50 EARTHWORMS AND THEIR ALLIES [ch. 



shows precisely the same state of affairs. These facts 

 gain additional significance in my opinion from the 

 fact that among the leeches which are now univer- 

 sally admitted to be allies of the earthworms the 

 same position of the vent is met with. This abnormal 

 position of the end of the alimentary canal may thus 

 be fairly quoted in connection with structui-es modi- 

 fied by the aquatic life. 



Finally, and this seems to be very important, the 

 only genus among the Megadrili which possesses gills 

 is the Nile worm Alma nilotiea. 



Marine Species. 



There are a few, but relatively speaking very few, 

 worms of the order Oligochaeta which lead a marine 

 life. And of these the majority are shore forms not 

 extending into the waters of the sea. The most 

 salient example, at any rate the best known perhaps, 

 is the genus Pontodrilus, the name of which fixes its 

 habitat, and was naturally given to it on that account. 

 It was originally found on the sea shore of the South 

 of France, and I have myself examined examples from 

 Nice. The worm lives among bunches of sea- weed cast 

 up by the sea, and which are thoroughly salt. Besides 

 the two forms that have been met with in this Mediter- 

 ranean region but which are united by Dr Michaelsen 

 into but one species, other Pontodrilus have been 



