JELLY FISHES. 55 



are produced. The eggs make their way through the stomach 

 to the mouth of the manubrium, where there are little cavities 

 for their reception, and here they stay until they have devel- 

 oped a fringe of cilia, when they swim off. In this condition 

 they are quite flat, and of old they were regarded as a distinct 

 species of animal under the name of Planula. It afterwards 

 becomes pear-shaped, tires of wandering, and settles down on 

 a rock or shell to undergo the series of developments we have 

 already described, every stage of which was formerly consid- 

 ered a different animal and bore its special name. 



In spite of the structureless appearance presented by these 

 Jellies owing to the presence of a thick layer of transparent 

 gelatinous material they are endowed with true muscular 

 fibres, which are confined to the under surface of the umbrella, 

 to the manubrium and tentacles, and to a flap of the umbrella 

 margin which is directed inwards and known as the 'velum. 

 It is by the contraction of the velum that water is expelled 

 from beneath, and this has the effect of forcing the Jelly-fish 

 in the opposite direction. 



Somewhat similar to the Aurelia in general form is the 

 Hairy Stinger (Cyancea capillata), to which allusion has already 

 been made. Its umbrella is not so disk-like, but has a raised 

 central dome, and its edges are beautifully fringed with long 

 threads. The lobes around the mouth are developed into 

 very long appendages, all frills and furbelows. An allied 

 species, Cyancea chrysaora, has a very thick and bulging man- 

 ubrium, but no long streamers depending from it. 



A very common form which swarms in harbours is Thau- 

 mantias, of which there are several species. In these the jelly 

 is very thick at the crown of the umbrella, which is more bell- 

 shaped than in Aurelia or Cyancea. The nutrient tubes are 

 four, and the ovaries are beside them. A very small species, 

 Turris digitalis, is bell-shaped, with a conical top and a deep 

 fringe of tentacles round the margin. It originates as a poly- 

 pite on a so-called coralline similar to those described in 

 Chapter IV. 



