30 EARTHWORMS AND THEIR ALLIES [ch. 



and in certain Eudrilids, e.g. Hyperiodrilus. The 

 main peculiarity of the family is that the sperm 

 ducts are very short and open on to the next segment 

 to that which contains the spermaries, as in the 

 water-living Oligochaeta generally. The terminal 

 sac into which the male ducts open is moreover 

 rather like that of such a family as the Lumbriculidae. 



The Aquatic Families of Oligochaeta. 



It would seem to be quite possible that when the 

 fresh waters of the world have been as well examined 

 for Oligochaeta as have so many parts of the land 

 areas, the number of purely aquatic Oligochaeta 

 will be found to equal those inhabiting the land. In 

 any case we are quite justified at the present moment 

 in stating that there are rather more families of 

 these smaller Oligochaeta than there are of the bulkier 

 terrestrial forms. But while there are certainly 

 seven or eight distinct families, these do not between 

 them contain at present so many genera as do the 

 fewer families of earthworms; and the number of 

 species of the latter that are known to science 

 enormously exceeds that of the 'Limicolae' as the 

 fresh- water worms were at one time called in common. 

 The fact that there are purely marine forms of these 

 water worms was hardly appreciated at the time that 

 the term Limicolae was used; now however we are 



