THE STKUGTUKE AND AFFINITIES OF SACCOCIRRUS. 421 



which pass down ou either side of the CESophagus to join 

 below it in the ventral vessel ; in the male genital region 

 the nephridia which open into the coelom by wide funnels 

 spreading over the front of the septa, pass backwards to 

 open by a narrow tube into the ducts of the sperm-sacs 

 before their eut ranee into the penes ; the penis is provided 

 with a number of supporting cuticular rods in its wall; in the 

 female the nephridium of the genital region opens in front 

 by a small ccelomic funnel, and runs backwards to open by a 

 minute pore into the base of the spermathecal duct. 



Although we cannot hope, in the present state of our 

 knowledge, to definitely determine the affinities of Saccor 

 cirrus, yet a general review of the question may be made 

 with some proht. 



Marion and Bobretzky (10) considered Saccocirrus to be 

 allied to Polygordius ; Hatschek (6), followed by Fraipont 

 (2), believing the Polygordiidee to represent an Archi-an- 

 nelidan group outside the Polychaeta, places Saccocirrus at 

 the beginning of the Polychaetes, between the Archi-annelids 

 and the Opheliidae.^ It is obvious that to determine the 

 position of Saccocirrus, we must first of all inquire into the 

 affinities of the Polygordiidae. The Polygordiidae comprise 

 the two genera Polygordius and Protodrilus. The cha- 

 racters on which Hatschek founds his opinion that these 

 worms form a group ancestral to the remainder of the Anne- 

 lida are the following : — the absence of parapodia and 

 chsetse ; the homonomy of the segments, and the fact that 

 segmentation is chiefly internal (a statement which scarcely 

 agrees with the structure of Protodrilus, however) ; the 

 restriction of the pharynx to the buccal segment; the close 

 connection of the nervous system with the epidermis; the 

 absence of ventral ganglia ; the simplicity of the muscula- 

 ture, there being no circular muscles (except in Polygor- 

 dius Villoti, described by Perrier [11] ) ; the presence of 

 dorsal and ventral mesenteries, and the simplicity of the 



' Ferrier, iu liis 'Traile de Zoologie ' (1897), places tue Polygordiidae near 

 the Phyliodocidse. 



