70 Papers from the Marine Biological Laboratory at Tortugas. 



intermediate portions of the body a transverse section is horseshoe- 

 shaped (fig. 175). The lateral margins, beginning in 2 thick muscular 

 folds a short distance behind the oral sucker, are bent downward and 

 inward until the gap between the edges may be no more than one-third 

 the whole breadth of the body thus folded. The edges are muscular, 

 being provided with strong, longitudinal muscle fibers. The body 

 throughout is supplied with numerous fascicles of strong muscle fibers 

 which connect the morphologically dorsal and ventral surfaces (figs. 

 175, 178-180). There is no pharynx, but there is a slender esophagus 

 (fig. 183) . The intestinal rami extend to the posterior end, with numerous 

 short branches throughout. In one set of sections they were observed 

 to anastomose (fig. 177). In other sets of sections the rami of the intes- 

 tines do not appear to anastomose, although their walls were seen in 

 juxtaposition in two sets of sections. In the most satisfactory set they 

 were entirely separated by parenchymatous tissue. The genital aperture 

 is on the left margin approximately at the anterior third. The cirrus- 

 pouch is relatively large, cylindrical, the basal half consisting of the 

 conspicuous prostate. The seminal vesicle, as a convoluted tube, lies 

 caudad of the basal portion of the cirrus-pouch and enters the distal end 

 of the prostatic portion. The testes are 2, somewhat lobed, and lie oppo- 

 site to each other at the extreme posterior end of the body. The ovary, 

 also more or less lobed, lies on the median line a little in front of the testes, 

 its posterior margin about on a level with the anterior edges of the testes. 

 The seminal receptacle lies anterior and dorsal to the ovary, and the shell- 

 gland is behind the ovary and between the testes. The vitelline glands 

 are massed laterally on the margins immediately in front of the testes, 

 extending from the anterior border of the testes for a short distance 

 along the margin. The folds of the uterus lie in close, transverse loops 

 running from margin to margin between the testes and the cirrus-pouch. 

 The ova have a slender filament at each pole. The excretory vessels are 

 conspicuous, being in most cases filled with black pigment, which remains 

 in the mounted specimens. The excretory vessels begin at the head in 

 a net-work of fine vessels. These soon unite into 2 main lateral branches 

 about half-way between the mouth and the bifurcation of the intestine. 

 They pursue a somewhat irregular, meandering course, but mainly lat- 

 eral, to the posterior end, where they unite just before entering the excre- 

 tory pore. 



One of the most characteristic features of this singular worm is the 

 musculature, especially as seen in the numerous fascicles of transverse 

 fibers and in the strong marginal fibers (fig. 175 tm, Im). 



Host, Angelichthys isabelita: 



1906, July 10, 1 fish, 2 trematodes. 

 1908, July 3, 1 fish, 3 trematodes. 



These trematodes were boat-shape, pinkish, anterior end lighter 

 colored; dark-brown intestines, branched; genitalia white. Length 2.5 

 to 3 mm. 



Host, Pomacanthus arcuatus : 



1907, July 3, 1 fish, 1 trematode; July 11, 1 fish, 8 trematodes; July 

 15, 1 fish, 1 trematode. 



