244 ALTERNATE GENERATIONS. 



themselves organic structure, and had begun to 

 live and move. It swims by means of rapid 

 contractions and expansions of its disk, thus 

 impelling itself through the water, its tentacles 

 floating behind it and measuring many times 

 the length of the body. The disk is very con- 



Little Jlly-Fish, called Sarsia, the free Medusa of Coryne mirabilis. 



vex, as will be seen by the wood-cut ; four tubes 

 radiate from the central cavity to the periphery, 



