AXD ZOOGEOGRAPHY OF INDIAX OLIGOCH.ETA. 137 



experiment on the subject of worms and salt water ; the statement 

 that they are destroyed by it seems to be commonly accepted, 

 without comment and without reference. 



There are, of course, other possibilities of transport for worms, 

 or for their cocoons — the mud on birds' feet for example ; Benhani 

 calculates that a strongly flying bird could pass from Australia to 

 New Zealand (1200 miles) in 36 hours. But the possibility that 

 I most wish to insist on, after that of the occuri'ence of rafts — 

 because I do not think that it has as yet received any attention — 

 is that of the polyphyletic origin of some, at least, of the genera 

 common to the Indian and Australian regions. I believe that 

 this will go some distance towards explaining the presence of 

 these common elements in the two faunas ; evolution has pro- 

 ceeded on parallel lines, and the younger genera ha,ve not wandered 

 from India to Australia or from Australia to India — the}' have 

 been independently evolved in each region. 



In my first sketch of the present argument the whole question 

 of polyphyly in these genera was discussed in this place ; it was, 

 in fact, in reviewing their geographical distribution that I was 

 brought up against the subject. But the space that I was obliged 

 to devote to it seemed too great to assign to a subordinate head- 

 ing, and I decided to treat it independently. The whole of the 

 previous article, however, may logically be placed here, as a con- 

 tribution towards a more satisfactory explanation of the facts of 

 distribution. 



We may finally proceed to a separate consideration of the 

 several bridges which have been postulated ; and here I shall 

 usually takeThe conclusions of Michaelsen (with whom Beddard 

 is in general agreement) as the basis of my own discussion, since 

 he is the author who has treated the matter most fully. Michael- 

 sen requires all the bridges to be mentioned, and the splitting up 

 of India into islands as well ; however, he regards himself as 

 conservative in this matter. In a controversy with F. Sarasin 

 (11) he says, " I am reproached with being too wanton in my 

 bridge-building. I do not think that such a charge can be sub- 

 stantiated ; on the contrary, I believe that we do not reckon 

 sufficiently with the mobilitj^ of the earth's crust in this region "' 

 (^. e. the Indo-Australian region). 



These bridges are as follows : — A bridge between Asia and N. 

 America, to explain the occurrence of Plutellus and Megascolides 

 in the western part of N. America ; a transatlantic bridge between 

 the W. Indies and Central America on the west and Africa on 

 the east, and a bridge between Africa and India, to explain the 

 occurrence in India of the Trigastrinas ; one between Australia 

 and Eui'ther India over the present Malay Archipelago, and one 

 across the present Bay of Bengal, said to be requisite to account 

 for the distribution of the Megascolecinaj and Moniligastridae ; a 

 particular bridge, at a particular time, between India and New 



