AVIAN CESTODES. 433 



serves, as I imagine, as a retractoi' of the cirrus. The vagina 

 opens at the junction of the neck and. the flask-shaped region, a 

 fact which rather tends to prove that the neck region really 

 belongs to the cloaca genitalis, unless it be remembered that the 

 male and female genitalia have really a common origin and are 

 parts of a single sytem. The various facts to which attention 

 has been called are illustrated in the accompanying figure of the 

 cirrus-sac and its external orifice (text-fig. 2), 



Text -figure 2. 



L 



:^-4 I 



:-> ■< 



^_ 



■^ 





Horizontal section througli cirrus-sac. 



In the lower figure the junction of the two parts of the cirrus-sac is shown 



more highlj^ magnified. 



g.c. Genital cloaca, c. Cirrus, v. Muscular valve-fold separating the narrow 



part of the cirrus-sac from the wider region. I. Water-vascular tube. 



The earliest appearance of the xitenis is represented in text- 

 fig. 3. It is there seen to consist of a modified tract of medullary 

 tissue lying anteriorly to the male and female gonads, at about 



