. Fresh-water biology. Freshwater biology. 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. Protone

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. Fresh-water biology. Freshwater biology. 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