332 ZOOLOGY SECT, vu 



system takes the form of ciliated tubes (ex.), closed internally, and showing a 

 tendency to metamerism : these in Straliodrilus extend into the head. The 

 sexes are distinct : the male has a protrusible penis, directed ventrally. 

 There is no metamorphosis. 



There seems to be some reason for believing that Dinophilus and the 

 Histriobdellea may help to bridge over the interval between the Trochelminthes 

 and the higher, segmented, worms or Annulata. In this connection the 

 Echinoderidse, which were noticed in an appendix to the last Section (p. 313), 

 have also to be kept in view. 



