THE ANATOMY. GEOGRAPHICAL DISTRIBUTION 



153 



7. Desmogaster. 



8. Bilimba. 



9. Perichaeta. 

 10. Megascolex. 



13. Benhamia. 



II. Perionyx. 

 13. Pleionogaster. 



1. Megascolex. 

 3. Perichaeta. 

 3. Cryptodrilus. 



1. All Eudrilidae. 

 a. Benhamia. 



3. Pygmaeodrilus. 



4. Gordiodrilus. 



5. Microchaeta. 



6. Kynotus. 



1. Plutellus. 



Australian. 



4. Megascolides. 



5. Acanthodrilus. 



6. Octochaetus. 



10. Digaster. 



Ethiopian. 



Nearctic. 

 a. Lumbricus. 



Palaearctic. 



I. Lumbricus. 

 a. Hormogaster. 



7. Deinodrilus. 



8. Plagiochaeta. 



9. Diporochaeta. 



7. Ilyogenia. 



8. Callidrilus. 



9. Millsonia. 



10. Nannodrilus. 



11. Siphonogaster. 



3. Diplocardia. 



3. Sparganophilus. 



4. Criodrilus. 



The genera can in reality (in my opinion) be sorted in a better way. It is not 

 obvious from the above lists that there is a close resemblance between the Nearctic 

 and Palaearctic regions; and yet there is, owing to the fact that Lumbricus (s. Z.) is 

 the dominant genus in both. But it is a question how far this fact ought to lead 

 one. I have pointed out (p. 150) that although Lumbricus is a genus of world-wide 

 distribution, the exotic species are invariably identical with European forms ; were the 

 former indigenous to those countries instead of being, as is probable, introduced by 

 man's agency, they might be fairly expected to be not identical with European forms. 

 To the case of N. America this argument cannot perhaps be so readily applied, on 

 the grounds of its recent continuity with Asia. It must be borne in mind, however, 

 that there are but few American species which are not also met with in Europe. 



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