REPORT ON THE SPHENISCID^. 



37 



rounding fluid. In the backward or effective stroke, on the other hand, a broad surface 

 is presented to the water, and instead of the wing being carried backwards, the body of 

 the bird is propelled forwards. In accordance with the requirements of the animal, 

 moreover, the movements permissible between the separate segments of the limbs are 

 much more limited than in other birds — so much so that movements of pure flexion and 

 extension in the joints Ijcyond the shoulder can scarcely be said to be possible. These 

 articulations, however, admit of a very considerable amount of rotation, and consequently 

 instead of the limb being converted into an absolutely rigid paddle or oar, the rotation 

 in question converts the wing into a screw-like blade, the curvatures of which are 

 constantly varying in accordance with the amount of rotation which the forms of the 

 different joints permit. 



Upon carefully watching a living specimen of Aptenodytes which some time since 

 formed a portion of the menagerie of the Zoological Society, I observed that the 

 wing of the Penguin is never used in the manner of a rigid oar, which would 

 imply the simultaneous movement of both wings in the same direction in order to 

 propel the bird. On the contrary, the wings are often, and indeed I may say usually, 

 brought into use alternately, much in the same manner as the pectoral fins of a fish, 

 and in every movement of the wing, screw-like curvatures, which are due to the 

 rotation of the different segments of the limb upon one another, are strongly developed. 

 In fact, a constant screwing and unscrewing of the separate alar segments upon one 



