TiENIOID CESTODES OF NORTH AMERICAN BIRDS. 51 



In the anterior half of the segment in the median line the vas 

 deferens is swollen to form a prominent seminal vesicle (figs. 39, 41, 

 ■oes. sem.) , 150//, or more in diameter. Usually the seminal vesicle is 

 dorsal of, occasionally ventral of, the proximal end of the cirrus 

 pouch. The cirrus pouch (figs. 39, 41, c. p.), usually somewhat curved, 

 extends transversely across the anterior portion of the segment, 

 measuring 250 to 300/x in length by 30 to 40/x in thickness. It is 

 somewhat longer than the cirrus pouch of D. acuminata and usually 

 extends bej^ond the median line of the segment. As in the latter 

 species, the pouch is covered with a prominent layer of longitudinal 

 muscles, thickest near the middle of the pouch. The vas deferens is 

 enlarged to form a seminal reservoir within the cirrus pouch. In 

 sharp contrast to D. acuminata^ the cirrus (fig. 39, cir.) is very 

 slender without bulbous enlargement at the base, measuring but 1.5 

 to 2/x in diameter when extruded, whereas in the other species it is 

 from 6 to S/x in diameter, and has a bulbous enlargement at the base 

 14 to IG/x in diameter. As in the latter species, it is unarmed. Its 

 length when fully extruded is at least 100/x. 



Female reprochictive organs. — The vagina (figs. 40, 42, vag.), at 

 first very narrow, becomes swollen beyond the excretory canals to 

 form an elongated seminal receptacle (figs. 40, 42, sem. 7rcept.), 

 which lies against the ventral side of the cirrus pouch and extends 

 as far as the inner end of the latter. 



The ovary (figs. 39, 40, ov.), as in D. acuminata, is trilobed with 

 occasionally a fourth lobe on the left-hand side, and when fully de- 

 veloped it extends laterally as far as the excretory canals, and its 

 median lobe reaches the anterior border of the segment. It is located 

 on the ventral side of the cirrus pouch, seminal vesicle, and seminal 

 receptacle. The yolk gland (figs. 39, 40, y. g.) is similar in shape 

 and size to that of D. acuminata and is similarly located. 



The uterus (figs. 41, 42, ut.) is a simple sac, without partitions, and 

 develops behind and dorsal of the ovary and ventral of the testicles. 

 As the uterus increases in size and becomes filled with eggs the ovary 

 degenerates and disappears. AVhen fully developed the uterus extends 

 from the posterior to the anterior border of the segment, and later- 

 ally beyond the excretory canals on each side, dorsal of the canals 

 on the right side and ventral of the canals on the left side. 



The eggs when they first enter the uterus measure 12 to 15/a in 

 diameter and are closely surrounded by a very thin membrane. Eggs 

 containing fully formed oncospheres were not present in the speci- 

 mens studied. 



