Plaie XXIII. 



Tristomum ovale. 



Fig. 1. The whole worm viewed from the ventral side. The testes are represented 



only on one side. 

 ,, 2. One of the hooks of the posterior sucker, x 70 diara. 

 „ 3. Tangential section of the marginal membrane of the posterior sucker. 



X 204 diam. 

 „ 4. Median sagittal section through the region of the pharynx, x 50 diam. 

 „ 5. Cross-section through the region of the left anterior sucker, x 50 diam. 

 ,, G. Cross-section through the anterior part of the pharynx, x 50 diam. 

 ,, 7. A small portion of the ventral side of a cross-section of the body, x 204 



diam. The contents of the testes are only partially drawn. 

 „ 8. Central portion of the genital organs viewed as a transparent object from 



the ventral side, x 29 diam. 



