Monocotyle Floridana, a New Monogenetic Trematode. 5 



The large mouth opens through a small passage into the pharynx, 

 receiving at the juncture a circular pocket which lies over the anterior 

 end of the pharynx (fig. 3, p.p.). The pharynx is of enormous size, being 

 0.19 mm. long, 0.18 mm. wide, and 0.17 mm. thick in the worm selected 

 for description, and is the most conspicuous organ in the body (figs. 1 

 and 3, ph.) ; but it varies considerably in relative size in different indi- 

 viduals, being relatively smallest in the youngest individuals. In the 

 smallest worms in my collection its length is one-twelfth that of the 

 body; in the largest this proportion is 1 to 6. The small lumen is three- 

 cornered in cross-section and the walls are very thick and composed of 

 closely compacted, deeply staining radial muscle -fibers. Sparsely dis- 

 tributed throughout these fibers are large oval cells, which are probably 

 nerve-ganglia. Surrounding the radial fibers is a thin layer of delicate 

 circular fibers. 



The intestine branches just back of the pharynx, there being no esoph- 

 agus present (figs. 1 and 3). The two intestinal trunks pass directly to 

 the right and left sides of the body. They then pass first forward a 

 short distance, and then, turning abruptly, run posteriorly along the 

 medial surfaces of the voluminous yolk-glands and parallel to the lateral 

 margins of the body to the hinder part of it, where their posterior ends 

 meet and unite (figs. 1 and 4). In the two other species of this genus the 

 hinder ends of the intestinal trunks do not thus join, but remain apart. 



The diameter of each trunk is about 0.04 mm. in a large individual. 

 Projecting posteriorly from the point of juncture of the two lateral 

 trunks in all the individuals examined by me (about twenty-five), is a 

 median trunk which extends to the extreme hinder end of the body (figs. 

 1 and 4 m. t.). This median trunk has exactly the same structure as 

 the lateral trunks and about the same diameter (figs. 9, 10, 11); but 

 in several individuals it was much thicker than they and took stains 

 much more deeply. 



In two individuals examined the median trunk opens to the outside 

 by means of a median, dorsal, thick-lipped pore, situated at the extreme 

 posterior end of the body and just in front of the point of attachment 

 of the sucking-disk (fig. 4, t. p.). In all other individuals examined no 

 such pore could be seen and the median trunk ends blind, forming thus 

 a caecum. 



The occurrence of a median, posterior intestinal caecum similar to 

 the one here described is exceedingly rare among trematodes, the only 

 other species with which I am acquainted in which it occurs being Vallisia 

 striata, which has been described by Perugia and Parona (1890). The 

 terminal pore is difficult to explain and may be simply an accidental 

 opening in the two individuals in which it was seen, although its well- 

 defined form and broad lips would seem to preclude this interpretation. 



The excretory system has not been distinctly seen, but has undoubt- 

 edly the same arrangement as that described by Goto in M. ijimce and 

 in other monogenetic trematodes. The longitudinal trunks are small 

 and delicate tubes which open to the outside through a pair of lateral 

 pores situated at about the level of the hinder part of the pharynx, each 



