Variation in Hooks of Dog-Tapezvorms n 



end and then tapered sharply to the end; however, the root may 

 continue evenly toward the end and be gently rounded or drawn 

 out to a point (pi. Ill, figs. 22, 23). Only in rare cases is the 

 upward bend of the end of the dorsal root wanting. The out- 

 line of the dorsal root is, as a rule, quite regular, but occasion- 

 ally presents elevations and depressions at irregular intervals. 

 The upper margin may pass gradually into the back boundary 

 of the blade, but quite frequently a slight angle marks the tran- 

 sition. The blade tapers regularly, but in a few instances is 

 abruptly pointed (pi. Ill, fig. 20). It is to be noted that the 

 dorsal root varies extensively in length and that the ventral root 

 is often a broad, flat, solid body. 



large hooks of Taenia serialis 



The large hooks of Taenia serialis vary greatly in general form 

 and comparative volume, some being heavier-bodied than others. 

 The ventral root is undivided, its anterior margin slanting for- 

 ward in a gentle curve to its base, where it then turns abruptly 

 backward for a short space, then passes into the lower boundary 

 of the blade which varies in the angle of the curvature, as in the 

 case of the hooks of Taenia serrata; also, it often has the point 

 bent sharply downward. The back margin of the blade passes 

 in an even course to its base, where it makes an angle with the 

 upper boundary of the dorsal root, which has almost invariably 

 in its course a single depression and elevation, though frequently 

 a second depression and elevation are present. The end of the 

 dorsal root is usually rounded, but very often is either blunt or 

 tapering. The lower margin of the dorsal root is uniform in its 

 course, excepting for a slight downward inclination where it 

 meets the posterior boundary of the ventral root. In many of 

 the hooks there are, however, along this margin, depressions and 

 elevations at irregular intervals. The end of the dorsal root may 

 or may not be bent upward or downward from its general direc- 

 tion. 



In general the shape and form of the hooks of the two species 

 are similar, but in detail of outline the hooks of Taenia serialis 

 are the most variable. The hooks of both species are flattened 



201 



