202 LEISURE-TIME STUDIES. 



range amongst the human populations of the earth. It is a 

 tolerably well-ascertained fact, that our common tapeworms 

 may affect inhabitants of any climate, but the "broad- 

 headed" species affects a singularity in its distribution in 

 that it has never been known to occur outside the European 

 province, that is, it has never been found in any other 

 continent save in cases where it has been conveyed to other 

 continents by European hosts. But the " broad-head " is 

 moreover found to affect certain districts or regions within 

 this European area, so that its distribution in Europe is 

 itself of peculiar kind. Its head-quarters appear to be 

 the cantons of Western Switzerland and the nearest French 

 provinces. Its affects Poland, Russia, and Sweden in the 

 north and north-western parts, and it also occurs, but less 

 typically, in Holland and Belgium. In Eastern Prussia 

 and Pomerania the " broad-head " has occasionally ap- 

 peared ; but the latter districts are probably to be regarded 

 in the light of occasional habitats rather than of stated 

 and permanent kind. 



The reasons for the restriction of the parasite to such a 

 limited field are by no means clear. We are not yet 

 sufficiently acquainted with its development and life -history 

 to make generalisations, but one significant fact remains to 

 be noted, namely, that the " broad-head " flourishes in the 

 regions in which the common tapeworm is an unknown or 

 comparatively rare visitant. Now this observation is exactly 

 paralleled by the peculiarities of the distribution of higher 

 animals. In one country we may find what are termed 

 "representative species'"' of the animals which occur in 

 another and distant region. Thus the puma in the New 

 World assumes the place of the lion of the Eastern hemis- 

 phere ; the tapirs of the Eastern Archipelago are balanced 

 in the opposite side of the world by the American species ; 

 and the llamas of South America represent their camel- 

 neighbours of the Old World. There thus appears in such 

 cases to be a balancing of animal life : the one species in 

 one region or continent assuming the functions of the nearly 



