4 Papers from the Marine Biological Laboratory at Tortugas. 



mouth is a powerful sucker which entirely fills the anterior end of the 

 body, but is not separated from the parenchyma by a definite boundary. 

 Goto describes a similar structure in M. iiimce as a sucker-like organ 

 which, as he says, undoubtedly functions as a sucker. He refuses, how- 

 ever, to recognize it morphologically as a sucker because of the lack of 

 definite boundaries. 



The posterior sucking-disk is not so large relatively as in the other 

 two species of the genus, having a diameter of 0.52 mm., which is some- 

 what less than that of the body (figs. 1 and 4). It is circular in outline 

 and shaped more or less like a saucer, having a curled rim, and is sub- 

 terminal in position, being attached to the body by a short, thick pe- 

 duncle. The ventral surface of the disk is divided by eight radial ridges 

 into as many segments, each of which contains a large oval sucker about 

 ci mm. in diameter. The sucker occupies about two-thirds of the space 

 in the segment, extending from the outer rim or margin of the disk to 

 the peduncle. The center of the disk, where the peduncle is attached, 

 is somewhat depressed (fig. 5, c.d.) and contains no muscular tissue. The 

 parenchyma, however, immediately beneath the cuticula in the center is 

 arranged in parallel lines perpendicular to the cuticula and has some- 

 what the appearance of a musculature. Extending from the outer 

 margin of the sucking-disk is a lip or flange of non -muscular tissue (figs. 



5 and 6, /?.) similar to the lip at the anterior end of the body. It will be 

 seen that the sucking-disk is not a single sucker, as it is described as 

 being in the other two species of the genus, but a pedunculated plate 

 containing eight distinct suckers. 



Two small hooks (fig. i,h., fig. 7) are embedded in two of the posterior 

 radii of the sucking-disk, but do not usually extend beyond the margin. 

 Each hook has two parts, a crescentic portion 0.027 mm. in diameter 

 and a straight portion extending from it, 0.034 mm. long. 



On the dorsal or reverse side of the sucking disk, opposite to the two 

 posterior segments and between the two hooks, are two groups of short 

 finger-like projections (figs. 4 and 5, d.p.). Each group is V-shaped, with 

 the apex directed towards the center of the disk, and each projection 

 has the same structure as the suckers. No similar structures, so far as 

 I know, have been observed in any other trematode. 



Goto has called attention to the unusual structure of the musculature 

 of the sucking-disk in M. ijimce, the radial muscle-fibers composirg the 

 main mass of the disk being striated. In M. floridana identical relations 

 exist. The musculature of the suckers of the disk is made up principally 

 of perpendicular striated fibers (fig. 6, 5. m.), most of which run inde- 

 pendently from the cuticula on one side of the sucker to that on the other. 

 Between the ends of these fibers are very delicate non-striated fibers 

 which run parallel to the cuticula. The muscle-fibers composing the 

 dorsal finger-like projections have a direction transverse to that of those 

 of the suckers (fig. 5, d.p.). 



The body of the worm is smooth. The chitinous pieces on the radial 

 elevations of the sucking-disk which have been described by Goto in 

 M. ijimce are not present. 



