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, 7. ¢., 
among birds whose ancestry in the diving line 
isnotalongone. 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. 
ist. 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. 
ed. 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 
