Helminth Fauna of the Dry Tortugas. 47 



Outline of body very long ovate, broadest near posterior end and 

 tapering rather uniformly to the anterior end; smooth, but neck crossed 

 by fine wrinkles; oral sucker nearly terminal, much smaller than ventral 

 sucker; neck one-third the entire length; prepharynx long, pharynx 

 large. There seems to be a short esophagus, and the wide intestinal 

 branches extend to the posterior end of the body. Reproductive opening 

 on median line at anterior border of ventral sucker; cirrus smooth and 

 cylindrical; cirrus-pouch slender, prostate not seen; seminal vesicle 

 cylindrical, on median line, its anterior end at the caudal border of the 

 ventral sucker; testes 2, near together on median line, one behind the 

 other and contiguous ; posterior testis larger and longer than the anterior. 

 Ovary suboval, at anterior border of anterior testis; seminal receptacle 

 in front of ovary a little to right of median line. Vitelline glands diffuse, 

 dense, with a peculiar transverse arrangement of the lobes, from posterior 

 end to ventral sucker. Uterus median, the ova lying between the ovary 

 and the caudal end of the seminal vesicle. 



Dimensions in balsam: Length 2.10; breadth 0.61 ; oral sucker 0.13 ; 

 pharynx, length 0.18, breadth 0.14; ventral sucker 0.29; ova 0.052 by 

 0.034. 



Mesorchis urna gen. et sp. nov. (Figs. 88 93.) 



Etymology: ;j.iao<s t middle; 8p%t?, testicle. 



Body variable in shape but usually fusiform, truncate anteriorly, 

 and tapering to a blunt point posteriorly, covered, at least anteriorly, 

 with minute, short spines; oral sucker terminal, vase-shape, broad in 

 front, narrowing at posterior end; ventral border of lip usually rather 

 deeply notched; pharynx close to oral sucker; esophagus long and slender; 

 intestinal rami short, with thick walls, as a rule diverging widely, in which 

 case they do not reach the ventral sucker. The ventral sucker is rather 

 weak and often hard to distinguish in living specimens, its anterior 

 border about the middle of the length of the body. Genital aperture 

 at anterior edge of ventral sucker; cirrus-pouch large, median, vertical; 

 seminal vesicle a large convoluted tube inclosed in the cirrus-pouch and 

 lying dorsal to the ventral sucker. The metraterm passes on dorsal side 

 of ventral sucker, ventral to seminal vesicle. Testes 2, lateral, their 

 anterior borders in front of level of anterior edge of ventral sucker. In 

 what is perhaps an average case a line joining the middle points of the 

 testes passes along the anterior edge of the ventral sucker. Ovary dorsal 

 to ventral sucker, extending a short distance caudad of ventral sucker. 

 At its posterior border is the shell-gland which, in turn, is followed by 

 the seminal receptacle. A short distance back of the seminal receptacle 

 on the dorsal side is the opening of Laurer's canal, which is exceptionally 

 conspicuous. The opening is thick-lipped and surrounded by strongly 

 staining nuclei. The vitelline glands are lateral, mostly in front of the 

 testes, and extending about half-way from the testes to the anterior end. 

 Each lateral gland is composed of a considerable number of compact, 

 rounded, and comparatively small masses. The folds of the uterus are 

 ventral and occupy the greater part of the space behind the testes. The 

 excretory vessel is capacious, with a short, thick stem at the posterior 



