T^NIOTD CESTODES OF NORTH AMERICAN BIRDS. 



43 



The genital pores are unilateral. In each segment the pore is 

 located near the middle of the right-hand margin. 



Internal anatom,y. 



Nervous system. — The lateral longitudinal nerves (fig. 34, I. n.) 

 are about midway between the lat- 

 eral borders of the segment and the 

 excretory vessels. 



Musculature. — The longitudinal 

 muscles are arranged in two lay- 

 ers. The outer layer (fig. 34, ext. 

 muse.) is composed of numerous 

 small bundles of fibers close to 

 the surface of the segment. The 

 inner layer (fig. 34, int. muse.) 

 consists of eight bundles, as a rule 

 somewhat larger than the outer 

 bundles, and conspicuous only in 

 young segments. 



Transverse muscle fibers are well 

 developed only at the junction of 

 the segments. The dorso-ventral 

 fibers are very weakly developed. 



Excretory system. — The longi- 

 tudinal excretory vessels (figs. 34, 

 V. ex., d. ex./ 35, v. ex.) in the 

 older segments are located near the 

 ventral surface on the right-hand 

 (pore) side of the segment and near the dorsal surface on the left- 

 hand side. The dorsal vessel is close to and dorsal of the ventral 

 vessel. The ventral vessels are not connected by 

 transverse vessels. 



The cirrus pouch aiid vagina pass dorsal of the 

 nerve and excretory vessels. 



Male reproductive organs. — The testicles (fig- 

 33, t.) are two in number, located near the dorsal 

 surface in the jDosterior portion of the segment, 

 one on either side of the median line, and reach 

 a maximum size of 100 to 130/*. A portion of the 

 vas deferens is swollen to form a seminal vesicle 

 (figs. 33, 34, ves. sem.) , which attains a size of 80 to 

 130/x, in diameter. This seminal vesicle is located in 

 the median line close to the anterior border of the 

 segment near the dorsal surface. 



The cirrus pouch (figs. 33, 34, c. p.) is elongated, extending trans- 

 versely across the segment. As a rule its inner end does not reach 



lOQil. 



Fig. 31. — Diorchis acdminata : Head 

 with retracted kostellum. 



5Q«.. 



Fig. 32. — Diorchis 

 acuminata : hook 

 from rostellum. 



