IV 



COELENTERATA 



75 



the summer. This is very much the same phenomenon as the 

 " strobilization " of the Scyphistoma, when the first " Ephyra-head " 

 is budded off. 



ten 



FIG. 55. Longitudinal section through the sense organ of a young Ephyra. 



cole, calcareous concretions in the sense-tentacle ; I, lobe of disc of Ephyra ; r.c, wall of radial canal ; 



toi 1 , sense-tentacle. 



FIG. 56. Three stages in the development of the Ephyra larva into the adult Aurelia. 



(After Glaus.) 



ad, adradial cushion ; c.c, circular canal ; g.f, gastral filament ; I, lobe sheltering sense tentacle ; 

 per, per-radial canal ; ten 1 , sense-tentacle. (The reference line without letter in the first figure points 

 to an inter-radial canal.) 



Then in both groups the sexually mature person is typically a 

 person which breaks loose from the colony and develops a swimming- 

 web. In Hydrozoa such a person breaks loose in such a way as 



