A LABRADOR SPRING 



the extremes of specialization for the posterior 

 and anterior extremity respectively. Where 

 either habit is not firmly established we should 

 expect at times a return to the primitive 

 method, and we should expect to find it in 

 young birds. This is well shown in the case 

 of the loon. We should expect to find it at 

 all times in behinners in the art of diving, i. e., 

 among birds whose ancestry in the diving line 

 is not a long one. The mallard, the black duck, 

 the moorhen, the spotted sand piper and the 

 water ouzel may perhaps illustrate this con- 

 tention. 



In conclusion the following tentative in- 

 ferences from these preliminary studies on 

 diving birds may be set down. 



i st. That progression by both the wings and 

 feet under water in diving birds is the primitive 

 method, and is therefore to be looked for 

 among beginners and young birds. 



2d. That specialization towards the use of 

 the wings alone leads to a diminution in the 

 size of the wings, and finally to a form of bird 

 that is flightless in the air; for wings of flipper 

 proportions, too small for aerial flight, are 

 more efficient than large wings for subaqueous 

 204 



