FIN-FOOTED CARNIVORES 55 



speed of a shark, and with equal ease on its back or belly or side. 

 Indeed it performs all kinds of gambols in the water, diving down into 

 the depths with the speed of an arrow, and again shooting up to the 

 surface with equal rapidity. It is able to remain seven minutes under 

 the water without breathing. 



Differing thus in the manner of its life from most other mammals, we 

 , may expect to meet with special arrangements in the structure of its body. 



1. The head passes straight into the short thick neck, and this again 

 is continuous with the cylindrical elongated trunk, the whole body thus 

 acquiring the form of a spindle, which cuts through the water with ease. 

 (Compare with fishes.) 



2. In consequence of the strength and thickness of the neck, the 

 head must follow the direction in which the trunk is moving ; were the 

 neck short and thin, it would be deflected 

 — by the resistance of the water — from 

 the direction of motion, and consequently 

 impede progress. 



3. The fore and hind limbs form the 

 oars and rudder of the boat-shaped 

 body. 



(a) The feet, the toes of which are s -- °* !Zsl S^^* 

 connected by webs, form broad finlike 



plates. In their backward movement the toes are spread out ; in the 

 forward movement they are laid together, so as to offer the least possible 

 resistance to the water. (Compare the duck.) 



(b) Both the upper and lower segments of the limbs are much 

 shortened, and, for the most part, hidden within the body. Thus, only 

 the finlike hands and feet project into the water, so that their strokes 

 are short and quick. 



The shoulder-blade, and the upper and lower bones of the limbs are 

 very broad, and thus, in spite of their shortness, offer the necessary 

 surface of attachment to the muscles. (Compare the mole.) 



(c) The limbs are not, as in animals which progress by walking, 

 directed downwards. The hands (as in the mole, which, as it were, 

 swims in the earth) are directed obliquely outwards, and the feet, between 

 which the remnant of a tail is visible, are directed posteriorly, their inner 

 surfaces being turned towards the middle line of the body. By power- 

 fully striking its feet together, the animal pushes away the water between 

 them, and propels its body forwards. The feet, in this action, are 

 assisted by the hands, which at the same time are used for steering. 

 (Illustrate this method of steering by means of a small boat which is 

 steered by means of the oars only.) 



