T^NIOTD CESTODES OF NORTH AMERICAN BIRDS. 



27 



genital glands. The vas deferens (figs. 20, 21, v. clef.) forms a mass 

 of coils in the anterior third of the segment extending from the 

 median line to the base of the cirrus pouch. The cirrus pouch (figs. 

 IT, 19, 21, 22, c. p.) is elon- 

 gated, broadest near the base 

 and tapering toward its outer 

 end. It measures 350 to 380/x 

 in length by 80 to lOOfx in 

 thickness. It is covered with 

 a layer of muscle fibers inter- 

 lacing and crossing diago- 

 nally, forming a sort of basket 

 work (fig. 19). In the distal 

 three-fifths of the pouch this 

 layer is very thick, but is thin 

 in the proximal or basal por- 

 tion of the pouch. The cirrus 

 (figs. 19, 20, cir.) is from 250 

 to 350/x in length, about lOfx 

 in diameter when evaginated, 

 with a lumen about 2^ in 

 diameter, and is armed with short spines 2 to Sfi long. A number of 

 slender muscles, which extend from its inner end to attach to the 

 distal portion of the pouch, serve as protractors. The portion of the 





lOOjU/. 



Fig. 16. — Rhabdometra nullicollis : Head 

 and anterior portion of stkobila^ median 

 horizontal section. 



vag. 



lOQu,. 



Fig. 17. — Rhabdometra nullicollis : Sexually mature segment, c. p.. Cirrus pouch. 

 or.. Ovary, t.. Testicles, rag.. Vagina, y. g., Yolk gland. 



vas deferens which lies within the cirrus pouch possesses a thick 

 muscular wall. From the base of the cirrus pouch a prominent re- 

 tractor muscle (fig. 19, retr.) extends diagonally inwards and for- 

 wards to the anterior end of the segment near the median line. The 



