212 OLIGOCHAETA 



considered that these discrepancies were due to errors on the part of GBUBE. DIEFFENBACH'S 

 paper was published about the same time as VEJDOVSKY'S great work upon the Oligochaeta (24), 

 and is, accordingly, not referred to there. VEJDOVSKY, however, has not passed over the divergent 

 accounts given by GRUBE and CLAPAEEDE, and has pointed out that CLAPAREDE'S 'Lumbriculus' 

 is really identical with Claparedilla ; as this name, instituted by VEJDOVSKY in 1883, has the 

 priority over DIEFFENBACH'S name Pseudolumbriculus, it must clearly be retained. 



Our knowledge of the structure of this genus is principally due to VEJDOVSKY (24), RATZEL (3), 

 and to DIEFFENBACH, and is restricted to that of the species Lumbriculus variegatus. This knowledge 

 is, unfortunately, far from being complete, as the sexual organs have been, as yet, only imperfectly 

 described. 



The setae are disposed in pairs, and are bifid at their free extremity. 



There is, as LEYDIO first discovered, a pore upon the dorsal side of the prostomium, 

 which is not always evident ; it puts the cavity of the prostomium into communication 

 with the exterior. DIEFFENBACH states that in the neighbourhood of the pore there 

 are cilia present ; and BULOW (1) describes nerves which arise from the cerebral 

 ganglia and supply this region, which he regards as an organ of taste. 



The nervous system of Lumbriculus is formed upon the same plan as that of 

 other Oligochaeta ; the cerebral ganglia are figured by VEJDOVSKY (24, Taf. xii, p. 28), 

 the cerebral ganglia and the commencement of the ventral cord by RATZEL (3, fig. 10, 

 Taf. xlii.), and LEYDIG (7> Taf. iv. fig. 6). The brain (cerebral ganglia) consists of two 

 ganglia, which are composed of nerve-cells anteriorly and fibres posteriorly; the two 

 masses of cells are united by a narrow row of cells. The commissures passing round 

 the oesophagus have no ganglionic cells ; where they join the ventral chain there 

 is a group of cells in front of, and behind, the point of junction. The neuro-chord 

 forks at the commissure, and extends along the commissure for a very short way 

 on each side. VEJDOVSKY represents the brain as more extensively cellular than does 

 RATZEL, whose account has been followed above. According to VEJDOVKSY, the ventral 

 nerve-chord gives off only a single pair of nerves in each segment, which almost 

 immediately perforate the muscles of the parietes. Transverse sections show the 

 presence of these 'giant fibres.' A pair of lateral ganglionated nerves are present. 



The sense-organs of Lumbriculus consist, according to RATZEL, of 'a sharply- 

 marked white stripe in the median ventral line,' which gradually fades away 

 posteriorly. This streak is composed of irregular spots, which consist of groups of 

 cells in intimate connexion with the nerve-chord. VEJDOVSKY has denied the 

 existence of this sense-organ ; he describes, however, the cup-shaped tactile organs 

 of which mention has already been made. 



The alimentary canal is, with the exception of the buccal cavity, ciliated 

 throughout. It commences with a strong muscular pharynx, which can be everted 



