AQUATIC MAMMALS 



If one drop a cutworm into a dish of water the worm is unable to 

 progress, or to do aught but bend first to one side and then to the 

 other. The reason for this is that the center of gravity and center of 



r-A. 



FIGURE 1. Diagrams illustrative of some swimming principles of vertebrates: 

 (1) a cut worm or similar form; (2) mud turtle swimming freely; 

 (3) mud turtle with fore legs bound down by adhesive tape; (4) fish with 

 its snout held rigid; (.5 and 6) fish swimming free; (7) the sea-lion prin- 

 ciple: (a) pivot of movement; (b) fulcrum; (r) power arm; (d) weight 

 to be moved (i.e. the water) ; (e) lever. 



motion are at the middle of the body, and both the form and mass of 

 the anterior and of the posterior parts are equal, and hence, any motion 

 by one end is equalized by a corresponding motion of the other. Bend- 

 ing of the body in a curve hitches it first an infinitesimal distance to 



[14] 



