SciiAKFi'' — Former Land-Bridge hchuecn N. Europe mid N. America. 15 



species of freshwater sponges were detected in various lakes at some distance 

 from the sea on the west coast. Only one of tliese sponges, viz., Tnhrlla 

 pennstjhanica, has since liecn observed in another European locality, in 

 Loch Baa in Scotland, but all of tbcia are identical with American species.' 

 Dr. Hanitsch identified them as Ephydatia cratcriformis, Heteromeycnia 

 Rydcri and TuhcUa pcnnsylvanica. Being unaware of the theory advanced 

 by botanists as to the existence of a former direct land-bridge to America, 

 he speculated on the origin of these freshwater sponges by appealing to 

 accidental means of transport, such as winds, ocean-currents, and birds, and 

 argued that any of these modes of conveyance might have carried tlie 

 gemmules across the Atlantic. 



Of all the occasional means of transmission, only that by birds deserves, 

 to my mind, serious consideration. The two others are clearly out of the 

 question as far as the gemmules of freshwater sponges .are concerned. As 

 I shall endeavour to show later on (p. 21), birds probably never fly directly 

 across the Atlantic ; nor is there any reason to believe that they set foot on 

 the west coast of Ireland first on reaching Europe. That they imported the 

 gemmules of the freshwater sponges on their feet or feathers, from the 

 mainland of America, is therefore extremely improbable. It is of interest 

 to note that Dr. Stejneger argues in favour of a former discontinuous land- 

 connexion between Scotland and Greenland from the route of migration 

 followed by a bird. Because the large-winged race of the Common AMieatear 

 {Saxicola cenanthe leucorhoa) is known to breed in Greenland and eastern 

 arctic America, migrating in winter to the British Islands and France by 

 way of Iceland, the Faroes, and Shetland Islands, he contends that greater 

 land-masses than at present must have existed formerly along this migration 

 route. He does not suggest a complete land-connexion such as I now 

 advocate, but merely a series of large islands separated by ocean straits. 

 He believes this incomplete or discontinuous land-bridge to have existed 

 during part of the Glacial period. = 



In my more recent work on European Animals, I have incidentally 

 dwelt on the past range of the Great Auk (Alca impcnnis) as indicating the 

 presence of a former more continuous coast-line between the British Islands, 

 Iceland, Greenland, and Newfoundland, in all of which countries this bird 

 was known to have been abundant.^ 



Yet, after all, the best evidence in favour of a North Atlantic land-bridge 



1 Hanitsch, R., "Freshwater Sponges of Ireland," p. 126. Annandale, " Freshwater Sponges 

 in Scotland." 



^ Stejneger, L., " Scharfif s History of the European Fauna," pp. 107-108. 

 3 Scharff, R. F., " European Animals," pp. 37-39. 



