122 



muscle seems to be a further development of the second layer from the 

 membrane mentioned above, as on transverse sections it is continued into 

 it. Its fibres are also found under the cuticula, fewest in the middle of 

 the sucker, in greatest abundance at the margins. 



All the muscles of the suckers are embedded in parenchym. A layer 

 of cells, with small round nuclei, measuring on an average about 4 "5 /«, is 

 found between the radial fibres quite close to the cuticula. These cells 

 are rather poor in plasma, their nucleus is vesicular, contains a fairly large 

 nucleolus and one or two chromatin bodies. These cells may represent a 

 much modified subcuticula, for which their arrangement in a definite layer 

 under the cuticula and the cuticular muscles (ring muscle) would seem to 

 speak; on the other hand, their plasma bodies do not resemble the normal 

 subcuticular cells of this worm. 



The Longitudinal Canals. 



The longitudinal canals have already been shown to be very con- 

 spicuous in the posterior part of the strobila. It is, however, only the 

 ventral canals which one sees ; the dorsal canals become rudimentary at 

 50 cm. from the scolex, though they can be traced as a solid line of tissue 

 throughout the strobila. In the proglottids, the dorsal canal gets dis- 

 placed and runs laterally and internally to the ventral canal. In the base 

 of the scolex we find them lying dorsal and ventral to each other ; even 

 here the difference in calibre is very apparent. 



The left ventral canal on reaching the level of the base of the suckers 

 turns at right angles and proceeds horizontally to the base of the left 

 dorsal sucker, rising vertically and laterally to the sucker to just above 

 the first sections showing the lumen of the sucker ; it then turns over 

 and proceeds downwards parallel to its ascent ; arrived near the base of 

 the sucker it gives off a short branch which terminates abruptly in about 

 the same height as the loop just mentioned (i.e. after the first sections 

 showing the lumen of the sucker). 



The main canal, however, twists around, internal to its initial hori" 

 zontal portion and ahnost parallel to it, crossing the scolex externally to 

 the dorsal canal ; arrived at the base of the left ventral sucker, ,it ascends 

 the median side of the sucker until the external opening of the sucker is 

 reached, it then runs downwards parallel to its ascent, until the base of 

 the sucker is reached ; passing round the external face of the base of the 

 sucker and forming a few spiral loops at its base, it ascends the lateral 

 inner side of the sucker as far as the cross commissure, then it sends off 

 a branch which proceeds a short distance to the outer surface of the dorsal 

 sucker, where it terminates abruptly. The main canal, however, continues 

 ascending just between the two suckers, after making a single spiral loop, 

 to the summit of the scolex, where it bends over, descends in the inner 

 angle formed by the two suckers until the cross conunissure is reached ; 

 here it bends inwards, then upwards, and runs parallel and ventral to the 



