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. MESENCHYTIUETTS Eisen. Setae sigmoid; blood usually colorless; 



no salivary glands: 30 species. 



M. bemneri (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, 

 in wet places; Europe. 



Fig. 487 Diagram of anterior por- 

 tion of a naid (Walton). 1, prosto- 

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

 5, pharynx ; 6, O3sophagus ; 7, blood 

 vessel ; 8, testis ; 9, ovary ; 10, hair- 

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

 testine ; 13, clitellum. 



FAMILY 5. NAIDIDAE.' 



Small aquatic, transparent worms 

 (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: 



a x Hair-like setae present dorsally. 



Z>! Prostomium not tentacular. 



Cj Without retractile rear appendages 1. NAIS 



c 2 Retractile rear appendages present 4. DEBO 



6 2 Prostomium long and tentacular. 



Cj Dorsal setae begin on 5th or 6th segment 2. STYLABIA 



c 2 Dorsal setae begin on 2d segment 5. PBISTINA 



a, Hair-like setae absent dorsally. 



&! No dorsal setae present 6. CIOSTOGASTEB 



& 2 Forked dorsal setae present 3. PABANAIS 



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 Mull. (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 Point," by L. B. Walton, Am. Nat, Vol. 40, p. 683, 1906. 



