v] RELATIVE FREQUENCY 89 



has been stated the earthworms of Europe amount 

 to perhaps 130, at any rate well over one hundred. 

 In tropical America there are hardly more. But in 

 the latter case the number of genera is very greatly 

 in excess of that of Europe. We cannot however say 

 that an abundance of generic types is quite charac- 

 teristic of the tropics. For the Eastern Archipelago, 

 though rich in species, is but poor in genera, not 

 possessing more than half a dozen or so. And on 

 the other hand the temperate climate of New Zealand 

 has produced a very considerable series of genera, 

 much more than those of the islands of the East 

 and nearly as many as those of, for instance, Central 

 America and the West Indies. 



This conclusion is in its turn contradicted by 

 the conditions observable in Chili and the temperate 

 regions of South America, where the number of 

 species is large but the number of genera small. 

 In short no general laws, in the present state of our 

 knowledge, can be laid down as to the connection 

 between species and genera on the one hand and 

 climatic conditions on the other. In this department 

 of our subject we cannot do more than has already 

 been done, i.e. to state the actual facts. One is 

 tempted in comparing the rich fauna of tropical 

 Africa with the very limited fauna of Madagascar 

 to associate a richness of types with extent of land 

 surface. In the two cases cited this conclusion is 



