ii] MODE OF LIFE 49 



find gizzard and calciferous glands absent or rudi- 

 mentary. 



Another not unusual feature among these aquatic 

 Geoscolecidae is the quadrangular form of the posterior 

 end of the body. This is shown as its specific name 

 denotes by GlypMdrilus quadrangidus, by species 

 of Alma and in all the species of the genus Criodrilus. 

 It is to be noted in this connection that a species of 

 the partly aquatic Eiseniella has been named tetrae- 

 drus on account of precisely the same phenomenon. 

 In these cases it is the posterior part of the body 

 which is thus quadrangular ; the anterior segments 

 down to the ninth in Criodrilus being rounded in 

 the usual Oligochaetous fashion. As the paired setae 

 are apt to lie in the four projections of the quad- 

 rangular body, one is tempted to see in this arrange- 

 ment of structures a faint approach to the dorsal and 

 ventral parapodia of the marine worms, and in any 

 case it seems possible that by this means the worms 

 can cling more effectively and continuously to the 

 stems and leaves of aquatic plants among which they 

 so largely live. 



It is a very remarkable fact that in the genera 

 Criodrilus and Alma the vent is dorsal in position 

 instead of being surrounded as in earthworms 

 generally by the last segment of the body. This fact 

 might be put down to the near affinity between these 

 two genera, were it not for the fact that GlypMdrilus 



B. E. 4 



