6 THEEL, PRIAPULIDS AND SIPUNCULIDS OF THE SWEDISH ANTARCTIC EXPEDITION 1901 — 1903. 



water faunas of the two polar seas can have any noticeable exchange of species either 

 in the adult or in the larval state. 



In proceeding to discuss these views I must begin by remarking that I omit the 

 deep water fauna, which presents more cosmopolitan features, and that I also prefer 

 to leave out all the representatives of Holoplankton which spend their whole life floating 

 on the surface of the sea or in the water layers beneath, because they might happen 

 to be transported far away from the native-place by means of sea-currents. 



Though I am conscious of deviating from the actual subject of this paper, I 

 nevertheless avail myself of the opportunity to express in a note below my opinion 

 with regard to the holoplankton animals, because there seem to exist views which 

 do not correspond with my own. 



Note. It has been asserted that a permanent exchange of plankton animals is going on 

 between the two polar seas and that the communication takes place in the deeper and colder 

 water-layers under the tropic and subtropic zones. This may be true, but certainly to a very 

 limited extent. 



When Steinhaus states that Sagitta hamata, common in arctie and northern seas, is caught 

 from the cold water in the South under the 40th latitude, and Lohmann relätes that Michaelsen 

 has found the northern Fritillaria borealis in abundance off the coasts of Tierra del fuego, then 

 I think it is an open question, whether the animals in question really have been transported by 

 sea-currents from pole to pole, or whether at the present era they have two or, more probably, 

 several birth-places in the oceans. To my conviction, they are capable of producing an offspring 

 in allmost all the places where the adult animals have been met with. 



We know several instances of plankton forms with a very wide distribution, und here I 

 will refer to the Copepods, marine animals of the greatest importance for supporting the animal 

 life in the oceans. 



In arctie and northern seas we have two forms of rather large Copepods, Calanus firmar- 

 chicus (Gunn.) and Calanus hyperboreus Kröyer, both very representative species and charac- 

 terising the cold northern water by their appearance in enormous masses. Both of them are very 

 resistant and are evidently capable of living in far different depths. For among their relatives 

 there are several forms which posses the necessary qualities of enduring a life at the surface of 

 the sea as well as at depths of 500, 1,000 or even down to 4,000 m. 



According to Giesbrecht, 1 Brady 2 and Aurivillius 3 these two species have a quite dif- 

 ferent extent of their horizontal distribution. In spite of the fact that they pass their life side 

 by side in a sea-area comprising about 16 degrees of latitude or more, the former is distributed 

 in the Atlantic and the Pacific between 85° N. and 52° S., while Calanus hyperboreus is confined 

 to the North Atlantic between 85° N. and 60° N. and is to be looked upon as a genuine arctie form. 



The copepods are in possession of a certain motive power of their own, but, considering 

 the immense distances which they are thought to pass över, this must be minimal, their migra- 

 tion and distribution in the oceans being mainly due to the sea-currents. Now, it seems to be 

 indisputable that the two species in question, living side by side in or under an arctie sea-area 

 of about 16 degrees of latitude, must be subjected to the influences of the same currents. Then 

 it remains to explain, why Calanus finmarchicus alone can be disposed by those currents in every 

 direction, in the Atlantic, Baltic, Mediterranean, Pacific etc, while Calanus hyperboreus still 

 dwells in its native arctie water. 



1 Das Tierreich. Copepoda. I. Gymnoplea. VI. Berlin 1898. 

 ' Challenger Report. Zool. Vol. 8. 1883. 

 :i Kungl. Vet. Handl. Vol. 30. 1905. 



