T^NIOID CESTODES OF NORTH AMERICAN BIRDS. 



13 



side of the medullary portion, to form the vas deferens, which ex- 

 tends forward nearly to the anterior border of the segment, and then 

 laterally in a very tortuous course toward the genital pore. The 

 mass of coils formed by the vas deferens occupies most of the anterior 

 third of the medullary portion of the segment on the left-hand side 

 of the median line. The middle portion of the vas deferens is com- 

 monly dilated in older segments, forming a capacious seminal reser- 

 voir measuring 40 to QO/x in diameter ; the remainder of the vas defer- 

 ens measures about 10/x in diameter. 



The cirrus pouch (figs. 3, 4, c. p.) measures 115 to 135/^ in length 

 and has the pyriform shape common in the genus Davainea. The 

 outer muscular layer is very thin, 2 to 3/^, the fibers running mostly 

 lengihwise in the basal portion and transversely in the distal portion 

 of the pouch. The vas deferens after entering the cirrus pouch is 



vag 



Fig. 



lOQu. 

 4. — Davainea bhynchota : Grayid segment, horizontal section. 

 PODCH. emh., Eggs, vag., Vagina, y. g.. Yolk gland. 



c. p., Cirrus 



supplied with a muscular wall, and its terminal portion is modified 

 to form the cirrus, which in the retracted condition measures 50 to 

 60ju, in length and 2 to 4^ in diameter, without apparent spines. 



Female reproductive organs. — The vagina (fig. 4, vag.) opens into 

 the genital sinus immediately behind the male opening, and extends 

 inwards along the posterior side of the cirrus pouch. The distal por- 

 tion of the vagina has a thick muscular wall and measures from 200 

 to 235/x in length. Before crossing the excretory canals the vagina 

 becomes very thin-walled, and in older segments the thin-walled por- 

 tion is dilated to form an elongated seminal receptacle (fig. 3, sem. 

 recept.) . Near the center of the segment the vagina joins the oviduct. 



The ovary (fig. 3, ov.) is situated in the middle of the segment, and 

 measures about 250 to 320/x in width when fully developed. It is a 

 compact lobulated organ deeply hollowed out behind. In this space 



