8 EDWARD T. BROWNE. 



In the collection from the Falklands there are seventeen species of Hydromedusse (for 

 names, see Browne, 1902) belonging to sixteen genera. Not one of these species has 

 yet been found in the Antarctic, and only two of the genera, namely, Eleutheria and 

 Phialidium, are represented there. Among the Scyphomedusse the genus Desmonema 

 is common to the Magellanic and Antarctic regions, but the species are distinct. 

 Eleutheria charcoti, found off the Antarctic continent near Wandel Island (south of 

 the Falklands), is more like E. hodgsoni from McMurdo Sound than like E. vallentini 

 from the Falklands. If we compare the Antarctic Medusae with the records (which 

 are still very meagre) from Australia and New Zealand, we find that only one genus 

 (Margelopsis] and no species are common to both regions. 



The recent Antarctic explorations have produced a fair number of new Medusae, 

 many of which have well-marked and interesting specific characters, but there are only 

 about three new genera. I expect that ultimately not one of them will remain 

 peculiar to the Antarctic fauna. All the genera, except those recently described, have 

 representatives in other parts of the world, frequently living under totally different 

 conditions and in localities far apart. As the littoral Hydromedusse of the Antarctic 

 have not yet been found in the Magellanic, South Australian, and New Zealand areas, 

 it looks as if they belonged to an ancient stock which has long been isolated by the 

 Great Southern Ocean from the rest of the world. 



Sir John Murray, K.C.B. (1896), says: "In water of a low temperature the 

 metabolism in cold-blooded animals would be much less rapid than in water of a 

 high temperature, and all those changes which result in the evolution of new species 

 would proceed at a much slower rate at the poles than in the tropical belt." If the 

 Medusas of the Antarctic region have long been isolated, and their evolution has 

 proceeded at a slow rate on account of the coldness of the water, then, when an Antarctic 

 species is compared with another species of the same genus inhabiting warmer water 

 we ought to be able to see a difference and mark the course of evolution. As evolution 

 is proceeding at a much slower rate in cold than in warm regions, the characters of 

 an Antarctic Medusa should be more primitive than those of one from warmer seas. 



The following are instances of this primitive condition : 



The genus Solmundella has a very wide geographical range, extending from the 

 tropics to the Antarctic. It has only two opposite perradial tentacles, and the genus 

 is descended, without doubt, from a genus which had four perradial tentacles. Beneath 

 the two tentacles there is always a deep groove in the wall of the umbrella. In the 

 Antarctic form there is still a conspicuous groove present in the two perradii without 

 tentacles. The grooves have disappeared from the two perradii without tentacles in 

 the species found off Ceylon. The species from Ceylon has not only lost all traces of 

 the grooves, but in addition has developed about four times the number of sense 

 organs found in the Antarctic species. 



A new species of Sibogita found in the Antarctic has only four centripetal canals, 

 whereas the other species have eight or more centripetal canals. 



