294: EVENINGS AT THE MICROSCOPE 



CHAPTEK XV 



WORMS 



AN examination of the diverse modes in which locomo- 

 tion is performed among animals, and the various 

 organs and modifications of organs that subserve 

 this important purpose, would 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 va- 

 riations. 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 muscular disk; the Scallop 

 leaps about by puffs of water driven from its appressed 

 lips; the Lobster shoots several 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 Centiped winds slowly along upon a hun- 

 dred pairs of feet; the Beetle darts like an arrow upon 

 three; and the Butterfly sails on the atmosphere with those 

 painted fans which are properly "aerial gills." How ele- 

 gantly does the Planaria swim by the undulation of its 

 thin body, and the Medusa by the pumping forth of the 

 water held within its umbrella! How wondrously does the 



