DESCRIPTIONS OF GENERA AND SPECIES 303 



Genus Amphichaeta, Tauber. 



Dbfinitioit. Prostomium elongate. Setae in four rows ; several segments without 

 setae after second setigerous segment No perioesophageal vessels. Sperm-sacs 

 and egg-sacs present ; no genital setae. 



This genus was first described by Taubee (1) ; the description, however, is 

 limited to the following brief definition : — 



'Praestomium dilatatum. Os inferum. Fasciculi uncinorum tam dorsalium quam 

 ventralium.' 



This definition is nevertheless sufiicient to show that the worm in question is difierent 

 from Chaetogaster. The genus has been fully established by the investigations of 

 Kallstenius. Previously to the paper of the last-named, Levinsen (2) had sought 

 to identify Amphichaeta with Uncinais. Since Levinsen wrote upon this subject 

 Uncinais has been re-investigated by Bourne (5) ; and there is no longer any doubt 

 of the complete distinctness of these two Oligochaeta. 



In the most distinctive feature of the organization of the Chaetogastridae, 

 Amphichaeta agrees with Chaetogaster; there are, that is to say, a considerable 

 number of segments intercalated between the second and third seta-bearing segment ; 

 in Chaetogaster there are six intervening between the first segment and the second 

 segment, provided with ganglia. The oesophageal segment has no setae ; in Amphi- 

 chaeta there are the same number; but as there are two ventral bundles of setae 

 immediately following the mouth, and as the oesophageal segment is provided with 

 setae, the same number of ganglia separate the anterior and the posterior seta-bundles. 



This genus also differs from Chaetogaster in the absence of a perivisceral vessel 

 in the oesophageal segment. A peculiar fact about the nephridia is their asymmetrical 

 condition ; they commence in the segment following that which contains the ovaries ; 

 occasionally they are symmetrical (paired), but more often one or other only of the 

 two nephridia of a segment are present; they are closely adherent to the ventral 

 blood-vessel, and are entirely without a pre-septal portion, that is, there is no 

 funnel. 



The reproductive organs have been fully described by Kallstenius; the two 

 testes lie in the segment immediately following the oesophageal; they arise from 

 the peritoneum covering the nervous cord; the unpaired ovary arises in a similar 

 fashion in the next segment; the efferent apparatus of the testes consists of the 

 usual funnel-duct and terminal gland ; it opens on to the ovarian segment ; an 



