590 THE AMERICAN NATURALIST [Vol. XXXIII. 



Lastly, we have a paper, by O. Buerger, 1 treating of a group 

 of worms, the nemertines. Buerger does not go much into 

 detail, but we must attribute this chiefly to our scant knowl- 

 edge of this group. Again, there are no bipolar species ; the 

 only two species which have been found in corresponding lati- 

 tudes on both hemispheres are circum-tropical, and enter extra- 

 tropical parts only on the northern and southern limits of their 

 range. As regards the genera, all Antarctic genera (9) are 

 also found in the Arctic. Buerger says that a general simi- 

 larity of both polar faunas is thus indicated, but the lack of 12 

 Arctic genera in the Antarctic does not support this view ; and 

 since he says, further, that neither of the faunas seems to possess 

 very characteristic types, as do the tropics, it is evident that 

 these 9 genera common to both polar faunas are also repre- 

 sented in the tropics. There is, however, one genus that seems 

 to be bipolar ; Carinoma, which has been found on the coast 

 of England (C. armandi) and in the Straits of Magellan 

 (C. patagonica). 



There is no doubt that the facts presented here do not at all 

 support the theory of bipolarity. The contention of Pfeffer 

 and Murray is that bipolarity forms a very striking feature of 

 the polar faunas. This has been denied by the present writer 

 with regard to the decapod crustaceans, and now von Ihering 

 has confirmed this latter opinion for the mollusks, Breitfuss 

 for the Calcispongiae, Herdman for the tunicates, d'Arcy W. 

 Thompson for the fishes, isopods, and amphipods, Ludwig for 

 the holothurians, crinoids,and ophiuroids, Buerger for the nemer- 

 tines, and Chun for the entire bulk of the pelagic fauna. 



Two cases of bipolarity of species and one of genera have 

 been discovered, and when we add these to the single case 

 previously established (Crangon), we have altogether four cases 

 of true bipolarity which are to be explained by a theory. In 

 all other cases the supposed bipolar range of a species or group 

 has been connected by intermediate localities, and these con- 

 nections are of two kinds : (1) connection along the bottom of 

 the deep sea or in deeper strata of the tropical parts of the open 



1 Hamburger Magalhaensische Sammelreise. Nemertinen, 1899. 



