IX] GEOGRAPHICAL DISTRIBUTION 141 



East are not strong. But there is on the other 

 hand no doubt that the Indian Etidichogaster is very 

 closely allied to it. But it is by no means excluded 

 from this argument to suppose that these Trigastrinae 

 owe their likeness to convergence. At any rate there 

 are examples of equally marked convergence which 

 seem to be as nearly proved as can be in another 

 though allied group. The New Zealand Neodrilus is 

 to all intents and purposes a Maoridrilus in which 

 one of the two pairs of spermiducal glands and 

 spermathecae has disappeared. It retains the charac- 

 teristic alternation in the position of the nephridia of 

 Maoridrilus, and other structural similarities unite 

 the two genera. In the same way species of Micro- 

 scolex seem as easily derivable from Notiodrdus. 

 MicrosGolex and Neodrilus are so near that had we 

 no such hint of their origin it would be reasonable to 

 place them in the same genus. They at least show a 

 marked convergence. 



It will be noticed therefore that the facts of 

 their distribution agree, as it would appear, with the 

 structure of the terrestrial Oligochaeta. The primi- 

 tive characters of the genus Notiodrilus are to be 

 seen in the double spermaries and glands appended 

 to the (hict, and the corresponding spermatheca, 

 in the absence, or very slight development, of the 

 papillae, so fre(iuent in more specialised genera such 

 as Fheretima, and in the general simplicity of many 



