KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 47. N:() I. '.I 



is more significant in some respects than thc agreement of fche plankton Algae, which 

 have a more stable environment than thc littoral forms.» 



From thc above we are entitled to drovv thc conclusion, that the shallow-watcr 

 faunas and floras of the two polar seas present very much the same features, bhal 

 they are more closely related to each other than to any fauna and flora in the in- 

 tervcning tropical and subtropical regions, and that they in ma ny instances present 

 such a great conformity, that several species of the same genus occur in both of them. 



If we take for granted that the general feature of the marine faunas of thc 

 two cold seas presents a striking resemblanee, a fact that cannot be disputed, and, 

 besides, that a limited number of specifically related forms is to be met with in both 

 of them, but absent in the whole intervening tropical and subtropical regions, then 

 we have to seek for the cause of this phenomenon. In order to arrive at an expla- 

 nation it will be necessary, as I think, to reflect upon and endeavour to throw light 

 on the following particulars: 



1. Consequence and extent of convergence with regard to shallow-water animals 

 of cold waters. 



2. Faculty of free moving of shallow-water animals in the adult state. 



3. Power of larvse of shallow-water animals to sustain transport by sea-currents, 

 and duration of such a larval period, dependent of currents. 



4. Directions and rapidity of sea-currents. 



5. Animals devoid of free larvae. 



6. »Relicta»-theory. 



With regard to the first particula.r, every investigator of biology knows that 

 similar physical and chemical conditions call forth an astonishing resemblanee between 

 animals and plants of two far separate regions, but up to date nobody has been 

 able to present a single instance which proves that two separate species have 

 become identical only by means of a convergence phenomenon produced solely by 

 the influence of similar physical and chemical conditions. According to our present 

 views, two species never can reunite to one, after they have once separated into two. 

 Supposing these views to be wrong, then the present prevailing conviction of the 

 significance of a true relationship between animals or plants would be a fable and 

 the arranging of a natural system an impossibility. 



With regard to the second question, which concerns the possibility of free 

 moving of adult marine invertebrates from polar cirele to polar cirele, I think it 

 may be possible in some instances, but considering that we are here only consi- 

 dering shallow-water forms and, moreover, that they have to pass över an enormous 

 space, this possibility must be very restricted indeed. Supposing such a migration 

 to be taking place in the present time, then the animals must make their way 

 along the west coasts of Europa and Africa or along the west coast of America, both 

 ways almost devoid of coral-reefs. Their progress is certainly not along the bottom 

 of the deep sea. But who can say for certain that communication-ways exist along 

 the west coasts of the continents? 



K. Sv. Vet. Aliad. Handl. Band 47. N:o 1 2 



