74 ILLINOIS BIOLOGICAL MONOGRAPHS [354 



the median line, the caudal testis is almost in the center of the body, and 

 the cephalic testis is about 0.2 mm. in front of it. They are about the 

 same size, lobulated, oval, crosswise of the body, almost touching the 

 cecum of either side. They are ventral in position, almost touching the 

 ventral body wall and not extending far into the dorsal half of the worm. 

 They vary in size from 0.2 by 0.3 mm. in the smallest to 0.55 by 0.78 mm. 

 in the largest specimen. The vasa efferentia arise from the anterior 

 dorsal margins, the right tube from the anterior and the left tube from 

 the posterior testis. Near the genital pore they unite and form a much 

 coiled seminal vesicle which has a thickened muscular wall. This struc- 

 ture extends thru twenty-five cross sections cut 10/a thick. The termi- 

 nal part that leads ventrad to the genital pore is expanded, the walls are 

 thinner, and this part is surrounded by the cells of prostate gland. A 

 cirrus sac is absent, the male and female tubes open to the exterior in- 

 dependently at the apex of a slight ventral prominence. The opening 

 of the male duct is immediately anterior to that of the female (Fig. 78), 



Female Reproductive Organs.— The ovary is oval, lobulated, cross- 

 wise of the body, about the shorter diameter of the testis behind that or- 

 gan. In the smallest specimens it is 0.2 by 0.33 mm. and in the largest 

 0.33 by 0.52 mm. The oviduct arises at the dorsal margin as a very small 

 tube and passes dorsad where Laurer's canal is given off. This canal 

 winds in short curves to the dorsal surface, opening anterior to the ex- 

 cretory pore (Fig. 79). After the origin of Laurer's canal the oviduct 

 passes posteriad and ventrad into Mehlis' gland where a short common 

 vitelline duct is received. The uterus then coils irregularly in close folds 

 to the genital pore. The uterine coils are largely in the dorsal part of 

 the worm altho they may extend into the ventral portion and coil around 

 the testes. Laterally the coils of the uterus are limited by the ceca. The 

 terminal part has a slight thickening of the wall but net a distinct de- 

 limited metraterm. The vitellaria are well developed, large follicles ex- 

 tending in the extracecal areas from the level of the pssterior edge of 

 the oral sucker to the anterior margin of the opening of the acetabulum. 

 They are limited medially by the ceca and laterally extend almost to the 

 body wall. They are more ventral than dorsal in position. 



Eggs are present in large numbers. In size they average 0.14 by 

 0.083 mm. 



Comparison. — Zygocotyle ceratosa agrees with Z. lunata in length, 

 width, and size of oral sucker, but in the former species the oral evagi- 

 nations are smaller, the esophagus is much shorter, the testes and ovary 

 are oval and lobed instead of circular, and the ceca do not extend to the 

 opening of the acetabulum. In Z. ceratosa the acetabulum is nearer the 

 ovary, and the vitellaria are entirely extracecal while in Z. lunata they 

 extend between the ceca. 



