AVES 



413 



should be remembered, however, that the classification is not 

 the best possible, inasmuch as forms in reality not very closely 

 related in structure are, according to it, placed together because 

 of similar habits. The student is asked to refer to other texts 

 for different arrangements. 



FIG. 213. 



PIG. 213. Ross 1 Gull (Rhodostethia rosea). Upper figure adult male; lower, young female. From 

 "Chapters on Natural History"; drawn by Dr. R. W. Shufeldt after Ridgway. 



Questions on the figure. What indications of structural adaptation to habits 

 do you find in the figure? What sexual dimorphism is perceptible? 



The Pygopodes (feet on the rump) include the auks, penguins, 

 grebes, and loons. These are all aquatic birds and are expert 

 divers and swimmers. Their feet are poorly adapted for the 

 land, and in consequence the birds are awkward. The auks 

 and penguins have poorly developed wings. The loons however 

 are good fliers. The penguins, auks, and puffins are marine 



