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down their exterior surfaces, recross the scolex, run up and down the 

 median surfaces of the ventral suckers, pass round the base of the same 

 suckers, run up the outer lateral angle formed by the dorsal and ventral 

 suckers, cross over the anterior angle formed by the same suckers, run 

 down the inner angle, pass under the commissure, and then vertically to 

 the summit of the scolex parallel and ventral to the dorsal canal, joining 

 the dorsal canal at the summit. The dorsal canal runs straight through 

 the scolex, uniting at the summit with the ventral canals, and joined near 

 the summit by a short loop. Blind branches are given off by both right 

 and left canals (perhaps rudiments of a ring canal ?). 



I have not found any trace of commissures between the lateral canals 

 in the proglottids ; in S. hepatica anastomosing canals connect the ventral 

 canals, these commissures lying at the end posterior of the segment. 



The longitudinal canals, when cut transversely to their long axis are 

 more or less circular or oval in outline. Their diameter varies consider- 

 ably in various parts of the body, as can be seen from the following : 



Scolex, at apex 

 ,, at base 

 Strobila, near scolex . . 



,, 10 cm. from scolex 



,, 20 cm. ,, 



,, 30 cm. ,, 

 40 cm. 



,, 50 cm. ;, 



,, 60 cm. ,, 

 70 cm. 



Segments with nearly ripe ova obliterated 192 

 of the lateral canals are formed of a membrane, staining with orange g. 

 In the apex of the scolex, in sections tangential to the course of the canals 

 a very fine cross-striping becomes apparent; the stripes are 2 /* across, 

 separated from each other by an almost invisible fine dark fine. I have 

 been able to find this structure in material fixed in Zenker's solution or 

 formaline, stained with haematoxyhn and orange g. The walls of the 

 canals are covered with a layer of cells, probably belonging to the 

 parenchym. In the strobila the cross-stripes are much harder to make 

 out. 



On sections in the proglottids the dorsal and ventral canals differ 

 considerably. 



The ventral canals have thin walls, and the nuclei of the surrounding 

 parenchym cells lie quite close and tangentially to it. The dorsal canals, 

 on the other hand, have much thicker walls, often thicker than the lumen ; 

 these walls have three different layers, the innermost very thin, dark : the 

 middle about 1 /^ thick staining orange, the outer about 2 [j, thick, staining 

 with haematoxyhn ; they are surrounded by closely radially arranged 



