TiENIOID CESTODES OP NORTH AMERICAN BIRDS. 



41 



Female reproductive onjaiis. — In sexually mature seguieuts the va- 

 gina is swollen to form a- prominent seminal receptacle located near, 

 the right-hand border of the segment ventral of the cirrus jjouch, 

 oval in shape, and attaining a maximum of 30 to 35/a by 45 to 

 50jti in width and length. 



The ovary when fully developed is transversely elongated, extend- 

 ing laterally as far as the excretory canals and measuring 135/x in 

 its longest dimension. It extends forward to the anterior border of 

 the segment, but does not reach the posterior border. In the median 

 line behind the ovary is the small rounded yolk gland, which, 

 measures about 20;u, in di- 

 ameter. 



The uterus develops as 

 a simple sac on the ven- 

 tral side of the ovary, and 

 the latter rapidly degen- 

 erates after the appear- 

 ance of the former. When 

 fully developed the uterus 

 occupies practically the 

 entire segment, and as its 

 wall becomes folded in- 

 ward in various places its 

 cavity is divided into a 

 number of incompletely 

 separated chambers. The 

 number of eggs in the 

 gravid segment is small, 

 18 to 20, but on account of the large size which they finally attain 

 the cavity of the uterus is fully occupied. 



When they first enter the uterus the eggs have but a single thin 

 membrane and measure but 20/x in diameter. Later other membranes 

 are developed, and the o^^g (fig. 29) in the final stage of development 

 possesses two well-defined shells, an inner one 27 to 35/x, in diameter 

 and an outer one 45 to 60/x in diameter. Between the outer and inner 

 shell is an intermediate finely granular layer limited by a very thin 

 membrane internally and externally. The oncosphere measures 22 to 

 25/A in diameter with hooks 13 to 14/x in length. 



5Qa. 



Fig. 29. — Hyjienolepis cantanian.\ : Egg. 



