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- 
* Birds of Essex County, Cambridge, 1005, p. 80. 
198 
