BY S. J. JOHNSTON. 305 



of blood from the contracting ventricle. Then the muscle- 

 fibres of this part of the sucker are arranged in such a way 

 that this central plug can be drawn far back from the surface 

 to which the worm is attached, so as to give the sucker a very 

 powerful clinging action. 



The cells of the body-parenchyma are very large and thin- 

 walled, and more or less filled with finely granular contents. 

 Between these cells are two longitudinal vessel-like spaces, 

 which Looss (55, p. 432) has described, in A. spinulosum, as 

 lymphatics. They run from the oral to the posterior sucker, 

 and enter into intimate relation with the suckers. 



The excretory vesicle lies in the body directly behind the 

 posterior sucker. From its anterior end, a pair of large ves- 

 sels come off, running first pretty straight outwards to the 

 sides; then they turn forwards, and run in a somewhat wavy 

 course up to the level of the oral sucker diverticula ; crossing 

 the intestine on the ventral side, they then bend sharply back, 

 and run as much finer tubes to the posterior end of the body, 

 giving off', at various points, capillaries that end in excretory 

 cells. Some branches of the excretory system enter the pos- 

 terior sucker, but the arrangement of these has not been 

 closely followed out. At its posterior end, the vesicle gradu- 

 ally narrows into a moderately fine duct with muscular tissue 

 in its walls, and this duct opens on the exterior by an exceed- 

 ingly minute pore, less than 0-005 mm. in diameter, in every 

 one of my sectioned specimens, more than a dozen in number. 

 This pore is situated right at the posterior end of the body, 

 just near the posterior rim of the sucker. 



The genital opening (Fig. 39) lies in the middle line on the 

 ventral surface, just behind the intestinal fork. It leads into 

 a small genital chamber, into which the male and female 

 ducts open. 



There is a single testis, in the form of a large, somewhat 

 cubical or rectangular body, laterally placed near the intes- 

 tine and internal to it. 'J'his testis is inconspicuously marked 

 off into two lobes by a groove running along its ventral and 



