dorsal canal until the summit of the scolex is reached ; here it again bends 

 over horizontally and dorsally to join the left dorsal canal in a simple 

 loop. 



Explanation oj Figure. — ^I'.v.c. riglit ventral canal. 

 l.T.o. left ventral canal, 

 r.d.c. right dorsal canal, 

 l.d.o. left dorsal canal. 

 The scolex is seen obliquely, the left central sucker facing the observer. 



The right ventral canal, having reached the base of the suckers, also 

 bends over dorsally and horizontally, running to the right dorsal sucker, 

 then it ascends the median internal face of the right dorsal sucker and 

 runs almost the whole length of the sucker, veering over more and more 

 to the right until it at last appears on the dorsal summit of the sucker ; 

 then it turns over, descends parallel to the direction it came, until the base 

 of the sucker is again reached ; it now turns and runs horizontally through 

 the scolex, remaining exterior to the dorsal canal but interior to its first 

 horizontal winding ; arrived at the median internal base of the right 

 ventral sucker, it ascends and descends its internal ventral side, reaching 

 the height of the opening of the sucker. Passing around the base of the 

 right ventral sucker on its posterior surface, it ascends the outer angle of 

 the two right suckers ; at about the same level as the left canal branches, 

 the right canal does the same, but unhke the left canal, it sends off two 

 ramifications, one to the outer surface of the dorsal, the other to the outer 

 surface of the ventral sucker. After the branches have been given off, 

 it ascends almost to the summit, bends over laterally and inwards, descends 

 in the inner angle of the right suckers until the cross commissure is 

 reached ; here it turns inwards, passes under the nerve commissure, then 

 proceeds in a straight hne anteriorly, parallel, and ventral to the dorsal 

 canal ; arrived at the summit it bends over dorsally and joins the dorsal 

 canal. The two dorsal canals ascend the scolex in a straight line until 

 they are joined to the ventral canals ; the right and left dorsal canals are 

 connected at the summit by a short loop. 



The course of these canals can be summed up as follows : The ventral 

 canals on entering the scolex pass over to the dorsal suckers, run up and 



