90 ILLINOIS BIOLOGICAL MONOGRAPHS [90 



ripe proglottids does the length exceed the breadth. The nervous and 

 excretory systems, and the musculature have not been studied. 



The common genital sinus (Figs. 66, 67) is situated very near the 

 middle of the lateral margin of the segment or in ripe proglottids 

 slightly posterior to the middle. It alternates irregularly. There is no 

 genital papilla. In a worm of 52 proglottids the anlagen of the sexual 

 organs appear in the 10th-12th segment as two darkly staining masses 

 the one representing the cirrus and vagina and the other the ovaries. 

 In the 20th segment the anlagen of the testes appear. Beginning with 

 the 24th segment the sexual organs are mature while with segment 40 

 a number of eggs begin toi appear in the uterus. 



The cirrus-pouch (Figs. 66, 67) in mature proglottids is about 

 0.221 mm. long while in ripe proglottids its length measures 0.185-0.212- 

 0.228 mm. It is an elongated ovoid in shape being broadest near the 

 inner end. In mature proglottids it extends just a short distance 

 through the vitellaria. In ripe proglottids it may barely reach through 

 the vitellaria. The ratio of the length of the cirrus-pouch to the 

 breadth of the proglottid varies from 2 :9 in mature to 1 :5, 1 :6, 1 :7 in 

 ripe proglottids. The protruded cirrus has not been seen. Within the 

 cirrus-pouch the distal portion of the cirrus is slender and straight. 

 The ductus ejaculatorius is thrown into 1-3 coils. The vas deferens in 

 scarcely mature proglottids is thrown into coils which extend in a 

 straight narrow mass nearly to the middle of the proglottid, never past 

 the middle. In ripe proglottids coils of the vas deferens are massed 

 at the inner end of the cirrus-pouch and "there is no large mass of coils 

 in the middle of the segment. In P. fallax La Rue the coils of the vas 

 deferens form a dense mass in the mid-field of the segment. In P. neg- 

 lectus La Rue the large mass of coils of vas deferens lies in the middle 

 of the proglottid. The testes (Fig. 67) about 70 in number, apparently 

 lie in one layer. They are irregularly scattered between the vitellaria 

 anterior to the ovary. They measure 0.085-0.130 mm. in diameter. They 

 are thus more numerous and larger than in P. fallax and P. dubius, 

 somewhat more numerous and larger than in P. percae and much larger 

 than in P. neglectus. 



The vagina (Figs. 66, 67) always opens anterior to the cirrus- 

 pouch which it never crosses in its course to the interovarial space. It 

 passes to the middle of the proglottid in a smooth, gentle curve, then 

 it bends posteriad toward the interovarial space. There are no coils of 

 vagina anterior to the ovary but at that place it may be slightly sinu- 

 ous. This straight or nearly straight condition of the vagina is evi- 

 dence that the worm is in a normal state of contraction for usually 

 when a proglottid is unduly contracted the vagina is very sinuous. In 



