muscular partitions arranged in a more or less complicated fashion are 

 formed on the internal surface of such attaching discs, among many species 

 ( Trochopus , Fig. 28, Capsala , Fig. 1). The main part of the suction discs 

 have a precisely rounded form, and in rare cases are laterally elongated 

 (as for instance^ Tetraonchoides , Fig. 29) or longitudinally elongated (for 

 example Thaumatocoty le , Fig. 30). 



fl/nf 



p. 26 



Fig. 25. Octostoma minor (Goto), 

 adult worm with weakly developed 

 attaching disc, from the gills of 

 Pneumatophorus japonicus (Hout. ) 

 from the region Yablochnoii 

 (Southern Sakhalin, Sea of Japan). 



Fig. 26. Protogyrodactylus quadratus 

 Johnston and Tiegs, adult worm, size 

 is about 0. 23 mm. The worm con- 

 tracted strongly during fixation, 

 apparently in normal condition it is 

 more elongated. (According to 

 Johnston and Tiegs, 1922). 



The following group of discs, not less well-delineated from the 

 body, and likewise supplied with a powerful musculature, but lacking the 

 suctorial form, is similar to the second type which was described. This 

 group is typical for the monogenetic trematodes in that the organs located 

 on the ventral side or along the sides of the disc are the main or basic 

 organs of attachment. 



One must note that the form of the disc can fluctuate considerably 

 from round to very elongate, while the edge of the disc changes from the 

 equally round one to a highly indented one. Often the disc forms paired and 

 odd growths of different extent, as a rule they are symmetrically arranged. 

 The discs of Polystomatidae (Fie. 22) and Hexobothriidae (Fig. 2) can be con- 

 sidered as samples of discs of this type. Here also can be placed the disc 



18 



