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LECTURES ON BIOLOGY 



are often littered with the brilliant blue-tinted jelly-fish, Aurelia 

 aurita. From the ovum of these animals originates a little ciliated 

 free-swimming larva, the Planula. After a short life of freedom 

 it attaches itself to the sea-floor and changes into a polyp, the 

 sixteen-armed Scyphostoma. On the body of this polyp soon 

 appear numerous circular grooves which gradually increase in 

 depth, resembling a pile of tea-cups. This is the beginning of 



FIG. 62. DEVELOPMENT OF Aurelia aurita. 



On the left, above, the free-swimming larva form a Planula ; below, on the 

 the rock, a Planula about to become a Scyphostoma. Three other fixed forms show 

 the process of strobilation and the formation of the Ephyra-form ; on the left, 

 swimming, an Ephyra soon after separation from the Strobila ; on the right, an 

 adult Aurelia aurita. 



sexual reproduction by means of terminal gemmation. The 

 Scyphostoma has thereby become a Strobila. Now the polyp- 

 tentacle in the most extreme bud begins to degenerate, and the 

 bud separates. The others quickly follow, and in a short time 

 numerous so-called Ephyrae are swimming about. But there is 

 still a long road to travel. Only a slow and complicated meta- 

 morphosis, during which the larvae must pass many different 



