6 P. T. CLEVE, PLANKTON-RESEAKCHES. 



ilowiiig- currents along the bottom, partly by warm surface-currents». The plankton that 

 inay take its origin in the fjords must then be cavried out in the ocean to raore or less 

 distant regions. Without such fresh intlow of water, the deeper layers in the fjords must 

 become sterile, as the Swedish hydrographers have pointed out long ago. There will be 

 formed in the bottom-mud sulphuretted compounds destructive to animal life, just as is 

 the case on a large scale in the Black Sea. 



The bottom-fauna of the fjords frequently contains a number of arctic forms, A\hich 

 are usually believed to l)e remnants or »relics» from the giacial epoch. It seems really 

 stränge that such a fauna should remain for so long a time, when ^vaters in the fjords 

 undergo at least an annual change. It has been a favourite theme for biologists to look 

 for »relics» everywhere, since Loven published his genial theory on the relicforms of the 

 Baltic. Lovén's theory is doubtlees true as concerns such forms as can exist in fresh 

 water, f. i. Glyptonotus entomon, l)ut it is not ajjplicable to marine forms such as Astarte 

 horealis and Tellina calcarea, Avhich occur in the Bornholm depth of the Baltic. Such 

 forms have certainly not existed there since the giacial epoch. After the giacial epoch 

 followed the ancylus-epoch, when the Baltic basin was filled with fresh water. The fresh 

 water became exchanged for salt water in the oak- or litorina-epoch. Just as little as 

 the named molluscs can be relics form the giacial epoch can the arctic Baltic alga Spha- 

 celaria raceviosa be such a relic. Dr. Svedelius "'■■) agrees with we so far when he says 

 that the named species eould not have endured the fresh water of the ancylus sea. He 

 believes that the arctic flora and fauna retired from the baltic during the ancylus epoch, 

 but returned with the salter water, when it entered during the litorina epoch. Unfortu- 

 nately for this hypothesis the Kattegatt had then much salter and warmer water than in 

 our time, a fact that seems not to be favourable to the existence of an arctic colony 

 in the Kattegatt. Dr. Svedelius has borrowed his theory from Dr. E. Lönnbekg. *) The 

 latter author emphazises as »absolutely» impossible that the arctic animals, Avhich in our 

 time live in the Öresund, could derive from arctic currents in the present epoch. He 

 tries to prove that especially by the occurrence in the Oresiuid of two stariishes, Cri- 

 hrella sangvinolenta and Asterias Midleri, which have no pelagic sta.ges. 



The Cribrella has been fouiid at Greenland, along the east coast of North America, 

 at Iceland and the Färöes, Shetland (MTntosh), off W. England (Cladwick), S. W. of 

 Ireland (Jeff. Bell), in Moray Firth (Peakcey), in La?sö Rcnde, between Anholt and 

 Hesselö as well as betwen Sjajllands Ödde and Djursland (Petersen). 



The Asterias MuUeri occurs, besides in the arctic regions, at Iceland, Färöes, Shet- 

 land (Norman), E. England (Norman), in the Kattegatt, north of Djursland and in the 

 Österrende towards Kullen (Petersen). It was collected last February by the Swedish 

 Commission inside Väderöboda, and Mr. Lönnberg has approved of the correctness of 

 ray determination. 



The geographical distribution of these two species seems to me to make the theory 

 af Mssrs Lönnberg and Svedelius superfluous. On the ther hand the hydrographical data 



*) Studier öfver Östersjöns hafsalgflora p. 70 — 71. Akad. Diss. Upsala 1901. 



*) Undersökningar rörande Öresunds Djurlif. Medd. fr. K. Landtbruksakademien n:r 1 1898 p. 05. 



