112 MANUAL OF ZOOLOGY SECT. 



processes grow out, forming the first two tentacles; soon 

 two others appear at right angles to these. Subsequently 

 other tentacles appear. At the same time the attached or 

 proximal end is narrowed into a stalk-like organ of attach- 

 ment (E). 



The outcome of all these changes is the metamorphosis 

 of the planula into a polype (F), not unlike a Hydra. The 

 Scyphozoon-polype is called a Scyphula. The Scyphula some- 

 times multiplies by budding. After a time it undergoes a 

 process of transverse fission (G), becoming divided by a series 

 of constrictions which deepen until the polype assumes the 

 appearance of a pile of saucers, each with its edge produced 

 into eight bifid lobes. Soon the process of constriction is 

 completed, the saucer-like bodies separate from one another, 

 and each, except the first topmost one, which falls off and 

 dies, turning upside down, begins to swim about as a small 

 jellyfish called an Ephyrula (H, I), which grows rapidly 

 and eventually develops into the adult Aurelia. 



The rest of the Scyphozoa resemble Aurelia in the gen- 

 eral features of their structure, but there is a good deal 

 of variation in certain points (Fig. 52). Thus the umbrella, 

 instead of being a saucer-shaped disc, as in Aurelia, is often 

 conical or cup-shaped or cubical. In some, tentaculocysts 

 are not developed, and in others the oral arms are absent. 

 Lucernaria differs somewhat widely from the rest in being 

 attached by means of a short stalk developed from the centre 

 of the ex-umbrella. In the Rhizostomece the mouth is 

 obliterated by the union of the bases of the oral arms, the 

 food being taken in through a large number of minute orifices 

 scattered over the surface of the arms, and leading into a 

 system of fine canals, which join together to form larger 

 canals, eventually opening into the gastric cavity. Many of 

 the Scyphozoa pass through an alternation of generations 



