V] RELATIVE FREQUENCY 91 



are moreover connected by forms with an intermediate 

 range. There is no doubt whatever that the genus 

 with the widest range is Notiodrilus of which species 

 are found throughout the antarctic region, viz., in 

 Patagonia, the islands of the Antarctic Ocean, the 

 Cape of Good Hope, New Zealand, and also further 

 to the north, sometimes even to and beyond the 

 tropics in America, Australia, and Africa. There is 

 no other genus of which the genuine extension 

 {i.e. not in any way due to man) is so great as this 

 genus Notiodrilus. And this fact gains much signi- 

 ficance from the now generally accepted view that 

 in its anatomical structure Notiodrilus comes near 

 to the original type of earthworm. 



Perhaps the next most widely distributed genus 

 is Helodrilus of the family Lumbricidae which oc- 

 cupies Europe and Asia to the extreme east, and is 

 thought also to be indigenous to certain parts of 

 North America. But this range, though equally wide 

 perhaps in mileage, is less impressive than that of 

 Notiodrllns, since the land areas inhabited by the 

 genus are continuous almost so if we accept North 

 America as its real habitat. Here we have a case 

 precisely the opposite of that of Notiodrllns ; for 

 while there are reasons for regaixling Notiodrilus as 

 an ancient form of Lumbricid, there are e(pially good 

 reasons for regarding the Lumbricidae as the most 

 modern ftimily of earthworms. 



