Incursion of Atlantic Forms into the Noi'th Sea. 37 



If the records of the isolated eggs aud larvae of Lophius are considered, the spawning 

 area must be looked for to the north and west, in a direction contrary to that of the 

 prevailing current. 



There is abundant proof from recent investigations that, on the European side 

 of the Atlantic, there occurs annually a northerly extension of true Atlantic passive 

 organisms. The magnitude of this phenomenon varies greatly from year to year, 

 but in some years it may be so great that the drift carries great numbers of these 

 passive forms over the Faeroe-Shetland Channel into the Norwegian Sea and to the 

 coast of Norway, and, in addition, large numbers may be brought into the North 

 Sea through the Scotland-Shetland entrance. For example, Leqms fascicularis, 

 the floating barnacle, which is not a true North Sea form, may often be picked up 

 from the surface in the northern North Sea in the summer months. The following 

 few records show that these forms may penetrate well into the North Sea, and that 

 the phenomenon is a recurring one :— 60° 7' N. ; 0° 32' E., 10/8/11 ; 57° N. ; 0° E., 

 1/8/12 ; 58° 13' N. ; 0° 49' E., 25/8/04 ; 57° 50' N. ; 0° 30' E., 25/8/04 ; 58° 34' N. ; 

 0° 47' E., 20/7/05 ; 57° N. ; 0° 5' W., 15/8/12. 



The year 1905 seems to have been particularly favourable for the immigration 

 of passive Atlantic forms into the North Sea. In that year, there was an im- 

 migration of considerable magnitude of the true Atlantic form, Salpa fusiformis, 

 which is extremely well represented in the Goldseeker collections for that year. 

 The Umits of distribution of the Salps in the different summer months are graphi- 

 cally described by Schmidt, who had exceptional opportunities for studying the 

 phenomenon that year. At the end of the month of May, the northern boundary 

 of the Salps in the Atlantic had not extended beyond the latitude of the Hebrides, 

 but by the month of August this boundary had been gradually pushed northwards 

 and eastwards until it included a part of the North Sea and the Orkney and Shetland 

 Islands. 



Perhaps of more interest and importance in the present instance is the ap- 

 pearance in this northern section of the North Sea of fish larvae which are admitted 

 to belong to the Atlantic, or to areas to the west and south. Fierasfer, a form which 

 does not belong to the North Sea but to the warmer water-masses of the Atlantic 

 and Mediterranean, and which has often been compared with Lophius p)iscatorius, 

 on account of its mode of spawning and the similarity of the post-larval stages in 

 the development of filamentous rays on the head, has been captured a large number 

 of times in the North Sea in the autumn and winter months, at stages both with 

 and without the filamentous ray on the head. 



Mention may be made here of the occurrence in the North Sea of pelagic stages 

 of Arnoglossus imperialis. This is a species, the adult stages of which have never 

 been recorded from the North Sea. although it is hardly likely that its occurrence 

 would have been overlooked in an area so intensively fished. According to Kyle 

 (1913), the adults are common in 60-70 metres at the western mouth of the English 

 Channel, and are not rare south and south-west of Ireland. The j)ost-larval stages 

 were found in these areas and southwards, as well as in the Mediterranean. There 

 is one record from the north of Scotland. It was taken in September 1905. Dr. 

 Kyle, in reviewing the captures of these pelagic stages, says, " The small specimens 

 occur in practically every month in which investigations were made, whilst the 

 large are most abundant in September ; one large specimen occurs in January. 

 According to Holt, the spawning period should be in Spring, and with this agrees 

 the large number of the large specimens (eleven altogether, including the earlier) 

 taken in September. But the occurrence of small specimens in February, as well 

 as of a large specimen in January, would indicate that here, just as in the case of 

 A. Thori and A. Laterna, we have to deal with an indefinitely prolonged sj)awning 

 period, with the main spawning in Spring. The presence of both small and large 

 specimens over very deep water points to both a prolonged j)ost-larval life and also 

 to a deep-water habitat." The two captures of Arnoglossus imperialis in the North 

 Sea are in complete accord with these statements. One specimen, 16'5 mm. in 

 length in the preserved condition, was taken in the Petersen Young Fish Trawl at 

 58° 34' N. ; 0° 47' E., at a depth of 66 metres below the surface, on 26th November 

 1904 ; the other specimen 18 mm. long, was captured by the same apparatus at 

 58° N. ; 2° 54' W., at a depth of 27 metres, on 21st November 1904. Both these 

 specimens, even of such a large size, were symmetrical ; the position of the eyes 



