16 



which the specimens of the various species occiir. — It does not seem to be tlie 

 diatomacem only wlncli occur iu the said mauner iu a flowing mass of water; 

 somethiug like thi s is known also of the pelagic foraminifera, eveu out iu the 

 great oceanic currents. John Murray writes tlius in Natural Science, vol. XI, 

 July 1897, p. 21, where he discusses the distribution of the pelagic /orawm;- 

 fera: »The gradual disappearance of the tropieal species, and their replace- 

 ment by other species, as the colder water to the north aud south of the 

 equatoi'ial regions is eutered, has always appeared to me rather puzzliug, 

 especiallj' when it is remembered tliat tjicse changes take place in a continuous 

 oceanic current, like the Gulf Stream, flowing from the equator towards the 

 poles.« I take it for granted, however, that we must be able to find guide- 

 organisms (aualogous guide-fossils) in the jjlankton also, M-hich could give 

 us information of the parts of the globe from wliich they come; but 

 not till we know the geographical distribution of tliese guide- organisms, 

 and the conditions under which they live, we shall be able to get the 

 full profit out of them and recognise them as guide- organisms. I must 

 beheve,,for instance, that none of our specimens of Cfenophores properly 

 belong to our seas within the Skaw, but oflen quite disappear from them till 

 the currents carry them agaiu in great numbei-s into the Cattegat. Whence 

 these currents come I do not know, but they are scarcely identical with those 

 that carry Pilenia ociopus. another supposed guide - organism , to the west- 

 ern Limfjord almost every autumn; perhaps they are the same currents as 

 now and theu carry Clione limacina to Bohusian and the Little Belt. These 

 animals, the CtenopJwres as well as Clione, are so large that they could 

 scarcely escape notice if they lived liere constantly; at least it is this suppo- 

 sition which makes me look upon them as visitors here only, but I grant that 

 the whole matter is in great need of renewed investigations. Probably we 

 shall also amoug the smaller organisms, for instance among the diatomaceæ, 

 be able to find such guide -organisms, and perhaps for instance Uhiso- 

 solenia styliformis is such a one; but it will be necessary, before it is raised 

 to its dignity as such, to pro ve that it is not »stationary« in our seas at any 

 time. It would be desirable to point out such organisms among the smaller 

 organisms, for instance amoug the diatomaceæ, because they are so uume- 

 rous that they are found uearly in every, even the smallest, sample of 

 plankton. 



The above mentioned rich diatom-plankton with Ch. boreale in the north- 

 ern Cattegat can, as it is seen from table II, in whicia the localitics are 

 arranged from north to south, follow the liottom-currcnt down tlirougli the 



