140 DR. J. STEPHE^g^SON ON THE MORPHOLOGY, CLASSIFICATION, 



regions between the islands of Bali and Lombok; this is the 

 interval where the assmnption of a land-bridge raises many more 

 ditnculties than it explains. But the interval is only fifteen miles ; 

 and while birds' feet and natural rafts oft'er a sufficient mode of 

 transfer for worms and their cocoons, they cannot serve to trans- 

 plant the mammals — not a whole mammalian fauna at any rate. 

 It is, too, in the genera of the Megascolecinte, the group which is 

 common to India and Australia, that Ave have seen most reason 

 to believe in polyphyletic origins ; as bearing on the probability 

 of polyphyly it is interesting to recall what Michaelsen says (7) 

 concerning the broad differences between the Indian and 

 Australian groups of Mec/ascolex — that the Australian species are 

 simpler, at a lower level of evolution, and more uniform, while 

 the Ceylonese species are often further advanced and in many 

 cases approach Phereiima. We can thus manage quite well with 

 the verse causse we know, but the bridge would only embarrass ws. 



The distance to be overcome in the case of New Zealand is 

 greater ; but the general faunistic objections to a land connection 

 with S.W. Asia (which is supposed to have avoided Australia) 

 are greater also. We are compelled, therefore, to invoke the same 

 agencies as before. 



Michaelsen's plea for a bridge across the Bay of Bengal, by 

 which worms from Australia, and also frOm Further India, could 

 reach the south of the peninsula and Ceylon without going round 

 by the head of the Bay, depends for its force on the presence in 

 S. India and Ceylon of genera which are not found elsewhere in 

 India ; the argument is that if these genera had passed through 

 the lai:ids about the head of the Bay, they would have left tliere 

 some trace of their passage. Thus Drctwida, a Moniligastrid, 

 common in S. India, and descended from a form which was 

 proba,bly not unlike Desmogasier (now found in Burma, Sumatra, 

 and Borneo), was, when Michaelsen wrote, unknown from the 

 intervening region, except for a few records of peregrine species. 

 But naore recent discoveries have shown that, both in the E. 

 Himalayas and near the coast at the head of the Bay, there ai"e 

 a number of endemic species of Drawida ; and it can no longer 

 be urged that the Moniligastridte cannot have passed round that 

 way because they have left no trace of their passage. Certain 

 genera of the Megascolecinse also were supposed to show the saiiie 

 limitation of distribution. JVotoscole.v was only known from 

 S. India and Ceylon, and the same was true of its descendant 

 Merfascolex. Lately, however, the E. Himalayas have been shown 

 to harbour three species (and a variety) of Notoscolex (31ef/ascoUdes 

 oneilli is a Notoscolex) ; so that here again it can no longer be 

 claimed that a bridge across the Bay of Bengal is necessaiy because 

 otherwise the genus would have left some trace of its passage 

 round the head of the Bay. And the polyphyletic origin of 

 Megascolex is, I think, clear enough to allow us to dispense with 

 the supposition, that it migrated into India from outside, whether 

 round the head of the Bay or by a land-bridge across it. 



