainly piscivorous, 

 pursuing their prey under water after the fashion of the Alcidse, the 

 Diving Ducks, and the Penguins, and hence the common resemblances 

 of structure which these several types present. A careful study of the 

 skeletons of these diverse types affords one of the most instructive 

 object-lessons on " adaptation to environment " to be found in the 

 whole animal kingdom. But considerations of space make such a 

 survey impossible in these pages. It must suffice to remark that the 

 Grebes and Divers on the one hand, and the Penguins on the other, 

 mark the extremes of specialisation in the direction of sub-aqueous 

 locomotion among birds. In so far as the Grebes and Divers are con- 

 cerned, it is interesting to note that while they possess, as might be 

 supposed, much in common, they reveal also some curiously contra- 

 dictory features. Thus, for example, in the Divers the sternum is 

 extremely long, in the Grebes it is short and wide. Both agree in 

 having a remarkably elongated and narrow pelvis, comparable only, 

 strangely enough, to certain flightless members of the ostrich tribe, 

 such as the Apteryx. Both agree in having the knee-joint prolonged 

 upwards beyond the end of the femur, but while in the Divers this 

 upstanding spur is formed by the cnemial crest of the tibia or " shank " 

 bone, in the Grebes it is formed, mainly, at any rate, by the knee-cap, 



