72 land and 90 km from Rugen, the nearest locality where relics are found, is of great interest. An immigration in recent time is out of the question, and even in late-glacial times it can scarcely have spread across the sea. Geologicai facts prove that Bornholm, at some epoch after the latest glaciation, has been situated consider- ably higher than it is now-a-days; undoubtedly the island was connected with North Germany (an upheaval of little more than 20 m would be sufficient to change the sea-bottom between Bornholm and the district E. of Riigen into land). Obviously Planarui nipina has immigrated to Bornholm during this time. By the Danish geologists (Milthers and others) this land- connection is assigned to the Ancylus epoch. According to recent researches the improvement of climate advanced, however, very rapidly ; already early in the Ancylus period the climate was at least as warm as it is to-day. Even during the latest part of the late-glacial period (De Geers fini-glacial epoch) the climate was, to judge from many facts, so warm that Plannria alpina, when existing as far from the ice-border as in the latitudes of Bornholm, certainly could no longer spread into new regions. The immigra- tion must, therefore, date from an earlier epoch. Geological facts do not contradict this assumption. On the con- trary, it is well known that in southern Scandinavia an intensive upheaval of land began very soonly after the retreat of the ice- border. Munthe has come to the conclusion that in the latest part of the late-glacial period the recession of the sea perhaps pro- ceeded to such an extent that even that time Gottland was con- nected with North Germany. It may be assumed even more easily that Bornholm was connected with the continent at a still ear- lier date. Planaria alpina has consequently immigrated to Bornholm from the south by means of a connection with North Germany, presum- ably very early after the retreat of the ice-border. Some remarks upon the immigration of the land-fauna to Bornholm. In the second part of the paper the immigration of the land- fauna to Bornholm is discussed, in particular the immigration of animals that can cross the sea only by more or less rare and ex- I
73 ceptional accidents and whose occurence in Bornholm therefore supports the assumption that this island has been connected with the continent during the late-quaternary period. Such animals are Erinaceiis europæiis (which, however, was possibly imported by man), the reptiles, the amphibians, the land-moUuscs, many insects (butterflies, etc.) and other Invertebrates. The theory that Bornholm has been connected with North Ger- many is supported by many positive geologicai facts. If, however, the island of Gottand has never been more or less closely con- nected with the continent since the ice-age, it must be admitted that the animals in question may have immigrated to Bornholm just as well after the disappearance of the land-bridge as before, and no conclusions with regard to the time of immigration can be drawn. Munthe has pointed out that there are evidences of a considerable upheaval of land in the southern Baltic area in early post-glacial time and supposes that a land-connection was establ- ished between North Germany and Gottland— Oland (an upheaval of abaut 60 m E. of Bornholm would be sufficient, cf. the map fig. 2); this hypothesis, though not proved, is strengthened by the occurence of the above-mentioned animals and can for the present be maintained as a working hypothesis. The fauna of Bornholm contains, inter alia, many species with a more or less southerly distribution, the northern boundary pas- sing through Denmark or Southern Sweden. If these animals have immigrated over the land-connection, this was still in existence at a time when the climate was as warm as it is to-day. Several of these species occur in the southern Baltic district only at isolated localities, outside the area of continuous distribution, and are pre- sumably, in Bornholm and in the other Scandinavian localities, relics from a warmer period. Such animals are Rana agilis, the land-shells Pupa avenacea, P. cijlindracea and Clausilia plicata, several insects (the butterflies Coscinia striata, Agroiis glareosa, A. janthina, A. cinerea, Selidosema ericetaria and others). To judge from the occurrence of these species, the land-connection between Bornholm and the continent existed during the first part of the post-glacial period of warmth. Probably Emys orbicularis and Sus scrofa fems, which are now extinct over the whole of Scandinavia, also immigrated during this time.