168 ILLINOIS BIOLOGICAL MONOGRAPHS [168 



end and also toward the neck. Its anterior region is conical. At the 

 apex of the head is a slight depression which structurally is not a fifth 

 sucker. There is no rostellum. The suckers are round in outline and 

 they measure 0.34 mm. in diameter. 



The youngest proglottids in the proliferation zone are narrow trans- 

 verse bands 0.135 mm. long by 0.612 mm. broad. With increasing age 

 the proglottids elongate until mature and ripe proglottids may be quad- 

 rate and the oldest proglottids even longer than broad. An end-proglot- 

 tid was not seen. The margins of the segments are nearly straight. At 

 the place of the opening of the genital passages the surface is slightly 

 raised to form a small genital papilla. 



In the head the excretory vessels run close together. Near the 

 suckers a circular anastomosis unites the vessels. In the space between 

 the suckers is a complicated plexus. The two pairs of main lateral 

 excretory vessels run through the length of the worm in nearly a straight 

 course. In the posterior margin of each proglottid is a transverse anas- 

 tomosis connecting the main vessels. In this region also and in the 

 neck short ducts arise from the main ventral vessels only and pass to 

 the exterior, opening on the surface near the posterior angle of the 

 proglottid. The lumen of such ducts becomes smaller near the periph- 

 ery of the work. The passage through the cuticula is quite small. 



The genital aperture is marginal, irregularly alternating, situated 

 a little anterior to the middle of the proglottid. A very small genital 

 papilla is present, due largely to a thickening of the margin of the 

 sinus. The anlagen of the genital organs appear in about the twentieth 

 segment. The testes (Fig. 180) number 120-150 and are relatively 

 small, 0.5 mm. in diameter, round or polygonal in outline. They fill 

 the whole field between the two vitelline glands and the anterior and 

 posterior margins of the proglottid. The vas deferens forms a loose 

 mass of coils between the cirrus-pouch and the middle of the proglottid. 

 The mass lies posteriad to the cirrus-pouch and is excentric to it, lying 

 on the porose side of the proglottid. In the cirrus-pouch the ductus 

 ejaculatorius forms a few coils and then it passes over into the cirrus. 

 The cirrus is enlarged into a thick vesicle which fills up nearly the 

 outer half of the cirrus-pouch. The cirrus-pouch, which is about 0.30 

 mm. long, reaches about J^ across the proglottid breadth. It is an 

 elongated oval in shape. 



The vagina which always opens anterior to the cirrus-pouch has a 

 small sphincter near its opening. Further within, the lumen of the 

 vagina enlarges into an ovoidal vesicle which may be almost as volumi- 

 nous and as long as the cirrus-pouch. The vagina forms no coils ante- 

 rior to the ovary. Riggenbach found no receptaculum seminis but he 



