22 



February, If this migrates directly across tlie Gulf Stream, it 

 must thus take 5 months to perform the journey, and during that 

 period be exposed to great hydrographical changes. It has, however, 

 never as yet been observed on its way, so that there exists nothing 

 whatsover to allow of our assuming the probability of such a 

 migration. 



We, therefore, have come to the conclusion that the Plankton 

 Diatoms cannot be used as indicatory organisms in the comparison 

 of far separated places, as their migratory powers are not great, 

 and the same kinds of Plankton can, in all probability, be deve- 

 loped at different places under like conditions. 



With the large animals of the Plankton, matters are, however, 

 very different. The Animal Plankton has been very thoroughly 

 gone in to by Aueivillius, who. especially in his latest great work 

 [98] gives a general account of their relation to the ocean currents. 



Aueivillius bases his observations on the Plankton of the 

 Skagerak, which is partly endogenous, and partly allogonus. 



The allogenus species he separates into 5 groups. 



1. Forms from the Jiitland current. 



2. Forms from the amalgamated waters in the Noi'thern Ocean. 



3. Forms from the northern parts of the Gult Stream. 



4. Forms from the Arctic current. 

 .5. Forms from the Baltic waters. 



This classification has been partly founded on the distribution 

 of the species in the Northern Ocean &c., which however, is to 

 some extent but little known, and partly, and especially on tlieii- 

 periodical appearance in tlie Skagerak. 



Thus, for instance, the forms in the Jutland curi'ent attain 

 their maximum in September — October ; those of the Arctic curient 

 iu February. 



The Author, however, says (1. c. p. 127) "Wenn ferner die 

 Erscheinungszeiten der Formen einer jeden dieser fiinf hinnen 

 Jahresfrist auftretenden Klassen unter sich verglichen werden, so 

 geht hervoi-, dass sie nicht in der Meinung von einander gesondert 

 sind, dass die eint; auftritt, wenn die andere verschwindet oder im 

 Riickgang begriffen ist, sondern vielmehr greifen die Perioden in 

 einander liber so dass gleichzeitig his auf vier Kategorien vertreten 

 sein konneri. So ist z. B. im Januar der Fall, wo inich einige 

 Formen der Jiitschen Striimung zu treffen sind, wahrend dass 

 gleichzeitig alle drei Gruppen nordlichen Ursprungs rnehi- oder 

 weniger zahlreiche Vertreter haben." 



In this, in our opinion, lies the kernel of the question. We 

 consider it as settled that, throughout the year, bodies of oceanic 

 water flow into the Skagerak, especially along the coast of Jutland 

 where the strong current which pours in has long been recognised. 



And the water must convey with it Oceanic organisms, provided 

 they have sufficient powers of resistance to withstand the changes 

 that occur in the surrounding water. 



But we regard it as being doubtful, whether, from the solitary 

 species or group, it is possible to indicate w'ith certainty the pale 

 of sea, or the ocean currents from which they originate. 



Two stretches of ocean or land, with not too difi'eront ;i climate, 

 own, as is known, most species in common, whilst but a minority, of 

 most often rare, sensitive forms, are typical of individual spheres. 



And even were it possible with certainty to say that certain 

 species but existed, for instance in the Pohu' current (sucli as 

 Cakmus hyperhoreus, Clionu lim,acina), one cannot, therefore, either 

 in the North Sea or Skagerak point out certain layers of water 

 as being, or having been direct continuations of the Polar current. 



This current shews its influence by giving the northern poi'- 

 tion of the Gulf Stream a lower temperature and lesser salinity than 

 elsewhere. Wc saw on PI. 4, that the great development of the 

 Polar current, during the winter and spring of 1897. inwered the 

 maximum temperature on the line Sogne Fjord - Jan Mayen (12th — 

 IBth May) to 7".2, whilst in 189f), at the same period it was 9". 6. 

 The Polar current is clieckel to the north of the Shetland Islands, 

 but as all the Ar'ctic organisms can thrive in water of ."i" to 7'' 

 (see Aueivillius 1. c. p. 87 — 91), they may be conveyed on in 

 the amalgamated layers to the North Sea and Skagerak. 



As Aueivillius, genei'ally finds his geographical gron])s inter- 

 mingled, this surely likewise indicates that the waters become 

 mixed, and tliat it is, thereby, impossible to point out strata of any 

 certain origin. 



The oceanic waters which flow into the Skagerak must pass, 

 partly, through the English Clumnel, partly through the northern 

 entrance to the North Sea, and the Norwegian Channel. The 

 nature of the in-flowing layers are therefore determined by the 

 hydrographical conditions existing in those parts. 



There, as everywhere else, the changes of the seasons affect 

 the ocean water and its organisms, so that the temperature, and 

 the Pehigic Fauna and B'lora obtain an annual period. This compli- 

 cation alone can, in our opinion, cause great yearly changes in 

 the Pl.ankton of the Skagerak. To this must be added the fact, 

 that the Gulf Stream during winter, in the northern portion of 

 the North Sea, becomes chilled by the proximity of the Arctic 

 current, and that, possibly, its fauna is supplemented with Arctic 

 animals. 



The biological conditions can, thus, not afl'ect the results of 

 our hydrographical studies. The general result of the combined 

 investigations we may sum up in the following manner. 



i 



■: 



