432 THE GEOGRAPHICAL DISTRIBUTION OF THE SCYPHOMEDUS^E, 



If a current flows by the entrance of a harbour in which Rhizos- 

 tomse have found a home, then they can spread to a great distance 

 even without breeding places, but only in the direction of 

 the current. Harbours connected by a current often contain 

 exactly the same species, although they are often very distant 

 one from the other. On the contrary harbours not so connected 

 mostly contain different species. From one harbour to another, 

 even if they be very near one another, this distribution of the 

 Medusae cannot take place against the current. If we, therefore, 

 find llhizostoma? in several harbours, the centre of distribution 

 is not in the middle, but at the extreme upper end of the down 

 current. 



If we now pass over the limits of our district and consider 

 all the Rhizostomidae, we shall discover some interesting facts 

 on the distribution of this group of Medusa?, which will be 

 easily seen in the table published in one of my former 

 papers. ( 1 ) 



The adult Medusae will, for the most part emigrate from their 

 birth place and seek the open sea, swimming about without 

 particular aim, they must be carried on by the current. Whilst 

 the Medusae swim about in the open sea they cannot produce 

 young in case their young consist of Scyphostomaa ; as these 

 only flourish in quiet and shallow water, but if they get into a 

 harbour then they can propagate their species, as here the Scypho- 

 stomee flourish and such a harbour will become a new centre 

 of distribution. 



It appears to be proved, as already mentioned, that Rhizostomee 

 propagate by means of a change of generation, and that their 

 Scyphostomse flourish best or perhaps solely in quiet and shallow 

 water. 



And, therefore, the above can be applied to Rhizostoma? and 

 we must come to the conclusion that the Rhizostomae can spread 



(1.) R. von Lendenfeld. Proceedings of the Linnean Society of New 

 South Wales. Vol., IV., May 1884. 



