SECT, iv PHYLUM CCELENTERATA 113 



other, and each, turning upside down, begins to swim 

 about as a small jelly-fish called an Ephyrula (H, I), which 

 grows rapidly and eventually develops into the adult 

 Aurelia. 



The rest of the Scyphozoa resemble Aurelia in the 

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

 of variation in certain points (Fig. 51). 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. Lucern- 

 aria 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, eventu- 

 ally opening into the gastric cavity. Many of the Scypho- 

 zoa pass through an alternation of generations similar to 

 that which has been described in the case of Aurelia, with a 

 fixed scyphistoma stage ; but in others the ciliated larvae 

 developed from the ova give rise directly to jelly-fishes 

 like the parent, without the intercalation of any fixed 

 stage. 



The Scyphozoa are all marine, and the majority are 

 pelagic, i.e., swim freely in the surface waters of the ocean. 

 A few inhabit the deep sea, and have been dredged from 

 as great a depth as 2,000 fathoms. Nearly all are free- 

 swimming in the adult state ; some, however, live on coral- 

 reefs or mud-banks, and are found resting, in an inverted 

 position, on the ex-umbrella ; and a few, such as Lucernaria, 

 are able to attach themselves at will by a peduncle. Many 

 are semi-transparent and glassy, but often with brilliantly- 



