ON TEMNOCEPHALA. 289 



versely or obliquely through the parenchyma from the dorsal 

 to the ventral aspect, and inserted at their extremities into the 

 basement membrane. In the region of the intestine, however, 

 the muscular fibres of the parenchyma form a series of about 

 twelve incomplete transverse dissepiments (PI. XXI, fig. 8, 

 sept.), constricting the intestine at regular intervals, and 

 dividing the peri-intestinal region into a series of incompletely 

 separated segments. Continuous with these are the layers of 

 muscular fibres investing the alimentary canal and the repro- 

 ductive organs. 



The muscular fibres of the sucker are derived both from 

 the muscle of the body wall and from that of the parenchyma. 

 There are six sets of fibres to be distinguished, viz. (1) fibres 

 which pass from the dorsal wall of the body to near the centre 

 of the concavity of the sucker ; (2) oblique fibres which run 

 through the substance of the outer part of the sucker from the 

 dorsal to the ventral surface ; (3) fibres which run longi- 

 tudinally from the ventral body wall obliquely through the 

 lateral parts of the stalk; (4) radial fibres; (5) circular fibres 

 running round the margin ; (6) accessory fibres. 



Alimentary Canal. 



The mouth is situated on the ventral surface, near the 

 anterior end of the body, rather behind the plane of the eyes 

 and the excretory openings. It is a transverse opening of 

 considerable width, leading directly into the cavity of the 

 muscular pharynx. The latter is a subspherical organ with 

 thick walls and a relatively small cavity. The wall of the 

 organ (Plate XXI, fig. 6) is constituted as follows. Most inter- 

 nally is a thick membrane (ep.), almost homogeneous in cha- 

 racter, but very finely granular, and very finely striated in a 

 vertical direction. The substance of which this membrane is 

 composed is not cuticular, but, though entirely devoid of 

 nuclei, is to be taken as the equivalent of an internal epithe- 

 lium. Running right through the substance of the wall of the 

 pharynx is a series of radially arranged muscular fibres (rad.) ; 



