10 Earlc C. Stevenson 



shaped, but it is often pointed or broad and blunt (pi. IV, fig. 

 33; pi. V, fig. 43). On the lower margin of the dorsal root at 

 its origin usually occurs a more or less abrupt elevation, but 

 frequently this is graduated in its origin and termination. The 

 posterior end of the dorsal root is usually broader than the mid- 

 dle portion, but not infrequently it is narrower. The upper 

 boundary is very rough in outline, there being in some hooks 

 one or more deep notches ; and in many cases at the base of the 

 blade is found an abrupt shoulder, marking the point of pro- 

 jection of the blade from the tissues. 



In many of the hooks the back margin of the blade just in 

 front of the shoulder is undulate or ridged (pi. IV, figs. 34, 35). 

 The prong of many of the large hooks is sharply bent downward 

 at the extreme point. One peculiar feature noticed is shown in 

 pi. Ill, fig. 19, where the anterior and posterior extremities of 

 the hook have apparent additions to the original length, though 

 the length with the added parts corresponds to the usual magni- 

 tude of the mature hook. This peculiarity, also occurring in 

 some of the small hooks of this species, is presumed to be caused 

 by a greater deposit of chitin on the inner walls of the hook 

 during its growth. 



small hooks of Taenia serialis 



The hooks of Taenia serialis are easily distinguished from 

 those of Taenia serrata by means of their lesser magnitude and 

 their characteristic differences in shape and outline. The small 

 hooks are bifid and also present a wide difference in the depth 

 of the cleft between the branches of the ventral root. The body 

 of the hook is more slender and the anterior root much longer 

 than in the small hooks of Taenia serrata. The branches of the 

 ventral root vary in their mutual positions as in Taenia serrata. 

 Usually the outline of the branches is regular and even, gently 

 rounding at the point, but frequently the root may be broadened 

 and flattened (pi. Ill, fig. 20). At the base of the root on the 

 posterior side there may occur a deep notch, though more fre- 

 quently the margin passes in a gradual curve into the lower 

 boundary of the dorsal root, which is usually enlarged near its 



200 



