166 THE MINUTE. 



in a sort of shell or transparent case, much arched along 

 the back, nearly straight along the belly, and hollowed 

 out at each extremity. This shell is a very beautiful 

 object, when we meet with it, as we often do, completely 

 cleaned of the softer parts, the animal having died. It is 

 hard, perfectly transparent, but marked all over with 

 minute pits. It is closed on all sides, except before and 

 behind, where, as I have said, it is cut away, as it were, 

 for the egress of the head, and the forked foot : along the 

 back it rises into two tall, longitudinal, sharp ridges with 

 a deep furrow between them, and the appearance of this 

 double ridge, from the perfect transparency of the material, 

 has a curious effect as the animal moves about. Both 

 before and behind, the ridges run out into projecting 

 points, those of the front arching over the head like curv- 

 ing horns. These little animals derive their nourishment 

 likewise from the soft vegetable tissues, or the half-dis- 

 solved matter that accumulates on the stems and leaves 

 of the aquatic plants. On this they feed greedily, and 

 nearly the whole of their time is spent in munching away 

 this with the mouth. To do this the foot, which consists 

 of two stiff unjointed styles, is brought into requisition. 

 These are capable of being opened or closed like the feet 

 of a pair of compasses, and of being brought round into 

 any position through the flexibility of the base, which 

 forms false or telescopic joints. The tips of these foot- 

 styles are used as a pivot on which the animal moves ; 

 they are placed perpendicularly to the stem, or other sub- 

 stance, on which it means to crawl or feed, and the body 



