134 DR. J. STEPHENSON ON THE MORPHOLOGY, CLASSIFICATION, 



for the quick-moving Carnivora ; in asking for land-bridges to 

 explain the distribution of the Oligochseta we get much more than 

 we want. There can never have been a land connection between 

 Australia and the great land mass to the north-west since 

 the Eocene. 



Still stronger is the case of the supposed connection between 

 India and New Zealand. This is a necessity, according to 

 Michaelsen, in order to explain the occurrence of the Octo- 

 chretinae in both lands; and since the Octochsetinse do not 

 occur in Australia, the bridge in this case avoided Australia. 

 New Zealand does not even contain Marsupials ; yet Octochcetus, 

 the genus common to India and New Zealand, is not a particularly 

 archaic genus, and its occurrence in both India and New Zealand 

 would, on Michaelsen's view, have to be explained by, presumably, 

 late or middle Tertiary land connections. But New Zealand is 

 an oceanic island, and probably lias never been connected at any 

 time* with the larger land-masses, certainly not in Tertiary 

 times. 



It is quite possible that similar objections might be brought 

 against the other land-bridges which have been postulated to 

 explain the existence of related or identical genera of earthworms 

 in distant lands. I have specially mentioned the above because 

 it is so obvious, once attention has been drawn to it. The general 

 principle is that, earthworms being a recent group, and requiring, 

 on the hypothesis of dispersal by land, connections of some 

 considerable permanence, other groups will have been a.ble to 

 pass even more easily ; and the dispersal of earthworms by land- 

 bridges cannot be assumed unless there is a latge degree of 

 similarity between other elements of the fauna also. 



(4) Contributions towards a more satisfactory Solution. 



I trust that, in what follows, I shall not be considered to be 

 treating too lightly tire claims of zoogeography to a hearing in 

 the discussion of the problems of palseogeograph}--. As Michaelsen 



* Michaelsen's time-scheme can be put together somewhat as follows : — The 

 oldest components of the Indian earth worm fauna date from the Upper Jurassic, 

 when India was connected broadly with both Angara and Australia; Plutellus and 

 Megascolides wandered oft' into Angara, reaching western N. America in the later 

 Cretaceous. The chief part of the evolution took place in the Tertiary, the period 

 of the changing land-bridges. In the Pliocene the now consolidated Indian 

 peninsula became connected on the W. or N.W. with lands which had earlier 

 received their earthworms from Tropical Africa (JEudichogaster). 



It will be seen that he puts the evolution of the group earlier than I do; but I do 

 not find anj'thing which invalidates the line of argument and general conclusions of 

 section 3a- above, especially that, of the quite recent origin of the phyletically youngest 

 genera such as Megascolex. The word used by Michaelsen for the period of the 

 crigin of the Indian Oligochnete fauna is "Malm," which corresponds (Ziegler, 

 Zool. Worterbuch) to the Upper Jura. PluteUus and Megascolides are supposed 

 to have then been in existence ; is there any other example of genera ot a variable and 

 evolving group persisting since that period, especially genera, such as these, which 

 are connected by intermediate gradations not only with each other, but with the 

 genera below and above them (Diplotreuia and Notoscolex) , genera, that is, which 

 are still not sharply marked off from their ancestors and descendants? 



