28 



BULLETIN 69, UNITED STATES NATIONAL MUSEUM. 



axis of the cirrus pouch is nearly transverse in younger segments, 

 with its inner end slightly tilted forward, but as the segments be- 

 come older the cirrus pouch becomes more and more oblique. 



Female repvoductive organs. — The vagina (figs. 17, 18, 20, 21. 

 22, vag.)^ which opens into the genital sinus immediately behind the 



d.ex. /;;^_.,^^^^J^^^ sem. recept. 



l.n, 



v.ex. 



ov. 



vag, 



10 QU/. 



Fig. 18. — Rhabdometra ndllicolli.s : Sexually mature segment, transverse section. 

 d. ex., Dorsal excretory vessel. I. m.. Nerve cord, ov., Ovary, spwj.. recept.. 

 Seminal receptacle, t.. Testicle, ut.. Uterus, rag.. Vagina, r. def., Vas 



DEFERENS. I!. eX., VENTRAL EXCRETORY VESSEL. 



male opening, has three distinct portions. The first is very short 

 with a narrow lumen and is surrounded by a spherical muscle bulb 

 25 to 30/x in diameter which serves as a sphincter (fig. 20, sph. vag.). 

 The second portion is 250 to 300/;. long, and possesses a muscular wall 

 by the expansion or contraction of which the size of the lumen may 

 be varied; this portion is lined with closely set cilia-like projections 



v.def. 



lOQu.. 



Fig. 19. — Rhabdometra nullicollis : Section through cirrus pouch, dr.. Cirrus. 

 c. p., Cirrus pouch, retr.. Retractor of cirrus pouch, v. clef., Vas deferens. 



8 to 10|U, long. The third portion has a thin membranous v^all, and 

 its lumen is at first very narrow, about 2/x, but toward its inner end 

 it swells out to form a seminal receptacle (figs. 18, 20, sem. recept.) 

 about 50/x, in diameter and 75 to lOOp long. 



The ovary (figs. 17, 18, on.) is small, compact, and but slightly 

 lobed. At its maximum of development it does not exceed 175/x 



