22 T. B. ROSSETER ON DREPANIDOT^ENIA VENUSTA. 



act, and one act only, of coitus, ever takes place. When the 

 cirrus is extruded from the vaginal canal it is seen in every 

 instance to be denuded of the hooked termination, broken off 

 no doubt by the rows of inverted spines which line the interior 

 of the vaginal canal. Their utility is to secure the cirrus from 

 being drawn back by the retraction of the elevator muscles during 

 the flow of the sperm or emptying of the vas deferens. The 

 act is somewhat slow, as the cirrus aperture is small. Once 

 the looped vas deferens in the vesicula seminalis is emptied, it is 

 never refilled by the testes. 



Explanation of Plates 1 and 2. 



Fig. 1. Scolex of Drepanidotcenia venusta. Fresh specimen 

 taken from the mucous membrane of the intestine 

 of a duck, a, suckers; b, rostellum inverted; c, ring 

 formation caused by inversion of rostellum ; d, neck. 

 X 21. 



Fig. 2. Young testes, to show pyriform glands in interior. Each 

 circle of glands is composed of an uneven number, the 

 central number being nine. I have not figured the 

 two primary layers of three and one. x 210. 



Fig. 3. Vesicula seminalis, with cirrus previous to coitus. In 

 the interior of the pouch is the looped vas deferens, a, 

 filled with spermatozoa ; b, attachment of vas deferens 

 to root of cirrus, c ; d, spines in interior of canal ; 

 e, annular orifice of canal, x 210. 



Fig. 4. Cirrus pouch in oblique section ; c, cirrus after coitus, 

 with loss of terminal hook ; e, longitudinal muscles ; 

 /, ductus efferens of vagina in cross section. x 210. 



Fig. 5. Vertical section through anterior portion of papilla, A , 

 cirrus and portion of canal ; a, circular muscles 

 surrounding neck of pouch ; b, longitudinal muscles of 

 papillae in section. B, vagina ; a, circular muscles ; c, 

 vaginal canal; b, longitudinal muscles of same, x 210. 



Fig. 6. Flattened cloaca of papilla, as seen in prepared segment. 

 a, cirrus after coitus ; b, orifice of canal ; c, vagina ; 

 c', vaginal opening of canal, x 210. 



Figs. 7 and 8. Two genital papilla?. 7, cirrus within pouch, 

 previous to coitus ; 8, cirrus partially protruded and 

 entering the cloaca, x 93. 



