232 RADIATES: JELLY-FISHES. 



swarms near the surface of the water. About the 

 middle of summer they become full grown. Towards 

 the close of summer they lay their eggs, and in the 

 autumn they perish. At length the eggs hatch, and 

 the little planulce, as the newly hatched jelly-fishes are 

 called, swim about in the water by means of little ap- 

 pendages which naturalists call vibratile cilia. Soon 

 each becomes attached to a rock, shell, or sea-weed, 

 and is then called Scyphostoma, Figure 475. Then 

 the body begins to divide by horizontal constrictions, 

 and soon appears as in Figures 4T4 and 476, and is 

 then called Strobila. At length the segments become 

 more and more separated, and the uppermost one 

 drops off, then the next one, then the next, and so on 

 till each in turn has separated from the one below it- 

 self. Each disk, as it separates, turns over and floats 

 away, and is known as Ephyra. Soon each Ephyra 

 assumes the form of a perfect jelly-fish, as shown in 

 Figure 477. Thus one scyphostoma which comes from 

 a single egg becomes a strobila, and this strobila di- 

 vides into numerous parts, each of which becomes a. 

 jelly-fish. 



+ 



HYDROIDS. 



The Hydroids are jelly-fishes which are almost more 

 wonderful in their mode of development than those 

 already described. Occurring, as they do in many 

 cases, in their early stages of existence, as mere dis- 

 colored patches on sea-weeds, stones, or shells, or in 

 appearance like little tufts of, moss, or miniature shrubs, 

 the untrained eye might well mistake the fact that 

 they are animals. But naturalists have shown that 

 these plant-like forms produce medusae-buds, which 



