woKMs. 297 



CIIArTER XY. 



WOKMS. 



An examination of tlic diverse modes in which loco- 

 motion is performed among animals, and the vai'ions 

 oi'gans and modifications of organs that subserve this 

 important purpose, Avould form no uninteresting chap- 

 ter in natural history. You have two feet, your dog 

 has four; in the bird, two of these are converted into 

 wings, with which it rises into the air ; in the fish all 

 of them are become fins, with which it strikes the water. 

 But it is in the invertebrate classes that we discover the 

 strongest variations. The Poulpe " flops" awkwardly 

 but vigorously along, by the alternate contractions and 

 expansions of the web that unites its arms ; the Snail 

 glides evenly over the herbage by means of its muscu- 

 lar disk ; the Scallop leaps about by puffs of water 

 driven from its appressed lips ; the Lobster shoots sev- 

 eral yards in a second by the blow of its tail upon the 

 water ; the Gossamer Spider floats among the clouds 

 upon a balloon that it has spun from its own body ; the 

 Centipede winds slowly along upon a hundred pairs of 

 feet ; the Beetle darts like an arrow upon three ; and 

 the Butterflj' sails on the atmosphere with those painted 

 fans which are properly " aerial gills." How elegantly 

 does the Planaria swim by the undulation of its thin 

 body, and the Medusa by the pumping forth of the 

 .vater held witliin its umbrella ! How wondrously does 

 1.* 



