168 ILLINOIS BIOLOGICAL MONOGRAPHS [456 



The vitelline duct at its union with the oviduct has a diameter of S/x; but 

 just beyond this, in the direction of the follicles, it soon enlarges to form a 

 somewhat irregular vitelline reservoir which when filled with yolk may attain 

 a diameter of SO^i. Its general course is towards the opposite side of the 

 generative space almost parallel to either surface of the body; but beyond this 

 it could not be traced with satisfaction. 



The vitelline follicles fill up ahnost the whole of the cortical parenchyma 

 from the layer of longitudinal body muscles to the nuclei of the subcuticula, 

 the thickness of the stratum averaging 0.05mm. (Fig. 90). They form a con- 

 tinuous layer aroimd the margins of the proglottides (in transverse sections) 

 and also from proglottis to proglottis, as mentioned above, even extending 

 well into the posterior borders. They are not arranged in lateral fields, but 

 are interrupted only where the uterus sac and genital sinus pierce the body- 

 wall, or in the former case greatly press against the latter. The individual 

 follicles attain a size of dQp. and are very closely crowded together. The 

 number in cross-sections of the proglottis averages 55 and in sagittal sections 

 13, thus making the average total munber for each proglottis 715. 



The shell-gland is situated in the dorsal portion of the genital space, that 

 part of the oviduct showing the connections being almost horizontal in position 

 and about 18ju m diameter, that is, a little larger than the oviduct behind that 

 region. The individual cells of the gland are much attenuated, closely ar- 

 ranged and have their nuclei situated in their shghtly enlarged distal ends. 

 Their connections with the oviduct give the wall of the latter a honeycombed 

 appearance when it is seen in longitudinal section. 



Beyond this region the oviduct gradually enlarges as it passes above the 

 ovarian isthmus to become the uterine tube, the coils of which are accommo- 

 dated opposite the cirrus pouch just behind the uterus-sac. As it proceeds 

 its wall gets thinner and the nuclei protrude more and more into the lumen 

 untU many of them are evidently lost. It is noteworthy that the uterine 

 tube in many cases as well as the uterus -sac, especially in younger proglottides, 

 alternates irregularly from right to left according as the cirrus and vas deferens 

 do. These three structures are, in fact, fitted very nicely into the space be- 

 tween the uterus-sac ahead and the ovarian isthmus behind. 



The uterus-sac is elliptical in outline, has its longitudinal axis directed 

 anteroposterior^, and is situated in the anterior half of the proglottis. In 

 very mature segments it occupies almost the whole of the medullary region, or 

 to be more precise, the middle three-fifths of the diameter of the proglottis, its 

 anterior end extending forward close to the ovary of the proglottis immediately 

 ahead (Fig. 75). Luhe (1902a:326) figured the uterus as, to use his own words, 

 " . . . in der Regel erne geraumige Uterushohle bildend, welche die ubrigen 

 Genitalorgane, ohne dass freilich deren Ruckbildung eintritt, buchstablich 

 an die Wand drangen kann. indem die ganze Proglottis in reifen Proglottiden 

 vielfach als ein einziger sackformiger Eibehalter mit verhaltnissmassig sehr 

 diinnen Wandungen erscheint. " But such a degree of restriction of the other 

 genitalia was seen by the writer only in a few of the ripe proglottides of strobilas 



