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ZOOLOGY 



student. It should be remembered, however, that the classifi- 

 cation 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. Some of the 

 important orders are as follows: 



Fig. 213. 



FfG. 213. — Koss's 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 nimp) include the auks, grebes, 

 and loons. These are all aquatic birds and are expert divers 

 and swimmers. Their feet are poorly adapted for the land, and 

 in consecjuence the birds are awkward. Auks have poorly 



