308 ANNELIDA 



segment 25, then 2; color opaline white: among damp leaves, in the 

 woods. 



F. agilis Smith. Length 30 mm.; number of segments 57 to 66; 

 dorsal blood vessel begins at segment 19 ; salivary glands much branched : 

 in the soil (Illinois). 



4. MESENCHYTRa:us Eiseu. Setae sigmoid; blood usually colorless; 



no salivaiy glands: 30 species. 



M. beumeri (Michaelsen). Length 



30 mm. ; setae 3 to 5 in lateral bundles 



^ -^ ^ ^ ' "'' "■ ' and 5 to 8 in ventral ones ; clitellum 



^__ on segments 11 to 13: Philadelphia, 



I f-^^=='"''^^y^=*^^ ^^[^'^%^^ ^^ in wet places; Europe. 



•5 8 9 ~^' 



Fig. 487 — Diagram of anterior por- r ^t a ttat-tv a tt. * 



tion of a naid (Walton). 1, prosto- FAMILY 5. NAIDIDAE.* 



raium ; 2, eye ; 3, brain ; 4, mouth ; 

 5, pharynx ; 6, oesophagus ; 7, blood 



vessel ; 8, testis ; 9, ovary ; 10, hair- Small aquatic, transparent worms 



like setae; 11, forked setae; 12, in- 

 testine; 13, clitellum. (Fig. 487) with 2 to 4 groups of setae 



on each segment, and often with a 

 distinct head; ventral setae forked; testes and ovaries usually in seg- 

 ments 5 to 7; the worms reproduce principally by transverse division, 

 forming animal chains : 15 genera and 50 species, mostly in fresh water. 

 Key to the genera of Naididae here described: 



Ri Hair-like setae present dorsally. 

 bi Prostomium not tentacular. 



Ci Without retractile rear appendages 1. Nais 



Ca Retractile rear appendages present 4. Dero 



62 Prostomium long and tentacular. 



Ci Dorsal setae begin on 5th or 6th segment 2. Stylaria 



C2 Dorsal setae begin on 2d segment 5. Pristina 



flj Hair-like setae absent dorsally. 



61 No dorsal setae present 6. Ch^togaster 



62 Forked dorsal setae present 3. Paranais 



1. Nais 0. F. Miiller. Head distinct ; dorsal setae begin on segment 

 6 and are partly acicular and partly long and hair-like; ventral setae 

 short, with cleft ends; blood yellow or red; eyes usually present: in 

 standing or flowing water, in mud or on plants ; reproduction by budding 

 very common; 10 species, 5 American. 



N. elinguis Miill. (N. rivulosa Leidy). Two or 3 dorsal hair-like 

 setae present; length 2 to 10 mm., with 15 to 37 segments; color light 

 brown; eyes usually present: often abundant on algae; Europe. 



N. parvula Walton. Prostomium blunt; eyes present; dorsal bundle 

 composed of 1 hair-like and 2 cleft setae; length 1.2 mm.: Cedar Point, 

 Lake Erie. 



* See "Naididae of Cedar Toint," by L. B. Walton, Am. Nat., Vol. 40, p. 683, 1906. 



