AND ZOOGEOGRAPHY OF INDIAN OLIGOCH^TA. 117 



I now wish to argue that a number of genera of Megascole- 

 cidae are probably polyphyletic. I take as a text a sentence of 

 Benham's, in his paper on the Oligochaetes of the Subantarctic 

 Islands of New Zealand (4) : — " According to Michaelsen, species 

 of Microswlex may arise at different times, in different parts of the 

 world, from different species of Notiqdrilus. This thesis involves 

 so profound a modification in the accepted ideas of evolution that 

 space will not permit me to discuss the problem here." I think 

 we may take it, then, that the general view with regard to the 

 multiple origin of species, genera, and larger groups is one of 

 scepticism; the orthodox view is that each group has arisen 

 once and once only. 



But we have to remember that the essential variations in the 

 genera of this family are not innumerable, but limited. It is 

 not the case that the modes ©f variation are so numerous, and 

 the possible combinations therefore so greatly more numerous 

 still, that there is no reasonable chance of the same combination 

 of characters ever being repeated---this seems to be the foundation 

 of the orthodox view. The combinations of characters that 

 distinguish the various genera can be obtained in more than one 

 way, and the characters and their combinations are few enough 

 to render it possible that this has happened ; I would even say 

 probable that this has happened, and perhaps often. 



Let us remember that the perichastine arrangement of seta^ is 

 secondary to the lumbricine, the micronephridial condition 

 secondary to the meganephridial, and the racemose prostate to 

 the tubular, and that these changes have demonstrably taken 

 place more than once ; and let us take such a form as Megascolex, 

 with perichaetine setae, micronephridia, and racemose prostates. 

 It may have arisen from a form with lumbricine seta?, micro- 

 nephridia, and racemose prostates (i.e. Notoscolex) by the multipli- 

 cation of the setae; or it may have arisen from a form with 

 perichaetine setae, racemose prostates, and meganephridia 

 (i. e. Perionyx) by breaking up of the nephridia. Both these 

 modes of origin have, in fact, been suggested; the point seems to 

 be decided — for some species of Megascolex, at any rate — by 

 finding a number of intermediate forms between Notoscolex and 

 Megascolex. There is a third possibility, from a form with 

 perichastine setae, micronephridia. and tubular prostates, by 

 the change of the tubular into the racemose prostate — this 

 would mean that Spenceriella was the ancestor. 



Or take Perionyx, with perichaetine setae, racemose prostates, 

 and meganephridia. It might be derived from a form with 

 lumbricine setae, meganephridia, and racemose prostates (i. e. 

 Woodwardia) by multiplication of setae; or from one with peri- 

 chaetine setae, tubular prostates, and meganephridia (i. e. 

 Diporochceta) by the branching of the prostatic lumen. Here the 

 existence of intermediate forms has decided in favour of the 

 latter. 



Spenceriella is a very small genus, with one species in India 



