268 
Amoehotaenia sjiJienoides 
Excretory System. 
The excretory system (PI. XXI, fig. 9) consists as usual of four longi¬ 
tudinal vessels, one dorsal {d.l.c.) and one ventral {d'.l'.c'.) each side, 
running the whole length of the strobilus. Of these four vessels, the 
two ventral are much smaller than the two dorsal and at times become 
so small that they appear to vanish. The course of each longitudinal 
vessel is not straight. In each proglottis it has the form of an arc vdth 
the convex side directed towards the exterior : the arc extends externally 
approximately to the level of the inner end of the cirrus sac ; it passes 
from one proglottis to another about at one-third of the width of the 
strobilus and has there its innermost margin. The four canals are 
joined at the end of each segment by an elhptical commissure : the 
transverse commissures {t.c.) between the two dorsal and the two 
ventral vessels are approximately the wddth of the respective longi¬ 
tudinal vessels and are therefore fairly obvious : those between the two 
vessels of the same side are very minute {v.c.). 
The excretory system in the scolex is much more complex, although 
it still conforms to a definite plan. There is no neck, so that the longi¬ 
tudinal vessels pass straight into the head system. At the level of the 
posterior margin of the suckers each longitudinal vessel curves shghtly 
towards the interior and then runs in a straight fine along the rostellum 
to the level of the anterior border of the sucker. Half-way along its 
course each sends off a wide branch to the rostellum (r.c.) : and at each 
third of the course the two vessels of each side communicate with one 
another by small transverse commissures. Arrived at the anterior 
margin of the sucker, each describes a semicircle under the cuticle of 
the scolex : the two semicircles of each side converge as they approach 
the exterior and finally join on the lateral margin of the strobilus, half¬ 
way between the suckers. The common vessel thus formed only extends 
for a short distance, splitting again into two, each of which (lat.c.) runs 
posteriorly, equidistant from and in the same horizontal plane as its 
corresponding longitudinal vessel. Arrived at the posterior margin of 
the sucker, each lateral vessel describes another semicircle, opening into 
its corresponding longitudinal vessel. Two loops are thus formed on 
each side, communicating with one another at their extreme antero¬ 
lateral limits. The two lateral vessels on each side communicate with 
each other by small transverse commissures and at about the posterior 
third of its course each gives off a small vessel running to the correspond¬ 
ing sucker (.s.c.). The corresponding lateral and longitudinal vessels 
