DIFFEEENTIAL DIAGNOSIS OF T^NIA MARGINATA. 567 



rostellum measures 0'64 mm., and bears a double circlet of from 

 thirty- eight to forty-eight powerful hooks, M'hich (Fig. 306) are fully 

 a third longer and stronger than those of T. marginata. The total 

 length of the large hooks is about 0'25 mm., of the smaller 0'14 mm. 

 In the latter, the point of the anterior root is at an almost equal 

 distance from the two extremities (0'084 mm.), while the same distances 

 in the larger hooks are O'l mm. in front, and 0'167 mm. behind. 



In T. marginata the suckers and the rostellum measure about 

 0'34 mm. On the latter are from 32 to 42 hooks, which in form 

 (Fig. 304) are not unlike those of T. serrata, but are less in strength 

 and size, having a length of only 0-19-0'21 mm. and 0'12-0'16 mm. 

 respectively. Specially distinctive are the comparatively great length 

 and the slender form of the anterior processes (compare Fig. 304). 

 This is most striking in the case of the small hooks whose anterior 

 root, as in the related species, has almost a Y-shape. The distances 

 between the two extremities of the hook and of the anterior root are, 

 in the larger hooks, about O'09-O'l mm. in front, and OH-0'14 mm. 

 behind, while in the smaller they sink to 0'077 mm. and 0'08 mm. 

 Between the hooks one sometimes sees (as also in the Cysticercus) 

 isolated black pigment granules, like those of Tcenia solium. 



Fio. 307. — Larger and smaller hooks of Tcenia ccenurus. ( x 280.) 



The head of Tcenia ccenurus is of a more slender, pear-shaped form, 

 with a transverse diameter of 0'8 mm., and with somewhat insignificant 

 suckers (0-29 mm.). The rostellum has a diameter of 0-3 mm., and 

 carries usually twenty-eight (from twenty-four to thirty-two) hooks, of 

 which the larger are 0-16 mm. long, while the smaller measure only 

 01 mm. (Fig. 307). The distances between the extremities of the hooks 

 and the anterior process are in the larger hooks each 0'09 mm., and in 

 the smaller 0-084 mm. and 0-064 mm. respectively. Notewortliy, as 

 being diagnostic, is the heart-shaped structure of the anterior root on 

 the large hooks, and we have also to remark on the smaller and more 

 slender form of the posterior root. 



But not only do these three worms differ from one another in 

 their external characters, and in the nature of the hooks, the liberated 

 proglottides also exhibit many differences in size and in the structure 

 of the uterus. 



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