134 THE APODOUS HOLOTHUHIANS 



We know too little about the range of the great majority of the species to 

 attempt any study of geographical distribution more in detail; but it is inter- 

 esting to note the striking difference between the Arctic and Antarctic faunas, 

 for, excepting Chiridota Icevis and Leptosynnpta inhcerens, both of which are 

 very wide-ranging and very poorly delimited, none of the 25 species occurring 

 in the Arctic and Boreal subregions have any near relatives in the Antarctic 

 region, and the 10 species occurring in the latter region are, with one or two 

 possible exceptions, entirely confined within its limits. Moreover, the northern 

 regions have five very characteristic genera, entirely unrepresented south of the 

 equator, while the southern fauna possesses two characteristic genera, each 

 of which seems to have only an aberrant member north of the equator. It is 

 difficult to reconcile these facts with any rational "theory of bipolarity. " 



