A LABRADOR SPRING 



feet habitually. These facts would seem to 

 indicate that the method of posterior propulsion 

 in loons and grebes has not been long developed 

 nor permanently fixed, and that the young 

 show the ancestral or primitive form of loco- 

 motion. The close resemblance in the legs of 

 the loons and grebes on the one hand, and 

 hesperornis on the other, would suggest either 

 a case of parallelism from similar functions, or 

 that they were all descended from the same 

 stock. In the " Birds of Essex County " ' I 

 spoke of the loon as " approaching the wingless 

 conditions." The present studies would, how- 

 ever, lead me to believe that the loon, in per- 

 fecting the method of posterior propulsion 

 under water, has no need to reduce the size of 

 its wings for use there. It can, however, with 

 advantage increase their size, provided it does 

 not use them under water, for the wings are 

 now so small that on calm days it is unable to 

 rise into the air. 



Cormorants on the other hand have for so 

 long a time perfected the posterior propulsion 

 method that they do not use the wings under 

 water even apparently when young. In con- 



1 Birds of Essex County, Cambridge, 1905, p. 80. 

 198 



