188 OLIGOCHAETA 



Haplotaxis, subsequently (1, p. 40) altered to Phreoryctes for the reason that Ilaplo- 

 taxis had been previously used in Botany. Schlotthaubee altered the name to 

 Georyctes for the reason that the worm is not exclusively an inhabitant of 'wells,' but 

 is occasionally found in the soil. This change cannot of course be allowed. Claparede 

 (2) applied the name Nemodrilus to a worm found by him in the Rhone, in ignorance 

 of its identity with Phreoryctes'^. Accordingly the name Phreoryctes must stand, 

 unless, indeed, it be thought that the same name may be allowed to an animal and 

 a plant : but in any case the name Phreoryctes is now so well established that it 

 seems hardly worth while to make a change. The genus Phreoryctes has been found 

 in a good many parts of Europe (not in England), and in New Zealand, and in North 

 America. 



The species or the genus are of considerable length and thinness (this is less the 

 case with P. smithii), and the prostomiuTn is generally divided into two by 

 a transverse constriction — a character also met with in the Capitellidae, which 

 were at one time, not, however, for this reason, included in the Oligochaeta. The 

 setae in the European Phreoryctes are of the typical Lumbricid pattern, sigmoid 

 and not cleft at the free extremity. As a rule there are only four setae to each 

 segment, which are implanted singly and at equal distances from each other ; each 

 has commonly a nearly complete ' soie de remplacement ' beside it. Each of these 

 setae, together with the incomplete seta lying beside it, represents the pair of setae 

 in other Oligochaeta. The dorsal and ventral setae are usually of different sizes. 

 A more normal arrangement of the setae is met with in P. smithii, where they are 

 distinctly paired ; here, however, we still find the same difference in size between 

 the dorsal and ventral pairs. The dorsal setae are largely obsolete in P. emissarius. 

 The clitellum is not extensive ; it occupies segments xi-xiii inclusive and a portion 

 of segment x. 



The ventral nerve-cord is provided in each segment with a peculiar appendage, 

 first described by Leydig (6), and afterwards by Timm and Forbes ; these struc- 

 tures, the ' ventral organs ' of Timm, are pyramidal masses of nucleated cells which 

 support the nerve-cord as the ' chairs ' support the railway lines ; they are hollowed 

 out where the nerve-cord rests upon them. These organs are regarded by Timm as 

 of sensory function. Similar organs occur in the Enchytraeidae. 



The most remarkable feature about the vascular system is that (according to 

 Clapar^de) the ventral vessel is contractile - a condition which is, so far as we are 

 aware, unique among the Oligochaeta. 



The reproductive system is in several respects peculiar and interesting. The 



' This identity w-aa first pointed out by Vaillant (3, p. 249). 



