II] MODE OF LIFE 57 



terrestrial Oligochaeta that this mode of progression 

 occurs. It might also be urged, and with some 

 reason, that the retention of rather longer setae 

 upon the clitellum in the Lumbricidae and Geoscole- 

 cidae, and the possession of equally long or in many 

 cases much longer setae corresponding to one of the 

 two pairs of setae of the generative segment in certain 

 Megascolecidae, is a feature in which an aquatic 

 condition so to speak is retained. The setae would 

 represent a vestige of the general presence of long 

 setae over the body generally such as is convenient 

 or at least not inconvenient to an Annelid living in 

 water or soft mud. But probably it will be thought 

 the modified genital setae are a recent development 

 and not a retention. 



There is no more thoroughly terrestrial family of 

 earthworms than that of the Moniligastridae and yet 

 this family in its general anatomical characters shows 

 many points of likeness to aquatic forms as has been 

 now pointed out by many observers. It is true that 

 these characters are not those which might be 

 associated at first sight with an aquatic life. But 

 none the less they are characteristic of most of the 

 families which live in the waters of the earth. Thus 

 Monlligaster and its allies {Eiqmlygaster, Drawida, 

 etc.) have quite short sperm ducts which open on to 

 the exterior at furthest in the segment next to that 

 in which their internal funnel lies. Again the 



