154 ILLINOIS BIOLOGICAL MONOGRAPHS [154 



The worm shows a very evident strobilation, the angles of the pro- 

 glottids being sharp and well marked. The posterior border of one 

 proglottid overlaps the anterior end of the one following. Segmenta- 

 tion begins about 0.5-0.6 mm. from the head. Here the segments are 

 much broader than long. Gradually the length increases in proportion 

 to the breadth until in nearly mature proglottids the dimensions may 

 be 1.70 mm. broad by 0.595 mm. long. Further down the strobila nearly 

 ripe proglottids may be about quadrate 1.02 mm. broad by 1.10 mm. 

 long. Ripe proglottids are longer than broad, 1.75 mm. long by 0.510 

 mm. broad. In all but ripe proglottids the genital pore is not promi- 

 nent but in these long proglottids the pore is situated on an eminence. 

 Moreover in this part of the strobila the posterior region of the seg- 

 ment is much broader than the anterior or middle region. The neck is 

 0.5-0.6 mm. long. It is broad and thick, not as broad, however, as the 

 head. 



The genital pore is situated on the lateral margin at the end of the 

 first one-fourth to one-half of the proglottid. The pores alternate irreg- 

 ularly. In mature and nearly ripe proglottids there is no genital 

 papilla but in elongated ripe proglottids a genital prominence is noted. 

 Into the common genital sinus both vagina and cirrus open, the vagina 

 always anterior to the cirrus. The male organs (Fig. 65) much resem- 

 ble the male organs of P. anibloplitis but here again certain differences 

 exist. The cirrus-pouch in P. perplexus is not as voluminous nor as 

 long as in P. amhloplitis. It measures 0.300-0.344 mm. long. Its length 

 goes into the proglottid breadth 3-4-5 times depending somewhat upon 

 the state of contraction of the proglottid. "Within the cirrus-pouch are 

 1-3 coils of ductus ejaculatorius, a much smaller number than in P. 

 amhloplitis. The coils of the vas deferens outside the cirrus-pouch are 

 very numerous. They form in mature proglottids a thick compact mass 

 extending from the cirrus-pouch to the middle of the segment. The 

 cirrus itself is well muscled. When protruded it is a long spindle- 

 shaped organ slightly thicker near the base than elsewhere. It is nearly 

 0.60 mm. long. The testes are very numerous, 135-155 in number. They 

 are arranged in one layer, occupying the entire dorsal field anterior to 

 the ovaries and as far laterad as the vitellaria, with the exception of 

 the small region taken up by a portion of the cirrus-pouch and the vas 

 deferens. The testes measure as much as 0.069 mm. long by 0.037 mm. 

 broad, their short axis Ijang parallel to the long axis of the worm. 



The vagina (Fig. 64) in its first part is considerably dilated. 

 Throughout the full length of this dilated region there is a weak cir- 

 cular musculature. At the end of the dilatation is a strong sphincter 

 vaginae 0,053 mm. long and 0.015 mm. thick. P. amhloplitis has a long 



