DESCRIPTIONS OF GENERA AND SPECIES 309 



pores ; this family is the only one of the aquatic Oligochaeta which have dorsal 

 pores. The setae are entirely absent in Anachaeta; there are only two bundles in 

 Diktichopus (if this genus be really an Enchytraeid), but six in Chirodrilus (con- 

 cerning which genus also more information is wanted) ; all the others have the 

 usual four bundles of setae to a segment. The setae are either straight or bent in 

 the prevalent ./-shape ; their extremities are never cleft. The setae in this family 

 are always short and generally fairly numerous in each bundle. One genus only is 

 entirely achaetous the genus Anachaeta. The setae are here represented by large 

 cells which depend into the body-cavity (see p. 5). The setae when present are of 

 two kinds ; there are curved sigmoid setae and straight setae ; the former are found 

 in certain genera, such as Pachydrilus ; and the latter in other genera, such as 

 Enchytraeus. The setae of a bundle are disposed in a fan-like fashion, the setae on 

 one side of a bundle diverging from those upon the other side. The number of 

 setae in a bundle varies from one (Enchytraeus monochaetus) or two (Fridericia 

 bisetosa) to fourteen, which is the greatest number that has been hitherto recorded 

 (in Pachydrilus minutus). Very commonly there is an inequality in number 

 between the setae of the lateral and ventral bundles respectively ; in this case, 

 the lateral bundles have usually the fewest setae ; thus in Pachydrilus pagen- 

 stecheri there are 7-10 setae in the ventral bundles and 3-5 in the lateral. The 

 setae of a given bundle are usually of a size ; but this is not always the case ; 

 the most conspicuous exception is seen in the genus Fridericia ; here the outer 

 setae of a bundle are always larger than the inner, which are at the same 

 time the younger. There are sometimes differences in size between the setae of 

 the four bundles of a given segment ; for example in Fridericia bulbosa the setae 

 of the lateral bundles are smaller than those of the ventral. In Mesenchytraeus 

 setosus there is something like a formation of genital setae ; the lateral bundles of 

 segments v-viii (inclusive) are made up of 14 setae, which are very much larger 

 than those of adjacent segments. In Enchytraeus monochaetus the anterior setae are 

 more slender than those of the posterior segments. Enchytraeus 'monochaetus is 

 unique in the group by reason of the fact that the setae are entirely wanting upon 

 the first few segments of the body. The nephridia are peculiar in their form ; they 

 are stout and solid-looking organs, often lobed, with a lumen which (according to 

 BOLSIUS) forms a plexus in their interior. They frequently begin as far forward as 

 the second segment, though they are wanting in those segments which contain the 

 generative organs. Some Enchytraeidae are characterized by the possession of 

 a single gland, or a pair of glands, which seem to be the equivalents of the 

 calciferous glands of other worms (see p. 61). The family is also characterized by 



