138 DR. J. STEPHEN'SON OX THE MORPHOLOGY, CLASSIFICATTON, 



Zealand, to explain the distribution of the Octochfetin?e ; and lastly, 

 we may add, in the opposite sense, a number of arms of the sea, 

 stretching across India and dividing it into a number of islands, 

 which formed a western extension of what is now the Malay 

 Archipelago. 



The bridge to JST. America may be admitted. It would pass from 

 the eastern end of Siberia to Alaska, and demands no considerable 

 elevation of the floor of the ocean — indeed, a rise of 1000 feet 

 would convert the N. Pacific into dry land as far south as the 

 60th parallel. 



The case is otherwise with the bridge between Africa and India. 

 What is asked for is something like the Lemuria of Wallace, or 

 the Gondwana continent postulated by many geologists. The 

 important question here concerns Eudichocj aster ^ according to 

 Michaelsen a member of the Trigastrinte, and descended from 

 Trufaster, which is endemic in the W. Indies and Mexico. 

 Michaelsen supposes that either TriV/osifej' crossed the Atlantic (by 

 an Americo-African bridge) and made its way across Africa, and 

 thence by the bridge now under discussion to India, where it 

 evolved into EudichogciHter (suffering extermination in the African 

 part of its range) ; or Eadidiogaster originated from Trigaster on 

 the American side, passed across in the same way, and was exter- 

 minated in Africa but maintained itself in India. But I think 

 I have shown in a previous section that it is at least equally 

 probable that EadicJiogaster originated from Octochcetus (or 

 Rcmiiella) ; on this supposition EudicJiog aster arose in India, to 

 which it has thus always been confined. 



I have myself argued that the Indian genius Hojylochoitella 

 may be descended from Jloirascolex, found in Madagascar (20), 

 and Lemuiia or Gondwana would form an easy path for its 

 transport. But Hoplocha'teUa is — or at any rate a number of 

 species are — euryhaline, and are found on the shores of western 

 India ; and we must i^eckon with the possibility of transport 

 from Madagascar in seaweed or other tangle ; the S,W. monsoon 

 blows in the required direction for several months of the yenr. 



Dlchogaster has reached most of the islands of the Malay 

 Archipelago, and some of the Polynesian islands, as well as India, 

 and there is no doubt that small species of this genus are 

 frequently transported by man in the way of trade. It is admitted 

 that there is no need whatever to introduce land-bridges to 

 explain the Avide occurrence of these species all over the East. 



The last reason for assuming the former existence of the 

 Indo- African bridge would be the presence of a Moniligastrid 

 (though one widely difTerent from the Oriental Moniligastrid ?e) 

 in tropical East Africa. This African Moniligastrid is not 

 descended from the Oriental branch of the family, nor the Oriental 

 from the African ; this follows from the position of the gizzards — 

 in front of the genital segments in the African, behind in the 

 Oriental worms. The alimentary tube, without special thickening 

 in the common ancestor, has developed into a series of gizzards 



