ECTOPARASITIC TREMATODES. 287 



the attempt to clean off the fragments of the tissue of the host. 

 In connection with the sucker there are numerous unicellular 

 glands in the posterior part of the hody free from the genital 

 organs. They are of various size and form accordino; to the 

 stages of secretory activity (fig. 22). The smaller ones are irregu- 

 larly polyhedral and measure about 20 ff- or less in diameter ; 

 the nuclei are very small and the cytoplasm is very finely granu- 

 lar, and has a strong affinity for stains. In this stage no dis- 

 tinct membrane could be observed. The larger gland cells are 

 mostly of a globular shape, and the nuclei are large. There is 

 a thin but distinct external membrane, the cytoplasm is coarse- 

 ly granular and has less affinity for stains. There are also 

 some spacious vacuoles of irregular form. These larger gland 

 cells always send out large ducts, which form a bundle on either 

 side of the body, and proceeding backwards, finally open, each 

 bundle by itself, near the hind border of the sucker. The 

 smaller cells above described are evidently gland cells in the 

 interval of secretor}^ activity, and the contents of the vacuoles 

 in the larsjer cells are the mucus. 



Along the antero-lateral borders of the body there are 

 openings of numerous mucous glands, which impart a dark as- 

 pect to this portion. These glands are unicellular and goblet- 

 shaped. The cell bodies lie at some distance from the external 

 margin of the body, and contain either a finely or a somewliat 

 coarsely granular cytoplasm according to the stages of secretory 

 activity. The finely granular cytoplasm stains more deeply than 

 the coarsely granular, but not very deeply after all. The 

 nuclei are always very small and lie near the periphery. The 

 ducts are very long, and open on the ventral side of the body 

 close to the margin (figs. 19 & 24). 



