^^ VESMES— SYSTEMATIC REVIEW 181 



mentally arranged, with special efferent ducts ending in a single median external 

 aperture. A pan- of germaria placed in front of the testes ; female aperture behind 

 the male ; both m the anterior end of the body. Parasites or carnivorous ; fresh 

 water, in the sea, or on land. 



Sub-Order 1. Ehynchobdellidse. 

 With cylindrical tubular pharynx lying free in the pharyngeal pouch, and pro- 

 ti-usible through the mouth. Clepsinc, Poniobdella, Brmichellion (with gill-like 

 appendages on the back). The two latter in the sea, parasitic on sharks. 



Sub-Order 2. Gnathobdellidae. 



The pharynx is a muscular thickening of the oesophageal wall, which projects 

 into the lumen in the shape of 3 plates or ridges occasionally toothed. 



Hirudo medicinalis (the ordinary leech), Hcemopis Aulastamura (horse-leech), 

 Kephdis. Some Hintdinidce live on land. The remaining ChiathobdeUidx are 

 fresh-water forms. 



Order 2. Chsetopoda. 



The external segmentation of the body mostly corresponds with an inner segmenta- 

 tion. In special segmentally arranged glandular saccules of the outer integument 

 (setigerous glands) arise setfe, which project freely above the skin. Body cavity 

 well developed, separated from the blood - vascular system. The sexual products 

 develop in special regions of the epithelial lining (endothelium) of the body cavity, 

 into which they generally soon fall, and escape thence through more or less 

 strongly modified nephridia (vasa deferentia, oviducts, genital pouches, segmental 

 organs) . The following division is artificial, and is only retained from practical con- 

 siderations. 



Sub-Order 1. Oligochseta. 



The setigerous glands do not open on special blunt processes of the body 

 (parapodia) ; outer appendages (antennae, feelers, feeler - cirri, cirri, gills, etc.) are 

 wanting. Hermaphrodite. Direct development. In fresh water or on land. Fam. 

 Aphanmiciira : jSolosoma. Fam. Naidomorpha: Nais, Dero, Stylaria. Fam. 

 Chmtogastridce : Clicetogaster. Fam. Discodrilidm (posterior end of body modified 

 into a sucker ; parasitic on Crustacea) : SrancMoMella. Fam. EnchytrmidcB : Fachy- 

 drilus, Enchytrcetts, A'nachoeta. Fam. Tuhificidce: Tubifex, Psammoryctcs, ClitelUo, 

 Limnodrilus. Fam. Phreoryctidoe : Phreoryctes. Fam. Lumhriculidce : Luinbriculus, 

 Bhynchelmis, Stylodrilus. Fam. Criodrilidce : Criodrilus. Fam. Lumbricidce : 

 Allurus, Dendroloena, AllolohopTiora, Lumbricus (earth-worm). And the related 

 forms UrocJueta, Eudrilus, Acanthodrilus, Perichceta, PleurocJueta, McmiUgastcr. 



An uncertain position within the ChcBtopoda is taken by the so-called Archi- 

 anndida {Polygordius, Protodrilus, OUnodrilus, Histriobddla) and Saccocirrus — 

 forms whose organisation exhibits simple embryonic characteristics. 



Between the Oligochceta and the Polychceta stand the families of the Capitellidcc 

 (Oapitella, Noto'mastus, Dasybranchus), and Oplidiacea {Op>hdia, Travisia, Polyopli- 

 thalmus). The first have no blood-vessels. In both the parapodia are much reduced. 

 Gills may be present or absent. Head not distinctly separated. 



Sub-Order 2. Polychssta. 



The setffi stand on very strongly developed segmentally arranged elevations or 

 parapodia. On the head, antennse or feeler-cirri ; on the trunk segments, cirri, gills, 



