172 MODE OF GROWTH OF THE RADIATES. 



been mistaken forand described as an adult animal under that 



After assuming this scy phi stoma condition, transverse constric- 

 tions appear at regular intervals, dividing the column, as it were, 

 into a pile of saucers ; the edges rise, tentacles bud out, and the 

 animal assumes the form seen in Fig. 65 (after Agassiz). The 

 Fig. gg. uppermost disk becomes detached, the rest 



separate one after the other and float away in 

 the form of an "Ephyra" (Fig. 66, after A. 

 Agassiz) and after some weeks assume the 

 aurelia or adult condition (Fig. 67). The gi- 

 gantic Cyanea arctica, which attains a diam- 

 eter of from three to five feet across the disk, 

 as Agassiz remarks, is produced from "a hy- 

 droid measuring not more than half an inch when full-grown." 



On the other hand there are several exceptions known to this 

 mode of development, a few growing directly from the egg, with- 



rig.a7. 



out passing through a hydra, or scyphistoma stage. Such is the 

 large Pelagia, as observed by Krohn. Mr. A. Agassiz has ob- 

 served the same fact in Campanella pachydermia, a minute jelly 

 fish. 



The Discophores, then, develop in two ways :— 



A. Directly from the egg (Pelagia and Campanella). 



