Art. 8.— S. Goto and Y. Matsudaira : 



Text-fig. 1 and 2. Dissotrema papillalum. 



X 18 diam. 



1. Ventral view. 2. Lateral view, m — mouth, 



gp — genital pore, ac — acetabulum. 



longitudinally concave on the ventral side, slightly tapering in 

 front where it ends bluntly, and simply rounded at the hind end. 



Frequently the worm rounds 

 itself up on the ventral side. 

 The openings of the oral and 

 posterior suckers and the 

 genital aperture near the 

 middle are very conspicuous. 

 Another peculiarity of this 

 worm is the presence of a 

 relatively large papilla near 

 the hind end in the dorsal 

 median line, on the top of 

 which the excretory system 

 opens. The surface of the 

 body is perfectly smooth, 

 except for the minute conical 

 sensory papillae, which are 

 more numerous in the anterior parts of the body. The colour 

 is light yellowish brown, owing to the presence of numerous 

 fine pigment granules in the parenchyma. The cuticle or invest- 

 ing membrane is 4/* thick on the dorsal side at the middle of the 

 body and slightly less on the ventral side. 



The mouth is subterminal and transversely oval and sur- 

 rounded by a lip-like prolongation of the body. The oral sucker 

 which immediately follows is usually ellipsoidal; in four specimens 

 mounted in toto it was respectively 298 x 260/*, 268x275/*, 275 x 

 260/* and 253x253/*. Its lumen is flattened dorsoventrally and 

 lined by the direct continuation of the cuticle. The oral sucker is 

 surrounded by a very thin but distinct external limiting mem- 

 brane, in which run very fine circular muscle fibres, mostly 

 arranged in band-like groups separated from one another by narrow 

 but distinct spaces. Under the microscope these fibres look exact- 

 ly like the circular fibres of the body wall. Along the lateral 

 margin of the lumen of the oral sucker there project into it in its 

 posterior two-thirds a number of sharp dentiform spines stained 



