[duff] THE BEAVER FLUKE 93 



external layer of the parenchyma. This view is set forth in a recent 

 paper by Pratt (28) who draws the conclusions from his study that the 

 subcuticular tissue belongs genetically to the parenchyma and that 

 the cuticle is the peripheral portion of the parenchyma, composed 

 mainly of secretions of it. This last hypothesis offers I think the 

 best explanation of the facts as I have observed them in Amph. subtri- 

 quetrum. The subcuticular cells are undoubtedly connected every- 

 where with cuticle, and their protoplasmic net-work on the other 

 hand passes directly into that of the typical parencyhma tissue 

 (Figs. 6, 9 & 10). 



Parenchyma. 



The parenchyma of Amph. subtriquetrum is formed of thin strands 

 of connective tissue which enclose large irregular spaces. These, 

 spaces appear filled with a loose coagulum of the body fluid of the 

 living Trematode; and in this flocculent mass are scattered numerous 

 iree nuclei in various stages of degeneration. 



At intervals through the parenchyma and especially numerous 

 in the muscles of the pharynx and of the posterior sucker are conspic- 

 uous "large" or "giant" cells. Those in the parenchyma occupy 

 various positions. Some are near the circular muscles of the body 

 wall, some lie alongside parenchyma fibres and occasionally I have 

 found them closely approximated to the walls of the body organs. 

 The acetabular cells, i.e., those in the pharynx and sucker muscles, 

 are regularly arranged in zones mid-way between the cuticle and the 

 inner boundaries of the muscles. The layer of "large" cells is more 

 easily distinguished in the pharyngeal muscle, because the fibres 

 there are farther apart, but the cells are as numerous though less 

 distinct in the sucker (Figs. 4, 8 & 12). 



The nuclei of the " large" cells are generally oval in shape, bounded 

 by a distinct dark membrane, (Fig. 13). The nuclear contents are 

 granular and a large densely staining nucleolus is present as a rule. 

 In some cases, however, I found the nucleus irregular in outline as 

 though in process of budding off daughter nuclei, and in such cases 

 there were several smaller nucleoli (Figs. 14 & 15). The protoplasm 

 shows thread-like prolongations in all directions which give the outer 

 border of the cell a netted appearance. These long branching fibres 

 of protoplasm show direct connections with the extensions of the 

 subcuticular cells mentioned above. This is especially clear in the 

 acetabular cells of the pharynx (Fig. 14). 



At first these "large" cells were almost universally called "Gang- 

 lion cells." According to Looss (29) it was Stieda (30) who first 



