BY S. J. JOHNSTON. 303 



The integument is perfectly smooth, without any trace of 

 spines or tubercles. The opening of the oral sucker is termi- 

 nal : that of the posterior sucker subterminal or postero-ven- 

 tral. The average diameter of the oral sucker is 0-313 mm., 

 of the posterior 1085 mm. : the ratio of oral to posterior 1 : 346 

 or about 3:10. 



The oral sucker is a thick, muscular subglobular structure, 

 deeply embedded in the body of the worm, with a pair of 

 diverticula, the so-called "pharyngeal pockets," given off 

 laterally from its base. These diverticula are about as deep 

 (0-33 mm.) as the main body of the sucker, and are joined 

 together in the middle line for the most part of their length, 

 only being completely separated from one another near their 

 terminations (Figs. 37, 38). The structure of the walls of 

 these pockets is exactly similar to that of the oral sucker, and 

 the arrangement of its muscle-fibres, radial, circular, longi- 

 tudinal and oblique, together with the embedded cells, agrees 

 very closely with the detailed description given by Looss (55) 

 for the oral sucker of Amphisto/iiuni spintilosum. At the bot- 

 tom of the sucker, lies the opening of the oesophagus, running 

 . into it from a ventral position, and lying very close to the 

 openings of the diverticular (Fig. 38). The oesophagus is a long 

 tube with fairly thin walls, running almost straight back to 

 the forking of the intestinal limbs, with a length of about 0-52 

 mm. At its posterior end, the muscular wall of this tube 

 becomes considerably thickened so as to form a pharynx (01 2 

 mm. long), which opens into the intestine. Fischoeder (19), 

 Daday (16), and others have sought to make the structure, 

 which I have called the oral sucker, homologous with the 

 pharynx of other trematodes. I cannot agree with this, but 

 concur with Looss' contention (55, p. 440) that here we have 

 to do with a real oral sucker. Leaving out of account for the 

 moment the A nrjjIiii^fonirf<, one finds, in most of the Mahiroco- 

 tyha, an oral sucker, out of the base of which, that })art of the 

 alimentary tract lying between it and the intestine, and called 

 the oesophagus, opens. On the course of the oesophagus some- 



