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



III. Some General Considerations on the Geographical, 

 Distribution of Indian Oligoch/Eta. 



The geographical distribution of Indian Oligochseta lias been 

 treated at length by Beddard and Michaelsen (Beddard 1, 2; 

 Michaelsen 7, 10. 11). The earlier writings of both authors are 

 valuable for the discussions of the means by which the migrations 

 of Oligocbseta are in general effected ; but the large collections of 

 Indian worms investigated by Michaelsen in 1909 and 1910 (10, 

 11) increased our knowledge of the actual facts of distribution to 

 such an extent that the special conclusions in the later works 

 supersede those arrived at in the earlier. 



(1) The Migrations of Oligochceta. 



Oligochaata may for the present purpose be divided into three 

 groups — limnic, littoral, and terrestrial, each with its distinctive 

 modes of spreading. 



Limnic forms have a great diversity of means of dispersal. 

 They may spread directly throughout a river system, through all 

 the canals and into all the tanks and reservoirs supplied from it. 

 Their cocoons are easily transported in the mud which adheres 

 to the feet of wading birds ; some forms are known to encyst, and 

 hence may be transported in this manner even in the adult state. 

 An Enchytraeid has been found frozen in a block of ice, and 

 recovered (Beddard, 1). 



As a consecpience the same genera — sometimes the same species 

 even — are found in widely distant places. The case is similar to 

 that of the Rotifera and Protozoa, of which the same genera and 

 species are found in ponds and streams all over the world. There 

 appears to be but one genus. Branchiodri/us, of the limnic 

 Oligochaeta which is peculiar to India, while a number of species 

 are found both in England and India,, or in Europe and India 

 (species of Nais, C Junto g aster, Dero, Aulophorus, Pristina, etc.). 



Littoral forms live on the shore, exposed at times to submersion 

 in salt water. Like the last group, these have a wide distri- 

 bution ; being, unlike earthworms in general, immune to salt 

 water, they can be transported in masses of seaweed, or more 

 commonly their cocoons are so transported, entangled in masses 

 of weed or other detritus. Not only can they take possession 

 of a whole coast, and spread along the shore line, but they may 

 in this way travel over sea for long distances. The most note- 

 worthy genus is Pontodrilus, which occurs along the coasts of 

 India, and has a circummundane distribution. 



Terrestrial forms constitute the bulk of the Oligochaeta.. Here 

 the means of spreading are more limited ; for the most part 

 earthworms are dependent on their own activities for reaching 

 new regions, and hence their wanderings must be very slow. 

 According to Michaelsen, worms which are found outside their 

 burrows apparently wandering about have for the most part been 



