58 



GUIDE TO THE CORAL GALLERY. 



Case 3, jecting from the stomach walls are four groups of gastral filaments 

 Upright part, loaded with thread-cells. The purple reproductive masses project 

 from the floor of the stomach cavity ; at the base of the manubrium 

 outside are four pockets, which bring the water very near to these 

 masses. Aurelia has no velum in the adult state. The fertilised 

 egg develops into a hollow oval ciliated embryo, which settles down 

 and becomes a small polyp with mouth and stomach and sixteen 

 tentacles ; this phase was formerly supposed to be a distinct 

 individual, which was named Hydra tuba, or the Trumpet Polypus. 

 A v^ery fine example sent by the Plymouth Biological Station is 

 exhibited in Case 3 (Fig. 19a), numerous specimens of the little 



Fig. 21. 



£nd. 



Coil \ 



Teutaculocyst and marginal lappets of Aurelia atirita. In the left-hand figure 

 — ml, marginal lappets ; t, tentaculocyst ; «, superior olfactory pit ; mt, mar- 

 ginal tentacles of the disc, magnified about 50 diameters. In the right- 

 hand figure — a, superior olfactory pit; b, inferior olfactory pit; h, hood or 

 bridge joining the marginal lappets ; t, tentaculocyst ; eon, auditory con- 

 cretion ; oc, ocellus. (After Eimer, from Encyc. Britannica.) 



polyp being attached to a shell ; this fixed phase of Aurelia is now 

 called the " Scyphistoma " stage, on account of the shallow cup- 

 like oral region, contrasting in this respect with the elongated narrow 

 conical oral region of Hydra and Hydroid polyps. In course of 

 time the little Scyphistoma undergoes " transverse fission," and 

 resembles a pile of saucers with crenulated rims (Fig. 19b). 

 Presently the saucers detach themselves (specimens. Case 3) and 

 swim away ; they are now known as Ephyra Medusa3, or the 

 Ephyra stage (Fig. 19c ; specimens. Case 3) ; the last stage in this 

 wonderful transformation consists in the filling in of the spaces 

 between the eight bifid arms of the Ephyra and the development of 



