AND ZOOGEOGRAPHY OF INDIAN OLIGOCII^TA. 119 



Benham, however, is wrong if, in the sentence I have quoted 

 above, he means to imply that Michaelsen holds heretical views 

 on evolution. Michaelsen is strictly orthodox ; he will not have 

 it that different species of a genus may arise at different places 

 from different species of a parent genus ; he merges the two 

 genera concerned, and calls all the species Microscolex (8). 



Again, in the Abor country, in a remote spot in the 

 Eastern Himalayas, a worm is found named by me Perionyx 

 annulatus (18); like other examples of the genus it has racemose 

 prostates and perichaetine seta? ; but while the rest of the genus 

 has only meganephridia this worm has, in addition to mega- 

 nephridia, micronephridia also in all the postgenital segments. 

 But the presence of micronephridia is just what distinguishes 

 Megascolex from Perionyx, and by definition the worm should go 

 in Megascolex. A large number of species of Perionyx, however, 

 have a rather characteristic appearance — the dorsal surface is 

 deeply pigmented, of a dark purple colour; the setae are 

 exceptionally numerous, and the breaks in the middorsal and 

 midventral lines are very small; the male pores and spermathecal 

 pores are close together near the midventral line and, internally, 

 the gizzard is considerably reduced. These characters are not set 

 down in bhe generic diagnosis ; some of them are scarcely definite 

 enough, and they are not features of all the species, though, in 

 varying degree, they are of many ; they are, however, all possessed 

 by Perionyx annulatus. Lastly, Perionyx annulatus occurs in the 

 heart of the Perionyx region,' and more than a thousand miles 

 from the Indian Megascolex region. There is only one possible 

 conclusion — that this worm, by definition a Megascolex, has 

 evolved where we find it from a, Perionyx, and that it has nothing 

 to do in its origin with any other Indian or Australian Megascolex. 

 Very similar is Megascolex dubius, which also seems to have 

 arisen, far away from the Megascolex region, from a Perionyx. 



I have already said, however, that Megascolex has originated 

 from Notoscolex (lumbricine setae, micronephridia, and racemose 

 prostates) by increase in the number of the setae ; and indeed we 

 get so many intermediate stages in this increase that this is no 

 doubt true for at any rate a large number of species ; Megascolex 

 is therefore cliphyletic. 



But this does not end the complexity. Michaelsen (14) has 

 pointed out the close relation of certain Ceylon species of 

 Megascolex to certain Ce}don species of Notoscolex — the group 

 of Megascolex travancorensis to that of Notoscolex ponmuxlianus. 

 The argument is the same as in the case of the Notiodrilus and 

 Microscolex of Possession Island ; the species of Megascolex have in 

 all probability arisen from the local representatives of Notoscolex. 

 There is also a similar correspondence between species of 

 Notoscolex and species of Megascolex in another restricted area, 

 the TST. Island of New Zealand; here, too, the inference is that 

 the second have arisen from the former. 



