244 Townsend, Use of Wings and Feet by Diving Birds. [xuiy 



The tibia, however, is of great strength and size, provided with a 

 keel or crest for the attachment of powerful muscles, and the patella 

 is enormously developed. It is evident that Hesperornis pursued 

 its prey under water by means of the feet alone, and that through 

 many generations it had gradually lost the use of the wings, which 

 must have been, therefore, a hindrance rather than a help in its 

 subaqueous flight. It had long since given up aerial flight. Loons 

 and Grebes, however, although apparently allied to Hesperornis, 

 do at times, as we have seen, use their wings in addition to their 

 feet under water, yet it seems to me probable from the evidence 

 adduced that as a rule they progress by the feet alone. The young 

 appear to use the wings as well as the 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 

 locomotion. 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' (26) I spoke of the Loon as "approaching the 

 wingless conditions." The present studies would, however, lead 

 me to believe that the Loon in perfecting 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 consequence they 

 have been able to retain large wings for aerial flight. That they 

 can develop great speed under water and are very expert fish- 

 catchers is well known. 



The other line of evolution, the subaqueous flight by anterior 

 propulsion, or by the use of the wings alone, reaches its height in the 

 Penguins, and probably in the extinct Great Auk, two birds widely 

 separated genetically, but converging to the same result in this 

 particular. Both birds in developing speed under water by the 

 use of the wings, reduced them in size to the proportions of seal's 



