ZOOLOGY. 



61 



Sponges.' 



Among the lower forms of life, reference must be made to the recent 

 discovery by Dr. Hanitsch of three North American 

 species of freshwater sponges — Efhydatia crateri- 

 forniis, Tubella pennsylvamca, and Heteronieyenia 

 Ryderi — hitherto unknown in Europe, in various 

 lakes in the west of Ireland. This discovery shows that the peculiar assem- 

 blage of North American plants inhabiting western Ireland are accompanied 

 by animals — albeit lowly ones — of the same distributional group. Little 

 doubt can be entertained that these American forms, with their distribution 

 east of the Atlantic so greatly restricted, are older than the animals of the 

 ordinary Northern type with a wide circumpolar range. They support the 

 theory of an ancient land-connection to the north of the Atlantic by means 

 of which many of the Arctic species common to Europe and North America 

 were able to make their way between the two continents. 



Fig. 7. — American Freshwater Sponge (Heteromeyenia Ryderi), Co. Kerry. 

 Natural size. 



Fig. 8. — Spicules and amphidiscs of H. Ryderi. Magnified 200 times. 

 After Hanitsch, Irish Nat., vol. iv. • 



The remains of this old continental coast, connecting Scandinavia with 

 Scotland, and Scotland with Ireland, probably lasted until the Pleistocene 

 " Ice Age " had passed away. Across it passed the latest of those animals 

 that journeyed to Ireland overland. The fact that it broke down before so 

 many of the British animals could make their way thither explains the 

 poverty and interest of the Irish fauna. For, had the newer eastern group 



R. Hanitsch. " The Freshwater Sponges of Ireland." Irish Nat., vol. iv., 1805. 



