480 MICHAEL F. GUYER, 



In a few cases, in Segments wherc the uterus is just beginning 

 to brauch, the pore is a trifle decper than in niost of the sexually 

 mature ones, raeasuriug about 0.09 mm. It is also deeper in trans- 

 verse section than longitudinal (compare Figs. 6 and 7), tlius show- 

 iug that there is niore of an indenture on the dorsal and ventral 

 sides of the plug than on the anterior and posterior sides. The Ibllow- 

 ing measurenients will give sonie idea of the relative size of the pore 

 and plug in sexually mature proglottids. Dorso-veutrally the plug 

 measures 0.2 to 0.4 mm in diameter, the pore, 0.26 to 0.60 mm. 

 Longitudinally the plug measures 0.3 to 0.4 mm, the pore 0.5 to 

 0.6 mm in diameter. 



Femalc Organs. 



Vagina. The pore in adtlition to receiving the male duct is 

 also the termiuus for the female canal, or vagina, which opens directly 

 behind the plug (Fig. 7 v). The vagina is seen as a long thread-like 

 structure, niore or less siuuous but showing little tendency toward 

 the formation of complicated coils like those so characteristic of the 

 Vas deferens (Fig. 3 v). It extends into the proglottid sonie distance 

 parallel to the last nientioned orgau, and then makes a quarter circle 

 to the rear, where fmally, after uudergoing some modifications of 

 structure, it terminates in the shell-gland. The terminal end which 

 opens into the pore is also considerably modified, being much enlarged 

 in diameter. At this point, it Springs rathcr abruptly from its normal 

 narrow statc (about 24.5 /.i) to a breadth of 0.04 to 0.06 mm, and 

 then gradually tapers to the outer opening. The narrowing of the 

 canal again, which varies considerably in difterent proglottids is due 

 probably to the State of contraction of the pore itself. The eularge- 

 meut begins about 0.25 to 0.60 mm back from the outer opening and 

 has scattered along its walls, a great number of free nuclei (Fig. 7 

 f.n) similar to those of the cirrus pouch. These are also present 

 along the entire length of the vagina. 



A Short distance from the exterior, a well developed sphiucter 

 muscle (Fig. 7 sp.m) is found, which in section measures from 0.02 

 to 0035 mm across the cut end. It extends as a band or riug, com- 

 pletcly around the vagina and is present in all proglottids. It serves, 

 l)robably, to hold the cirrus firmly during copulatiou. In the sexu- 

 ally mature proglottids, the lumen of the vagina is usually considerably 

 narrower at the point where the sphincter surrounds it. 



Since the presence of such a muscle in either of the other human 



