TURBELLAFJA 



161 



Key to tlie families of Ilh ah doc eel a here described: 



Gi Forward end not in form of a proboscis, or where a proboscis is present 

 it cannot be retracted into a sheath. 

 &i Ovary and yolk glands not distinct. 



Ci Single median excretory trunk present 1. Catenulidae 



Ca A pair of excretory trunks present 2. Microstomidae 



60 Ovary and yolk glands distinct from each other. 



Ci Pharynx sac-shaped and parallel to ventral surface 3. Dalyelliidae 



C2 Pharynx rosette-shaped and perpendicular to ventral surface. 



4. Typhloplanidae 

 Oj Forward end in form of a proboscis which can be retracted into a sheath. 



6i One genital pore present 5. Polycystididae 



&2 Two genital pores present 6. Gyratricidae 



Family 1. CATENULIDAE. 



Mouth in ventral surface near forward end; no preoral branch of 

 intestine; pharynx simple; excretory pore at hinder end, with a single 

 median excretory trunk; testis and ovary median and single, the former 

 in front of the latter; pigment eyes wanting; reproduction asexual as 

 well as sexual, chains of individuals forming: 5 genera and about 25 

 species, 14 American. 



1. Stenostomum* Schmidt. Body colorless; intestine often colored 

 brown, reaching almost to the hinder end of the body; a pair of ciliated 

 sense pits in front of brain and 1 to 2 pairs of light-refracting organs 

 behind it: 16 species, 5 American, all but 



one in fresh water. 



S. leucops (Duges). Chain consisting 

 of 8 or less individuals up to 4 mm. long; 

 light-refracting organs concave and 2 in 

 number: eastern and central states; Eu- 

 rope; common. 



S. grande Child (Fig. 258). Chain 

 consisting of 4 to 6 individuals 2 to 2.6 

 mm. long ; color orange yellow^ : in fresh 

 and brackish water; common. 



2. Rhynchoscolex Leidy. Forward 

 end of cylindrical bodj^ elongated into 



proboscis-like appendage at the base of which are the mouth and a pair 

 of sense pits: 2 species. 



R. simplex Leidy. Body yellowish white, 5 mm. long: Philadelphia, 

 at the bottom of clear brooks. 



Fig. 258 — Stenostomum, grande 

 (von Graff). A, anterior cud 

 with tbe sense pits (s) ; B, pos- 

 terior end. 



* See "Studies on Regeneration, Fission, and Regulation of Stenostoma, 

 C. M. Child, Arch. f. Entwick., Vol. 15, p. 187, 1902. 



by 



