THE FREE-LIVING FLATWORMS (TURBELLARIA) 



339 



26 (25) Chitinous spicule of cirrus a straight narrow tube tapering to a 

 somewhat variably curved point. Vesicula seminalis and 

 vesicula granulorum separated by a short constriction. 



Macrostomum sensitivum (Silliman) 1885. 



Length 1.5 mm. Color grayish- 

 white. Intestine yellowish. Broad- 

 est through middle. Posterior end 

 narrowed. Rhabdites present in in- 

 tegument in large numbers, either 

 singly or in twos and threes. Rhab- 

 dite tracts conspicuous in anterior 

 end. Intestine with lateral diver- 

 ticula. Protonephridium communi- 

 cates through a pore with mouth 

 cavity. Chitinous organ somewhat 

 variable. Monroe Co., N.Y.; brack- 

 ish water, Falmouth, Mass. 



Fig. 601. Macrostomum sensitivum. (^) Anterior end: 6, 

 brain; e, eye with lens; k, protonephridium which opens 

 through the pore (p) into the mouth cavity; sh, sensory 

 hairs. X 15°. (After Silliman ) (B) Male copulatory organ 

 subjected to pressure. (C) Male copulatoiy organ not under 

 pressure: pj^ vesicula semmalis; pg, vesicula granulorum; ch, 

 chitinous point. Much enlarged. (B, C, after von Grifl.) 



27 (4) With a long cylindrical bulbous pharynx. . Family Prorhynchidae. 



The pharynx is remarkably large. The mouth is in the anterior end. Testes with numerous 

 follicles. Ovary not paired. Two sexual pores, the female pore on the ventral side. The male 

 sexual organs open near the mouth or unite with it. 



Only one genus Prorhynchus M. Schultze 



28 



28 (29) Without eyes. 

 -C/t 



Prorhynchus stagnalis M. Schultze 1851. 



i—pd 



-f 



i-OV 



Length to 6 mm., commonly much smaller. White, thread-like. Two cili- 

 ated pits. With numerous pear-shaped glands in the integument. Pharynx 

 about B of total length of body. Protonephridium with four principal branches, 

 two dorsal and two ventral. Chitinous portion of cirrus straight and stiletto- 

 shaped. Monroe Co., N. Y.; brackish water, Falmouth, Mass. 



Fig. 602. Prorhynchus stagnalis. ch, chitinous stiletto; ^6. bulb-like cirrus; w, semi- 

 nal vesicle; ds, ductus seminalis; /, testis follicle; opening of male sexual organs intc 

 pharyngeal pocket; ov, ovary; e, mature egg. X is. (After von Graff.) 



