THE FREE-LIVING FLATWORMS (TURBELLARIA) 



349 



62 (63) Genital pore in posterior third of body. . . Tribe Olisthanellini 



Excretory system opens on fdorsal surface with one asymmetrical or two symmetrically 

 placed openings. Testes dorsal to the yolk glands. Without atrial copulatory organ. 



Single genus thus far reported in America Olisthanella. 



Only one species in this country. . Olisthanella caeca (Silliman) 1885. 



Length 1.3 mm. Without eyes. Without long sensory hairs. Color 

 grayish- white. Sometimes apparently colored, due to food in intes- 

 tine. Pharynx rosette-shaped and nearly central in position. Intes- 

 tine large. Rhabdites and tracts prominent. Female organs only are 

 known. Sluggish and found only in mud under stones. Monrce Co., 

 N. Y. 



Fig. 619. Olisthanella caeca, ph, pharynx; i, intestine; b, brain; wi, yolk 

 gland; oi), ovary; go, genital pore; /i, rbabdite tracts. X 35. (After Silliman.) 



63 (62) Genital pore in anterior two-thirds 64 



64 (71) Testes ventral to the yolk glands. Rhabdites only in mesenchyma 

 tracts Tribe Typhloplanini . . 65 



Protonephridia with two main branches which communicate with the exterior through a 

 transverse branch which leads either to the mouth or to the genital atrium. With or without 

 atrial copulatory organs. 



65 (66) Anterior end of body a retractile proboscis. . . Rhynchomesostoma. 

 Only one species. . . Rhynchomesostoma rostratum (MiiUer) 1773. 



Length 2 mm. European specimens 



reach a length of s mm. when extended. 



Very transparent. Body fluid rose or 



yellowish-red in color. Intestine contains 



B yellowish-red oil droplets. Ventral surface 



flat, dorsal convex. Anterior end of body like a telescopic tube. 



Pharynx small, lying somewhat before the middle of the body. 



Rochester, N. Y. 



Fig. 620. Rhynchomesostoma rostratum. {A) Proboscis partly extended. 

 (S) Fully contracted. X 40. (After von Graff.) 



66 (65) Anterior end of body without retractile proboscis 67 



67 (70) Without atrial copulatory apparatus 68 



