DESCRIPTIONS OF GENERA AND SPECIES 213 



and retracted by means of special muscles attached to the body -wall; it occupies 

 segments ii-iv, the space in front belonging to the buccal cavity. The oesophagus 

 occupies the next two segments, the intestine commencing in the seventh. The 

 commencement of the intestine is marked by the chloragogen-cells which cover it 

 throughout ; it is lined by columnar ciliated cells which are narrow at their base ; 

 between them lie roundish cells, which appear to be young cells in course of growth ; 

 outside the lining epithelium is a delicate muscle-layer, consisting only (Dieffenbach) 

 of circularly-arranged fibres. An abundant plexus of excessively fine blood-vessels 

 surrounds the gut. 



The vascular system consists of a dorsal and ventral blood-vessel, which are 

 united by transverse trunks, and of a series of caecal appendages of the dorsal 

 vessel. The dorsal vessel lies close to the dorsal wall of the gut, being covered by 

 the chloragogen-cells ; in the first segment it divides into two the branches reuniting 

 on the ventral side of the gut in the sixth segment. The dorsal and ventral vessel 

 are united by pairs of non-contractile transverse vessels in every segment ; in the 

 first eight segments (DiEFFiSNBACH), or fifteen (Katzel), these transversely running 

 trunks give rise to branches which form a complicated and irregular network, 

 continuous from segment to segment. At the ninth segment the network entirely 

 ceases, and the simple vessels, which are at first much coiled, alone remain ; they 

 lie in the posterior region of each segment. In front of each, commencing with 

 the ninth segment, are a pair of lateral vessels, also arising from the dorsal trunk, 

 which branch and end blindly ; at first the branches are less numerous ; afterwards 

 each vessel has from eight to ten; they are attached to the parietes by slender 

 contractile fibres ; they are themselves contractile. 



Vejdovsky's account differs somewhat from that of Dieffenbach — so much 

 so that one is inclined to believe that the two naturalists studied different 

 species. 



According to Vejdovsky, who examined young specimens (and starving, so that the 

 vessels were specially clear, owing to the empty condition of the alimentary canal), 

 each segment from the ninth to the sixteenth, has only a pair of non-branched, but 

 contractile, vessels situated close to the posterior dissepiment ; from the seventeenth 

 segment onwards there is no trace of these vessels. In the thirteenth segment the 

 branched vessels commence, but in the thirteenth segment they are only short caecal 

 appendages of the dorsal vessel ; the branching becomes quite obvious at about the 

 seventeenth segment. 



The nephridia commence in the ninth segment; they are present, at least, in 

 some of the genital segments, when the worm is matured. Where the funnel passes 



