OLIGOCHAETA. 



By J. Stephknson. 



The Oligochaeta of brackish water are few, and do not form an independent 

 ethological group. They seem to be forms belonging to the freshwater or littoral 

 groups which possess the power of resisting a certain amount of admixture of salt or 

 fresh water respectively. 



Though the Oligochaeta have long been recognized as capable of contributing 

 valuable results to zoogeography, these results have been gained almost entirely 

 from a study of the terrestrial forms, to the exclusion of those of aquatic and littoral 

 habit. Nor in view of the modes of dispersal can it be expected that it will be 

 otherwise in the future. The following few remarks may serve briefly to illustrate 

 this statement. 



In the case of freshwater forms, it seems probable that birds are one of the chief 

 agents of dispersal; the mud which adheres to the feet of waders offers an easy 

 means of transport to small worms or their cocoons; and it is well known that small 

 animals, such as Nematodes and Rotifers, have been cultivated from such mud after 

 a prolonged flight, while small molluscs have also been found to be conveyed in this 

 way. Speaking of the probable introduction of Australian worms into New Zealand in 

 this way, Benham ( fC A note on the Oligochaeta of the New Zealand Lakes "-, Trans. 

 N . Z. Inst., XXXVI, 1903) calculates that a strong flier with the wind behind it 

 could cover the distance in 36 to 48 hours. The comparative valuelessness for 

 zoogeography of the data of distribution of freshwater Oligochaeta may be exempli- 

 fied by the fact that Nais paraguayensis, first found, as the name implies, in 

 material from Paraguay, has since been discovered in Lahore ; that Nais communis, 

 described first from Switzerland, has been found both in North and South India ; 

 Stylaria lacustris, also found at Lahore, occurs all over Europe, in the Baikal Sea, 

 and in North America; while the genus Chaetogaster , represented by several species in 

 India, is found throughout Europe, in North America, in the Baikal Sea, and in 

 Australia, and is indeed probably absolutely cosmopolitan. 



The littoral Oligochaeta are unfortunately capable of furnishing no more valu- 

 able results. " The animals usually lay their cocoons underneath and amongst the 



masses of detritus on the shore, often attaching them firmly to these When at 



more than usually high tides these masses are again washed into the sea, they may 

 be taken up by currents, carried far away, and thrown up with the cocoons they 

 bear on to the shore at some distant point. In this way littoral Oligochaetes may 

 spread not only along a continuous coast-line but over considerable stretches of 



