347] NORTH AMERICAN PARAMPHISTOMIDAE—STUNKARD 67 



two-thirds of the outer half is a nuclear zone and all the nuclei are col- 

 lected in this area. Half way between the nuclear zone and the lumen 

 there is a narrow band of circular fibers. The oral evaginations arise at 

 the caudal end of the oral sucker by two separate openings, one on either 

 side, and extend dorsad and caudad. They are 0.35 to 0.6 mm. long, 

 flattened dorso-ventrally, 0.15 to 0.2 mm. in width. These sacs are lined 

 with cuticula and their wall is continuous with that of the oral sucker. 

 Externally there is a layer of longitudinal fibers and inside this sets of 

 annular fibers (Fig. 63). Oblique and radial fibers are occasionally seen 

 but are very scanty. 



The esophagus is 0.6 to 1.3 mm. in length ; it is lined with cuticula 

 and the wall contains external longitudinal and internal annular fibers. 

 At the caudal end of the esophagus, just anterior to the bifurcation of 

 the alimentary tract, there is a prominent esophageal bulb. It varies 

 from 0.65 to 0.95 mm. in length and from 0.33 to 0.5 mm. in width ; it 

 is formed by a thickening of the annular fibers of the wall of the esoph- 

 agus. A cross section is represented in Figure 60 and shows the eighteen 

 concentric lamellae of muscles. No nuclei are present in these annular 

 muscles. Both the oral evaginations and the esophagus are surrounded 

 by clusters of deeply staining cells (Fig. 63). Looss (1896) described 

 similar cells in Gastrodiscus and believed they secrete the lining of the 

 esophagus. The ceca are flattened laterally and are of very unequal 

 caliber, small lateral evaginations occur on opposite sides at the same 

 level recalling the condition in some of the Turbellaria. The diverticula 

 extend almost to the acetablum, about 0.37 mm. intervening. They have 

 a muscular coat consisting of external annular and internal longitudinal 

 fibers and an epithelial lining of columnar cells which show faint long- 

 itudinal striations (Fig. 62). 



Male Reproductive Organs. — The testes are slightly lobed, oval, 

 longer in the transverse diameter, and vary in size from 0.27 by 0.35 mm. 

 to 0.45 by 0.9 mm. They are situated one behind the other or in con- 

 tracted specimens slightly on opposite sides of the median line. They 

 are approximately the same size in any one specimen and are separated 

 by about the length of one of the testes, tho in contracted specimens they 

 may lie closer together. The vasa efferentia arise from the dorsal anter- 

 ior margins, the duct from the posterior testis on the left and the duct 

 from the anterior testis on the right side of the body. They pass dorsad 

 and cephalad, and 0.4 to 0.5 mm. caudad of the bifurcation of the diges- 

 tive tract they unite to form a much coiled seminal vesicle, which near 

 the pore passes into a small, poorly developed cirrus sac. In sectioned 

 individuals it could be seen that the seminal vesicle was filled with sper- 

 matoza. In one specimen the coils of the vesicle extend thru twenty 



