T^NIOID CESTODES OF NORTH AMERICAN BIRDS. 



11 



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in a strobila 50 mm, long was about 175. The posterior 8 or 10 seg- 

 ments in this strobila contained fully formed eggs. In shape the seg- 

 ments are trapezoidal, broader than long, and the posterior border of 

 each segment overlaps more or less 

 the anterior portion of the next 

 following segment. 



The genital pores are unilateral 

 on the left-hand margin of the 

 strobila, located slightly in front of 

 the middle of each segment. 



Internal anatoiny. 



Nervous system. — The lateral 

 longitudinal nerves are well devel- 

 oped, situated toward the lateral 

 borders of the segment just within 

 the inner layer of longitudinal 

 muscles. 



Muscle system. — The longitudinal 

 muscles are arranged in two layers ; 

 a thicker outer layer of several 

 irregular rows of very numerous 

 small bundles and a thinner inner 

 layer of larger bundles in a single 

 row, about 40 in number, 20 in the 

 dorsal and 20 in the ventral half of 

 the segment. The dorso-ventral 

 and transverse muscle systems are 

 very weakly developed. 



Excretory system. — The dorsal 

 (fig. 3, d. ex.) and the ventral ex- 

 cretory canal are situated in about 

 the same vertical longitudinal plane 

 a short distance from the lateral 

 nerve on its inner side. The dorsal 

 canal is, as usual, the smaller and 

 its course more w^avy. 



In a segment in which the ventral 

 canals measured 60/a in diameter 

 the dorsal canals measured 15/x- 

 The ventral canals are connected by a transverse canal in the posterior 

 portion of each segment ; the dorsal canals (fig. 3) are also connected in 

 the same region in most of the segments by a slender transverse canal. 



100a. 



Fig. 1. — Davainba ehtnchota : Head 

 and anterior portion of strobila. 



