Some Points on the General Anatomy of Gyrocotyle. 731 



pronounced that the passage way is almost closed, but they flatten 

 out gradually and the lumen acquires a nearly circular outline which 

 continues unchanged until it passes suddenly but without any break 

 or structural change into the folds of the rosette. The maximum 

 diameter of the canal in the contracted stellate region is 160 to 

 240 ju; where the folds of the wall are flattened out this reaches 

 560 to 640 ii and gradually inereases to about 1,1 to 1,4 mm just 

 before the termination in the rosette. The lining of the canal is a 

 cuticular layer similar to. and directly continuous witli. that over 

 the general surface of the body but thinner and without spines. 

 Within it lies the same series of layers as formed in the body wall ; 

 the layer of nuclei noted by Watson is especially distinct here. 

 The oblique dorso-ventral muscles radiate from the wall of the canal 

 to the body wall. They occur as elsewhere in the form of separate 

 fibres and not in special bundles. At the posterior end the wall of 

 the canal merges insensibly into the walls of the rosette folds. Here 

 as at the anterior end one finds no special muscles or other pecu- 

 liar structures to mark the limits of the organ. Between the canal 

 and the outer surface of the body the space is filled by the charac- 

 teristic parenchymatous tissue, the various muscle layers and oblique 

 fibres, together with some few vitelline follicles, ducts and the nerve 

 trunks. At the level where the canal originates the follicles are 

 occasionally found near the median line but are mostly crowded 

 together within the circular muscles at the edge of the body and 

 in the lateral ruffles. They disappear entirely when the latter 

 terminate. At the beginning of the canal there are two heavy 

 centrolateral nerve trunks ; these connect with the posterior complex 

 near the posterior end of the canal. In brief then the wall of the 

 canal is merely a continuation of the body wall, and the canal itself 

 simply a ]»assage way from the apex of the posterior sucker to the 

 exterior. A slightly accentuated development of the circular muscles 

 near the middle of its course serves as a sphincter to close the canal. 

 The origin of the canal is possibly related to the formation of the 

 posterior rosette from a right and left fold of the posterior body 

 wall which fusing into a funnel left an open commnnication corre- 

 sponding to the stein of the funnel. An indication of this bilateral 

 origin is still to be seen in the groove which bisects the posterior 

 and ventral portions of the rosette. The funnel margin is highly 

 convoluted to form the rosette itself. The latter organ is clearly 



